Merge branch 'feature/OptimizeGame' into develop

Added Renderer_iface.h as a clean interface.
Replaced usages of old/ambiguous SDL calls in SDLRenderer.cpp to call SDL3 APIs: SDL_RenderTexture, SDL_RenderFillRect, SDL_RenderRect, SDL_RenderLine.
Converted copy() to call SDL_RenderTexture by converting integer rects to float rects.
Updated GameRenderer.cpp to include the new clean interface.

.copilot-rules.md

@@ -0,0 +1,168 @@
+# Copilot Rules — Spacetris (SDL3 / C++20)
+
+These rules define **non-negotiable constraints** for all AI-assisted changes.
+They exist to preserve determinism, performance, and architecture.
+
+If these rules conflict with `.github/copilot-instructions.md`,
+**follow `.github/copilot-instructions.md`.**
+
+---
+
+## Project Constraints (Non-Negotiable)
+
+- Language: **C++20**
+- Runtime: **SDL3** + **SDL3_ttf**
+- Build system: **CMake**
+- Dependencies via **vcpkg**
+- Assets must use **relative paths only**
+- Deterministic gameplay logic is mandatory
+
+Do not rewrite or refactor working systems unless explicitly requested.
+
+---
+
+## Repo Layout & Responsibilities
+
+- Core gameplay loop/state: `src/Game.*`
+- Entry point: `src/main.cpp`
+- Text/TTF: `src/Font.*`
+- Audio: `src/Audio.*`, `src/SoundEffect.*`
+- Effects: `src/LineEffect.*`, `src/Starfield*.cpp`
+- High scores: `src/Scores.*`
+- Packaging: `build-production.ps1`
+
+When adding a module:
+- Place it under `src/` (or an established subfolder)
+- Register it in `CMakeLists.txt`
+- Avoid circular includes
+- Keep headers minimal
+
+---
+
+## Build & Verification
+
+Prefer existing scripts:
+
+- Debug: `cmake --build build-msvc --config Debug`
+- Release:
+  - Configure: `cmake -S . -B build-release -DCMAKE_BUILD_TYPE=Release`
+  - Build: `cmake --build build-release --config Release`
+- Packaging (Windows): `./build-production.ps1`
+
+Before finalizing changes:
+- Debug build must succeed
+- Packaging must succeed if assets or DLLs are touched
+
+Do not introduce new build steps unless required.
+
+---
+
+## Coding & Architecture Rules
+
+- Match local file style (naming, braces, spacing)
+- Avoid large refactors
+- Prefer small, testable helpers
+- Avoid floating-point math in core gameplay state
+- Game logic must be deterministic
+- Rendering code must not mutate game state
+
+---
+
+## Rendering & Performance Rules
+
+- Do not allocate memory per frame
+- Do not load assets during rendering
+- No blocking calls in render loop
+- Visual effects must be time-based (`deltaTime`)
+- Rendering must not contain gameplay logic
+
+---
+
+## Threading Rules
+
+- SDL main thread:
+  - Rendering
+  - Input
+  - Game simulation
+- Networking must be **non-blocking** from the SDL main loop
+  - Either run networking on a separate thread, or poll ENet frequently with a 0 timeout
+  - Never wait/spin for remote inputs on the render thread
+- Cross-thread communication via queues or buffers only
+
+---
+
+## Assets, Fonts, and Paths
+
+- Runtime expects adjacent `assets/` directory
+- `FreeSans.ttf` must remain at repo root
+- New assets:
+  - Go under `assets/`
+  - Must be included in `build-production.ps1`
+
+Never hardcode machine-specific paths.
+
+---
+
+## AI Partner (COOPERATE Mode)
+
+- AI is **supportive**, not competitive
+- AI must respect sync timing and shared grid logic
+- AI must not “cheat” or see hidden future pieces
+- AI behavior must be deterministic per seed/difficulty
+
+---
+
+## Networking (COOPERATE Network Mode)
+
+Follow `docs/ai/cooperate_network.md`.
+If `network_cooperate_multiplayer.md` exists, keep it consistent with the canonical doc.
+
+Mandatory model:
+- **Input lockstep**
+- Transmit inputs only (no board state replication)
+
+Determinism requirements:
+- Fixed tick (e.g. 60 Hz)
+- Shared RNG seed
+- Deterministic gravity, rotation, locking, scoring
+
+Technology:
+- Use **ENet**
+- Do NOT use SDL_net or TCP-only networking
+
+Architecture:
+- Networking must be isolated (e.g. `src/network/NetSession.*`)
+- Game logic must not care if partner is local, AI, or network
+
+Robustness:
+- Input delay buffer (4–6 ticks)
+- Periodic desync hashing
+- Graceful disconnect handling
+
+Do NOT implement:
+- Rollback
+- Full state sync
+- Server-authoritative sim
+- Matchmaking SDKs
+- Versus mechanics
+
+---
+
+## Agent Behavior Rules (IMPORTANT)
+
+- Always read relevant markdown specs **before coding**
+- Treat markdown specs as authoritative
+- Do not invent APIs
+- Do not assume external libraries exist
+- Generate code **file by file**, not everything at once
+- Ask before changing architecture or ownership boundaries
+
+---
+
+## When to Ask Before Proceeding
+
+Ask the maintainer if unclear:
+- UX or menu flow decisions
+- Adding dependencies
+- Refactors vs local patches
+- Platform-specific behavior

.gitignore

@@ -18,6 +18,7 @@
 CMakeCache.txt
 cmake_install.cmake
 Makefile
+settings.ini
 
 # vcpkg
 /vcpkg_installed/
@@ -70,7 +71,4 @@ dist_package/
 # Local environment files (if any)
 .env
 
-# Ignore local settings file
-settings.ini
-
 # End of .gitignore

CMakeLists.txt

@@ -28,11 +28,14 @@ find_package(SDL3_ttf CONFIG REQUIRED)
 find_package(SDL3_image CONFIG REQUIRED)
 find_package(cpr CONFIG REQUIRED)
 find_package(nlohmann_json CONFIG REQUIRED)
+find_package(unofficial-enet CONFIG REQUIRED)
 
 set(TETRIS_SOURCES
     src/main.cpp
     src/app/TetrisApp.cpp
     src/gameplay/core/Game.cpp
+    src/gameplay/coop/CoopGame.cpp
+    src/gameplay/coop/CoopAIController.cpp
     src/core/GravityManager.cpp
     src/core/state/StateManager.cpp
     # New core architecture classes
@@ -43,25 +46,33 @@ set(TETRIS_SOURCES
     src/core/Settings.cpp
     src/graphics/renderers/RenderManager.cpp
     src/persistence/Scores.cpp
+    src/network/supabase_client.cpp
+    src/network/NetSession.cpp
     src/graphics/effects/Starfield.cpp
     src/graphics/effects/Starfield3D.cpp
     src/graphics/effects/SpaceWarp.cpp
     src/graphics/ui/Font.cpp
     src/graphics/ui/HelpOverlay.cpp
     src/graphics/renderers/GameRenderer.cpp
+    src/graphics/renderers/SyncLineRenderer.cpp
     src/graphics/renderers/UIRenderer.cpp
     src/audio/Audio.cpp
+    src/audio/AudioManager.cpp
+    src/renderer/SDLRenderer.cpp
     src/gameplay/effects/LineEffect.cpp
     src/audio/SoundEffect.cpp
+    src/video/VideoPlayer.cpp
     src/ui/MenuLayout.cpp
     src/ui/BottomMenu.cpp
     src/app/BackgroundManager.cpp
     src/app/Fireworks.cpp
     src/app/AssetLoader.cpp
     src/app/TextureLoader.cpp
+    src/resources/ResourceManager.cpp
     src/states/LoadingManager.cpp
     # State implementations (new)
     src/states/LoadingState.cpp
+    src/states/VideoState.cpp
     src/states/MenuState.cpp
     src/states/OptionsState.cpp
     src/states/LevelSelectorState.cpp
@@ -156,10 +167,17 @@ if(APPLE)
     endif()
 endif()
 
-target_link_libraries(spacetris PRIVATE SDL3::SDL3 SDL3_ttf::SDL3_ttf SDL3_image::SDL3_image cpr::cpr nlohmann_json::nlohmann_json)
+target_link_libraries(spacetris PRIVATE SDL3::SDL3 SDL3_ttf::SDL3_ttf SDL3_image::SDL3_image cpr::cpr nlohmann_json::nlohmann_json unofficial::enet::enet)
+
+find_package(FFMPEG REQUIRED)
+if(FFMPEG_FOUND)
+    target_include_directories(spacetris PRIVATE ${FFMPEG_INCLUDE_DIRS})
+    target_link_directories(spacetris PRIVATE ${FFMPEG_LIBRARY_DIRS})
+    target_link_libraries(spacetris PRIVATE ${FFMPEG_LIBRARIES})
+endif()
 
 if (WIN32)
-    target_link_libraries(spacetris PRIVATE mfplat mfreadwrite mfuuid)
+    target_link_libraries(spacetris PRIVATE mfplat mfreadwrite mfuuid ws2_32 winmm)
 endif()
 if(APPLE)
     # Needed for MP3 decoding via AudioToolbox on macOS
@@ -186,10 +204,25 @@ if(EXISTS "${CMAKE_SOURCE_DIR}/vcpkg_installed/x64-windows/include")
     target_include_directories(spacetris_tests PRIVATE "${CMAKE_SOURCE_DIR}/vcpkg_installed/x64-windows/include")
 endif()
 
+# GoogleTest-based board unit tests
+find_package(GTest CONFIG REQUIRED)
+add_executable(test_board
+    tests/test_board.cpp
+    src/logic/Board.cpp
+)
+target_include_directories(test_board PRIVATE ${CMAKE_SOURCE_DIR}/src)
+target_link_libraries(test_board PRIVATE GTest::gtest_main)
+add_test(NAME BoardTests COMMAND test_board)
+
+if(EXISTS "${CMAKE_SOURCE_DIR}/vcpkg_installed/x64-windows/include")
+    target_include_directories(test_board PRIVATE "${CMAKE_SOURCE_DIR}/vcpkg_installed/x64-windows/include")
+endif()
+
 # Add new src subfolders to include path so old #includes continue to work
 target_include_directories(spacetris PRIVATE
     ${CMAKE_SOURCE_DIR}/src
     ${CMAKE_SOURCE_DIR}/src/audio
+    ${CMAKE_SOURCE_DIR}/src/video
     ${CMAKE_SOURCE_DIR}/src/gameplay
     ${CMAKE_SOURCE_DIR}/src/graphics
     ${CMAKE_SOURCE_DIR}/src/persistence

docs/ai/cooperate_network.md

@@ -0,0 +1,271 @@
+# Spacetris — COOPERATE Mode  
+## Network Multiplayer (2 PLAYER – NETWORK)  
+### VS Code Copilot AI Agent Prompt
+
+You are integrating **online cooperative multiplayer** into an existing **C++ / SDL3 game** called **Spacetris**.
+
+This feature extends the existing **COOPERATE mode** to support:
+- Local 2 players
+- Human + AI
+- **Human + Human over network (NEW)**
+
+The networking solution must be **deterministic, lightweight, and stable**.
+
+---
+
+## 1. High-Level Goal
+
+Add **COOPERATE 2 PLAYER (NETWORK)** mode where:
+- Two players play together over the internet
+- Each player controls one half of the shared grid
+- A line clears only when both halves are filled
+- Gameplay remains identical to local COOPERATE mode
+
+---
+
+## 2. Technology Constraints
+
+- Language: **C++**
+- Engine: **SDL3**
+- Networking: **ENet (UDP with reliability)**
+- No engine rewrite
+- No authoritative server logic required (co-op only)
+
+SDL3 is used ONLY for:
+- Rendering
+- Input
+- Timing
+
+Networking is a **separate layer**.
+
+---
+
+## 3. Network Model (MANDATORY)
+
+### Use **Input Lockstep Networking**
+
+#### Core idea:
+- Both clients run the same deterministic simulation
+- Only **player inputs** are sent over the network
+- No board state is transmitted
+- Both simulations must remain identical
+
+This model is ideal for Tetris-like games.
+
+---
+
+## 4. Determinism Requirements (CRITICAL)
+
+To ensure lockstep works:
+
+- Fixed simulation tick (e.g. 60 Hz)
+- Identical RNG seed for both clients
+- Deterministic piece generation (bag system)
+- No floating-point math in core gameplay
+- Same gravity, rotation, lock-delay logic
+- Identical line clear and scoring rules
+
+Before networking:
+- Input recording + replay must produce identical results
+
+---
+
+## 5. Network Topology
+
+### Host / Client Model (Initial Implementation)
+
+- One player hosts the game
+- One player joins
+- Host is authoritative for:
+  - RNG seed
+  - start tick
+  - game settings
+
+This is sufficient and fair for cooperative gameplay.
+
+---
+
+## 6. Network Library
+
+Use **ENet** for:
+- Reliable, ordered UDP packets
+- Low latency
+- Simple integration with C++
+
+Do NOT use:
+- SDL_net
+- TCP-only networking
+- High-level matchmaking SDKs
+
+---
+
+## 7. Network Packet Design
+
+### Input Packet (Minimal)
+
+```cpp
+struct InputPacket {
+    uint32_t tick;
+    uint8_t buttons; // bitmask
+};
+````
+
+Button bitmask example:
+
+* bit 0 → move left
+* bit 1 → move right
+* bit 2 → rotate
+* bit 3 → soft drop
+* bit 4 → hard drop
+* bit 5 → hold
+
+Packets must be:
+
+* Reliable
+* Ordered
+* Small
+
+---
+
+## 8. Tick & Latency Handling
+
+### Input Delay Buffer (RECOMMENDED)
+
+* Add fixed delay: **4–6 ticks**
+* Simulate tick `T` using inputs for `T + delay`
+* Prevents stalls due to latency spikes
+
+Strict lockstep without buffering is NOT recommended.
+
+---
+
+## 9. Desync Detection (IMPORTANT)
+
+Every N ticks (e.g. once per second):
+
+* Compute a hash of:
+
+  * Both grid halves
+  * Active pieces
+  * RNG index
+  * Score / lines / level
+* Exchange hashes
+* If mismatch:
+
+  * Log desync
+  * Stop game or mark session invalid
+
+This is required for debugging and stability.
+
+---
+
+## 10. Network Session Architecture
+
+Create a dedicated networking module:
+
+```
+/network
+  NetSession.h
+  NetSession.cpp
+```
+
+Responsibilities:
+
+* ENet host/client setup
+* Input packet send/receive
+* Tick synchronization
+* Latency buffering
+* Disconnect handling
+
+SDL main loop must NOT block on networking.
+
+---
+
+## 11. Integration with Existing COOPERATE Logic
+
+* COOPERATE grid logic stays unchanged
+* SyncLineRenderer remains unchanged
+* Scoring logic remains unchanged
+* Network layer only injects **remote inputs**
+
+Game logic should not know whether partner is:
+
+* Local human
+* AI
+* Network player
+
+---
+
+## 12. UI Integration (Menu Changes)
+
+In COOPERATE selection screen, add a new button:
+
+```
+[ LOCAL CO-OP ]   [ AI PARTNER ]   [ 2 PLAYER (NETWORK) ]
+```
+
+### On selecting 2 PLAYER (NETWORK):
+
+* Show:
+
+  * Host Game
+  * Join Game
+* Display join code or IP
+* Confirm connection before starting
+
+---
+
+## 13. Start Game Flow (Network)
+
+1. Host creates session
+2. Client connects
+3. Host sends:
+
+   * RNG seed
+   * start tick
+   * game settings
+4. Both wait until agreed start tick
+5. Simulation begins simultaneously
+
+---
+
+## 14. Disconnect & Error Handling
+
+* If connection drops:
+
+  * Pause game
+  * Show “Reconnecting…”
+  * After timeout:
+
+    * End match or switch to AI (optional)
+* Never crash
+* Never corrupt game state
+
+---
+
+## 15. What NOT to Implement
+
+* ❌ Full state synchronization
+* ❌ Prediction / rollback
+* ❌ Server-authoritative gameplay
+* ❌ Complex matchmaking
+* ❌ Versus mechanics
+
+This is cooperative, not competitive.
+
+---
+
+## 16. Acceptance Criteria
+
+* Two players can complete COOPERATE mode over network
+* Gameplay matches local COOPERATE exactly
+* No noticeable input lag under normal latency
+* Desync detection works
+* Offline / disconnect handled gracefully
+* SDL3 render loop remains smooth
+
+---
+
+## 17. Summary for Copilot
+
+Integrate networked cooperative multiplayer into Spacetris using SDL3 + C++ with ENet. Implement input lockstep networking with deterministic simulation, fixed tick rate, input buffering, and desync detection. Add a new COOPERATE menu option “2 PLAYER (NETWORK)” that allows host/join flow. Networking must be modular, non-blocking, and transparent to existing gameplay logic.

src/app/AssetLoader.cpp

@@ -1,6 +1,10 @@
 #include "app/AssetLoader.h"
 #include <SDL3_image/SDL_image.h>
 #include <algorithm>
+#include "app/TextureLoader.h"
+
+#include "utils/ImagePathResolver.h"
+#include <filesystem>
 
 AssetLoader::AssetLoader() = default;
 
@@ -37,6 +41,10 @@ void AssetLoader::shutdown() {
     m_renderer = nullptr;
 }
 
+void AssetLoader::setResourceManager(resources::ResourceManager* mgr) {
+    m_resourceManager = mgr;
+}
+
 void AssetLoader::setBasePath(const std::string& basePath) {
     m_basePath = basePath;
 }
@@ -65,24 +73,25 @@ bool AssetLoader::performStep() {
 
     std::string fullPath = m_basePath.empty() ? path : (m_basePath + "/" + path);
 
-    SDL_Surface* surf = IMG_Load(fullPath.c_str());
-    if (!surf) {
-        std::lock_guard<std::mutex> lk(m_errorsMutex);
-        m_errors.push_back(std::string("IMG_Load failed: ") + fullPath + " -> " + SDL_GetError());
+    // Diagnostic: resolve path and check file existence
+    const std::string resolved = AssetPath::resolveImagePath(path);
+    bool exists = false;
+    try { if (!resolved.empty()) exists = std::filesystem::exists(std::filesystem::u8path(resolved)); } catch (...) { exists = false; }
+
+    // Use TextureLoader to centralize loading and ResourceManager caching
+    TextureLoader loader(m_loadedTasks, m_currentLoading, m_currentLoadingMutex, m_errors, m_errorsMutex);
+    loader.setResourceManager(m_resourceManager);
+    // Pass the original queued path (not the full resolved path) so caching keys stay consistent
+    SDL_Texture* tex = loader.loadFromImage(m_renderer, path);
+    if (!tex) {
+        // errors have been recorded by TextureLoader
     } else {
-        SDL_Texture* tex = SDL_CreateTextureFromSurface(m_renderer, surf);
-        SDL_DestroySurface(surf);
-        if (!tex) {
-            std::lock_guard<std::mutex> lk(m_errorsMutex);
-            m_errors.push_back(std::string("CreateTexture failed: ") + fullPath);
-        } else {
-            std::lock_guard<std::mutex> lk(m_texturesMutex);
-            auto& slot = m_textures[path];
-            if (slot && slot != tex) {
-                SDL_DestroyTexture(slot);
-            }
-            slot = tex;
+        std::lock_guard<std::mutex> lk(m_texturesMutex);
+        auto& slot = m_textures[path];
+        if (slot && slot != tex) {
+            SDL_DestroyTexture(slot);
         }
+        slot = tex;
     }
 
     m_loadedTasks.fetch_add(1, std::memory_order_relaxed);
@@ -104,12 +113,17 @@ void AssetLoader::adoptTexture(const std::string& path, SDL_Texture* texture) {
         return;
     }
 
+    // register in local map and resource manager
     std::lock_guard<std::mutex> lk(m_texturesMutex);
     auto& slot = m_textures[path];
     if (slot && slot != texture) {
         SDL_DestroyTexture(slot);
     }
     slot = texture;
+    if (m_resourceManager) {
+        std::shared_ptr<void> sp(texture, [](void* t){ SDL_DestroyTexture(static_cast<SDL_Texture*>(t)); });
+        m_resourceManager->put(path, sp);
+    }
 }
 
 float AssetLoader::getProgress() const {

src/app/AssetLoader.h

@@ -6,6 +6,7 @@
 #include <mutex>
 #include <atomic>
 #include <unordered_map>
+#include "../resources/ResourceManager.h"
 
 // Lightweight AssetLoader scaffold.
 // Responsibilities:
@@ -22,6 +23,7 @@ public:
     void shutdown();
 
     void setBasePath(const std::string& basePath);
+    void setResourceManager(resources::ResourceManager* mgr);
 
     // Queue a texture path (relative to base path) for loading.
     void queueTexture(const std::string& path);
@@ -49,6 +51,7 @@ public:
 private:
     SDL_Renderer* m_renderer = nullptr;
     std::string m_basePath;
+    resources::ResourceManager* m_resourceManager = nullptr;
 
     // queued paths (simple FIFO)
     std::vector<std::string> m_queue;

src/app/Fireworks.cpp

@@ -144,4 +144,7 @@ void draw(SDL_Renderer* renderer, SDL_Texture*) {
 
 double getLogoAnimCounter() { return logoAnimCounter; }
 int getHoveredButton() { return hoveredButton; }
+void spawn(float x, float y) {
+    fireworks.emplace_back(x, y);
+}
 } // namespace AppFireworks

src/app/Fireworks.h

@@ -6,4 +6,5 @@ namespace AppFireworks {
 	void update(double frameMs);
 	double getLogoAnimCounter();
 	int getHoveredButton();
+    void spawn(float x, float y);
 }

src/app/TextureLoader.cpp

@@ -6,6 +6,8 @@
 #include <mutex>
 #include <sstream>
 
+#include <filesystem>
+
 #include "utils/ImagePathResolver.h"
 
 TextureLoader::TextureLoader(
@@ -45,6 +47,18 @@ SDL_Texture* TextureLoader::loadFromImage(SDL_Renderer* renderer, const std::str
     const std::string resolvedPath = AssetPath::resolveImagePath(path);
     setCurrentLoadingFile(resolvedPath.empty() ? path : resolvedPath);
 
+    // Check filesystem existence for diagnostics (no console log)
+    bool fileExists = false;
+    try { if (!resolvedPath.empty()) fileExists = std::filesystem::exists(std::filesystem::u8path(resolvedPath)); } catch (...) { fileExists = false; }
+    // If resource manager provided, check cache first using the original asset key (path)
+    if (resourceManager_) {
+        if (auto sp = resourceManager_->get<SDL_Texture>(path)) {
+            clearCurrentLoadingFile();
+            loadedTasks_.fetch_add(1);
+            return sp.get();
+        }
+    }
+
     SDL_Surface* surface = IMG_Load(resolvedPath.c_str());
     if (!surface) {
         {
@@ -54,7 +68,7 @@ SDL_Texture* TextureLoader::loadFromImage(SDL_Renderer* renderer, const std::str
         }
         loadedTasks_.fetch_add(1);
         clearCurrentLoadingFile();
-        SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "Failed to load image %s (resolved: %s): %s", path.c_str(), resolvedPath.c_str(), SDL_GetError());
+        SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "Failed to load image %s (resolved: %s) exists=%s: %s", path.c_str(), resolvedPath.c_str(), fileExists ? "yes" : "no", SDL_GetError());
         return nullptr;
     }
 
@@ -66,6 +80,7 @@ SDL_Texture* TextureLoader::loadFromImage(SDL_Renderer* renderer, const std::str
     }
 
     SDL_Texture* texture = SDL_CreateTextureFromSurface(renderer, surface);
+    // surface size preserved in outW/outH; no console log
     SDL_DestroySurface(surface);
 
     if (!texture) {
@@ -80,6 +95,15 @@ SDL_Texture* TextureLoader::loadFromImage(SDL_Renderer* renderer, const std::str
         return nullptr;
     }
 
+    // No texture-size console diagnostics here
+
+    // cache in resource manager if present
+    if (resourceManager_) {
+        std::shared_ptr<void> sp(texture, [](void* t){ SDL_DestroyTexture(static_cast<SDL_Texture*>(t)); });
+        // store under original asset key (path) so callers using logical asset names find them
+        resourceManager_->put(path, sp);
+    }
+
     loadedTasks_.fetch_add(1);
     clearCurrentLoadingFile();
 

src/app/TextureLoader.h

@@ -6,6 +6,7 @@
 #include <mutex>
 #include <string>
 #include <vector>
+#include "../resources/ResourceManager.h"
 
 class TextureLoader {
 public:
@@ -16,6 +17,8 @@ public:
         std::vector<std::string>& assetLoadErrors,
         std::mutex& assetLoadErrorsMutex);
 
+    void setResourceManager(resources::ResourceManager* mgr) { resourceManager_ = mgr; }
+
     SDL_Texture* loadFromImage(SDL_Renderer* renderer, const std::string& path, int* outW = nullptr, int* outH = nullptr);
 
 private:
@@ -28,4 +31,6 @@ private:
     void setCurrentLoadingFile(const std::string& filename);
     void clearCurrentLoadingFile();
     void recordAssetLoadError(const std::string& message);
+
+    resources::ResourceManager* resourceManager_ = nullptr;
 };

src/audio/Audio.cpp

@@ -118,6 +118,7 @@ static bool decodeMP3(const std::string& path, std::vector<int16_t>& outPCM, int
     outCh = static_cast<int>(clientFormat.mChannelsPerFrame);
     return !outPCM.empty();
 }
+
 #else
 static bool decodeMP3(const std::string& path, std::vector<int16_t>& outPCM, int& outRate, int& outCh){
     (void)outPCM; (void)outRate; (void)outCh; (void)path;
@@ -184,6 +185,8 @@ void Audio::skipToNextTrack(){
 void Audio::toggleMute(){ muted=!muted; }
 void Audio::setMuted(bool m){ muted=m; }
 
+bool Audio::isMuted() const { return muted; }
+
 void Audio::nextTrack(){
     if(tracks.empty()) { current = -1; return; }
     // Try every track once to find a decodable one

src/audio/Audio.h

@@ -32,29 +32,27 @@ public:
     void setSoundVolume(float volume) override;
     bool isMusicPlaying() const override;
 
-    // Existing Audio class methods
-    bool init();                  // initialize backend (MF on Windows)
-    void addTrack(const std::string& path); // decode MP3 -> PCM16 stereo 44100
-    void addTrackAsync(const std::string& path); // add track for background loading
-    void startBackgroundLoading(); // start background thread for loading
-    void waitForLoadingComplete(); // wait for all tracks to finish loading
-    bool isLoadingComplete() const; // check if background loading is done
-    int getLoadedTrackCount() const; // get number of tracks loaded so far
-    void shuffle();               // randomize order
-    void start();                 // begin playback
-    void skipToNextTrack();       // advance to the next music track
-    void toggleMute();
+    // Additional IAudioSystem methods (forwarded to concrete implementation)
+    bool init() override;
+    void shutdown() override;
+    void addTrack(const std::string& path) override;
+    void addTrackAsync(const std::string& path) override;
+    void startBackgroundLoading() override;
+    bool isLoadingComplete() const override;
+    int getLoadedTrackCount() const override;
+    void start() override;
+    void skipToNextTrack() override;
+    void shuffle() override;
+    void toggleMute() override;
+    bool isMuted() const override;
     void setMuted(bool m);
-    bool isMuted() const { return muted; }
-    
-    // Menu music support
-    void setMenuTrack(const std::string& path);
-    void playMenuMusic();
-    void playGameMusic();
-    
-    // Queue a sound effect to mix over the music (pcm can be mono/stereo, any rate; will be converted)
-    void playSfx(const std::vector<int16_t>& pcm, int channels, int rate, float volume);
-    void shutdown();
+    void setMenuTrack(const std::string& path) override;
+    void playMenuMusic() override;
+    void playGameMusic() override;
+    void playSfx(const std::vector<int16_t>& pcm, int channels, int rate, float volume) override;
+
+    // Existing Audio class helper methods
+    void waitForLoadingComplete(); // wait for all tracks to finish loading
 private:
     Audio()=default; ~Audio()=default; Audio(const Audio&)=delete; Audio& operator=(const Audio&)=delete;
     static void SDLCALL streamCallback(void* userdata, SDL_AudioStream* stream, int additional, int total);

src/audio/AudioManager.cpp

@@ -0,0 +1,15 @@
+#include "AudioManager.h"
+#include "Audio.h"
+
+static IAudioSystem* g_audioSystem = nullptr;
+
+IAudioSystem* AudioManager::get() {
+    if (!g_audioSystem) {
+        g_audioSystem = &Audio::instance();
+    }
+    return g_audioSystem;
+}
+
+void AudioManager::set(IAudioSystem* sys) {
+    g_audioSystem = sys;
+}

src/audio/AudioManager.h

@@ -0,0 +1,11 @@
+#pragma once
+
+#include "../core/interfaces/IAudioSystem.h"
+
+class AudioManager {
+public:
+    // Get the currently registered audio system (may return Audio::instance())
+    static IAudioSystem* get();
+    // Replace the audio system (for tests or different backends)
+    static void set(IAudioSystem* sys);
+};

src/audio/SoundEffect.cpp

@@ -2,6 +2,7 @@
 #include "SoundEffect.h"
 #include <SDL3/SDL.h>
 #include "audio/Audio.h"
+#include "audio/AudioManager.h"
 #include <cstdio>
 #include <algorithm>
 #include <random>
@@ -93,7 +94,9 @@ void SimpleAudioPlayer::playSound(const std::vector<int16_t>& pcmData, int chann
         return;
     }
     // Route through shared Audio mixer so SFX always play over music
-    Audio::instance().playSfx(pcmData, channels, sampleRate, volume);
+    if (auto sys = AudioManager::get()) {
+        sys->playSfx(pcmData, channels, sampleRate, volume);
+    }
 }
 
 bool SoundEffect::loadWAV(const std::string& filePath) {

src/core/Settings.cpp

@@ -21,7 +21,11 @@ std::string Settings::getSettingsPath() {
 bool Settings::load() {
     std::ifstream file(getSettingsPath());
     if (!file.is_open()) {
-        SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION, "Settings file not found, using defaults");
+        SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION, "Settings file not found, using defaults. Creating settings file with defaults.");
+        // Persist defaults so next run has an explicit settings.ini
+        try {
+            save();
+        } catch (...) {}
         return false;
     }
     

src/core/Settings.h

@@ -48,7 +48,8 @@ private:
     Settings& operator=(const Settings&) = delete;
     
     // Settings values
-    bool m_fullscreen = false;
+    // Default to fullscreen on first run when no settings.ini exists
+    bool m_fullscreen = true;
     bool m_musicEnabled = true;
     bool m_soundEnabled = true;
     bool m_debugEnabled = false;

src/core/application/ApplicationManager.cpp

@@ -7,6 +7,7 @@
 #include "../interfaces/IInputHandler.h"
 #include <filesystem>
 #include "../../audio/Audio.h"
+#include "../../audio/AudioManager.h"
 #include "../../audio/SoundEffect.h"
 #include "../../persistence/Scores.h"
 #include "../../states/State.h"
@@ -25,15 +26,26 @@
 #include "../../graphics/effects/Starfield.h"
 #include "../../graphics/renderers/GameRenderer.h"
 #include "../../gameplay/core/Game.h"
+#include "../../gameplay/coop/CoopGame.h"
 #include "../../gameplay/effects/LineEffect.h"
 #include <SDL3/SDL.h>
 #include <SDL3_image/SDL_image.h>
 #include <SDL3_ttf/SDL_ttf.h>
 #include "../../utils/ImagePathResolver.h"
 #include <iostream>
+#include "../../video/VideoPlayer.h"
 #include <cmath>
 #include <fstream>
 #include <algorithm>
+#ifdef _WIN32
+#define WIN32_LEAN_AND_MEAN
+#ifndef NOMINMAX
+#define NOMINMAX
+#endif
+#include <windows.h>
+#include <shellapi.h>
+#endif
+// (Intro video playback is now handled in-process via VideoPlayer)
 
 ApplicationManager::ApplicationManager() = default;
 
@@ -54,7 +66,15 @@ void ApplicationManager::renderLoading(ApplicationManager* app, RenderManager& r
         if (winW_actual > 0 && winH_actual > 0) app->m_starfield3D->resize(winW_actual, winH_actual);
         app->m_starfield3D->draw(renderer.getSDLRenderer());
     }
-
+    // If intro video is playing, render it instead of the loading UI
+    if (app->m_introStarted && app->m_videoPlayer) {
+        SDL_Renderer* sdlR = renderer.getSDLRenderer();
+        int winW=0, winH=0; renderer.getWindowSize(winW, winH);
+        app->m_videoPlayer->render(sdlR, winW, winH);
+        SDL_SetRenderViewport(renderer.getSDLRenderer(), nullptr);
+        SDL_SetRenderScale(renderer.getSDLRenderer(), 1.0f, 1.0f);
+        return;
+    }
     SDL_Rect logicalVP = {0,0,0,0};
     float logicalScale = 1.0f;
     if (app->m_renderManager) {
@@ -248,7 +268,7 @@ void ApplicationManager::shutdown() {
     m_running = false;
 
     // Stop audio systems before tearing down SDL to avoid aborts/asserts
-    Audio::instance().shutdown();
+    if (auto sys = AudioManager::get()) sys->shutdown();
     SoundEffectManager::instance().shutdown();
 
     // Cleanup in reverse order of initialization
@@ -362,11 +382,11 @@ bool ApplicationManager::initializeManagers() {
 
                 // M: Toggle/mute music; start playback if unmuting and not started yet
                 if (!consume && sc == SDL_SCANCODE_M) {
-                    Audio::instance().toggleMute();
+                    if (auto sys = AudioManager::get()) sys->toggleMute();
                     m_musicEnabled = !m_musicEnabled;
-                    if (m_musicEnabled && !m_musicStarted && Audio::instance().getLoadedTrackCount() > 0) {
-                        Audio::instance().shuffle();
-                        Audio::instance().start();
+                    if (m_musicEnabled && !m_musicStarted && AudioManager::get() && AudioManager::get()->getLoadedTrackCount() > 0) {
+                        AudioManager::get()->shuffle();
+                        AudioManager::get()->start();
                         m_musicStarted = true;
                     }
                     consume = true;
@@ -374,11 +394,7 @@ bool ApplicationManager::initializeManagers() {
 
                 // N: Skip to next song in the playlist (or restart menu track)
                 if (!consume && sc == SDL_SCANCODE_N) {
-                    Audio::instance().skipToNextTrack();
-                    if (!m_musicStarted && Audio::instance().getLoadedTrackCount() > 0) {
-                        m_musicStarted = true;
-                        m_musicEnabled = true;
-                    }
+                    if (auto sys = AudioManager::get()) { sys->skipToNextTrack(); if (!m_musicStarted && sys->getLoadedTrackCount() > 0) { m_musicStarted = true; m_musicEnabled = true; } }
                     consume = true;
                 }
 
@@ -496,13 +512,13 @@ void ApplicationManager::registerServices() {
         SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION, "Registered IInputHandler service");
     }
     
-    // Register Audio system singleton
-    auto& audioInstance = Audio::instance();
-    auto audioPtr = std::shared_ptr<Audio>(&audioInstance, [](Audio*) {
-        // Custom deleter that does nothing since Audio is a singleton
-    });
-    m_serviceContainer.registerSingleton<IAudioSystem>(audioPtr);
-    SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION, "Registered IAudioSystem service");
+    // Register Audio system singleton (via AudioManager)
+    IAudioSystem* audioInstance = AudioManager::get();
+    if (audioInstance) {
+        std::shared_ptr<IAudioSystem> audioPtr(audioInstance, [](IAudioSystem*){});
+        m_serviceContainer.registerSingleton<IAudioSystem>(audioPtr);
+        SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION, "Registered IAudioSystem service");
+    }
     
     SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION, "Service registration completed successfully");
 }
@@ -561,6 +577,7 @@ bool ApplicationManager::initializeGame() {
         m_lineEffect->init(m_renderManager->getSDLRenderer());
     }
     m_game = std::make_unique<Game>(m_startLevelSelection);
+    m_coopGame = std::make_unique<CoopGame>(m_startLevelSelection);
     // Wire up sound callbacks as main.cpp did
     if (m_game) {
         // Apply global gravity speed multiplier from config
@@ -580,13 +597,25 @@ bool ApplicationManager::initializeGame() {
         });
     }
 
+    if (m_coopGame) {
+        // TODO: tune gravity with Config and shared level scaling once coop rules are finalized
+        m_coopGame->reset(m_startLevelSelection);
+        // Wire coop sound callback to reuse same clear-line VO/SFX behavior
+        m_coopGame->setSoundCallback([&](int linesCleared){
+            SoundEffectManager::instance().playSound("clear_line", 1.0f);
+            if (linesCleared == 2) SoundEffectManager::instance().playRandomSound({"nice_combo"}, 1.0f);
+            else if (linesCleared == 3) SoundEffectManager::instance().playRandomSound({"great_move"}, 1.0f);
+            else if (linesCleared == 4) SoundEffectManager::instance().playRandomSound({"amazing"}, 1.0f);
+        });
+    }
+
     // Prepare a StateContext-like struct by setting up handlers that capture
     // pointers and flags. State objects in this refactor expect these to be
     // available via StateManager event/update/render hooks, so we'll store them
     // as lambdas that reference members here.
 
     // Start background music loading similar to main.cpp: Audio init + file discovery
-    Audio::instance().init();
+    if (auto sys = AudioManager::get()) sys->init();
     // Discover available tracks (up to 100) and queue for background loading
     m_totalTracks = 0;
     std::vector<std::string> trackPaths;
@@ -602,15 +631,15 @@ bool ApplicationManager::initializeGame() {
     }
     m_totalTracks = static_cast<int>(trackPaths.size());
     for (const auto& path : trackPaths) {
-        Audio::instance().addTrackAsync(path);
+        if (auto sys = AudioManager::get()) sys->addTrackAsync(path);
     }
     if (m_totalTracks > 0) {
-        Audio::instance().startBackgroundLoading();
-    // Kick off playback now; Audio will pick a track once decoded.
-    // Do not mark as started yet; we'll flip the flag once a track is actually loaded.
-    if (m_musicEnabled) {
-            Audio::instance().shuffle();
-            Audio::instance().start();
+        if (auto sys = AudioManager::get()) sys->startBackgroundLoading();
+        // Kick off playback now; Audio will pick a track once decoded.
+        // Do not mark as started yet; we'll flip the flag once a track is actually loaded.
+        if (m_musicEnabled) {
+            if (auto sys = AudioManager::get()) { sys->shuffle(); sys->start(); }
+            m_musicStarted = true;
         }
         m_currentTrackLoading = 1; // mark started
     }
@@ -621,6 +650,7 @@ bool ApplicationManager::initializeGame() {
     {
         m_stateContext.stateManager = m_stateManager.get();
         m_stateContext.game = m_game.get();
+        m_stateContext.coopGame = m_coopGame.get();
         m_stateContext.scores = m_scoreManager.get();
         m_stateContext.starfield = m_starfield.get();
         m_stateContext.starfield3D = m_starfield3D.get();
@@ -765,17 +795,44 @@ void ApplicationManager::setupStateHandlers() {
                 m_starfield3D->update(deltaTime / 1000.0f);
             }
 
-            // Check if loading is complete and transition to menu
+            // Check if loading is complete and transition to next stage
             if (m_assetManager->isLoadingComplete()) {
-                SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION, "Loading complete, transitioning to Menu");
-                
+                SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION, "Loading complete, handling post-load flow");
+
                 // Update texture pointers now that assets are loaded
                 m_stateContext.backgroundTex = m_assetManager->getTexture("background");
                 m_stateContext.blocksTex = m_assetManager->getTexture("blocks");
-                
-                bool ok = m_stateManager->setState(AppState::Menu);
-                SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION, "setState(AppState::Menu) returned %d", ok ? 1 : 0);
-                traceFile("- to Menu returned");
+
+                            // If an intro video exists and hasn't been started, attempt to play it in-process
+                            std::filesystem::path introPath = m_introPath;
+                            if (!m_introStarted && std::filesystem::exists(introPath)) {
+                                SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION, "Intro video found: %s", introPath.string().c_str());
+                                try {
+                                    if (!m_videoPlayer) m_videoPlayer = std::make_unique<VideoPlayer>();
+                                    SDL_Renderer* sdlRend = (m_renderManager) ? m_renderManager->getSDLRenderer() : nullptr;
+                                    if (m_videoPlayer->open(introPath.string(), sdlRend)) {
+                                        m_introStarted = true;
+                                        SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION, "Intro video started in-process");
+                                    } else {
+                                        SDL_LogWarn(SDL_LOG_CATEGORY_APPLICATION, "VideoPlayer failed to open intro; skipping");
+                                        m_stateManager->setState(AppState::Playing);
+                                    }
+                                } catch (const std::exception& ex) {
+                                    SDL_LogWarn(SDL_LOG_CATEGORY_APPLICATION, "Exception while starting VideoPlayer: %s", ex.what());
+                                    m_stateManager->setState(AppState::Playing);
+                                }
+                            } else if (m_introStarted) {
+                                // Let VideoPlayer decode frames; once finished, transition to playing
+                                if (m_videoPlayer) m_videoPlayer->update();
+                                if (!m_videoPlayer || m_videoPlayer->isFinished()) {
+                                    SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION, "Intro video finished (in-process), transitioning to Playing");
+                                    m_stateManager->setState(AppState::Playing);
+                                }
+                            } else {
+                                // No intro to play; transition directly to Playing
+                                SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION, "No intro video; transitioning to Playing");
+                                m_stateManager->setState(AppState::Playing);
+                            }
             }
         });
 
@@ -881,15 +938,15 @@ void ApplicationManager::setupStateHandlers() {
             // Start music as soon as at least one track has decoded (don’t wait for all)
                 // Start music as soon as at least one track has decoded (don't wait for all)
             if (m_musicEnabled && !m_musicStarted) {
-                if (Audio::instance().getLoadedTrackCount() > 0) {
-                    Audio::instance().shuffle();
-                    Audio::instance().start();
-                    m_musicStarted = true;
+                if (auto sys = AudioManager::get()) {
+                    if (sys->getLoadedTrackCount() > 0) { sys->shuffle(); sys->start(); m_musicStarted = true; }
                 }
             }
             // Track completion status for UI
-            if (!m_musicLoaded && Audio::instance().isLoadingComplete()) {
-                m_musicLoaded = true;
+            if (!m_musicLoaded) {
+                if (auto sys = AudioManager::get()) {
+                    if (sys->isLoadingComplete()) m_musicLoaded = true;
+                }
             }
         });
 
@@ -917,8 +974,8 @@ void ApplicationManager::setupStateHandlers() {
                     m_showExitConfirmPopup = true;
                     return;
                 }
-                // S: toggle SFX enable state (music handled globally)
-                if (event.key.scancode == SDL_SCANCODE_S) {
+                // K: toggle SFX enable state (music handled globally)
+                if (event.key.scancode == SDL_SCANCODE_K) {
                     SoundEffectManager::instance().setEnabled(!SoundEffectManager::instance().isEnabled());
                 }
             }
@@ -1217,13 +1274,25 @@ void ApplicationManager::setupStateHandlers() {
                 // "GAME OVER" title
                 font.draw(renderer.getSDLRenderer(), LOGICAL_W * 0.5f - 120, 140, "GAME OVER", 3.0f, {255, 80, 60, 255});
                 
-                // Game stats
+                // Game stats (single-player or coop combined)
                 char buf[128];
-                std::snprintf(buf, sizeof(buf), "SCORE %d  LINES %d  LEVEL %d", 
-                    m_stateContext.game->score(), 
-                    m_stateContext.game->lines(), 
-                    m_stateContext.game->level());
-                font.draw(renderer.getSDLRenderer(), LOGICAL_W * 0.5f - 180, 220, buf, 1.2f, {220, 220, 230, 255});
+                if (m_stateContext.game && m_stateContext.game->getMode() == GameMode::Cooperate && m_stateContext.coopGame) {
+                    int leftScore = m_stateContext.coopGame->score(::CoopGame::PlayerSide::Left);
+                    int rightScore = m_stateContext.coopGame->score(::CoopGame::PlayerSide::Right);
+                    int total = leftScore + rightScore;
+                    std::snprintf(buf, sizeof(buf), "SCORE %d + %d = %d  LINES %d  LEVEL %d",
+                        leftScore,
+                        rightScore,
+                        total,
+                        m_stateContext.coopGame->lines(),
+                        m_stateContext.coopGame->level());
+                } else {
+                    std::snprintf(buf, sizeof(buf), "SCORE %d  LINES %d  LEVEL %d",
+                        m_stateContext.game ? m_stateContext.game->score() : 0,
+                        m_stateContext.game ? m_stateContext.game->lines() : 0,
+                        m_stateContext.game ? m_stateContext.game->level() : 0);
+                }
+                font.draw(renderer.getSDLRenderer(), LOGICAL_W * 0.5f - 220, 220, buf, 1.2f, {220, 220, 230, 255});
                 
                 // Instructions
                 font.draw(renderer.getSDLRenderer(), LOGICAL_W * 0.5f - 120, 270, "PRESS ENTER / SPACE", 1.2f, {200, 200, 220, 255});
@@ -1237,74 +1306,160 @@ void ApplicationManager::setupStateHandlers() {
     m_stateManager->registerUpdateHandler(AppState::Playing,
         [this](double frameMs) {
             if (!m_stateContext.game) return;
-            
+
+            const bool coopActive = m_stateContext.game->getMode() == GameMode::Cooperate && m_stateContext.coopGame;
+
             // Get current keyboard state
             const bool *ks = SDL_GetKeyboardState(nullptr);
-            bool left = ks[SDL_SCANCODE_LEFT] || ks[SDL_SCANCODE_A];
-            bool right = ks[SDL_SCANCODE_RIGHT] || ks[SDL_SCANCODE_D];
-            bool down = ks[SDL_SCANCODE_DOWN] || ks[SDL_SCANCODE_S];
-            
-            // Handle soft drop
-            m_stateContext.game->setSoftDropping(down && !m_stateContext.game->isPaused());
-            
-            // Handle DAS/ARR movement timing (from original main.cpp)
-            int moveDir = 0;
-            if (left && !right)
-                moveDir = -1;
-            else if (right && !left)
-                moveDir = +1;
-            
-            if (moveDir != 0 && !m_stateContext.game->isPaused()) {
-                if ((moveDir == -1 && !m_leftHeld) || (moveDir == +1 && !m_rightHeld)) {
-                    // First press - immediate movement
-                    m_stateContext.game->move(moveDir);
-                    m_moveTimerMs = DAS;  // Set initial delay
-                } else {
-                    // Key held - handle repeat timing
-                    m_moveTimerMs -= frameMs;
-                    if (m_moveTimerMs <= 0) {
-                        m_stateContext.game->move(moveDir);
-                        m_moveTimerMs += ARR;  // Set repeat rate
-                    }
-                }
-            } else {
-                m_moveTimerMs = 0;  // Reset timer when no movement
-            }
-            
-            // Update held state for next frame
-            m_leftHeld = left;
-            m_rightHeld = right;
-            
-            // Handle soft drop boost
-            if (down && !m_stateContext.game->isPaused()) {
-                m_stateContext.game->softDropBoost(frameMs);
-            }
-            
-            // Delegate to PlayingState for other updates (gravity, line effects)
-            if (m_playingState) {
-                m_playingState->update(frameMs);
-            }
 
-            // Update background fade progression (match main.cpp semantics approx)
-            // Duration 1200ms fade (same as LEVEL_FADE_DURATION used in main.cpp snippets)
-            const float LEVEL_FADE_DURATION = 1200.0f;
-            if (m_nextLevelBackgroundTex) {
-                m_levelFadeElapsed += (float)frameMs;
-                m_levelFadeAlpha = std::min(1.0f, m_levelFadeElapsed / LEVEL_FADE_DURATION);
-            }
-            
-            // Check for game over and transition to GameOver state
-            if (m_stateContext.game->isGameOver()) {
-                // Submit score before transitioning
-                if (m_stateContext.scores) {
-                    m_stateContext.scores->submit(
-                        m_stateContext.game->score(), 
-                        m_stateContext.game->lines(), 
-                        m_stateContext.game->level(), 
-                        m_stateContext.game->elapsed()
-                    );
+            if (coopActive) {
+                // Paused: suppress all continuous input so pieces don't drift while paused.
+                if (m_stateContext.game->isPaused()) {
+                    m_stateContext.coopGame->setSoftDropping(CoopGame::PlayerSide::Left, false);
+                    m_stateContext.coopGame->setSoftDropping(CoopGame::PlayerSide::Right, false);
+                    m_p1MoveTimerMs = 0.0;
+                    m_p2MoveTimerMs = 0.0;
+                    m_p1LeftHeld = false;
+                    m_p1RightHeld = false;
+                    m_p2LeftHeld = false;
+                    m_p2RightHeld = false;
+                    return;
+                }
+
+                auto handleSide = [&](CoopGame::PlayerSide side,
+                                      bool leftHeld,
+                                      bool rightHeld,
+                                      double& timer,
+                                      SDL_Scancode leftKey,
+                                      SDL_Scancode rightKey,
+                                      SDL_Scancode downKey) {
+                    bool left = ks[leftKey];
+                    bool right = ks[rightKey];
+                    bool down = ks[downKey];
+
+                    // Soft drop flag
+                    m_stateContext.coopGame->setSoftDropping(side, down);
+
+                    int moveDir = 0;
+                    if (left && !right) moveDir = -1;
+                    else if (right && !left) moveDir = +1;
+
+                    if (moveDir != 0) {
+                        if ((moveDir == -1 && !leftHeld) || (moveDir == +1 && !rightHeld)) {
+                            // First press - immediate movement
+                            m_stateContext.coopGame->move(side, moveDir);
+                            timer = DAS;
+                        } else {
+                            timer -= frameMs;
+                            if (timer <= 0) {
+                                m_stateContext.coopGame->move(side, moveDir);
+                                timer += ARR;
+                            }
+                        }
+                    } else {
+                        timer = 0.0;
+                    }
+
+                    // Soft drop boost: coop uses same gravity path; fall acceleration handled inside tickGravity
+                };
+
+                // Left player (WASD): A/D horizontal, S soft drop
+                handleSide(CoopGame::PlayerSide::Left, m_p1LeftHeld, m_p1RightHeld, m_p1MoveTimerMs,
+                           SDL_SCANCODE_A, SDL_SCANCODE_D, SDL_SCANCODE_S);
+                // Right player (arrows): Left/Right horizontal, Down soft drop
+                handleSide(CoopGame::PlayerSide::Right, m_p2LeftHeld, m_p2RightHeld, m_p2MoveTimerMs,
+                           SDL_SCANCODE_LEFT, SDL_SCANCODE_RIGHT, SDL_SCANCODE_DOWN);
+
+                // Update held flags for next frame
+                m_p1LeftHeld = ks[SDL_SCANCODE_A];
+                m_p1RightHeld = ks[SDL_SCANCODE_D];
+                m_p2LeftHeld = ks[SDL_SCANCODE_LEFT];
+                m_p2RightHeld = ks[SDL_SCANCODE_RIGHT];
+
+                // Gravity / effects
+                m_stateContext.coopGame->tickGravity(frameMs);
+                m_stateContext.coopGame->updateVisualEffects(frameMs);
+
+                // Delegate to PlayingState for any ancillary updates (renderer transport bookkeeping)
+                if (m_playingState) {
+                    m_playingState->update(frameMs);
+                }
+
+                // Game over transition for coop
+                if (m_stateContext.coopGame->isGameOver()) {
+                    m_stateManager->setState(AppState::GameOver);
+                }
+
+            } else {
+                bool left = ks[SDL_SCANCODE_LEFT] || ks[SDL_SCANCODE_A];
+                bool right = ks[SDL_SCANCODE_RIGHT] || ks[SDL_SCANCODE_D];
+                bool down = ks[SDL_SCANCODE_DOWN] || ks[SDL_SCANCODE_S];
+                
+                // Handle soft drop
+                m_stateContext.game->setSoftDropping(down && !m_stateContext.game->isPaused());
+                
+                // Handle DAS/ARR movement timing (from original main.cpp)
+                int moveDir = 0;
+                if (left && !right)
+                    moveDir = -1;
+                else if (right && !left)
+                    moveDir = +1;
+                
+                if (moveDir != 0 && !m_stateContext.game->isPaused()) {
+                    if ((moveDir == -1 && !m_leftHeld) || (moveDir == +1 && !m_rightHeld)) {
+                        // First press - immediate movement
+                        m_stateContext.game->move(moveDir);
+                        m_moveTimerMs = DAS;  // Set initial delay
+                    } else {
+                        // Key held - handle repeat timing
+                        m_moveTimerMs -= frameMs;
+                        if (m_moveTimerMs <= 0) {
+                            m_stateContext.game->move(moveDir);
+                            m_moveTimerMs += ARR;  // Set repeat rate
+                        }
+                    }
+                } else {
+                    m_moveTimerMs = 0;  // Reset timer when no movement
+                }
+                
+                // Update held state for next frame
+                m_leftHeld = left;
+                m_rightHeld = right;
+                
+                // Handle soft drop boost
+                if (down && !m_stateContext.game->isPaused()) {
+                    m_stateContext.game->softDropBoost(frameMs);
+                }
+                
+                // Delegate to PlayingState for other updates (gravity, line effects)
+                if (m_playingState) {
+                    m_playingState->update(frameMs);
+                }
+
+                // Update background fade progression (match main.cpp semantics approx)
+                // Duration 1200ms fade (same as LEVEL_FADE_DURATION used in main.cpp snippets)
+                const float LEVEL_FADE_DURATION = 1200.0f;
+                if (m_nextLevelBackgroundTex) {
+                    m_levelFadeElapsed += (float)frameMs;
+                    m_levelFadeAlpha = std::min(1.0f, m_levelFadeElapsed / LEVEL_FADE_DURATION);
+                }
+                
+                // Check for game over and transition to GameOver state
+                if (m_stateContext.game->isGameOver()) {
+                    // Submit score before transitioning
+                    if (m_stateContext.scores) {
+                        std::string gt = (m_stateContext.game->getMode() == GameMode::Challenge) ? "challenge" : "classic";
+                        m_stateContext.scores->submit(
+                            m_stateContext.game->score(), 
+                            m_stateContext.game->lines(), 
+                            m_stateContext.game->level(), 
+                            m_stateContext.game->elapsed(),
+                            std::string("PLAYER"),
+                            gt
+                        );
+                    }
+                    m_stateManager->setState(AppState::GameOver);
                 }
-                m_stateManager->setState(AppState::GameOver);
             }
         });
     // Debug overlay: show current window and logical sizes on the right side of the screen

src/core/application/ApplicationManager.h

@@ -17,6 +17,7 @@ class Starfield;
 class Starfield3D;
 class FontAtlas;
 class LineEffect;
+class CoopGame;
 
 // Forward declare state classes (top-level, defined under src/states)
 class LoadingState;
@@ -109,6 +110,7 @@ private:
     std::unique_ptr<ScoreManager> m_scoreManager;
     // Gameplay pieces
     std::unique_ptr<Game> m_game;
+    std::unique_ptr<CoopGame> m_coopGame;
     std::unique_ptr<LineEffect> m_lineEffect;
     
     // DAS/ARR movement timing (from original main.cpp)
@@ -118,6 +120,14 @@ private:
     static constexpr double DAS = 170.0;  // Delayed Auto Shift
     static constexpr double ARR = 40.0;   // Auto Repeat Rate
 
+    // Coop DAS/ARR per player
+    bool m_p1LeftHeld = false;
+    bool m_p1RightHeld = false;
+    bool m_p2LeftHeld = false;
+    bool m_p2RightHeld = false;
+    double m_p1MoveTimerMs = 0.0;
+    double m_p2MoveTimerMs = 0.0;
+
     // State context (must be a member to ensure lifetime)
     StateContext m_stateContext;
     
@@ -143,6 +153,11 @@ private:
     float m_logoAnimCounter = 0.0f;
     bool m_helpOverlayPausedGame = false;
 
+    // Intro video playback (in-process via FFmpeg)
+    bool m_introStarted = false;
+    std::string m_introPath = "assets/videos/spacetris_intro.mp4";
+    std::unique_ptr<class VideoPlayer> m_videoPlayer;
+
     // Gameplay background (per-level) with fade, mirroring main.cpp behavior
     SDL_Texture* m_levelBackgroundTex = nullptr;
     SDL_Texture* m_nextLevelBackgroundTex = nullptr; // used during fade transitions

src/core/assets/AssetManager.cpp

@@ -1,12 +1,15 @@
 #include "AssetManager.h"
 #include "../../graphics/ui/Font.h"
 #include "../../audio/Audio.h"
+#include "../../audio/AudioManager.h"
 #include "../../audio/SoundEffect.h"
 #include <SDL3/SDL.h>
 #include <SDL3_image/SDL_image.h>
 #include <SDL3_ttf/SDL_ttf.h>
 #include <filesystem>
 #include "../../utils/ImagePathResolver.h"
+#include "../../core/Config.h"
+#include "../../resources/AssetPaths.h"
 
 AssetManager::AssetManager() 
     : m_renderer(nullptr)
@@ -38,7 +41,7 @@ bool AssetManager::initialize(SDL_Renderer* renderer) {
     m_renderer = renderer;
     
     // Get references to singleton systems
-    m_audioSystem = &Audio::instance();
+    m_audioSystem = AudioManager::get();
     m_soundSystem = &SoundEffectManager::instance();
 
     m_initialized = true;
@@ -103,7 +106,34 @@ SDL_Texture* AssetManager::loadTexture(const std::string& id, const std::string&
 
 SDL_Texture* AssetManager::getTexture(const std::string& id) const {
     auto it = m_textures.find(id);
-    return (it != m_textures.end()) ? it->second : nullptr;
+    if (it != m_textures.end()) return it->second;
+
+    // Lazy fallback: attempt to load well-known short ids from configured asset paths.
+    std::vector<std::string> candidates;
+    if (id == "logo") {
+        candidates.push_back(std::string(Assets::LOGO));
+        candidates.push_back(Config::Assets::LOGO_BMP);
+    } else if (id == "logo_small") {
+        candidates.push_back(Config::Assets::LOGO_SMALL_BMP);
+        candidates.push_back(std::string(Assets::LOGO));
+    } else if (id == "background") {
+        candidates.push_back(std::string(Assets::MAIN_SCREEN));
+        candidates.push_back(Config::Assets::BACKGROUND_BMP);
+    } else if (id == "blocks") {
+        candidates.push_back(std::string(Assets::BLOCKS_SPRITE));
+        candidates.push_back(Config::Assets::BLOCKS_BMP);
+    } else if (id == "asteroids") {
+        candidates.push_back(std::string(Assets::ASTEROID_SPRITE));
+    }
+
+    for (const auto &candidatePath : candidates) {
+        if (candidatePath.empty()) continue;
+        AssetManager* self = const_cast<AssetManager*>(this);
+        SDL_Texture* tex = self->loadTexture(id, candidatePath);
+        if (tex) return tex;
+    }
+
+    return nullptr;
 }
 
 bool AssetManager::unloadTexture(const std::string& id) {

src/core/assets/AssetManager.h

@@ -7,12 +7,12 @@
 #include <memory>
 #include <functional>
 #include "../interfaces/IAssetLoader.h"
-#include "../interfaces/IAssetLoader.h"
 
 // Forward declarations
 class FontAtlas;
 class Audio;
 class SoundEffectManager;
+class IAudioSystem;
 
 /**
  * AssetManager - Centralized resource management following SOLID principles
@@ -121,7 +121,7 @@ private:
 
     // System references
     SDL_Renderer* m_renderer;
-    Audio* m_audioSystem;              // Pointer to singleton
+    IAudioSystem* m_audioSystem;              // Pointer to audio system (IAudioSystem)
     SoundEffectManager* m_soundSystem; // Pointer to singleton
 
     // Configuration

src/core/interfaces/IAudioSystem.h

@@ -1,6 +1,8 @@
 #pragma once
 
 #include <string>
+#include <vector>
+#include <cstdint>
 
 /**
  * @brief Abstract interface for audio system operations
@@ -52,4 +54,28 @@ public:
      * @return true if music is playing, false otherwise
      */
     virtual bool isMusicPlaying() const = 0;
+
+    // Extended control methods used by the application
+    virtual bool init() = 0;
+    virtual void shutdown() = 0;
+
+    virtual void addTrack(const std::string& path) = 0;
+    virtual void addTrackAsync(const std::string& path) = 0;
+    virtual void startBackgroundLoading() = 0;
+    virtual bool isLoadingComplete() const = 0;
+    virtual int getLoadedTrackCount() const = 0;
+
+    virtual void start() = 0;
+    virtual void skipToNextTrack() = 0;
+    virtual void shuffle() = 0;
+
+    virtual void toggleMute() = 0;
+    virtual bool isMuted() const = 0;
+
+    virtual void setMenuTrack(const std::string& path) = 0;
+    virtual void playMenuMusic() = 0;
+    virtual void playGameMusic() = 0;
+
+    // Low-level SFX path (raw PCM) used by internal SFX mixer
+    virtual void playSfx(const std::vector<int16_t>& pcm, int channels, int rate, float volume) = 0;
 };

src/core/state/StateManager.cpp

@@ -156,9 +156,19 @@ void StateManager::render(RenderManager& renderer) {
 }
 
 bool StateManager::isValidState(AppState state) const {
-    // All enum values are currently valid
-    return static_cast<int>(state) >= static_cast<int>(AppState::Loading) &&
-           static_cast<int>(state) <= static_cast<int>(AppState::GameOver);
+    switch (state) {
+        case AppState::Loading:
+        case AppState::Video:
+        case AppState::Menu:
+        case AppState::Options:
+        case AppState::LevelSelector:
+        case AppState::Playing:
+        case AppState::LevelSelect:
+        case AppState::GameOver:
+            return true;
+        default:
+            return false;
+    }
 }
 
 bool StateManager::canTransitionTo(AppState newState) const {
@@ -169,6 +179,7 @@ bool StateManager::canTransitionTo(AppState newState) const {
 const char* StateManager::getStateName(AppState state) const {
     switch (state) {
         case AppState::Loading: return "Loading";
+        case AppState::Video: return "Video";
         case AppState::Menu: return "Menu";
         case AppState::Options: return "Options";
         case AppState::LevelSelector: return "LevelSelector";

src/core/state/StateManager.h

@@ -12,6 +12,7 @@ class RenderManager;
 // Application states used across the app
 enum class AppState {
     Loading,
+    Video,
     Menu,
     Options,
     LevelSelector,

src/gameplay/LineEffect.cpp

@@ -3,6 +3,7 @@
 #include <algorithm>
 #include <cmath>
 #include "audio/Audio.h"
+#include "audio/AudioManager.h"
 
 #ifndef M_PI
 #define M_PI 3.14159265358979323846
@@ -266,6 +267,6 @@ void LineEffect::playLineClearSound(int lineCount) {
     const std::vector<int16_t>* sample = (lineCount == 4) ? &tetrisSample : &lineClearSample;
     if (sample && !sample->empty()) {
         // Mix via shared Audio device so it layers with music
-        Audio::instance().playSfx(*sample, 2, 44100, (lineCount == 4) ? 0.9f : 0.7f);
+        if (auto sys = AudioManager::get()) sys->playSfx(*sample, 2, 44100, (lineCount == 4) ? 0.9f : 0.7f);
     }
 }

src/gameplay/coop/CoopAIController.cpp

@@ -0,0 +1,317 @@
+#include "CoopAIController.h"
+
+#include "CoopGame.h"
+
+#include <algorithm>
+#include <array>
+#include <cmath>
+#include <limits>
+
+namespace {
+
+static bool canPlacePieceForSide(const std::array<CoopGame::Cell, CoopGame::COLS * CoopGame::ROWS>& board,
+                                 const CoopGame::Piece& p,
+                                 CoopGame::PlayerSide side) {
+    for (int cy = 0; cy < 4; ++cy) {
+        for (int cx = 0; cx < 4; ++cx) {
+            if (!CoopGame::cellFilled(p, cx, cy)) {
+                continue;
+            }
+
+            const int bx = p.x + cx;
+            const int by = p.y + cy;
+
+            // Keep the AI strictly in the correct half.
+            if (side == CoopGame::PlayerSide::Right) {
+                if (bx < 10 || bx >= CoopGame::COLS) {
+                    return false;
+                }
+            } else {
+                if (bx < 0 || bx >= 10) {
+                    return false;
+                }
+            }
+
+            // Above the visible board is allowed.
+            if (by < 0) {
+                continue;
+            }
+
+            if (by >= CoopGame::ROWS) {
+                return false;
+            }
+
+            if (board[by * CoopGame::COLS + bx].occupied) {
+                return false;
+            }
+        }
+    }
+    return true;
+}
+
+static int dropYFor(const std::array<CoopGame::Cell, CoopGame::COLS * CoopGame::ROWS>& board,
+                    CoopGame::Piece p,
+                    CoopGame::PlayerSide side) {
+    // Assumes p is currently placeable.
+    while (true) {
+        CoopGame::Piece next = p;
+        next.y += 1;
+        if (!canPlacePieceForSide(board, next, side)) {
+            return p.y;
+        }
+        p = next;
+        if (p.y > CoopGame::ROWS) {
+            return p.y;
+        }
+    }
+}
+
+static void applyPiece(std::array<uint8_t, CoopGame::COLS * CoopGame::ROWS>& occ,
+                      const CoopGame::Piece& p) {
+    for (int cy = 0; cy < 4; ++cy) {
+        for (int cx = 0; cx < 4; ++cx) {
+            if (!CoopGame::cellFilled(p, cx, cy)) {
+                continue;
+            }
+            const int bx = p.x + cx;
+            const int by = p.y + cy;
+            if (by < 0 || by >= CoopGame::ROWS || bx < 0 || bx >= CoopGame::COLS) {
+                continue;
+            }
+            occ[by * CoopGame::COLS + bx] = 1;
+        }
+    }
+}
+
+struct Eval {
+    double score = -std::numeric_limits<double>::infinity();
+    int rot = 0;
+    int x = 10;
+};
+
+static Eval evaluateBestPlacementForSide(const CoopGame& game, CoopGame::PlayerSide side) {
+    const auto& board = game.boardRef();
+
+    std::array<uint8_t, CoopGame::COLS * CoopGame::ROWS> occ{};
+    for (int i = 0; i < CoopGame::COLS * CoopGame::ROWS; ++i) {
+        occ[i] = board[i].occupied ? 1 : 0;
+    }
+
+    const CoopGame::Piece cur = game.current(side);
+
+    Eval best{};
+
+    // Iterate rotations and x positions. IMPORTANT: allow x to go slightly out of bounds
+    // because our pieces are represented in a 4x4 mask and many rotations have leading
+    // empty columns. For example, placing a vertical I/J/L into column 0 often requires
+    // p.x == -1 or p.x == -2 so the filled cells land at bx==0.
+    // canPlacePieceForSide() enforces the actual half-board bounds.
+    for (int rot = 0; rot < 4; ++rot) {
+        int xmin = (side == CoopGame::PlayerSide::Right) ? 6 : -3;
+        int xmax = (side == CoopGame::PlayerSide::Right) ? 22 : 13;
+        for (int x = xmin; x <= xmax; ++x) {
+            CoopGame::Piece p = cur;
+            p.rot = rot;
+            p.x = x;
+
+            // If this rotation/x is illegal at the current y, try near the top spawn band.
+            if (!canPlacePieceForSide(board, p, side)) {
+                p.y = -2;
+                if (!canPlacePieceForSide(board, p, side)) {
+                    continue;
+                }
+            }
+
+            p.y = dropYFor(board, p, side);
+
+            auto occ2 = occ;
+            applyPiece(occ2, p);
+
+            // Count completed full rows (all 20 cols) after placement.
+            int fullRows = 0;
+            for (int y = 0; y < CoopGame::ROWS; ++y) {
+                bool full = true;
+                for (int cx = 0; cx < CoopGame::COLS; ++cx) {
+                    if (!occ2[y * CoopGame::COLS + cx]) {
+                        full = false;
+                        break;
+                    }
+                }
+                if (full) {
+                    ++fullRows;
+                }
+            }
+
+            // Right-half column heights + holes + bumpiness.
+            std::array<int, 10> heights{};
+            int aggregateHeight = 0;
+            int holes = 0;
+
+            for (int c = 0; c < 10; ++c) {
+                const int bx = (side == CoopGame::PlayerSide::Right) ? (10 + c) : c;
+                int h = 0;
+                bool found = false;
+                for (int y = 0; y < CoopGame::ROWS; ++y) {
+                    if (occ2[y * CoopGame::COLS + bx]) {
+                        h = CoopGame::ROWS - y;
+                        found = true;
+                        // Count holes below the first filled cell.
+                        for (int yy = y + 1; yy < CoopGame::ROWS; ++yy) {
+                            if (!occ2[yy * CoopGame::COLS + bx]) {
+                                ++holes;
+                            }
+                        }
+                        break;
+                    }
+                }
+                heights[c] = found ? h : 0;
+                aggregateHeight += heights[c];
+            }
+
+            int bump = 0;
+            for (int i = 0; i < 9; ++i) {
+                bump += std::abs(heights[i] - heights[i + 1]);
+            }
+
+            // Reward sync potential: rows where the right half is full (10..19).
+            int sideHalfFullRows = 0;
+            for (int y = 0; y < CoopGame::ROWS; ++y) {
+                bool full = true;
+                int start = (side == CoopGame::PlayerSide::Right) ? 10 : 0;
+                int end = (side == CoopGame::PlayerSide::Right) ? 20 : 10;
+                for (int bx = start; bx < end; ++bx) {
+                    if (!occ2[y * CoopGame::COLS + bx]) {
+                        full = false;
+                        break;
+                    }
+                }
+                if (full) {
+                    ++sideHalfFullRows;
+                }
+            }
+
+            // Simple heuristic:
+            // - Strongly prefer completed full rows
+            // - Prefer making the right half complete (helps cooperative clears)
+            // - Penalize holes and excessive height/bumpiness
+            double s = 0.0;
+            // Strongly prefer full-line clears across the whole board (rare but best).
+            s += static_cast<double>(fullRows) * 12000.0;
+            // Heavily prefer completing the player's half — make this a primary objective.
+            s += static_cast<double>(sideHalfFullRows) * 6000.0;
+            // Penalize holes and height less aggressively so completing half-rows is prioritized.
+            s -= static_cast<double>(holes) * 180.0;
+            s -= static_cast<double>(aggregateHeight) * 4.0;
+            s -= static_cast<double>(bump) * 10.0;
+
+            // Reduce center bias so edge placements to complete rows are not punished.
+            double centerTarget = (side == CoopGame::PlayerSide::Right) ? 15.0 : 4.5;
+            const double centerBias = -std::abs((x + 1.5) - centerTarget) * 1.0;
+            s += centerBias;
+
+            if (s > best.score) {
+                best.score = s;
+                best.rot = rot;
+                best.x = x;
+            }
+        }
+    }
+
+    return best;
+}
+
+} // namespace
+
+void CoopAIController::reset() {
+    m_lastPieceSeq = 0;
+    m_hasPlan = false;
+    m_targetRot = 0;
+    m_targetX = 10;
+    m_moveTimerMs = 0.0;
+    m_moveDir = 0;
+    m_rotateTimerMs = 0.0;
+}
+
+void CoopAIController::computePlan(const CoopGame& game, CoopGame::PlayerSide side) {
+    const Eval best = evaluateBestPlacementForSide(game, side);
+    m_targetRot = best.rot;
+    m_targetX = best.x;
+    m_hasPlan = true;
+    m_moveTimerMs = 0.0;
+    m_moveDir = 0;
+    m_rotateTimerMs = 0.0;
+}
+
+void CoopAIController::update(CoopGame& game, CoopGame::PlayerSide side, double frameMs) {
+    const uint64_t seq = game.currentPieceSequence(side);
+    if (seq != m_lastPieceSeq) {
+        m_lastPieceSeq = seq;
+        m_hasPlan = false;
+        m_moveTimerMs = 0.0;
+        m_moveDir = 0;
+        m_rotateTimerMs = 0.0;
+    }
+
+    if (!m_hasPlan) {
+        computePlan(game, side);
+    }
+
+    const CoopGame::Piece cur = game.current(side);
+
+    // Clamp negative deltas (defensive; callers should pass >= 0).
+    const double dt = std::max(0.0, frameMs);
+
+    // Update timers.
+    if (m_moveTimerMs > 0.0) {
+        m_moveTimerMs -= dt;
+        if (m_moveTimerMs < 0.0) m_moveTimerMs = 0.0;
+    }
+    if (m_rotateTimerMs > 0.0) {
+        m_rotateTimerMs -= dt;
+        if (m_rotateTimerMs < 0.0) m_rotateTimerMs = 0.0;
+    }
+
+    // Rotate toward target first.
+    const int curRot = ((cur.rot % 4) + 4) % 4;
+    const int tgtRot = ((m_targetRot % 4) + 4) % 4;
+    int diff = (tgtRot - curRot + 4) % 4;
+    if (diff != 0) {
+        // Human-ish rotation rate limiting.
+        if (m_rotateTimerMs <= 0.0) {
+            const int dir = (diff == 3) ? -1 : 1;
+            game.rotate(side, dir);
+            m_rotateTimerMs = m_rotateIntervalMs;
+        }
+        // While rotating, do not also slide horizontally in the same frame.
+        m_moveDir = 0;
+        m_moveTimerMs = 0.0;
+        return;
+    }
+
+    // Move horizontally toward target.
+    int desiredDir = 0;
+    if (cur.x < m_targetX) desiredDir = +1;
+    else if (cur.x > m_targetX) desiredDir = -1;
+
+    if (desiredDir == 0) {
+        // Aligned: do nothing. Gravity controls fall speed (no AI hard drops).
+        m_moveDir = 0;
+        m_moveTimerMs = 0.0;
+        return;
+    }
+
+    // DAS/ARR-style horizontal movement pacing.
+    if (m_moveDir != desiredDir) {
+        // New direction / initial press: move immediately, then wait DAS.
+        game.move(side, desiredDir);
+        m_moveDir = desiredDir;
+        m_moveTimerMs = m_dasMs;
+        return;
+    }
+
+    // Holding direction: repeat every ARR once DAS has elapsed.
+    if (m_moveTimerMs <= 0.0) {
+        game.move(side, desiredDir);
+        m_moveTimerMs = m_arrMs;
+    }
+}

src/gameplay/coop/CoopAIController.h

@@ -0,0 +1,36 @@
+#pragma once
+
+#include <cstdint>
+#include "CoopGame.h"
+
+// Minimal, lightweight AI driver for a CoopGame player side (left or right).
+// It chooses a target rotation/x placement using a simple board heuristic,
+// then steers the active piece toward that target at a human-like input rate.
+class CoopAIController {
+public:
+    CoopAIController() = default;
+
+    void reset();
+
+    // frameMs is the frame delta in milliseconds (same unit used across the gameplay loop).
+    void update(CoopGame& game, CoopGame::PlayerSide side, double frameMs);
+
+private:
+    uint64_t m_lastPieceSeq = 0;
+    bool m_hasPlan = false;
+
+    int m_targetRot = 0;
+    int m_targetX = 10;
+
+    // Input pacing (ms). These intentionally mirror the defaults used for human input.
+    double m_dasMs = 170.0;
+    double m_arrMs = 40.0;
+    double m_rotateIntervalMs = 110.0;
+
+    // Internal timers/state for rate limiting.
+    double m_moveTimerMs = 0.0;
+    int m_moveDir = 0; // -1, 0, +1
+    double m_rotateTimerMs = 0.0;
+
+    void computePlan(const CoopGame& game, CoopGame::PlayerSide side);
+};

src/gameplay/coop/CoopGame.cpp

@@ -0,0 +1,600 @@
+#include "CoopGame.h"
+
+#include <algorithm>
+#include <cmath>
+#include <cstring>
+
+namespace {
+// NES (NTSC) gravity table reused from single-player for level progression (ms per cell)
+constexpr double NES_FPS = 60.0988;
+constexpr double FRAME_MS = 1000.0 / NES_FPS;
+
+struct LevelGravity { int framesPerCell; double levelMultiplier; };
+
+LevelGravity LEVEL_TABLE[30] = {
+    {48,1.0}, {43,1.0}, {38,1.0}, {33,1.0}, {28,1.0}, {23,1.0}, {18,1.0}, {13,1.0}, {8,1.0}, {6,1.0},
+    {5,1.0}, {5,1.0}, {5,1.0}, {4,1.0}, {4,1.0}, {4,1.0}, {3,1.0}, {3,1.0}, {3,1.0}, {2,1.0},
+    {2,1.0}, {2,1.0}, {2,1.0}, {2,1.0}, {2,1.0}, {2,1.0}, {2,1.0}, {2,1.0}, {2,1.0}, {1,1.0}
+};
+
+inline double gravityMsForLevelInternal(int level, double globalMultiplier) {
+    int idx = level < 0 ? 0 : (level >= 29 ? 29 : level);
+    const LevelGravity& lg = LEVEL_TABLE[idx];
+    double frames = lg.framesPerCell * lg.levelMultiplier;
+    return frames * FRAME_MS * globalMultiplier;
+}
+}
+
+namespace {
+// Piece rotation bitmasks (row-major 4x4). Bit 0 = (0,0).
+static const std::array<Shape, PIECE_COUNT> SHAPES = {{
+    Shape{ 0x0F00, 0x2222, 0x00F0, 0x4444 }, // I
+    Shape{ 0x0660, 0x0660, 0x0660, 0x0660 }, // O
+    Shape{ 0x0E40, 0x4C40, 0x4E00, 0x4640 }, // T
+    Shape{ 0x06C0, 0x4620, 0x06C0, 0x4620 }, // S
+    Shape{ 0x0C60, 0x2640, 0x0C60, 0x2640 }, // Z
+    Shape{ 0x08E0, 0x6440, 0x0E20, 0x44C0 }, // J
+    Shape{ 0x02E0, 0x4460, 0x0E80, 0xC440 }, // L
+}};
+}
+
+CoopGame::CoopGame(int startLevel_) {
+    reset(startLevel_);
+}
+
+namespace {
+uint64_t fnv1a64(uint64_t h, const void* data, size_t size) {
+    const uint8_t* p = static_cast<const uint8_t*>(data);
+    for (size_t i = 0; i < size; ++i) {
+        h ^= static_cast<uint64_t>(p[i]);
+        h *= 1099511628211ull;
+    }
+    return h;
+}
+
+template <typename T>
+uint64_t hashPod(uint64_t h, const T& v) {
+    return fnv1a64(h, &v, sizeof(T));
+}
+}
+
+void CoopGame::resetInternal(int startLevel_, const std::optional<uint32_t>& seedOpt) {
+    std::fill(board.begin(), board.end(), Cell{});
+    rowStates.fill(RowHalfState{});
+    completedLines.clear();
+    hardDropCells.clear();
+    hardDropFxId = 0;
+    hardDropShakeTimerMs = 0.0;
+    _score = 0;
+    _lines = 0;
+    _level = startLevel_;
+    startLevel = startLevel_;
+    gravityMs = gravityMsForLevel(_level);
+    gameOver = false;
+    pieceSequence = 0;
+    elapsedMs = 0.0;
+
+    left = PlayerState{};
+    right = PlayerState{ PlayerSide::Right };
+
+    auto initPlayer = [&](PlayerState& ps, uint32_t seed) {
+        ps.canHold = true;
+        ps.hold.type = PIECE_COUNT;
+        ps.softDropping = false;
+        ps.toppedOut = false;
+        ps.fallAcc = 0.0;
+        ps.lockAcc = 0.0;
+        ps.pieceSeq = 0;
+        ps.score = 0;
+        ps.lines = 0;
+        ps.level = startLevel_;
+        ps.tetrisesMade = 0;
+        ps.currentCombo = 0;
+        ps.maxCombo = 0;
+        ps.comboCount = 0;
+        ps.bag.clear();
+        ps.next.type = PIECE_COUNT;
+        ps.rng.seed(seed);
+        refillBag(ps);
+    };
+
+    if (seedOpt.has_value()) {
+        const uint32_t seed = seedOpt.value();
+        initPlayer(left, seed);
+        initPlayer(right, seed ^ 0x9E3779B9u);
+    } else {
+        // Preserve existing behavior: random seed when not in deterministic mode.
+        std::random_device rd;
+        initPlayer(left, static_cast<uint32_t>(rd()));
+        initPlayer(right, static_cast<uint32_t>(rd()));
+    }
+
+    spawn(left);
+    spawn(right);
+    updateRowStates();
+}
+
+void CoopGame::reset(int startLevel_) {
+    resetInternal(startLevel_, std::nullopt);
+}
+
+void CoopGame::resetDeterministic(int startLevel_, uint32_t seed) {
+    resetInternal(startLevel_, seed);
+}
+
+void CoopGame::setSoftDropping(PlayerSide side, bool on) {
+    PlayerState& ps = player(side);
+    auto stepFor = [&](bool soft)->double { return soft ? std::max(5.0, gravityMs / 5.0) : gravityMs; };
+    double oldStep = stepFor(ps.softDropping);
+    double newStep = stepFor(on);
+    if (oldStep <= 0.0 || newStep <= 0.0) {
+        ps.softDropping = on;
+        return;
+    }
+
+    double progress = ps.fallAcc / oldStep;
+    progress = std::clamp(progress, 0.0, 1.0);
+    ps.fallAcc = progress * newStep;
+    ps.softDropping = on;
+}
+
+uint64_t CoopGame::computeStateHash() const {
+    uint64_t h = 1469598103934665603ull;
+
+    // Board
+    for (const auto& c : board) {
+        const uint8_t occ = c.occupied ? 1u : 0u;
+        const uint8_t owner = (c.owner == PlayerSide::Left) ? 0u : 1u;
+        const uint8_t val = static_cast<uint8_t>(std::clamp(c.value, 0, 255));
+        h = hashPod(h, occ);
+        h = hashPod(h, owner);
+        h = hashPod(h, val);
+    }
+
+    auto hashPiece = [&](const Piece& p) {
+        const uint8_t type = static_cast<uint8_t>(p.type);
+        const int32_t rot = p.rot;
+        const int32_t x = p.x;
+        const int32_t y = p.y;
+        h = hashPod(h, type);
+        h = hashPod(h, rot);
+        h = hashPod(h, x);
+        h = hashPod(h, y);
+    };
+
+    auto hashPlayer = [&](const PlayerState& ps) {
+        const uint8_t side = (ps.side == PlayerSide::Left) ? 0u : 1u;
+        h = hashPod(h, side);
+        hashPiece(ps.cur);
+        hashPiece(ps.next);
+        hashPiece(ps.hold);
+        const uint8_t canHoldB = ps.canHold ? 1u : 0u;
+        const uint8_t toppedOutB = ps.toppedOut ? 1u : 0u;
+        h = hashPod(h, canHoldB);
+        h = hashPod(h, toppedOutB);
+        h = hashPod(h, ps.score);
+        h = hashPod(h, ps.lines);
+        h = hashPod(h, ps.level);
+        h = hashPod(h, ps.tetrisesMade);
+        h = hashPod(h, ps.currentCombo);
+        h = hashPod(h, ps.maxCombo);
+        h = hashPod(h, ps.comboCount);
+        h = hashPod(h, ps.pieceSeq);
+
+        const uint32_t bagSize = static_cast<uint32_t>(ps.bag.size());
+        h = hashPod(h, bagSize);
+        for (auto t : ps.bag) {
+            const uint8_t tt = static_cast<uint8_t>(t);
+            h = hashPod(h, tt);
+        }
+    };
+
+    hashPlayer(left);
+    hashPlayer(right);
+
+    // Session-wide counters/stats
+    h = hashPod(h, _score);
+    h = hashPod(h, _lines);
+    h = hashPod(h, _level);
+    h = hashPod(h, _tetrisesMade);
+    h = hashPod(h, _currentCombo);
+    h = hashPod(h, _maxCombo);
+    h = hashPod(h, _comboCount);
+    h = hashPod(h, startLevel);
+    h = hashPod(h, pieceSequence);
+
+    return h;
+}
+
+void CoopGame::move(PlayerSide side, int dx) {
+    PlayerState& ps = player(side);
+    if (gameOver || ps.toppedOut) return;
+    tryMove(ps, dx, 0);
+}
+
+void CoopGame::rotate(PlayerSide side, int dir) {
+    PlayerState& ps = player(side);
+    if (gameOver || ps.toppedOut) return;
+
+    auto minOccupiedY = [&](const Piece& p) -> int {
+        int minY = 999;
+        for (int cy = 0; cy < 4; ++cy) {
+            for (int cx = 0; cx < 4; ++cx) {
+                if (!cellFilled(p, cx, cy)) continue;
+                minY = std::min(minY, p.y + cy);
+            }
+        }
+        return (minY == 999) ? p.y : minY;
+    };
+
+    auto tryApplyWithTopKick = [&](const Piece& candidate) -> bool {
+        // If rotation would place any occupied cell above the visible grid,
+        // kick it down just enough to keep all blocks visible.
+        int minY = minOccupiedY(candidate);
+        int baseDy = (minY < 0) ? -minY : 0;
+
+        // Try minimal adjustment first; allow a couple extra pixels/rows for safety.
+        for (int dy = baseDy; dy <= baseDy + 2; ++dy) {
+            Piece test = candidate;
+            test.y += dy;
+            if (!collides(ps, test)) {
+                ps.cur = test;
+                return true;
+            }
+        }
+        return false;
+    };
+
+    Piece rotated = ps.cur;
+    rotated.rot = (rotated.rot + dir + 4) % 4;
+
+    // Simple wall kick: try in place, then left, then right.
+    if (tryApplyWithTopKick(rotated)) return;
+    rotated.x -= 1;
+    if (tryApplyWithTopKick(rotated)) return;
+    rotated.x += 2;
+    if (tryApplyWithTopKick(rotated)) return;
+}
+
+void CoopGame::hardDrop(PlayerSide side) {
+    PlayerState& ps = player(side);
+    if (gameOver || ps.toppedOut) return;
+
+    hardDropCells.clear();
+    bool moved = false;
+    int dropped = 0;
+    while (tryMove(ps, 0, 1)) {
+        moved = true;
+        dropped++;
+        // Record path for potential effects
+        for (int cy = 0; cy < 4; ++cy) {
+            for (int cx = 0; cx < 4; ++cx) {
+                if (!cellFilled(ps.cur, cx, cy)) continue;
+                int px = ps.cur.x + cx;
+                int py = ps.cur.y + cy;
+                if (py >= 0) {
+                    hardDropCells.push_back(SDL_Point{ px, py });
+                }
+            }
+        }
+    }
+    if (moved) {
+        _score += dropped; // 1 point per cell, matches single-player hard drop
+        ps.score += dropped;
+        hardDropShakeTimerMs = HARD_DROP_SHAKE_DURATION_MS;
+        hardDropFxId++;
+    }
+    lock(ps);
+}
+
+void CoopGame::holdCurrent(PlayerSide side) {
+    PlayerState& ps = player(side);
+    if (gameOver || ps.toppedOut) return;
+    if (!ps.canHold) return;
+    if (ps.hold.type == PIECE_COUNT) {
+        ps.hold = ps.cur;
+        spawn(ps);
+    } else {
+        std::swap(ps.cur, ps.hold);
+        ps.cur.rot = 0;
+        ps.cur.x = columnMin(ps.side) + 3;
+        // Match single-player spawn height (I starts higher)
+        ps.cur.y = (ps.cur.type == PieceType::I) ? -2 : -1;
+        ps.pieceSeq++;
+        pieceSequence++;
+    }
+    ps.canHold = false;
+    ps.lockAcc = 0.0;
+}
+
+void CoopGame::tickGravity(double frameMs) {
+    if (gameOver) return;
+
+    elapsedMs += frameMs;
+
+    auto stepPlayer = [&](PlayerState& ps) {
+        if (ps.toppedOut) return;
+        double step = ps.softDropping ? std::max(5.0, gravityMs / 5.0) : gravityMs;
+        ps.fallAcc += frameMs;
+        while (ps.fallAcc >= step) {
+            ps.fallAcc -= step;
+            if (!tryMove(ps, 0, 1)) {
+                ps.lockAcc += step;
+                if (ps.lockAcc >= LOCK_DELAY_MS) {
+                    lock(ps);
+                    break;
+                }
+            } else {
+                // Award soft drop points when actively holding down
+                if (ps.softDropping) {
+                    _score += 1;
+                    ps.score += 1;
+                }
+                ps.lockAcc = 0.0;
+            }
+        }
+    };
+
+    stepPlayer(left);
+    stepPlayer(right);
+
+    updateRowStates();
+}
+
+void CoopGame::updateVisualEffects(double frameMs) {
+    if (hardDropShakeTimerMs > 0.0) {
+        hardDropShakeTimerMs = std::max(0.0, hardDropShakeTimerMs - frameMs);
+    }
+}
+
+double CoopGame::hardDropShakeStrength() const {
+    if (hardDropShakeTimerMs <= 0.0) return 0.0;
+    return std::clamp(hardDropShakeTimerMs / HARD_DROP_SHAKE_DURATION_MS, 0.0, 1.0);
+}
+
+double CoopGame::gravityMsForLevel(int level) const {
+    return gravityMsForLevelInternal(level, gravityGlobalMultiplier);
+}
+
+bool CoopGame::cellFilled(const Piece& p, int cx, int cy) {
+    if (p.type >= PIECE_COUNT) return false;
+    const Shape& shape = SHAPES[p.type];
+    uint16_t mask = shape[p.rot % 4];
+    int bitIndex = cy * 4 + cx;
+    // Masks are defined row-major 4x4 with bit 0 = (0,0) (same convention as classic).
+    return (mask >> bitIndex) & 1;
+}
+
+void CoopGame::clearCompletedLines() {
+    if (completedLines.empty()) return;
+    clearLinesInternal();
+    completedLines.clear();
+    updateRowStates();
+}
+
+void CoopGame::refillBag(PlayerState& ps) {
+    ps.bag.clear();
+    ps.bag.reserve(PIECE_COUNT);
+    for (int i = 0; i < PIECE_COUNT; ++i) {
+        ps.bag.push_back(static_cast<PieceType>(i));
+    }
+    std::shuffle(ps.bag.begin(), ps.bag.end(), ps.rng);
+}
+
+CoopGame::Piece CoopGame::drawFromBag(PlayerState& ps) {
+    if (ps.bag.empty()) {
+        refillBag(ps);
+    }
+    PieceType t = ps.bag.back();
+    ps.bag.pop_back();
+    Piece p{};
+    p.type = t;
+    return p;
+}
+
+void CoopGame::spawn(PlayerState& ps) {
+    if (ps.next.type == PIECE_COUNT) {
+        ps.next = drawFromBag(ps);
+    }
+    ps.cur = ps.next;
+    ps.cur.rot = 0;
+    ps.cur.x = columnMin(ps.side) + 3; // center within side
+    // Match single-player spawn height (I starts higher)
+    ps.cur.y = (ps.cur.type == PieceType::I) ? -2 : -1;
+    ps.next = drawFromBag(ps);
+    ps.canHold = true;
+    ps.softDropping = false;
+    ps.lockAcc = 0.0;
+    ps.fallAcc = 0.0;
+    ps.pieceSeq++;
+    pieceSequence++;
+    if (collides(ps, ps.cur)) {
+        ps.toppedOut = true;
+        // Cooperative mode: game ends when any player tops out.
+        gameOver = true;
+    }
+}
+
+bool CoopGame::collides(const PlayerState& ps, const Piece& p) const {
+    int minX = columnMin(ps.side);
+    int maxX = columnMax(ps.side);
+    for (int cy = 0; cy < 4; ++cy) {
+        for (int cx = 0; cx < 4; ++cx) {
+            if (!cellFilled(p, cx, cy)) continue;
+            int px = p.x + cx;
+            int py = p.y + cy;
+            if (px < minX || px > maxX) return true;
+            if (py >= ROWS) return true;
+            if (py < 0) continue; // allow spawn above board
+            int idx = py * COLS + px;
+            if (board[idx].occupied) return true;
+        }
+    }
+    return false;
+}
+
+bool CoopGame::tryMove(PlayerState& ps, int dx, int dy) {
+    Piece test = ps.cur;
+    test.x += dx;
+    test.y += dy;
+    if (collides(ps, test)) return false;
+    ps.cur = test;
+    if (dy > 0) {
+        ps.lockAcc = 0.0;
+    }
+    return true;
+}
+
+void CoopGame::lock(PlayerState& ps) {
+    // Write piece into the board
+    for (int cy = 0; cy < 4; ++cy) {
+        for (int cx = 0; cx < 4; ++cx) {
+            if (!cellFilled(ps.cur, cx, cy)) continue;
+            int px = ps.cur.x + cx;
+            int py = ps.cur.y + cy;
+            if (py < 0 || py >= ROWS) continue;
+            int idx = py * COLS + px;
+            board[idx].occupied = true;
+            board[idx].owner = ps.side;
+            board[idx].value = static_cast<int>(ps.cur.type) + 1;
+        }
+    }
+    // Detect completed lines and apply rewards but DO NOT clear them here.
+    // Clearing is deferred to the visual `LineEffect` system (as in single-player)
+    findCompletedLines();
+    if (!completedLines.empty()) {
+        int cleared = static_cast<int>(completedLines.size());
+        applyLineClearRewards(ps, cleared);
+        // Notify audio layer if present (matches single-player behavior)
+        if (soundCallback) soundCallback(cleared);
+        // Leave `completedLines` populated; `clearCompletedLines()` will be
+        // invoked by the state when the LineEffect finishes.
+    } else {
+        _currentCombo = 0;
+        ps.currentCombo = 0;
+    }
+    spawn(ps);
+}
+
+void CoopGame::findCompletedLines() {
+    completedLines.clear();
+    for (int r = 0; r < ROWS; ++r) {
+        bool leftFull = true;
+        bool rightFull = true;
+        for (int c = 0; c < COLS; ++c) {
+            const Cell& cell = board[r * COLS + c];
+            if (!cell.occupied) {
+                if (c < 10) leftFull = false; else rightFull = false;
+            }
+        }
+        rowStates[r].leftFull = leftFull;
+        rowStates[r].rightFull = rightFull;
+        if (leftFull && rightFull) {
+            completedLines.push_back(r);
+        }
+    }
+}
+
+void CoopGame::applyLineClearRewards(PlayerState& creditPlayer, int cleared) {
+    if (cleared <= 0) return;
+
+    // Base NES scoring scaled by shared level (level 0 => 1x multiplier)
+    int base = 0;
+    switch (cleared) {
+        case 1: base = 40; break;
+        case 2: base = 100; break;
+        case 3: base = 300; break;
+        case 4: base = 1200; break;
+        default: base = 0; break;
+    }
+    _score += base * (_level + 1);
+    creditPlayer.score += base * (creditPlayer.level + 1);
+
+    // Also award a trivial per-line bonus to both players so clears benefit
+    // both participants equally (as requested).
+    if (cleared > 0) {
+        left.score += cleared;
+        right.score += cleared;
+    }
+
+    _lines += cleared;
+    // Credit both players with the cleared lines so cooperative play counts for both
+    left.lines += cleared;
+    right.lines += cleared;
+
+    _currentCombo += 1;
+    if (_currentCombo > _maxCombo) _maxCombo = _currentCombo;
+    if (cleared > 1) {
+        _comboCount += 1;
+    }
+    if (cleared == 4) {
+        _tetrisesMade += 1;
+    }
+
+    creditPlayer.currentCombo += 1;
+    if (creditPlayer.currentCombo > creditPlayer.maxCombo) creditPlayer.maxCombo = creditPlayer.currentCombo;
+    if (cleared > 1) {
+        creditPlayer.comboCount += 1;
+    }
+    if (cleared == 4) {
+        creditPlayer.tetrisesMade += 1;
+    }
+
+    // Level progression mirrors single-player: threshold after (startLevel+1)*10 then every 10 lines
+    int targetLevel = startLevel;
+    int firstThreshold = (startLevel + 1) * 10;
+    if (_lines >= firstThreshold) {
+        targetLevel = startLevel + 1 + (_lines - firstThreshold) / 10;
+    }
+    if (targetLevel > _level) {
+        _level = targetLevel;
+        gravityMs = gravityMsForLevel(_level);
+        if (levelUpCallback) levelUpCallback(_level);
+    }
+
+    // Per-player level progression mirrors the shared rules but is driven by
+    // that player's credited line clears.
+    {
+        int pTargetLevel = startLevel;
+        int pFirstThreshold = (startLevel + 1) * 10;
+        if (creditPlayer.lines >= pFirstThreshold) {
+            pTargetLevel = startLevel + 1 + (creditPlayer.lines - pFirstThreshold) / 10;
+        }
+        creditPlayer.level = std::max(creditPlayer.level, pTargetLevel);
+    }
+}
+
+void CoopGame::clearLinesInternal() {
+    if (completedLines.empty()) return;
+    std::sort(completedLines.begin(), completedLines.end());
+    for (int idx = static_cast<int>(completedLines.size()) - 1; idx >= 0; --idx) {
+        int row = completedLines[idx];
+        for (int y = row; y > 0; --y) {
+            for (int x = 0; x < COLS; ++x) {
+                board[y * COLS + x] = board[(y - 1) * COLS + x];
+            }
+        }
+        for (int x = 0; x < COLS; ++x) {
+            board[x] = Cell{};
+        }
+    }
+}
+
+// Sound callback (optional) - invoked when lines are detected so audio can play
+// (set via setSoundCallback)
+// NOTE: defined inline in header as a std::function member; forward usage above
+
+void CoopGame::updateRowStates() {
+    for (int r = 0; r < ROWS; ++r) {
+        bool leftFull = true;
+        bool rightFull = true;
+        for (int c = 0; c < COLS; ++c) {
+            const Cell& cell = board[r * COLS + c];
+            if (!cell.occupied) {
+                if (c < 10) leftFull = false; else rightFull = false;
+            }
+        }
+        rowStates[r].leftFull = leftFull;
+        rowStates[r].rightFull = rightFull;
+    }
+}

src/gameplay/coop/CoopGame.h

@@ -0,0 +1,167 @@
+#pragma once
+
+#include <array>
+#include <optional>
+#include <random>
+#include <functional>
+#include <vector>
+#include <cstdint>
+#include <SDL3/SDL.h>
+
+#include "../core/Game.h" // For PieceType enums and gravity table helpers
+
+// Cooperative two-player session with a shared 20-column board split into halves.
+// This is an early scaffold: rules and rendering hooks will be iterated in follow-up passes.
+class CoopGame {
+public:
+    enum class PlayerSide { Left, Right };
+
+    static constexpr int COLS = 20;
+    static constexpr int ROWS = Game::ROWS;
+    static constexpr int TILE = Game::TILE;
+
+    struct Piece { PieceType type{PIECE_COUNT}; int rot{0}; int x{0}; int y{-2}; };
+
+    struct Cell {
+        int value{0};              // 0 empty else color index (1..7)
+        PlayerSide owner{PlayerSide::Left};
+        bool occupied{false};
+    };
+
+    struct RowHalfState {
+        bool leftFull{false};
+        bool rightFull{false};
+    };
+
+    struct PlayerState {
+        PlayerSide side{PlayerSide::Left};
+        Piece cur{};
+        Piece hold{};
+        Piece next{};
+        uint64_t pieceSeq{0};
+        bool canHold{true};
+        bool softDropping{false};
+        bool toppedOut{false};
+        double fallAcc{0.0};
+        double lockAcc{0.0};
+        int score{0};
+        int lines{0};
+        int level{0};
+        int tetrisesMade{0};
+        int currentCombo{0};
+        int maxCombo{0};
+        int comboCount{0};
+        std::vector<PieceType> bag{}; // 7-bag queue
+        std::mt19937 rng{ std::random_device{}() };
+    };
+
+    explicit CoopGame(int startLevel = 0);
+    using SoundCallback = std::function<void(int)>;
+    using LevelUpCallback = std::function<void(int)>;
+    void setSoundCallback(SoundCallback cb) { soundCallback = cb; }
+    void setLevelUpCallback(LevelUpCallback cb) { levelUpCallback = cb; }
+
+    void reset(int startLevel = 0);
+    void resetDeterministic(int startLevel, uint32_t seed);
+    void tickGravity(double frameMs);
+    void updateVisualEffects(double frameMs);
+
+    // Determinism / desync detection
+    uint64_t computeStateHash() const;
+
+    // Per-player inputs -----------------------------------------------------
+    void setSoftDropping(PlayerSide side, bool on);
+    void move(PlayerSide side, int dx);
+    void rotate(PlayerSide side, int dir); // +1 cw, -1 ccw
+    void hardDrop(PlayerSide side);
+    void holdCurrent(PlayerSide side);
+
+    // Accessors -------------------------------------------------------------
+    const std::array<Cell, COLS * ROWS>& boardRef() const { return board; }
+    const Piece& current(PlayerSide s) const { return player(s).cur; }
+    const Piece& next(PlayerSide s) const { return player(s).next; }
+    const Piece& held(PlayerSide s) const { return player(s).hold; }
+    bool canHold(PlayerSide s) const { return player(s).canHold; }
+    bool isGameOver() const { return gameOver; }
+    int score() const { return _score; }
+    int score(PlayerSide s) const { return player(s).score; }
+    int lines() const { return _lines; }
+    int lines(PlayerSide s) const { return player(s).lines; }
+    int level() const { return _level; }
+    int level(PlayerSide s) const { return player(s).level; }
+    int comboCount() const { return _comboCount; }
+    int maxCombo() const { return _maxCombo; }
+    int tetrisesMade() const { return _tetrisesMade; }
+    int elapsed() const { return static_cast<int>(elapsedMs / 1000.0); }
+    int elapsed(PlayerSide) const { return elapsed(); }
+    int startLevelBase() const { return startLevel; }
+    double getGravityMs() const { return gravityMs; }
+    double getFallAccumulator(PlayerSide s) const { return player(s).fallAcc; }
+    bool isSoftDropping(PlayerSide s) const { return player(s).softDropping; }
+    uint64_t currentPieceSequence(PlayerSide s) const { return player(s).pieceSeq; }
+    const std::vector<int>& getCompletedLines() const { return completedLines; }
+    bool hasCompletedLines() const { return !completedLines.empty(); }
+    void clearCompletedLines();
+    const std::array<RowHalfState, ROWS>& rowHalfStates() const { return rowStates; }
+
+    // Simple visual-effect compatibility (stubbed for now)
+    bool hasHardDropShake() const { return hardDropShakeTimerMs > 0.0; }
+    double hardDropShakeStrength() const;
+    const std::vector<SDL_Point>& getHardDropCells() const { return hardDropCells; }
+    uint32_t getHardDropFxId() const { return hardDropFxId; }
+
+    static bool cellFilled(const Piece& p, int cx, int cy);
+
+private:
+    static constexpr double LOCK_DELAY_MS = 500.0;
+
+    void resetInternal(int startLevel_, const std::optional<uint32_t>& seedOpt);
+
+    std::array<Cell, COLS * ROWS> board{};
+    std::array<RowHalfState, ROWS> rowStates{};
+    PlayerState left{};
+    PlayerState right{ PlayerSide::Right };
+
+    int _score{0};
+    int _lines{0};
+    int _level{1};
+    int _tetrisesMade{0};
+    int _currentCombo{0};
+    int _maxCombo{0};
+    int _comboCount{0};
+    int startLevel{0};
+    double gravityMs{800.0};
+    double gravityGlobalMultiplier{1.0};
+    bool gameOver{false};
+
+    double elapsedMs{0.0};
+
+    std::vector<int> completedLines;
+
+    // Impact FX
+    double hardDropShakeTimerMs{0.0};
+    static constexpr double HARD_DROP_SHAKE_DURATION_MS = 320.0;
+    std::vector<SDL_Point> hardDropCells;
+    uint32_t hardDropFxId{0};
+    uint64_t pieceSequence{0};
+    SoundCallback soundCallback;
+    LevelUpCallback levelUpCallback;
+
+    // Helpers ---------------------------------------------------------------
+    PlayerState& player(PlayerSide s) { return s == PlayerSide::Left ? left : right; }
+    const PlayerState& player(PlayerSide s) const { return s == PlayerSide::Left ? left : right; }
+
+    void refillBag(PlayerState& ps);
+    Piece drawFromBag(PlayerState& ps);
+    void spawn(PlayerState& ps);
+    bool collides(const PlayerState& ps, const Piece& p) const;
+    bool tryMove(PlayerState& ps, int dx, int dy);
+    void lock(PlayerState& ps);
+    void findCompletedLines();
+    void clearLinesInternal();
+    void updateRowStates();
+    void applyLineClearRewards(PlayerState& creditPlayer, int cleared);
+    double gravityMsForLevel(int level) const;
+    int columnMin(PlayerSide s) const { return s == PlayerSide::Left ? 0 : 10; }
+    int columnMax(PlayerSide s) const { return s == PlayerSide::Left ? 9 : 19; }
+};

src/gameplay/core/Game.h

@@ -15,7 +15,7 @@ enum PieceType { I, O, T, S, Z, J, L, PIECE_COUNT };
 using Shape = std::array<uint16_t, 4>; // four rotation bitmasks
 
 // Game runtime mode
-enum class GameMode { Endless, Challenge };
+enum class GameMode { Endless, Cooperate, Challenge };
 
 // Special obstacle blocks used by Challenge mode
 enum class AsteroidType : uint8_t { Normal = 0, Armored = 1, Falling = 2, Core = 3 };

src/gameplay/effects/LineEffect.cpp

@@ -3,6 +3,7 @@
 #include <algorithm>
 #include <cmath>
 #include "audio/Audio.h"
+#include "audio/AudioManager.h"
 #include "gameplay/core/Game.h"
 
 #ifndef M_PI
@@ -188,10 +189,13 @@ void LineEffect::initAudio() {
     }
 }
 
-void LineEffect::startLineClear(const std::vector<int>& rows, int gridX, int gridY, int blockSize) {
+void LineEffect::startLineClear(const std::vector<int>& rows, int gridX, int gridY, int blockSize, int gridCols, int gapPx, int gapAfterCol) {
     if (rows.empty()) return;
     
     clearingRows = rows;
+    effectGridCols = std::max(1, gridCols);
+    effectGapPx = std::max(0, gapPx);
+    effectGapAfterCol = std::clamp(gapAfterCol, 0, effectGridCols);
     state = AnimationState::FLASH_WHITE;
     timer = 0.0f;
     dropProgress = 0.0f;
@@ -228,8 +232,11 @@ void LineEffect::startLineClear(const std::vector<int>& rows, int gridX, int gri
 
 void LineEffect::createParticles(int row, int gridX, int gridY, int blockSize) {
     const float centerY = gridY + row * blockSize + blockSize * 0.5f;
-    for (int col = 0; col < Game::COLS; ++col) {
+    for (int col = 0; col < effectGridCols; ++col) {
         float centerX = gridX + col * blockSize + blockSize * 0.5f;
+        if (effectGapPx > 0 && effectGapAfterCol > 0 && col >= effectGapAfterCol) {
+            centerX += static_cast<float>(effectGapPx);
+        }
         SDL_Color tint = pickFireColor();
         spawnGlowPulse(centerX, centerY, static_cast<float>(blockSize), tint);
         spawnShardBurst(centerX, centerY, tint);
@@ -337,8 +344,12 @@ void LineEffect::updateGlowPulses(float dt) {
         glowPulses.end());
 }
 
-void LineEffect::render(SDL_Renderer* renderer, SDL_Texture* blocksTex, int gridX, int gridY, int blockSize) {
+void LineEffect::render(SDL_Renderer* renderer, SDL_Texture* blocksTex, int gridX, int gridY, int blockSize, int gapPx, int gapAfterCol) {
     if (state == AnimationState::IDLE) return;
+
+    // Allow caller to override gap mapping (useful for Coop renderer that inserts a mid-gap).
+    effectGapPx = std::max(0, gapPx);
+    effectGapAfterCol = std::clamp(gapAfterCol, 0, effectGridCols);
     
     switch (state) {
         case AnimationState::FLASH_WHITE:
@@ -383,10 +394,11 @@ void LineEffect::renderFlash(int gridX, int gridY, int blockSize) {
     
     for (int row : clearingRows) {
         SDL_SetRenderDrawColor(renderer, 255, 255, 255, alpha);
+        const int gapW = (effectGapPx > 0 && effectGapAfterCol > 0 && effectGapAfterCol < effectGridCols) ? effectGapPx : 0;
         SDL_FRect flashRect = {
             static_cast<float>(gridX - 4),
             static_cast<float>(gridY + row * blockSize - 4),
-            static_cast<float>(10 * blockSize + 8),
+            static_cast<float>(effectGridCols * blockSize + gapW + 8),
             static_cast<float>(blockSize + 8)
         };
         SDL_RenderFillRect(renderer, &flashRect);
@@ -450,7 +462,7 @@ void LineEffect::playLineClearSound(int lineCount) {
     const std::vector<int16_t>* sample = (lineCount == 4) ? &tetrisSample : &lineClearSample;
     if (sample && !sample->empty()) {
         // Mix via shared Audio device so it layers with music
-        Audio::instance().playSfx(*sample, 2, 44100, (lineCount == 4) ? 0.9f : 0.7f);
+        if (auto sys = AudioManager::get()) sys->playSfx(*sample, 2, 44100, (lineCount == 4) ? 0.9f : 0.7f);
     }
 }
 

src/gameplay/effects/LineEffect.h

@@ -69,11 +69,11 @@ public:
     void shutdown();
     
     // Start line clear effect for the specified rows
-    void startLineClear(const std::vector<int>& rows, int gridX, int gridY, int blockSize);
+    void startLineClear(const std::vector<int>& rows, int gridX, int gridY, int blockSize, int gridCols = Game::COLS, int gapPx = 0, int gapAfterCol = 0);
     
     // Update and render the effect
     bool update(float deltaTime); // Returns true if effect is complete
-    void render(SDL_Renderer* renderer, SDL_Texture* blocksTex, int gridX, int gridY, int blockSize);
+    void render(SDL_Renderer* renderer, SDL_Texture* blocksTex, int gridX, int gridY, int blockSize, int gapPx = 0, int gapAfterCol = 0);
     float getRowDropOffset(int row) const;
     
     // Audio
@@ -120,4 +120,7 @@ private:
     std::array<float, Game::ROWS> rowDropTargets{};
     float dropProgress = 0.0f;
     int dropBlockSize = 0;
+    int effectGridCols = Game::COLS;
+    int effectGapPx = 0;
+    int effectGapAfterCol = 0;
 };

src/graphics/renderers/GameRenderer.h

@@ -3,6 +3,7 @@
 #include <vector>
 #include <string>
 #include "../../gameplay/core/Game.h"
+#include "../../gameplay/coop/CoopGame.h"
 
 // Forward declarations
 class FontAtlas;
@@ -61,6 +62,24 @@ public:
         int selectedButton
     );
 
+    static void renderCoopPlayingState(
+        SDL_Renderer* renderer,
+        CoopGame* game,
+        FontAtlas* pixelFont,
+        LineEffect* lineEffect,
+        SDL_Texture* blocksTex,
+        SDL_Texture* statisticsPanelTex,
+        SDL_Texture* scorePanelTex,
+        SDL_Texture* nextPanelTex,
+        SDL_Texture* holdPanelTex,
+        bool paused,
+        float logicalW,
+        float logicalH,
+        float logicalScale,
+        float winW,
+        float winH
+    );
+
     // Public wrapper that forwards to the private tile-drawing helper. Use this if
     // calling from non-member helper functions (e.g. visual effects) that cannot
     // access private class members.

src/graphics/renderers/SyncLineRenderer.cpp

@@ -0,0 +1,358 @@
+#include "SyncLineRenderer.h"
+
+#include <algorithm>
+#include <cmath>
+#include <cstdlib>
+
+SyncLineRenderer::SyncLineRenderer()
+    : m_state(SyncState::Idle),
+      m_flashTimer(0.0f),
+            m_time(0.0f) {
+        m_particles.reserve(MAX_PARTICLES);
+}
+
+static float syncWobbleX(float t) {
+    // Small, smooth horizontal motion to make the conduit feel fluid.
+    // Kept subtle so it doesn't distract from gameplay.
+    return std::sinf(t * 2.1f) * 1.25f + std::sinf(t * 5.2f + 1.3f) * 0.55f;
+}
+
+void SyncLineRenderer::SpawnParticle() {
+    if (m_particles.size() >= MAX_PARTICLES) {
+        return;
+    }
+
+    SyncParticle p;
+    const float centerX = (m_rect.x + (m_rect.w * 0.5f)) + syncWobbleX(m_time);
+    // Spawn around the beam center so it reads like a conduit.
+    const float jitter = -8.0f + static_cast<float>(std::rand() % 17);
+
+    p.x = centerX + jitter;
+    p.y = m_rect.y + m_rect.h + static_cast<float>(std::rand() % 10);
+
+    // Two styles: tiny sparkle dots + short streaks.
+    const bool dot = (std::rand() % 100) < 35;
+    if (dot) {
+        p.vx = (-18.0f + static_cast<float>(std::rand() % 37));
+        p.vy = 180.0f + static_cast<float>(std::rand() % 180);
+        p.w = 1.0f + static_cast<float>(std::rand() % 2);
+        p.h = 1.0f + static_cast<float>(std::rand() % 2);
+        p.alpha = 240.0f;
+    } else {
+        p.vx = (-14.0f + static_cast<float>(std::rand() % 29));
+        p.vy = 160.0f + static_cast<float>(std::rand() % 200);
+        p.w = 1.0f + static_cast<float>(std::rand() % 3);
+        p.h = 3.0f + static_cast<float>(std::rand() % 10);
+        p.alpha = 220.0f;
+    }
+
+    // Slight color variance (cyan/green/white) to keep it energetic.
+    const int roll = std::rand() % 100;
+    if (roll < 55) {
+        p.color = SDL_Color{110, 255, 210, 255};
+    } else if (roll < 90) {
+        p.color = SDL_Color{120, 210, 255, 255};
+    } else {
+        p.color = SDL_Color{255, 255, 255, 255};
+    }
+
+    m_particles.push_back(p);
+}
+
+void SyncLineRenderer::SpawnBurst(int count) {
+    for (int i = 0; i < count; ++i) {
+        SpawnParticle();
+    }
+}
+
+void SyncLineRenderer::SetRect(const SDL_FRect& rect) {
+    m_rect = rect;
+}
+
+void SyncLineRenderer::SetState(SyncState state) {
+    if (state != SyncState::ClearFlash) {
+        m_state = state;
+    }
+}
+
+void SyncLineRenderer::TriggerClearFlash() {
+    m_state = SyncState::ClearFlash;
+    m_flashTimer = FLASH_DURATION;
+
+    // Reward burst: strong visual feedback on cooperative clear.
+    SpawnBurst(56);
+}
+
+void SyncLineRenderer::Update(float deltaTime) {
+    m_time += deltaTime;
+    m_pulseTime += deltaTime;
+
+    // State-driven particle spawning
+    float spawnRatePerSec = 0.0f;
+    int particlesPerSpawn = 1;
+    switch (m_state) {
+        case SyncState::LeftReady:
+        case SyncState::RightReady:
+            spawnRatePerSec = 24.0f;  // steady
+            break;
+        case SyncState::Synced:
+            spawnRatePerSec = 78.0f;  // very heavy stream
+            particlesPerSpawn = 2;
+            break;
+        default:
+            spawnRatePerSec = 18.0f;  // always-on sparkle stream
+            break;
+    }
+
+    if (spawnRatePerSec <= 0.0f) {
+        m_spawnAcc = 0.0f;
+    } else {
+        m_spawnAcc += deltaTime * spawnRatePerSec;
+        while (m_spawnAcc >= 1.0f) {
+            m_spawnAcc -= 1.0f;
+            for (int i = 0; i < particlesPerSpawn; ++i) {
+                SpawnParticle();
+            }
+        }
+    }
+
+    // Update particles
+    for (auto& p : m_particles) {
+        p.x += p.vx * deltaTime;
+        p.y -= p.vy * deltaTime;
+        // Slow drift & fade.
+        p.vx *= (1.0f - 0.35f * deltaTime);
+        p.alpha -= 115.0f * deltaTime;
+    }
+    std::erase_if(m_particles, [&](const SyncParticle& p) {
+        // Cull when out of view or too far from the beam.
+        const float centerX = (m_rect.x + (m_rect.w * 0.5f)) + syncWobbleX(m_time);
+        const float maxDx = 18.0f;
+        return (p.y < (m_rect.y - 16.0f)) || p.alpha <= 0.0f || std::fabs(p.x - centerX) > maxDx;
+    });
+
+    if (m_state == SyncState::ClearFlash) {
+        m_flashTimer -= deltaTime;
+        if (m_flashTimer <= 0.0f) {
+            m_state = SyncState::Idle;
+            m_flashTimer = 0.0f;
+        }
+    }
+}
+
+SDL_Color SyncLineRenderer::GetBaseColor() const {
+    switch (m_state) {
+        case SyncState::LeftReady:
+        case SyncState::RightReady:
+            return SDL_Color{255, 220, 100, 235};
+
+        case SyncState::Synced:
+            return SDL_Color{100, 255, 120, 240};
+
+        case SyncState::ClearFlash:
+            return SDL_Color{255, 255, 255, 255};
+
+        default:
+            return SDL_Color{80, 180, 255, 235};
+    }
+}
+
+void SyncLineRenderer::Render(SDL_Renderer* renderer) {
+    if (!renderer) {
+        return;
+    }
+
+    // We render the conduit with lots of translucent layers. Using additive blending
+    // for glow/pulse makes it read like a blurred beam without shaders.
+    SDL_SetRenderDrawBlendMode(renderer, SDL_BLENDMODE_BLEND);
+
+    const float wobbleX = syncWobbleX(m_time);
+    const float centerX = (m_rect.x + (m_rect.w * 0.5f)) + wobbleX;
+    const float h = m_rect.h;
+    const float hotspotH = std::clamp(h * 0.12f, 18.0f, 44.0f);
+
+    // Flash factor (0..1)
+    const float flashT = (m_state == SyncState::ClearFlash && FLASH_DURATION > 0.0f)
+                             ? std::clamp(m_flashTimer / FLASH_DURATION, 0.0f, 1.0f)
+                             : 0.0f;
+
+    SDL_Color color = GetBaseColor();
+
+    // Synced pulse drives aura + core intensity.
+    float pulse01 = 0.0f;
+    if (m_state == SyncState::Synced) {
+        pulse01 = 0.5f + 0.5f * std::sinf(m_time * 6.0f);
+    }
+
+    // 1) Outer aura layers (bloom-like using rectangles)
+    auto drawGlow = [&](float extraW, Uint8 a, SDL_Color c) {
+        SDL_FRect fr{
+            centerX - (m_rect.w + extraW) * 0.5f,
+            m_rect.y,
+            m_rect.w + extraW,
+            m_rect.h
+        };
+        SDL_SetRenderDrawColor(renderer, c.r, c.g, c.b, a);
+        SDL_RenderFillRect(renderer, &fr);
+    };
+
+    SDL_Color aura = color;
+    // Slightly bias aura towards cyan so it reads “energy conduit”.
+    aura.r = static_cast<Uint8>(std::min(255, static_cast<int>(aura.r) + 10));
+    aura.g = static_cast<Uint8>(std::min(255, static_cast<int>(aura.g) + 10));
+    aura.b = static_cast<Uint8>(std::min(255, static_cast<int>(aura.b) + 35));
+
+    const float auraBoost = (m_state == SyncState::Synced) ? (0.70f + 0.80f * pulse01) : 0.70f;
+    const float flashBoost = 1.0f + flashT * 1.45f;
+
+    SDL_BlendMode oldBlend = SDL_BLENDMODE_BLEND;
+    SDL_GetRenderDrawBlendMode(renderer, &oldBlend);
+    SDL_SetRenderDrawBlendMode(renderer, SDL_BLENDMODE_ADD);
+
+    SDL_Color auraOuter = aura;
+    auraOuter.r = static_cast<Uint8>(std::min(255, static_cast<int>(auraOuter.r) + 10));
+    auraOuter.g = static_cast<Uint8>(std::min(255, static_cast<int>(auraOuter.g) + 5));
+    auraOuter.b = static_cast<Uint8>(std::min(255, static_cast<int>(auraOuter.b) + 55));
+
+    SDL_Color auraInner = aura;
+    auraInner.r = static_cast<Uint8>(std::min(255, static_cast<int>(auraInner.r) + 40));
+    auraInner.g = static_cast<Uint8>(std::min(255, static_cast<int>(auraInner.g) + 40));
+    auraInner.b = static_cast<Uint8>(std::min(255, static_cast<int>(auraInner.b) + 70));
+
+    // Wider + softer outer halo, then tighter inner glow.
+    drawGlow(62.0f, static_cast<Uint8>(std::clamp(12.0f * auraBoost * flashBoost, 0.0f, 255.0f)), auraOuter);
+    drawGlow(44.0f, static_cast<Uint8>(std::clamp(20.0f * auraBoost * flashBoost, 0.0f, 255.0f)), auraOuter);
+    drawGlow(30.0f, static_cast<Uint8>(std::clamp(34.0f * auraBoost * flashBoost, 0.0f, 255.0f)), auraOuter);
+    drawGlow(18.0f, static_cast<Uint8>(std::clamp(54.0f * auraBoost * flashBoost, 0.0f, 255.0f)), auraInner);
+    drawGlow(10.0f, static_cast<Uint8>(std::clamp(78.0f * auraBoost * flashBoost, 0.0f, 255.0f)), auraInner);
+
+    // 2) Hotspots near top/bottom (adds that “powered endpoints” vibe)
+    SDL_Color hot = auraInner;
+    hot.r = static_cast<Uint8>(std::min(255, static_cast<int>(hot.r) + 35));
+    hot.g = static_cast<Uint8>(std::min(255, static_cast<int>(hot.g) + 35));
+    hot.b = static_cast<Uint8>(std::min(255, static_cast<int>(hot.b) + 35));
+    {
+        const float hotW1 = 34.0f;
+        const float hotW2 = 18.0f;
+        SDL_FRect topHot1{ centerX - (m_rect.w + hotW1) * 0.5f, m_rect.y, m_rect.w + hotW1, hotspotH };
+        SDL_FRect botHot1{ centerX - (m_rect.w + hotW1) * 0.5f, m_rect.y + m_rect.h - hotspotH, m_rect.w + hotW1, hotspotH };
+        SDL_FRect topHot2{ centerX - (m_rect.w + hotW2) * 0.5f, m_rect.y + hotspotH * 0.12f, m_rect.w + hotW2, hotspotH * 0.78f };
+        SDL_FRect botHot2{ centerX - (m_rect.w + hotW2) * 0.5f, m_rect.y + m_rect.h - hotspotH * 0.90f, m_rect.w + hotW2, hotspotH * 0.78f };
+
+        Uint8 ha1 = static_cast<Uint8>(std::clamp((m_state == SyncState::Synced ? 85.0f : 55.0f) * flashBoost, 0.0f, 255.0f));
+        Uint8 ha2 = static_cast<Uint8>(std::clamp((m_state == SyncState::Synced ? 130.0f : 90.0f) * flashBoost, 0.0f, 255.0f));
+        SDL_SetRenderDrawColor(renderer, hot.r, hot.g, hot.b, ha1);
+        SDL_RenderFillRect(renderer, &topHot1);
+        SDL_RenderFillRect(renderer, &botHot1);
+        SDL_SetRenderDrawColor(renderer, 255, 255, 255, ha2);
+        SDL_RenderFillRect(renderer, &topHot2);
+        SDL_RenderFillRect(renderer, &botHot2);
+    }
+
+    // 3) Synced pulse wave (a travelling “breath” around the beam)
+    if (m_state == SyncState::Synced) {
+        float wave = std::fmod(m_pulseTime * 2.4f, 1.0f);
+        float width = 10.0f + wave * 26.0f;
+        Uint8 alpha = static_cast<Uint8>(std::clamp(150.0f * (1.0f - wave) * flashBoost, 0.0f, 255.0f));
+
+        SDL_FRect waveRect{
+            centerX - (m_rect.w + width) * 0.5f,
+            m_rect.y,
+            m_rect.w + width,
+            m_rect.h
+        };
+
+        SDL_SetRenderDrawColor(renderer, 140, 255, 220, alpha);
+        SDL_RenderFillRect(renderer, &waveRect);
+    }
+
+    // 4) Shimmer bands (stylish motion inside the conduit)
+    {
+        const int bands = 7;
+        const float speed = (m_state == SyncState::Synced) ? 160.0f : 95.0f;
+        const float bandW = m_rect.w + 12.0f;
+        for (int i = 0; i < bands; ++i) {
+            const float phase = (static_cast<float>(i) / static_cast<float>(bands));
+            const float y = m_rect.y + std::fmod(m_time * speed + phase * h, h);
+            const float fade = 0.35f + 0.65f * std::sinf((m_time * 2.1f) + phase * 6.28318f);
+            const float bandH = 2.0f + (phase * 2.0f);
+            Uint8 a = static_cast<Uint8>(std::clamp((26.0f + 36.0f * pulse01) * std::fabs(fade) * flashBoost, 0.0f, 255.0f));
+            SDL_FRect fr{ centerX - bandW * 0.5f, y, bandW, bandH };
+            SDL_SetRenderDrawColor(renderer, 200, 255, 255, a);
+            SDL_RenderFillRect(renderer, &fr);
+        }
+    }
+
+    // 5) Core beam (thin bright core + thicker body with horizontal gradient)
+    Uint8 bodyA = color.a;
+    if (m_state == SyncState::Synced) {
+        bodyA = static_cast<Uint8>(std::clamp(175.0f + pulse01 * 75.0f, 0.0f, 255.0f));
+    }
+    // Keep the center more translucent; let glow carry intensity.
+    bodyA = static_cast<Uint8>(std::clamp(bodyA * (0.72f + flashT * 0.35f), 0.0f, 255.0f));
+
+    // Render a smooth-looking body by stacking a few vertical strips.
+    // This approximates a gradient (bright center -> soft edges) without shaders.
+    {
+        // Allow thinner beam while keeping gradient readable.
+        const float bodyW = std::max(4.0f, m_rect.w);
+        const float x0 = centerX - bodyW * 0.5f;
+
+        SDL_FRect left{ x0, m_rect.y, bodyW * 0.34f, m_rect.h };
+        SDL_FRect mid{ x0 + bodyW * 0.34f, m_rect.y, bodyW * 0.32f, m_rect.h };
+        SDL_FRect right{ x0 + bodyW * 0.66f, m_rect.y, bodyW * 0.34f, m_rect.h };
+
+        SDL_SetRenderDrawColor(renderer, color.r, color.g, color.b, static_cast<Uint8>(std::clamp(bodyA * 0.60f, 0.0f, 255.0f)));
+        SDL_RenderFillRect(renderer, &left);
+        SDL_RenderFillRect(renderer, &right);
+
+        SDL_SetRenderDrawColor(renderer,
+                               static_cast<Uint8>(std::min(255, static_cast<int>(color.r) + 35)),
+                               static_cast<Uint8>(std::min(255, static_cast<int>(color.g) + 35)),
+                               static_cast<Uint8>(std::min(255, static_cast<int>(color.b) + 55)),
+                               static_cast<Uint8>(std::clamp(bodyA * 0.88f, 0.0f, 255.0f)));
+        SDL_RenderFillRect(renderer, &mid);
+    }
+
+    SDL_FRect coreRect{ centerX - 1.1f, m_rect.y, 2.2f, m_rect.h };
+    Uint8 coreA = static_cast<Uint8>(std::clamp(210.0f + pulse01 * 70.0f + flashT * 95.0f, 0.0f, 255.0f));
+    SDL_SetRenderDrawColor(renderer, 255, 255, 255, coreA);
+    SDL_RenderFillRect(renderer, &coreRect);
+
+    // Switch back to normal alpha blend for particles so they stay readable.
+    SDL_SetRenderDrawBlendMode(renderer, SDL_BLENDMODE_BLEND);
+
+    // 6) Energy particles (sparks/streaks traveling upward)
+    for (const auto& p : m_particles) {
+        Uint8 a = static_cast<Uint8>(std::clamp(p.alpha, 0.0f, 255.0f));
+
+        // Add a tiny sinusoidal sway so the stream feels alive.
+        const float sway = std::sinf((p.y * 0.045f) + (m_time * 6.2f)) * 0.9f;
+        SDL_FRect spark{ (p.x + sway) - (p.w * 0.5f), p.y, p.w, p.h };
+        SDL_SetRenderDrawColor(renderer, p.color.r, p.color.g, p.color.b, a);
+        SDL_RenderFillRect(renderer, &spark);
+
+        // A little aura around each spark helps it read at speed.
+        if (a > 40) {
+            SDL_FRect sparkGlow{ spark.x - 1.0f, spark.y - 1.0f, spark.w + 2.0f, spark.h + 2.0f };
+            SDL_SetRenderDrawColor(renderer, p.color.r, p.color.g, p.color.b, static_cast<Uint8>(a * 0.35f));
+            SDL_RenderFillRect(renderer, &sparkGlow);
+        }
+    }
+
+    // 7) Flash/glow overlay (adds “clear burst” punch)
+    if (m_state == SyncState::ClearFlash) {
+        SDL_SetRenderDrawBlendMode(renderer, SDL_BLENDMODE_ADD);
+
+        const float extra = 74.0f;
+        SDL_FRect glow{ centerX - (m_rect.w + extra) * 0.5f, m_rect.y, m_rect.w + extra, m_rect.h };
+        Uint8 ga = static_cast<Uint8>(std::clamp(90.0f + 140.0f * flashT, 0.0f, 255.0f));
+        SDL_SetRenderDrawColor(renderer, 255, 255, 255, ga);
+        SDL_RenderFillRect(renderer, &glow);
+
+        SDL_SetRenderDrawBlendMode(renderer, oldBlend);
+    }
+
+    // Restore whatever blend mode the caller had.
+    SDL_SetRenderDrawBlendMode(renderer, oldBlend);
+}

src/graphics/renderers/SyncLineRenderer.h

@@ -0,0 +1,54 @@
+#pragma once
+#include <SDL3/SDL.h>
+
+#include <vector>
+
+enum class SyncState {
+    Idle,
+    LeftReady,
+    RightReady,
+    Synced,
+    ClearFlash
+};
+
+class SyncLineRenderer {
+public:
+    SyncLineRenderer();
+
+    void SetRect(const SDL_FRect& rect);
+    void SetState(SyncState state);
+    void TriggerClearFlash();
+
+    void Update(float deltaTime);
+    void Render(SDL_Renderer* renderer);
+
+private:
+    struct SyncParticle {
+        float x;
+        float y;
+        float vx;
+        float vy;
+        float w;
+        float h;
+        float alpha;
+        SDL_Color color;
+    };
+
+    SDL_FRect m_rect{};
+    SyncState m_state;
+
+    float m_flashTimer;
+    float m_time;
+
+    float m_pulseTime{0.0f};
+    float m_spawnAcc{0.0f};
+    std::vector<SyncParticle> m_particles;
+
+    static constexpr float FLASH_DURATION = 0.15f;
+    static constexpr size_t MAX_PARTICLES = 240;
+
+    void SpawnParticle();
+    void SpawnBurst(int count);
+
+    SDL_Color GetBaseColor() const;
+};

src/graphics/renderers/UIRenderer.cpp

@@ -232,6 +232,6 @@ void UIRenderer::drawSettingsPopup(SDL_Renderer* renderer, FontAtlas* font, floa
     
     // Instructions
     font->draw(renderer, popupX + 20, popupY + 150, "M = TOGGLE MUSIC", 1.0f, {200, 200, 220, 255});
-    font->draw(renderer, popupX + 20, popupY + 170, "S = TOGGLE SOUND FX", 1.0f, {200, 200, 220, 255});
+    font->draw(renderer, popupX + 20, popupY + 170, "K = TOGGLE SOUND FX", 1.0f, {200, 200, 220, 255});
     font->draw(renderer, popupX + 20, popupY + 190, "ESC = CLOSE", 1.0f, {200, 200, 220, 255});
 }

src/graphics/ui/HelpOverlay.cpp

@@ -38,7 +38,7 @@ void Render(SDL_Renderer* renderer, FontAtlas& font, float logicalWidth, float l
         {"ESC", "Back / cancel current popup"},
         {"F11 or ALT+ENTER", "Toggle fullscreen"},
         {"M", "Mute or unmute music"},
-        {"S", "Toggle sound effects"}
+        {"K", "Toggle sound effects"}
     }};
 
     const std::array<ShortcutEntry, 2> menuShortcuts{{

src/logic/Board.cpp

@@ -0,0 +1,59 @@
+#include "Board.h"
+#include <algorithm>
+
+namespace logic {
+
+Board::Board()
+    : grid_(Width * Height, Cell::Empty)
+{
+}
+
+void Board::clear()
+{
+    std::fill(grid_.begin(), grid_.end(), Cell::Empty);
+}
+
+bool Board::inBounds(int x, int y) const
+{
+    return x >= 0 && x < Width && y >= 0 && y < Height;
+}
+
+Board::Cell Board::at(int x, int y) const
+{
+    if (!inBounds(x, y)) return Cell::Empty;
+    return grid_[y * Width + x];
+}
+
+void Board::set(int x, int y, Cell c)
+{
+    if (!inBounds(x, y)) return;
+    grid_[y * Width + x] = c;
+}
+
+int Board::clearFullLines()
+{
+    int cleared = 0;
+    // scan from bottom to top
+    for (int y = Height - 1; y >= 0; --y) {
+        bool full = true;
+        for (int x = 0; x < Width; ++x) {
+            if (at(x, y) == Cell::Empty) { full = false; break; }
+        }
+        if (full) {
+            // remove row y: move all rows above down by one
+            for (int yy = y; yy > 0; --yy) {
+                for (int x = 0; x < Width; ++x) {
+                    grid_[yy * Width + x] = grid_[(yy - 1) * Width + x];
+                }
+            }
+            // clear top row
+            for (int x = 0; x < Width; ++x) grid_[x] = Cell::Empty;
+            ++cleared;
+            // stay on same y to re-check the row that fell into place
+            ++y; // because next iteration decrements y
+        }
+    }
+    return cleared;
+}
+
+} // namespace logic

src/logic/Board.h

@@ -0,0 +1,32 @@
+#pragma once
+
+#include <vector>
+#include <cstdint>
+
+namespace logic {
+
+class Board {
+public:
+    static constexpr int Width = 10;
+    static constexpr int Height = 20;
+
+    enum class Cell : uint8_t { Empty = 0, Filled = 1 };
+
+    Board();
+
+    void clear();
+
+    Cell at(int x, int y) const;
+    void set(int x, int y, Cell c);
+    bool inBounds(int x, int y) const;
+
+    // Remove and return number of full lines cleared. Rows above fall down.
+    int clearFullLines();
+
+    const std::vector<Cell>& data() const { return grid_; }
+
+private:
+    std::vector<Cell> grid_; // row-major: y*Width + x
+};
+
+} // namespace logic

src/network/CoopNetButtons.h

@@ -0,0 +1,21 @@
+#pragma once
+
+#include <cstdint>
+
+namespace coopnet {
+// 8-bit input mask carried in NetSession::InputFrame.
+// Keep in sync across capture/apply on both peers.
+enum Buttons : uint8_t {
+    MoveLeft  = 1u << 0,
+    MoveRight = 1u << 1,
+    SoftDrop  = 1u << 2,
+    RotCW     = 1u << 3,
+    RotCCW    = 1u << 4,
+    HardDrop  = 1u << 5,
+    Hold      = 1u << 6,
+};
+
+inline bool has(uint8_t mask, Buttons b) {
+    return (mask & static_cast<uint8_t>(b)) != 0;
+}
+}

src/network/NetSession.cpp

@@ -0,0 +1,324 @@
+#include "NetSession.h"
+
+#include <enet/enet.h>
+
+#include <SDL3/SDL.h>
+
+#include <cstring>
+
+namespace {
+constexpr uint8_t kChannelReliable = 0;
+
+static bool netLogVerboseEnabled() {
+    // Set environment variable / hint: SPACETRIS_NET_LOG=1
+    const char* v = SDL_GetHint("SPACETRIS_NET_LOG");
+    return v && v[0] == '1';
+}
+
+template <typename T>
+static void append(std::vector<uint8_t>& out, const T& value) {
+    const uint8_t* p = reinterpret_cast<const uint8_t*>(&value);
+    out.insert(out.end(), p, p + sizeof(T));
+}
+
+template <typename T>
+static bool read(const uint8_t* data, size_t size, size_t& off, T& out) {
+    if (off + sizeof(T) > size) return false;
+    std::memcpy(&out, data + off, sizeof(T));
+    off += sizeof(T);
+    return true;
+}
+}
+
+NetSession::NetSession() = default;
+
+NetSession::~NetSession() {
+    shutdown();
+}
+
+bool NetSession::ensureEnetInitialized() {
+    static bool s_inited = false;
+    if (s_inited) return true;
+    if (enet_initialize() != 0) {
+        setError("enet_initialize failed");
+        m_state = ConnState::Error;
+        return false;
+    }
+    s_inited = true;
+    return true;
+}
+
+void NetSession::setError(const std::string& msg) {
+    m_lastError = msg;
+}
+
+bool NetSession::host(const std::string& bindHost, uint16_t port) {
+    shutdown();
+    if (!ensureEnetInitialized()) return false;
+
+    SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION, "[NET] host(bind='%s', port=%u)", bindHost.c_str(), (unsigned)port);
+
+    ENetAddress address{};
+    address.host = ENET_HOST_ANY;
+    address.port = port;
+
+    if (!bindHost.empty() && bindHost != "0.0.0.0") {
+        if (enet_address_set_host(&address, bindHost.c_str()) != 0) {
+            setError("enet_address_set_host (bind) failed");
+            m_state = ConnState::Error;
+            return false;
+        }
+    }
+
+    // 1 peer, 2 channels (reserve extra)
+    m_host = enet_host_create(&address, 1, 2, 0, 0);
+    if (!m_host) {
+        setError("enet_host_create (host) failed");
+        m_state = ConnState::Error;
+        return false;
+    }
+
+    m_mode = Mode::Host;
+    m_state = ConnState::Connecting;
+    return true;
+}
+
+bool NetSession::join(const std::string& hostNameOrIp, uint16_t port) {
+    shutdown();
+    if (!ensureEnetInitialized()) return false;
+
+    SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION, "[NET] join(remote='%s', port=%u)", hostNameOrIp.c_str(), (unsigned)port);
+
+    m_host = enet_host_create(nullptr, 1, 2, 0, 0);
+    if (!m_host) {
+        setError("enet_host_create (client) failed");
+        m_state = ConnState::Error;
+        return false;
+    }
+
+    ENetAddress address{};
+    if (enet_address_set_host(&address, hostNameOrIp.c_str()) != 0) {
+        setError("enet_address_set_host failed");
+        m_state = ConnState::Error;
+        return false;
+    }
+    address.port = port;
+
+    m_peer = enet_host_connect(m_host, &address, 2, 0);
+    if (!m_peer) {
+        setError("enet_host_connect failed");
+        m_state = ConnState::Error;
+        return false;
+    }
+
+    m_mode = Mode::Client;
+    m_state = ConnState::Connecting;
+    return true;
+}
+
+void NetSession::shutdown() {
+    if (m_host || m_peer) {
+        SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION, "[NET] shutdown(mode=%d state=%d)", (int)m_mode, (int)m_state);
+    }
+
+    m_remoteInputs.clear();
+    m_remoteHashes.clear();
+    m_receivedHandshake.reset();
+
+    m_inputsSent = 0;
+    m_inputsReceived = 0;
+    m_hashesSent = 0;
+    m_hashesReceived = 0;
+    m_handshakesSent = 0;
+    m_handshakesReceived = 0;
+    m_lastRecvInputTick = 0xFFFFFFFFu;
+    m_lastRecvHashTick = 0xFFFFFFFFu;
+    m_lastStatsLogMs = 0;
+
+    if (m_peer) {
+        enet_peer_disconnect(m_peer, 0);
+        m_peer = nullptr;
+    }
+
+    if (m_host) {
+        enet_host_destroy(m_host);
+        m_host = nullptr;
+    }
+
+    m_mode = Mode::None;
+    m_state = ConnState::Disconnected;
+    m_lastError.clear();
+}
+
+void NetSession::poll(uint32_t timeoutMs) {
+    if (!m_host) return;
+
+    ENetEvent event{};
+    while (enet_host_service(m_host, &event, static_cast<enet_uint32>(timeoutMs)) > 0) {
+        switch (event.type) {
+            case ENET_EVENT_TYPE_CONNECT:
+                m_peer = event.peer;
+                m_state = ConnState::Connected;
+                SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION, "[NET] connected (mode=%d)", (int)m_mode);
+                break;
+            case ENET_EVENT_TYPE_RECEIVE:
+                if (event.packet) {
+                    handlePacket(event.packet->data, event.packet->dataLength);
+                    enet_packet_destroy(event.packet);
+                }
+                break;
+            case ENET_EVENT_TYPE_DISCONNECT:
+                m_peer = nullptr;
+                m_state = ConnState::Disconnected;
+                SDL_LogWarn(SDL_LOG_CATEGORY_APPLICATION, "[NET] disconnected");
+                break;
+            case ENET_EVENT_TYPE_NONE:
+            default:
+                break;
+        }
+
+        // After first event, do non-blocking passes.
+        timeoutMs = 0;
+    }
+
+    // Rate-limited stats log (opt-in)
+    if (netLogVerboseEnabled()) {
+        const uint32_t nowMs = SDL_GetTicks();
+        if (m_lastStatsLogMs == 0) m_lastStatsLogMs = nowMs;
+        if (nowMs - m_lastStatsLogMs >= 1000u) {
+            m_lastStatsLogMs = nowMs;
+            SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION,
+                        "[NET] stats: sent(in=%u hash=%u hs=%u) recv(in=%u hash=%u hs=%u) lastRecv(inTick=%u hashTick=%u) state=%d",
+                        m_inputsSent,
+                        m_hashesSent,
+                        m_handshakesSent,
+                        m_inputsReceived,
+                        m_hashesReceived,
+                        m_handshakesReceived,
+                        m_lastRecvInputTick,
+                        m_lastRecvHashTick,
+                        (int)m_state);
+        }
+    }
+}
+
+bool NetSession::sendBytesReliable(const void* data, size_t size) {
+    if (!m_peer) return false;
+    ENetPacket* packet = enet_packet_create(data, size, ENET_PACKET_FLAG_RELIABLE);
+    if (!packet) return false;
+    if (enet_peer_send(m_peer, kChannelReliable, packet) != 0) {
+        enet_packet_destroy(packet);
+        return false;
+    }
+    // Let the caller decide flush cadence; but for tiny control packets, flushing is cheap.
+    enet_host_flush(m_host);
+    return true;
+}
+
+bool NetSession::sendHandshake(const Handshake& hs) {
+    if (m_mode != Mode::Host) return false;
+    m_handshakesSent++;
+    SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION, "[NET] sendHandshake(seed=%u startTick=%u startLevel=%u)", hs.rngSeed, hs.startTick, (unsigned)hs.startLevel);
+    std::vector<uint8_t> buf;
+    buf.reserve(1 + sizeof(uint32_t) * 2 + sizeof(uint8_t));
+    buf.push_back(static_cast<uint8_t>(MsgType::Handshake));
+    append(buf, hs.rngSeed);
+    append(buf, hs.startTick);
+    append(buf, hs.startLevel);
+    return sendBytesReliable(buf.data(), buf.size());
+}
+
+std::optional<NetSession::Handshake> NetSession::takeReceivedHandshake() {
+    auto out = m_receivedHandshake;
+    m_receivedHandshake.reset();
+    return out;
+}
+
+bool NetSession::sendLocalInput(uint32_t tick, uint8_t buttons) {
+    m_inputsSent++;
+    if (netLogVerboseEnabled() && (tick % 60u) == 0u) {
+        SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION, "[NET] sendInput(tick=%u buttons=0x%02X)", tick, (unsigned)buttons);
+    }
+    std::vector<uint8_t> buf;
+    buf.reserve(1 + sizeof(uint32_t) + sizeof(uint8_t));
+    buf.push_back(static_cast<uint8_t>(MsgType::Input));
+    append(buf, tick);
+    append(buf, buttons);
+    return sendBytesReliable(buf.data(), buf.size());
+}
+
+std::optional<uint8_t> NetSession::getRemoteButtons(uint32_t tick) const {
+    auto it = m_remoteInputs.find(tick);
+    if (it == m_remoteInputs.end()) return std::nullopt;
+    return it->second;
+}
+
+bool NetSession::sendStateHash(uint32_t tick, uint64_t hash) {
+    m_hashesSent++;
+    if (netLogVerboseEnabled()) {
+        SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION, "[NET] sendHash(tick=%u hash=%llu)", tick, (unsigned long long)hash);
+    }
+    std::vector<uint8_t> buf;
+    buf.reserve(1 + sizeof(uint32_t) + sizeof(uint64_t));
+    buf.push_back(static_cast<uint8_t>(MsgType::Hash));
+    append(buf, tick);
+    append(buf, hash);
+    return sendBytesReliable(buf.data(), buf.size());
+}
+
+std::optional<uint64_t> NetSession::takeRemoteHash(uint32_t tick) {
+    auto it = m_remoteHashes.find(tick);
+    if (it == m_remoteHashes.end()) return std::nullopt;
+    uint64_t v = it->second;
+    m_remoteHashes.erase(it);
+    return v;
+}
+
+void NetSession::handlePacket(const uint8_t* data, size_t size) {
+    if (!data || size < 1) return;
+    size_t off = 0;
+    uint8_t typeByte = 0;
+    if (!read(data, size, off, typeByte)) return;
+
+    MsgType t = static_cast<MsgType>(typeByte);
+    switch (t) {
+        case MsgType::Handshake: {
+            Handshake hs{};
+            if (!read(data, size, off, hs.rngSeed)) return;
+            if (!read(data, size, off, hs.startTick)) return;
+            if (!read(data, size, off, hs.startLevel)) return;
+            m_receivedHandshake = hs;
+            m_handshakesReceived++;
+            SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION, "[NET] recvHandshake(seed=%u startTick=%u startLevel=%u)", hs.rngSeed, hs.startTick, (unsigned)hs.startLevel);
+            break;
+        }
+        case MsgType::Input: {
+            uint32_t tick = 0;
+            uint8_t buttons = 0;
+            if (!read(data, size, off, tick)) return;
+            if (!read(data, size, off, buttons)) return;
+            m_remoteInputs[tick] = buttons;
+            m_inputsReceived++;
+            m_lastRecvInputTick = tick;
+            if (netLogVerboseEnabled() && (tick % 60u) == 0u) {
+                SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION, "[NET] recvInput(tick=%u buttons=0x%02X)", tick, (unsigned)buttons);
+            }
+            break;
+        }
+        case MsgType::Hash: {
+            uint32_t tick = 0;
+            uint64_t hash = 0;
+            if (!read(data, size, off, tick)) return;
+            if (!read(data, size, off, hash)) return;
+            m_remoteHashes[tick] = hash;
+            m_hashesReceived++;
+            m_lastRecvHashTick = tick;
+            if (netLogVerboseEnabled()) {
+                SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION, "[NET] recvHash(tick=%u hash=%llu)", tick, (unsigned long long)hash);
+            }
+            break;
+        }
+        default:
+            break;
+    }
+}

src/network/NetSession.h

@@ -0,0 +1,118 @@
+#pragma once
+
+#include <cstdint>
+#include <optional>
+#include <string>
+#include <unordered_map>
+#include <vector>
+
+struct _ENetHost;
+struct _ENetPeer;
+
+// Lockstep networking session for COOPERATE (network) mode.
+//
+// Design goals:
+// - Non-blocking polling (caller drives poll from the main loop)
+// - Reliable, ordered delivery for inputs and control messages
+// - Host provides seed + start tick (handshake)
+// - Only inputs/state hashes are exchanged (no board sync)
+class NetSession {
+public:
+    enum class Mode {
+        None,
+        Host,
+        Client,
+    };
+
+    enum class ConnState {
+        Disconnected,
+        Connecting,
+        Connected,
+        Error,
+    };
+
+    struct Handshake {
+        uint32_t rngSeed = 0;
+        uint32_t startTick = 0;
+        uint8_t startLevel = 0;
+    };
+
+    struct InputFrame {
+        uint32_t tick = 0;
+        uint8_t buttons = 0;
+    };
+
+    NetSession();
+    ~NetSession();
+
+    NetSession(const NetSession&) = delete;
+    NetSession& operator=(const NetSession&) = delete;
+
+    // If bindHost is empty or "0.0.0.0", binds to ENET_HOST_ANY.
+    bool host(const std::string& bindHost, uint16_t port);
+    bool join(const std::string& hostNameOrIp, uint16_t port);
+    void shutdown();
+
+    void poll(uint32_t timeoutMs = 0);
+
+    Mode mode() const { return m_mode; }
+    ConnState state() const { return m_state; }
+    bool isConnected() const { return m_state == ConnState::Connected; }
+
+    // Host-only: send handshake once the peer connects.
+    bool sendHandshake(const Handshake& hs);
+
+    // Client-only: becomes available once received from host.
+    std::optional<Handshake> takeReceivedHandshake();
+
+    // Input exchange --------------------------------------------------------
+    // Send local input for a given simulation tick.
+    bool sendLocalInput(uint32_t tick, uint8_t buttons);
+
+    // Returns the last received remote input for a tick (if any).
+    std::optional<uint8_t> getRemoteButtons(uint32_t tick) const;
+
+    // Hash exchange (for desync detection) ---------------------------------
+    bool sendStateHash(uint32_t tick, uint64_t hash);
+    std::optional<uint64_t> takeRemoteHash(uint32_t tick);
+
+    // Diagnostics
+    std::string lastError() const { return m_lastError; }
+
+private:
+    enum class MsgType : uint8_t {
+        Handshake = 1,
+        Input = 2,
+        Hash = 3,
+    };
+
+    bool ensureEnetInitialized();
+    void setError(const std::string& msg);
+
+    bool sendBytesReliable(const void* data, size_t size);
+    void handlePacket(const uint8_t* data, size_t size);
+
+    Mode m_mode = Mode::None;
+    ConnState m_state = ConnState::Disconnected;
+
+    _ENetHost* m_host = nullptr;
+    _ENetPeer* m_peer = nullptr;
+
+    std::string m_lastError;
+
+    std::optional<Handshake> m_receivedHandshake;
+
+    std::unordered_map<uint32_t, uint8_t> m_remoteInputs;
+    std::unordered_map<uint32_t, uint64_t> m_remoteHashes;
+
+    // Debug logging (rate-limited)
+    uint32_t m_inputsSent = 0;
+    uint32_t m_inputsReceived = 0;
+    uint32_t m_hashesSent = 0;
+    uint32_t m_hashesReceived = 0;
+    uint32_t m_handshakesSent = 0;
+    uint32_t m_handshakesReceived = 0;
+    uint32_t m_lastRecvInputTick = 0xFFFFFFFFu;
+    uint32_t m_lastRecvHashTick = 0xFFFFFFFFu;
+    uint32_t m_lastStatsLogMs = 0;
+};

src/network/supabase_client.cpp

@@ -0,0 +1,182 @@
+#include "supabase_client.h"
+#include <curl/curl.h>
+#include <nlohmann/json.hpp>
+#include <thread>
+#include <iostream>
+#include <algorithm>
+#include <cmath>
+
+using json = nlohmann::json;
+
+namespace {
+// Supabase constants (publishable anon key)
+const std::string SUPABASE_URL = "https://xzxpmvyamjvtxpwnjpad.supabase.co";
+const std::string SUPABASE_ANON_KEY = "sb_publishable_GqQx844xYDizO9-ytlBXfA_MVT6N7yA";
+
+std::string buildUrl(const std::string &path) {
+    std::string url = SUPABASE_URL;
+    if (!url.empty() && url.back() == '/') url.pop_back();
+    url += "/rest/v1/" + path;
+    return url;
+}
+
+size_t curlWriteCallback(void* contents, size_t size, size_t nmemb, void* userp) {
+    size_t realSize = size * nmemb;
+    std::string *s = reinterpret_cast<std::string*>(userp);
+    s->append(reinterpret_cast<char*>(contents), realSize);
+    return realSize;
+}
+
+struct CurlInit {
+    CurlInit() { curl_global_init(CURL_GLOBAL_DEFAULT); }
+    ~CurlInit() { curl_global_cleanup(); }
+};
+static CurlInit g_curl_init;
+}
+
+namespace supabase {
+
+static bool g_verbose = false;
+
+void SetVerbose(bool enabled) {
+    g_verbose = enabled;
+}
+
+
+void SubmitHighscoreAsync(const ScoreEntry &entry) {
+    std::thread([entry]() {
+        try {
+            CURL* curl = curl_easy_init();
+            if (!curl) return;
+
+            std::string url = buildUrl("highscores");
+
+            json j;
+            j["score"] = entry.score;
+            j["lines"] = entry.lines;
+            j["level"] = entry.level;
+            j["time_sec"] = static_cast<int>(std::lround(entry.timeSec));
+            j["name"] = entry.name;
+            j["game_type"] = entry.gameType;
+            j["timestamp"] = static_cast<int>(std::time(nullptr));
+
+            std::string body = j.dump();
+            struct curl_slist *headers = nullptr;
+            std::string h1 = std::string("apikey: ") + SUPABASE_ANON_KEY;
+            std::string h2 = std::string("Authorization: Bearer ") + SUPABASE_ANON_KEY;
+            headers = curl_slist_append(headers, h1.c_str());
+            headers = curl_slist_append(headers, h2.c_str());
+            headers = curl_slist_append(headers, "Content-Type: application/json");
+
+            std::string resp;
+            curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
+            curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);
+            curl_easy_setopt(curl, CURLOPT_POSTFIELDS, body.c_str());
+            curl_easy_setopt(curl, CURLOPT_TIMEOUT, 5L);
+            curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, curlWriteCallback);
+            curl_easy_setopt(curl, CURLOPT_WRITEDATA, &resp);
+
+            if (g_verbose) {
+                std::cerr << "[Supabase] POST " << url << "\n";
+                std::cerr << "[Supabase] Body: " << body << "\n";
+            }
+
+            CURLcode res = curl_easy_perform(curl);
+            if (res != CURLE_OK) {
+                if (g_verbose) std::cerr << "[Supabase] POST error: " << curl_easy_strerror(res) << "\n";
+            } else {
+                long http_code = 0;
+                curl_easy_getinfo(curl, CURLINFO_RESPONSE_CODE, &http_code);
+                if (g_verbose) {
+                    std::cerr << "[Supabase] POST response code: " << http_code << " body_len=" << resp.size() << "\n";
+                    if (!resp.empty()) std::cerr << "[Supabase] POST response: " << resp << "\n";
+                }
+            }
+
+            curl_slist_free_all(headers);
+            curl_easy_cleanup(curl);
+        } catch (...) {
+            // swallow errors
+        }
+    }).detach();
+}
+
+std::vector<ScoreEntry> FetchHighscores(const std::string &gameType, int limit) {
+    std::vector<ScoreEntry> out;
+    try {
+        CURL* curl = curl_easy_init();
+        if (!curl) return out;
+
+        std::string path = "highscores";
+        // Clamp limit to max 10 to keep payloads small
+        int l = std::clamp(limit, 1, 10);
+        std::string query;
+        if (!gameType.empty()) {
+            if (gameType == "challenge") {
+                query = "?game_type=eq." + gameType + "&order=level.desc,time_sec.asc&limit=" + std::to_string(l);
+            } else {
+                query = "?game_type=eq." + gameType + "&order=score.desc&limit=" + std::to_string(l);
+            }
+        } else {
+            query = "?order=score.desc&limit=" + std::to_string(l);
+        }
+
+        std::string url = buildUrl(path) + query;
+
+        struct curl_slist *headers = nullptr;
+        headers = curl_slist_append(headers, ("apikey: " + SUPABASE_ANON_KEY).c_str());
+        headers = curl_slist_append(headers, ("Authorization: Bearer " + SUPABASE_ANON_KEY).c_str());
+        headers = curl_slist_append(headers, "Content-Type: application/json");
+
+
+        std::string resp;
+        curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
+        curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);
+        curl_easy_setopt(curl, CURLOPT_TIMEOUT, 5L);
+        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, curlWriteCallback);
+        curl_easy_setopt(curl, CURLOPT_WRITEDATA, &resp);
+
+        if (g_verbose) std::cerr << "[Supabase] GET " << url << "\n";
+
+        CURLcode res = curl_easy_perform(curl);
+        if (res == CURLE_OK) {
+            long http_code = 0;
+            curl_easy_getinfo(curl, CURLINFO_RESPONSE_CODE, &http_code);
+            if (g_verbose) {
+                std::cerr << "[Supabase] GET response code: " << http_code << " body_len=" << resp.size() << "\n";
+                if (!resp.empty()) std::cerr << "[Supabase] GET response: " << resp << "\n";
+            }
+            try {
+                auto j = json::parse(resp);
+                if (j.is_array()) {
+                    for (auto &v : j) {
+                        ScoreEntry e{};
+                        if (v.contains("score")) e.score = v["score"].get<int>();
+                        if (v.contains("lines")) e.lines = v["lines"].get<int>();
+                        if (v.contains("level")) e.level = v["level"].get<int>();
+                        if (v.contains("time_sec")) {
+                            try { e.timeSec = v["time_sec"].get<double>(); } catch(...) { e.timeSec = v["time_sec"].get<int>(); }
+                        } else if (v.contains("timestamp")) {
+                            e.timeSec = v["timestamp"].get<int>();
+                        }
+                        if (v.contains("name")) e.name = v["name"].get<std::string>();
+                        if (v.contains("game_type")) e.gameType = v["game_type"].get<std::string>();
+                        out.push_back(e);
+                    }
+                }
+            } catch (...) {
+                if (g_verbose) std::cerr << "[Supabase] GET parse error" << std::endl;
+            }
+        } else {
+            if (g_verbose) std::cerr << "[Supabase] GET error: " << curl_easy_strerror(res) << "\n";
+        }
+
+        curl_slist_free_all(headers);
+        curl_easy_cleanup(curl);
+    } catch (...) {
+        // swallow
+    }
+    return out;
+}
+
+} // namespace supabase

src/network/supabase_client.h

@@ -0,0 +1,17 @@
+#pragma once
+#include <string>
+#include <vector>
+#include "../persistence/Scores.h"
+
+namespace supabase {
+
+// Submit a highscore asynchronously (detached thread)
+void SubmitHighscoreAsync(const ScoreEntry &entry);
+
+// Fetch highscores for a game type. If gameType is empty, fetch all (limited).
+std::vector<ScoreEntry> FetchHighscores(const std::string &gameType, int limit);
+
+// Enable or disable verbose logging to stderr. Disabled by default.
+void SetVerbose(bool enabled);
+
+} // namespace supabase

src/persistence/Scores.cpp

@@ -1,20 +1,18 @@
-// Scores.cpp - Implementation of ScoreManager with Firebase Sync
+// Scores.cpp - Implementation of ScoreManager
 #include "Scores.h"
 #include <SDL3/SDL.h>
 #include <fstream>
 #include <sstream>
 #include <algorithm>
-#include <cpr/cpr.h>
+#include "../network/supabase_client.h"
 #include <nlohmann/json.hpp>
 #include <iostream>
 #include <thread>
 #include <ctime>
+#include <filesystem>
 
 using json = nlohmann::json;
 
-// Firebase Realtime Database URL
-const std::string FIREBASE_URL = "https://tetris-90139.firebaseio.com/scores.json";
-
 ScoreManager::ScoreManager(size_t maxScores) : maxEntries(maxScores) {}
 
 std::string ScoreManager::filePath() const {
@@ -27,48 +25,19 @@ std::string ScoreManager::filePath() const {
 void ScoreManager::load() {
     scores.clear();
     
-    // Try to load from Firebase first
+    // Try to load from Supabase first
     try {
-        cpr::Response r = cpr::Get(cpr::Url{FIREBASE_URL}, cpr::Timeout{2000}); // 2s timeout
-        if (r.status_code == 200 && !r.text.empty() && r.text != "null") {
-            auto j = json::parse(r.text);
-            
-            // Firebase returns a map of auto-generated IDs to objects
-            if (j.is_object()) {
-                for (auto& [key, value] : j.items()) {
-                    ScoreEntry e;
-                    if (value.contains("score")) e.score = value["score"];
-                    if (value.contains("lines")) e.lines = value["lines"];
-                    if (value.contains("level")) e.level = value["level"];
-                    if (value.contains("timeSec")) e.timeSec = value["timeSec"];
-                    if (value.contains("name")) e.name = value["name"];
-                    scores.push_back(e);
-                }
-            } 
-            // Or it might be an array if keys are integers (unlikely for Firebase push)
-            else if (j.is_array()) {
-                for (auto& value : j) {
-                    ScoreEntry e;
-                    if (value.contains("score")) e.score = value["score"];
-                    if (value.contains("lines")) e.lines = value["lines"];
-                    if (value.contains("level")) e.level = value["level"];
-                    if (value.contains("timeSec")) e.timeSec = value["timeSec"];
-                    if (value.contains("name")) e.name = value["name"];
-                    scores.push_back(e);
-                }
-            }
-            
-            // Sort and keep top scores
+        // Request only 10 records from Supabase to keep payload small
+        auto fetched = supabase::FetchHighscores("", 10);
+        if (!fetched.empty()) {
+            scores = fetched;
             std::sort(scores.begin(), scores.end(), [](auto&a,auto&b){return a.score>b.score;});
             if (scores.size() > maxEntries) scores.resize(maxEntries);
-            
-            // Save to local cache
             save();
             return;
         }
     } catch (...) {
-        // Ignore network errors and fall back to local file
-        std::cerr << "Failed to load from Firebase, falling back to local file." << std::endl;
+        std::cerr << "Failed to load from Supabase, falling back to local file." << std::endl;
     }
 
     // Fallback to local file
@@ -86,11 +55,32 @@ void ScoreManager::load() {
         ScoreEntry e; 
         iss >> e.score >> e.lines >> e.level >> e.timeSec;
         if (iss) {
-            // Try to read name (rest of line after timeSec)
+            // Try to read name (rest of line after timeSec). We may also have a trailing gameType token.
             std::string remaining;
             std::getline(iss, remaining);
-            if (!remaining.empty() && remaining[0] == ' ') {
-                e.name = remaining.substr(1); // Remove leading space
+            if (!remaining.empty() && remaining[0] == ' ') remaining = remaining.substr(1);
+            if (!remaining.empty()) {
+                static const std::vector<std::string> known = {"classic","cooperate","challenge","versus"};
+                while (!remaining.empty() && (remaining.back() == '\n' || remaining.back() == '\r' || remaining.back() == ' ')) remaining.pop_back();
+                size_t lastSpace = remaining.find_last_of(' ');
+                std::string lastToken = (lastSpace == std::string::npos) ? remaining : remaining.substr(lastSpace + 1);
+                bool matched = false;
+                for (const auto &k : known) {
+                    if (lastToken == k) {
+                        matched = true;
+                        e.gameType = k;
+                        if (lastSpace == std::string::npos) e.name = "PLAYER";
+                        else e.name = remaining.substr(0, lastSpace);
+                        break;
+                    }
+                }
+                if (!matched) {
+                    e.name = remaining;
+                    e.gameType = "classic";
+                }
+            } else {
+                e.name = "PLAYER";
+                e.gameType = "classic";
             }
             scores.push_back(e);
         }
@@ -108,42 +98,28 @@ void ScoreManager::load() {
 void ScoreManager::save() const {
     std::ofstream f(filePath(), std::ios::trunc);
     for (auto &e : scores) {
-        f << e.score << ' ' << e.lines << ' ' << e.level << ' ' << e.timeSec << ' ' << e.name << '\n';
+        // Save gameType as trailing token so future loads can preserve it
+        f << e.score << ' ' << e.lines << ' ' << e.level << ' ' << e.timeSec << ' ' << e.name << ' ' << e.gameType << '\n';
     }
 }
 
-void ScoreManager::submit(int score, int lines, int level, double timeSec, const std::string& name) {
+void ScoreManager::submit(int score, int lines, int level, double timeSec, const std::string& name, const std::string& gameType) {
     // Add to local list
-    scores.push_back(ScoreEntry{score,lines,level,timeSec, name});
+    ScoreEntry newEntry{};
+    newEntry.score = score;
+    newEntry.lines = lines;
+    newEntry.level = level;
+    newEntry.timeSec = timeSec;
+    newEntry.name = name;
+    // preserve the game type locally so menu filtering works immediately
+    newEntry.gameType = gameType;
+    scores.push_back(newEntry);
     std::sort(scores.begin(), scores.end(), [](auto&a,auto&b){return a.score>b.score;});
     if (scores.size()>maxEntries) scores.resize(maxEntries);
     save();
-    
-    // Submit to Firebase
-    // Run in a detached thread to avoid blocking the UI? 
-    // For simplicity, we'll do it blocking for now, or rely on short timeout.
-    // Ideally this should be async.
-    
-    json j;
-    j["score"] = score;
-    j["lines"] = lines;
-    j["level"] = level;
-    j["timeSec"] = timeSec;
-    j["name"] = name;
-    j["timestamp"] = std::time(nullptr); // Add timestamp
-    
-    // Fire and forget (async) would be better, but for now let's just try to send
-    // We can use std::thread to make it async
-    std::thread([j]() {
-        try {
-            cpr::Post(cpr::Url{FIREBASE_URL}, 
-                      cpr::Body{j.dump()}, 
-                      cpr::Header{{"Content-Type", "application/json"}},
-                      cpr::Timeout{5000});
-        } catch (...) {
-            // Ignore errors
-        }
-    }).detach();
+    // Submit to Supabase asynchronously
+    ScoreEntry se{score, lines, level, timeSec, name, gameType};
+    supabase::SubmitHighscoreAsync(se);
 }
 
 bool ScoreManager::isHighScore(int score) const {
@@ -151,19 +127,28 @@ bool ScoreManager::isHighScore(int score) const {
     return score > scores.back().score;
 }
 
+void ScoreManager::replaceAll(const std::vector<ScoreEntry>& newScores) {
+    scores = newScores;
+    // Ensure ordering and trimming to our configured maxEntries
+    std::sort(scores.begin(), scores.end(), [](auto&a,auto&b){return a.score>b.score;});
+    if (scores.size() > maxEntries) scores.resize(maxEntries);
+    // Persist new set to local file for next launch
+    try { save(); } catch (...) { /* swallow */ }
+}
+
 void ScoreManager::createSampleScores() {
     scores = {
-        {159840, 189, 14, 972, "GREGOR"},
-        {156340, 132, 12, 714, "GREGOR"}, 
-        {155219, 125, 12, 696, "GREGOR"},
-        {141823, 123, 10, 710, "GREGOR"},
-        {140079, 71, 11, 410, "GREGOR"},
-        {116012, 121, 10, 619, "GREGOR"},
-        {112643, 137, 13, 689, "GREGOR"},
-        {99190, 61, 10, 378, "GREGOR"},
-        {93648, 107, 10, 629, "GREGOR"},
-        {89041, 115, 10, 618, "GREGOR"},
-        {88600, 55, 9, 354, "GREGOR"},
-        {86346, 141, 13, 723, "GREGOR"}
+        {159840, 189, 14, 972.0, "GREGOR"},
+        {156340, 132, 12, 714.0, "GREGOR"}, 
+        {155219, 125, 12, 696.0, "GREGOR"},
+        {141823, 123, 10, 710.0, "GREGOR"},
+        {140079, 71, 11, 410.0, "GREGOR"},
+        {116012, 121, 10, 619.0, "GREGOR"},
+        {112643, 137, 13, 689.0, "GREGOR"},
+        {99190, 61, 10, 378.0, "GREGOR"},
+        {93648, 107, 10, 629.0, "GREGOR"},
+        {89041, 115, 10, 618.0, "GREGOR"},
+        {88600, 55, 9, 354.0, "GREGOR"},
+        {86346, 141, 13, 723.0, "GREGOR"}
     };
 }

src/persistence/Scores.h

@@ -3,14 +3,18 @@
 #include <vector>
 #include <string>
 
-struct ScoreEntry { int score{}; int lines{}; int level{}; double timeSec{}; std::string name{"PLAYER"}; };
+struct ScoreEntry { int score{}; int lines{}; int level{}; double timeSec{}; std::string name{"PLAYER"}; std::string gameType{"classic"}; };
 
 class ScoreManager {
 public:
     explicit ScoreManager(size_t maxScores = 12);
     void load();
     void save() const;
-    void submit(int score, int lines, int level, double timeSec, const std::string& name = "PLAYER");
+    // Replace the in-memory scores (thread-safe caller should ensure non-blocking)
+    void replaceAll(const std::vector<ScoreEntry>& newScores);
+    // New optional `gameType` parameter will be sent as `game_type`.
+    // Allowed values: "classic", "versus", "cooperate", "challenge".
+    void submit(int score, int lines, int level, double timeSec, const std::string& name = "PLAYER", const std::string& gameType = "classic");
     bool isHighScore(int score) const;
     const std::vector<ScoreEntry>& all() const { return scores; }
 private:

src/renderer/Renderer.h

@@ -0,0 +1,38 @@
+// Renderer abstraction (minimal scaffold)
+#pragma once
+
+#include <memory>
+#include <SDL3/SDL.h>
+
+namespace renderer {
+
+class Renderer {
+public:
+    virtual ~Renderer() = default;
+
+    // Create/destroy textures
+    virtual SDL_Texture* createTextureFromSurface(SDL_Surface* surf) = 0;
+    virtual void destroyTexture(SDL_Texture* tex) = 0;
+
+    // Draw operations (minimal)
+    // Copy a texture (integer rects)
+    virtual void copy(SDL_Texture* tex, const SDL_Rect* src, const SDL_Rect* dst) = 0;
+    // Copy a texture using floating-point rects (SDL_FRect)
+    virtual void renderTexture(SDL_Texture* tex, const SDL_FRect* src, const SDL_FRect* dst) = 0;
+    // Set alpha modulation on a texture
+    virtual void setTextureAlphaMod(SDL_Texture* tex, Uint8 a) = 0;
+    // Draw a line (floating-point coordinates)
+    virtual void renderLine(float x1, float y1, float x2, float y2) = 0;
+    // Set draw color and draw filled/floating rects
+    virtual void clear(const SDL_Color& color) = 0;
+    virtual void setDrawColor(const SDL_Color& color) = 0;
+    virtual void fillRectF(const SDL_FRect* rect) = 0;
+    virtual void drawRectF(const SDL_FRect* rect) = 0;
+    virtual void present() = 0;
+};
+
+// Factory helper implemented by SDL-specific backend
+std::unique_ptr<Renderer> MakeSDLRenderer(SDL_Renderer* rdr);
+
+} // namespace renderer
+

src/renderer/Renderer_iface.h

@@ -0,0 +1,27 @@
+// Clean renderer interface for local use
+#pragma once
+
+#include <memory>
+#include <SDL3/SDL.h>
+
+namespace renderer {
+
+class Renderer {
+public:
+    virtual ~Renderer() = default;
+    virtual SDL_Texture* createTextureFromSurface(SDL_Surface* surf) = 0;
+    virtual void destroyTexture(SDL_Texture* tex) = 0;
+    virtual void copy(SDL_Texture* tex, const SDL_Rect* src, const SDL_Rect* dst) = 0;
+    virtual void renderTexture(SDL_Texture* tex, const SDL_FRect* src, const SDL_FRect* dst) = 0;
+    virtual void setTextureAlphaMod(SDL_Texture* tex, Uint8 a) = 0;
+    virtual void renderLine(float x1, float y1, float x2, float y2) = 0;
+    virtual void clear(const SDL_Color& color) = 0;
+    virtual void setDrawColor(const SDL_Color& color) = 0;
+    virtual void fillRectF(const SDL_FRect* rect) = 0;
+    virtual void drawRectF(const SDL_FRect* rect) = 0;
+    virtual void present() = 0;
+};
+
+std::unique_ptr<Renderer> MakeSDLRenderer(SDL_Renderer* rdr);
+
+} // namespace renderer

src/renderer/SDLRenderer.cpp

@@ -0,0 +1,80 @@
+#include "Renderer_iface.h"
+#include <SDL3/SDL.h>
+
+namespace renderer {
+
+class SDLRendererImpl : public Renderer {
+public:
+    explicit SDLRendererImpl(SDL_Renderer* rdr) : rdr_(rdr) {}
+    ~SDLRendererImpl() override = default;
+
+    SDL_Texture* createTextureFromSurface(SDL_Surface* surf) override {
+        if (!rdr_ || !surf) return nullptr;
+        return SDL_CreateTextureFromSurface(rdr_, surf);
+    }
+
+    void destroyTexture(SDL_Texture* tex) override {
+        if (tex) SDL_DestroyTexture(tex);
+    }
+    void copy(SDL_Texture* tex, const SDL_Rect* src, const SDL_Rect* dst) override {
+        if (!rdr_ || !tex) return;
+        // Convert integer rects to float rects and call SDL_RenderTexture (SDL3 API)
+        SDL_FRect fs{}; SDL_FRect fd{};
+        const SDL_FRect* ps = nullptr;
+        const SDL_FRect* pd = nullptr;
+        if (src) { fs.x = static_cast<float>(src->x); fs.y = static_cast<float>(src->y); fs.w = static_cast<float>(src->w); fs.h = static_cast<float>(src->h); ps = &fs; }
+        if (dst) { fd.x = static_cast<float>(dst->x); fd.y = static_cast<float>(dst->y); fd.w = static_cast<float>(dst->w); fd.h = static_cast<float>(dst->h); pd = &fd; }
+        SDL_RenderTexture(rdr_, tex, ps, pd);
+    }
+
+    void renderTexture(SDL_Texture* tex, const SDL_FRect* src, const SDL_FRect* dst) override {
+        if (!rdr_ || !tex) return;
+        SDL_RenderTexture(rdr_, tex, src, dst);
+    }
+
+    void setTextureAlphaMod(SDL_Texture* tex, Uint8 a) override {
+        if (!tex) return;
+        SDL_SetTextureAlphaMod(tex, a);
+    }
+
+    void clear(const SDL_Color& color) override {
+        if (!rdr_) return;
+        SDL_SetRenderDrawColor(rdr_, color.r, color.g, color.b, color.a);
+        SDL_RenderClear(rdr_);
+    }
+
+    void setDrawColor(const SDL_Color& color) override {
+        if (!rdr_) return;
+        SDL_SetRenderDrawColor(rdr_, color.r, color.g, color.b, color.a);
+    }
+
+    void fillRectF(const SDL_FRect* rect) override {
+        if (!rdr_ || !rect) return;
+        SDL_RenderFillRect(rdr_, rect);
+    }
+
+    void drawRectF(const SDL_FRect* rect) override {
+        if (!rdr_ || !rect) return;
+        SDL_RenderRect(rdr_, rect);
+    }
+
+    void renderLine(float x1, float y1, float x2, float y2) override {
+        if (!rdr_) return;
+        SDL_RenderLine(rdr_, x1, y1, x2, y2);
+    }
+
+    void present() override {
+        if (!rdr_) return;
+        SDL_RenderPresent(rdr_);
+    }
+
+private:
+    SDL_Renderer* rdr_ = nullptr;
+};
+
+// Factory helper
+std::unique_ptr<Renderer> MakeSDLRenderer(SDL_Renderer* rdr) {
+    return std::make_unique<SDLRendererImpl>(rdr);
+}
+
+} // namespace renderer

src/resources/ResourceManager.cpp

@@ -0,0 +1,41 @@
+#include "ResourceManager.h"
+#include <future>
+
+namespace resources {
+
+ResourceManager::ResourceManager() = default;
+ResourceManager::~ResourceManager() = default;
+
+std::future<std::shared_ptr<void>> ResourceManager::loadAsync(const std::string& key, std::function<std::shared_ptr<void>(const std::string&)> loader)
+{
+    // Quick check for existing cached resource
+    {
+        std::lock_guard<std::mutex> lk(mutex_);
+        auto it = cache_.find(key);
+        if (it != cache_.end()) {
+            // Return already-available resource (keep strong ref)
+            auto sp = it->second;
+            if (sp) {
+                return std::async(std::launch::deferred, [sp]() { return sp; });
+            }
+        }
+    }
+
+    // Launch async loader
+    return std::async(std::launch::async, [this, key, loader]() {
+        auto res = loader(key);
+        if (res) {
+            std::lock_guard<std::mutex> lk(mutex_);
+            cache_[key] = res; // store strong reference
+        }
+        return res;
+    });
+}
+
+void ResourceManager::put(const std::string& key, std::shared_ptr<void> resource)
+{
+    std::lock_guard<std::mutex> lk(mutex_);
+    cache_[key] = resource; // store strong reference so callers using raw pointers stay valid
+}
+
+} // namespace resources

src/resources/ResourceManager.h

@@ -0,0 +1,43 @@
+#pragma once
+
+#include <string>
+#include <memory>
+#include <unordered_map>
+#include <mutex>
+#include <future>
+#include <functional>
+
+namespace resources {
+
+class ResourceManager {
+public:
+    ResourceManager();
+    ~ResourceManager();
+
+    // Return cached resource if available and of the right type
+    template<typename T>
+    std::shared_ptr<T> get(const std::string& key)
+    {
+        std::lock_guard<std::mutex> lk(mutex_);
+        auto it = cache_.find(key);
+        if (it == cache_.end()) return nullptr;
+        auto sp = it->second;
+        if (!sp) { cache_.erase(it); return nullptr; }
+        return std::static_pointer_cast<T>(sp);
+    }
+
+    // Asynchronously load a resource using the provided loader function.
+    // The loader must return a shared_ptr to the concrete resource (boxed as void).
+    std::future<std::shared_ptr<void>> loadAsync(const std::string& key, std::function<std::shared_ptr<void>(const std::string&)> loader);
+
+    // Insert a resource into the cache (thread-safe)
+    void put(const std::string& key, std::shared_ptr<void> resource);
+
+private:
+    // Keep strong ownership of cached resources so they remain valid
+    // while present in the cache.
+    std::unordered_map<std::string, std::shared_ptr<void>> cache_;
+    std::mutex mutex_;
+};
+
+} // namespace resources

src/states/MenuState.h

@@ -2,6 +2,12 @@
 #pragma once
 #include "State.h"
 
+#include <cstdint>
+#include <memory>
+#include <string>
+
+class NetSession;
+
 class MenuState : public State {
 public:
     MenuState(StateContext& ctx);
@@ -19,9 +25,13 @@ public:
     void showHelpPanel(bool show);
     // Show or hide the inline ABOUT panel (menu-style)
     void showAboutPanel(bool show);
+
+    // Show or hide the inline COOPERATE setup panel (2P vs AI).
+    // If `resumeMusic` is false when hiding, the menu music will not be restarted.
+    void showCoopSetupPanel(bool show, bool resumeMusic = true);
     
 private:
-    int selectedButton = 0; // 0 = PLAY, 1 = LEVEL, 2 = OPTIONS, 3 = HELP, 4 = ABOUT, 5 = EXIT
+    int selectedButton = 0; // 0=PLAY,1=COOPERATE,2=CHALLENGE,3=LEVEL,4=OPTIONS,5=HELP,6=ABOUT,7=EXIT
     
     // Button icons (optional - will use text if nullptr)
     SDL_Texture* playIcon = nullptr;
@@ -94,4 +104,37 @@ private:
     double aboutTransition = 0.0; // 0..1
     double aboutTransitionDurationMs = 360.0;
     int aboutDirection = 1; // 1 show, -1 hide
+
+    // Coop setup panel (inline HUD like Exit/Help)
+    bool coopSetupVisible = false;
+    bool coopSetupAnimating = false;
+    double coopSetupTransition = 0.0; // 0..1
+    double coopSetupTransitionDurationMs = 320.0;
+    int coopSetupDirection = 1; // 1 show, -1 hide
+    // 0 = Local co-op (2 players), 1 = AI partner, 2 = 2 player (network)
+    int coopSetupSelected = 0;
+
+    enum class CoopSetupStep {
+        ChoosePartner,
+        NetworkChooseRole,
+        NetworkEnterAddress,
+        NetworkWaiting,
+    };
+    CoopSetupStep coopSetupStep = CoopSetupStep::ChoosePartner;
+
+    // Network sub-flow state (only used when coopSetupSelected == 2)
+    int coopNetworkRoleSelected = 0; // 0 = host, 1 = join
+    std::string coopNetworkBindAddress = "0.0.0.0";
+    std::string coopNetworkJoinAddress = "127.0.0.1";
+    uint16_t coopNetworkPort = 7777;
+    bool coopNetworkHandshakeSent = false;
+    std::string coopNetworkStatusText;
+    std::unique_ptr<NetSession> coopNetworkSession;
+
+    SDL_FRect coopSetupBtnRects[3]{};
+    bool coopSetupRectsValid = false;
+    // Optional cooperative info image shown when coop setup panel is active
+    SDL_Texture* coopInfoTexture = nullptr;
+    int coopInfoTexW = 0;
+    int coopInfoTexH = 0;
 };

src/states/OptionsState.cpp

@@ -2,6 +2,7 @@
 #include "../core/state/StateManager.h"
 #include "../graphics/ui/Font.h"
 #include "../audio/Audio.h"
+#include "../audio/AudioManager.h"
 #include "../audio/SoundEffect.h"
 #include <SDL3/SDL.h>
 #include <algorithm>
@@ -220,7 +221,7 @@ void OptionsState::toggleFullscreen() {
 }
 
 void OptionsState::toggleMusic() {
-    Audio::instance().toggleMute();
+    if (auto sys = AudioManager::get()) sys->toggleMute();
     // If muted, music is disabled. If not muted, music is enabled.
     // Note: Audio::instance().isMuted() returns true if muted.
     // But Audio class doesn't expose isMuted directly in header usually?

src/states/PlayingState.cpp

@@ -1,13 +1,16 @@
 #include "PlayingState.h"
 #include "../core/state/StateManager.h"
 #include "../gameplay/core/Game.h"
+#include "../gameplay/coop/CoopGame.h"
 #include "../gameplay/effects/LineEffect.h"
 #include "../persistence/Scores.h"
 #include "../audio/Audio.h"
 #include "../audio/SoundEffect.h"
+#include "../graphics/Font.h"
 #include "../graphics/renderers/GameRenderer.h"
 #include "../core/Settings.h"
 #include "../core/Config.h"
+#include "../network/CoopNetButtons.h"
 #include <SDL3/SDL.h>
 
 // File-scope transport/spawn detection state
@@ -18,12 +21,23 @@ PlayingState::PlayingState(StateContext& ctx) : State(ctx) {}
 
 void PlayingState::onEnter() {
     SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION, "[PLAYING] Entering Playing state");
-    // Initialize the game based on mode: endless uses chosen start level, challenge keeps its run state
+    // Initialize the game based on mode: endless/cooperate use chosen start level, challenge keeps its run state
     if (ctx.game) {
-        if (ctx.game->getMode() == GameMode::Endless) {
+        if (ctx.game->getMode() == GameMode::Endless || ctx.game->getMode() == GameMode::Cooperate) {
             if (ctx.startLevelSelection) {
                 SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION, "[PLAYING] Resetting game with level %d", *ctx.startLevelSelection);
-                ctx.game->reset(*ctx.startLevelSelection);
+                const bool coopNetActive = (ctx.game->getMode() == GameMode::Cooperate) && ctx.coopNetEnabled && ctx.coopNetSession;
+
+                // For network co-op, MenuState already performed a deterministic reset using the negotiated seed.
+                // Re-resetting here would overwrite it (and will desync).
+                if (!coopNetActive) {
+                    ctx.game->reset(*ctx.startLevelSelection);
+                    if (ctx.game->getMode() == GameMode::Cooperate && ctx.coopGame) {
+                        ctx.coopGame->reset(*ctx.startLevelSelection);
+                    }
+                } else {
+                    ctx.game->setPaused(false);
+                }
             }
         } else {
             // Challenge run is prepared before entering; ensure gameplay is unpaused
@@ -42,127 +56,248 @@ void PlayingState::onExit() {
         SDL_DestroyTexture(m_renderTarget);
         m_renderTarget = nullptr;
     }
+
+    // If we are leaving gameplay during network co-op, tear down the session so
+    // hosting/joining again works without restarting the app.
+    if (ctx.coopNetSession) {
+        ctx.coopNetSession->shutdown();
+        ctx.coopNetSession.reset();
+    }
+    ctx.coopNetEnabled = false;
+    ctx.coopNetStalled = false;
+    ctx.coopNetDesyncDetected = false;
+    ctx.coopNetTick = 0;
+    ctx.coopNetPendingButtons = 0;
 }
 
 void PlayingState::handleEvent(const SDL_Event& e) {
+    if (!ctx.game) return;
+
     // If a transport animation is active, ignore gameplay input entirely.
     if (GameRenderer::isTransportActive()) {
         return;
     }
-    // We keep short-circuited input here; main still owns mouse UI
-    if (e.type == SDL_EVENT_KEY_DOWN && !e.key.repeat) {
-        if (!ctx.game) return;
 
-        auto setExitSelection = [&](int value) {
-            if (ctx.exitPopupSelectedButton) {
-                *ctx.exitPopupSelectedButton = value;
-            }
-        };
+    const bool coopActive = ctx.game->getMode() == GameMode::Cooperate && ctx.coopGame;
 
-        auto getExitSelection = [&]() -> int {
-            return ctx.exitPopupSelectedButton ? *ctx.exitPopupSelectedButton : 1;
-        };
+    auto setExitSelection = [&](int idx) {
+        if (ctx.exitPopupSelectedButton) {
+            *ctx.exitPopupSelectedButton = idx;
+        }
+    };
+    auto getExitSelection = [&]() -> int {
+        return ctx.exitPopupSelectedButton ? *ctx.exitPopupSelectedButton : 1;
+    };
 
-        // Pause toggle (P)
-        if (e.key.scancode == SDL_SCANCODE_P) {
-            bool paused = ctx.game->isPaused();
-            ctx.game->setPaused(!paused);
+    if (e.type != SDL_EVENT_KEY_DOWN || e.key.repeat) {
+        return;
+    }
+
+    // If exit-confirm popup is visible, handle shortcuts here
+    if (ctx.showExitConfirmPopup && *ctx.showExitConfirmPopup) {
+        // Navigate between YES (0) and NO (1) buttons
+        if (e.key.scancode == SDL_SCANCODE_LEFT || e.key.scancode == SDL_SCANCODE_UP) {
+            setExitSelection(0);
+            return;
+        }
+        if (e.key.scancode == SDL_SCANCODE_RIGHT || e.key.scancode == SDL_SCANCODE_DOWN) {
+            setExitSelection(1);
             return;
         }
 
-        // If exit-confirm popup is visible, handle shortcuts here
-        if (ctx.showExitConfirmPopup && *ctx.showExitConfirmPopup) {
-            // Navigate between YES (0) and NO (1) buttons
-            if (e.key.scancode == SDL_SCANCODE_LEFT || e.key.scancode == SDL_SCANCODE_UP) {
-                setExitSelection(0);
-                return;
-            }
-            if (e.key.scancode == SDL_SCANCODE_RIGHT || e.key.scancode == SDL_SCANCODE_DOWN) {
-                setExitSelection(1);
-                return;
-            }
-
-            // Activate selected button with Enter or Space
-            if (e.key.scancode == SDL_SCANCODE_RETURN || e.key.scancode == SDL_SCANCODE_KP_ENTER || e.key.scancode == SDL_SCANCODE_SPACE) {
-                const bool confirmExit = (getExitSelection() == 0);
-                *ctx.showExitConfirmPopup = false;
-                if (confirmExit) {
-                    // YES - Reset game and return to menu
-                    if (ctx.startLevelSelection) {
-                        ctx.game->reset(*ctx.startLevelSelection);
-                    } else {
-                        ctx.game->reset(0);
-                    }
-                    ctx.game->setPaused(false);
-                    if (ctx.stateManager) ctx.stateManager->setState(AppState::Menu);
+        // Activate selected button with Enter or Space
+        if (e.key.scancode == SDL_SCANCODE_RETURN || e.key.scancode == SDL_SCANCODE_KP_ENTER || e.key.scancode == SDL_SCANCODE_SPACE) {
+            const bool confirmExit = (getExitSelection() == 0);
+            *ctx.showExitConfirmPopup = false;
+            if (confirmExit) {
+                // YES - Reset game and return to menu
+                if (ctx.startLevelSelection) {
+                    ctx.game->reset(*ctx.startLevelSelection);
                 } else {
-                    // NO - Just close popup and resume
-                    ctx.game->setPaused(false);
+                    ctx.game->reset(0);
                 }
-                return;
-            }
-            // Cancel with Esc (same as NO)
-            if (e.key.scancode == SDL_SCANCODE_ESCAPE) {
-                *ctx.showExitConfirmPopup = false;
                 ctx.game->setPaused(false);
-                setExitSelection(1);
-                return;
+                if (ctx.stateManager) ctx.stateManager->setState(AppState::Menu);
+            } else {
+                // NO - Just close popup and resume
+                ctx.game->setPaused(false);
             }
-            // While modal is open, suppress other gameplay keys
             return;
         }
-
-        // ESC key - open confirmation popup
+        // Cancel with Esc (same as NO)
         if (e.key.scancode == SDL_SCANCODE_ESCAPE) {
-            if (ctx.showExitConfirmPopup) {
-                if (ctx.game) ctx.game->setPaused(true);
-                *ctx.showExitConfirmPopup = true;
-                setExitSelection(1); // Default to NO for safety
-            }
-            return;
-        }
-
-        // Debug: skip to next challenge level (B)
-        if (e.key.scancode == SDL_SCANCODE_B && ctx.game && ctx.game->getMode() == GameMode::Challenge) {
-            ctx.game->beginNextChallengeLevel();
-            // Cancel any countdown so play resumes immediately on the new level
-            if (ctx.gameplayCountdownActive) *ctx.gameplayCountdownActive = false;
-            if (ctx.menuPlayCountdownArmed) *ctx.menuPlayCountdownArmed = false;
+            *ctx.showExitConfirmPopup = false;
             ctx.game->setPaused(false);
+            setExitSelection(1);
+            return;
+        }
+        // While modal is open, suppress other gameplay keys
+        return;
+    }
+
+    // ESC key - open confirmation popup
+    if (e.key.scancode == SDL_SCANCODE_ESCAPE) {
+        if (ctx.showExitConfirmPopup) {
+            ctx.game->setPaused(true);
+            *ctx.showExitConfirmPopup = true;
+            setExitSelection(1); // Default to NO for safety
+        }
+        return;
+    }
+
+    // Debug: skip to next challenge level (B)
+    if (e.key.scancode == SDL_SCANCODE_B && ctx.game->getMode() == GameMode::Challenge) {
+        ctx.game->beginNextChallengeLevel();
+        // Cancel any countdown so play resumes immediately on the new level
+        if (ctx.gameplayCountdownActive) *ctx.gameplayCountdownActive = false;
+        if (ctx.menuPlayCountdownArmed) *ctx.menuPlayCountdownArmed = false;
+        ctx.game->setPaused(false);
+        return;
+    }
+
+    // Pause toggle (P) - matches classic behavior; disabled during countdown
+    if (e.key.scancode == SDL_SCANCODE_P) {
+        // Network co-op uses lockstep; local pause would desync/stall the peer.
+        if (ctx.coopNetEnabled && ctx.coopNetSession) {
+            return;
+        }
+        const bool countdown = (ctx.gameplayCountdownActive && *ctx.gameplayCountdownActive) ||
+                               (ctx.menuPlayCountdownArmed && *ctx.menuPlayCountdownArmed);
+        if (!countdown) {
+            ctx.game->setPaused(!ctx.game->isPaused());
+        }
+        return;
+    }
+
+    // Tetris controls (only when not paused)
+    if (ctx.game->isPaused()) {
+        return;
+    }
+
+    if (coopActive && ctx.coopGame) {
+        // Network co-op: route one-shot actions into a pending bitmask for lockstep.
+        if (ctx.coopNetEnabled && ctx.coopNetSession) {
+            const bool localIsLeft = ctx.coopNetLocalIsLeft;
+            const SDL_Scancode sc = e.key.scancode;
+            if (localIsLeft) {
+                if (sc == SDL_SCANCODE_W) {
+                    ctx.coopNetPendingButtons |= coopnet::RotCW;
+                    return;
+                }
+                if (sc == SDL_SCANCODE_Q) {
+                    ctx.coopNetPendingButtons |= coopnet::RotCCW;
+                    return;
+                }
+                if (sc == SDL_SCANCODE_LSHIFT || sc == SDL_SCANCODE_E) {
+                    ctx.coopNetPendingButtons |= coopnet::HardDrop;
+                    return;
+                }
+                if (sc == SDL_SCANCODE_LCTRL) {
+                    ctx.coopNetPendingButtons |= coopnet::Hold;
+                    return;
+                }
+            } else {
+                if (sc == SDL_SCANCODE_UP) {
+                    const bool upIsCW = Settings::instance().isUpRotateClockwise();
+                    ctx.coopNetPendingButtons |= upIsCW ? coopnet::RotCW : coopnet::RotCCW;
+                    return;
+                }
+                if (sc == SDL_SCANCODE_RALT) {
+                    ctx.coopNetPendingButtons |= coopnet::RotCCW;
+                    return;
+                }
+                if (sc == SDL_SCANCODE_SPACE || sc == SDL_SCANCODE_RSHIFT) {
+                    ctx.coopNetPendingButtons |= coopnet::HardDrop;
+                    return;
+                }
+                if (sc == SDL_SCANCODE_RCTRL) {
+                    ctx.coopNetPendingButtons |= coopnet::Hold;
+                    return;
+                }
+            }
+            // If coopNet is active, suppress local co-op direct action keys.
+        }
+
+        const bool coopAIEnabled = (ctx.coopVsAI && *ctx.coopVsAI);
+
+        // Player 1 (left): when AI is enabled it controls the left side so
+        // ignore direct player input for the left board.
+        if (coopAIEnabled) {
+            // Left side controlled by AI; skip left-side input handling here.
+        } else {
+            // Player 1 manual controls (left side)
+            if (e.key.scancode == SDL_SCANCODE_W) {
+                ctx.coopGame->rotate(CoopGame::PlayerSide::Left, 1);
+                return;
+            }
+            if (e.key.scancode == SDL_SCANCODE_Q) {
+                ctx.coopGame->rotate(CoopGame::PlayerSide::Left, -1);
+                return;
+            }
+            // Hard drop (left): keep LSHIFT, also allow E for convenience.
+            if (e.key.scancode == SDL_SCANCODE_LSHIFT || e.key.scancode == SDL_SCANCODE_E) {
+                SoundEffectManager::instance().playSound("hard_drop", 0.7f);
+                ctx.coopGame->hardDrop(CoopGame::PlayerSide::Left);
+                return;
+            }
+            if (e.key.scancode == SDL_SCANCODE_LCTRL) {
+                ctx.coopGame->holdCurrent(CoopGame::PlayerSide::Left);
+                return;
+            }
+        }
+        if (e.key.scancode == SDL_SCANCODE_UP) {
+            bool upIsCW = Settings::instance().isUpRotateClockwise();
+            ctx.coopGame->rotate(CoopGame::PlayerSide::Right, upIsCW ? 1 : -1);
+            return;
+        }
+        if (e.key.scancode == SDL_SCANCODE_RALT) {
+            ctx.coopGame->rotate(CoopGame::PlayerSide::Right, -1);
+            return;
+        }
+        // Hard drop (right): SPACE is the primary key for arrow controls; keep RSHIFT as an alternate.
+        if (e.key.scancode == SDL_SCANCODE_SPACE || e.key.scancode == SDL_SCANCODE_RSHIFT) {
+            SoundEffectManager::instance().playSound("hard_drop", 0.7f);
+            ctx.coopGame->hardDrop(CoopGame::PlayerSide::Right);
+            if (coopAIEnabled) {
+                // Mirror human-initiated hard-drop to AI on left
+                ctx.coopGame->hardDrop(CoopGame::PlayerSide::Left);
+            }
+            return;
+        }
+        if (e.key.scancode == SDL_SCANCODE_RCTRL) {
+            ctx.coopGame->holdCurrent(CoopGame::PlayerSide::Right);
+            return;
+        }
+    } else {
+        // Single-player classic controls
+        // Hold / swap current piece (H)
+        if (e.key.scancode == SDL_SCANCODE_H) {
+            ctx.game->holdCurrent();
             return;
         }
 
-        // Tetris controls (only when not paused)
-        if (!ctx.game->isPaused()) {
-            // Hold / swap current piece (H)
-            if (e.key.scancode == SDL_SCANCODE_H) {
-                ctx.game->holdCurrent();
-                return;
-            }
+        // Rotation (still event-based for precise timing)
+        if (e.key.scancode == SDL_SCANCODE_UP) {
+            // Use user setting to determine whether UP rotates clockwise
+            bool upIsCW = Settings::instance().isUpRotateClockwise();
+            ctx.game->rotate(upIsCW ? 1 : -1);
+            return;
+        }
+        if (e.key.scancode == SDL_SCANCODE_X) {
+            // Toggle the mapping so UP will rotate in the opposite direction
+            bool current = Settings::instance().isUpRotateClockwise();
+            Settings::instance().setUpRotateClockwise(!current);
+            Settings::instance().save();
+            // Play a subtle feedback sound if available
+            SoundEffectManager::instance().playSound("menu_toggle", 0.6f);
+            return;
+        }
 
-            // Rotation (still event-based for precise timing)
-            if (e.key.scancode == SDL_SCANCODE_UP) {
-                // Use user setting to determine whether UP rotates clockwise
-                bool upIsCW = Settings::instance().isUpRotateClockwise();
-                ctx.game->rotate(upIsCW ? 1 : -1);
-                return;
-            }
-            if (e.key.scancode == SDL_SCANCODE_X) {
-                // Toggle the mapping so UP will rotate in the opposite direction
-                bool current = Settings::instance().isUpRotateClockwise();
-                Settings::instance().setUpRotateClockwise(!current);
-                Settings::instance().save();
-                // Play a subtle feedback sound if available
-                SoundEffectManager::instance().playSound("menu_toggle", 0.6f);
-                return;
-            }
-
-            // Hard drop (space)
-            if (e.key.scancode == SDL_SCANCODE_SPACE) {
-                SoundEffectManager::instance().playSound("hard_drop", 0.7f);
-                ctx.game->hardDrop();
-                return;
-            }
+        // Hard drop (space)
+        if (e.key.scancode == SDL_SCANCODE_SPACE) {
+            SoundEffectManager::instance().playSound("hard_drop", 0.7f);
+            ctx.game->hardDrop();
+            return;
         }
     }
 
@@ -172,7 +307,21 @@ void PlayingState::handleEvent(const SDL_Event& e) {
 
 void PlayingState::update(double frameMs) {
     if (!ctx.game) return;
-    
+
+    const bool coopActive = ctx.game->getMode() == GameMode::Cooperate && ctx.coopGame;
+
+    if (coopActive) {
+        // Visual effects only; gravity and movement handled from ApplicationManager for coop
+        ctx.coopGame->updateVisualEffects(frameMs);
+        // Update line clear effect for coop mode as well (renderer starts the effect)
+        if (ctx.lineEffect && ctx.lineEffect->isActive()) {
+            if (ctx.lineEffect->update(frameMs / 1000.0f)) {
+                ctx.coopGame->clearCompletedLines();
+            }
+        }
+        return;
+    }
+
     ctx.game->updateVisualEffects(frameMs);
     // If a transport animation is active, pause gameplay updates and ignore inputs
     if (GameRenderer::isTransportActive()) {
@@ -204,6 +353,8 @@ void PlayingState::update(double frameMs) {
 void PlayingState::render(SDL_Renderer* renderer, float logicalScale, SDL_Rect logicalVP) {
     if (!ctx.game) return;
 
+    const bool coopActive = ctx.game->getMode() == GameMode::Cooperate && ctx.coopGame;
+
     // Get current window size
     int winW = 0, winH = 0;
     SDL_GetRenderOutputSize(renderer, &winW, &winH);
@@ -231,6 +382,31 @@ void PlayingState::render(SDL_Renderer* renderer, float logicalScale, SDL_Rect l
     // But countdown should definitely NOT show the "PAUSED" overlay.
     bool shouldBlur = paused && !countdown && !challengeClearFx;
 
+    auto renderNetOverlay = [&]() {
+        if (!coopActive || !ctx.coopNetEnabled || !ctx.pixelFont) return;
+        if (!ctx.coopNetDesyncDetected && !ctx.coopNetStalled) return;
+
+        const char* text = ctx.coopNetDesyncDetected ? "NET: DESYNC" : "NET: STALLED";
+        SDL_Color textColor = ctx.coopNetDesyncDetected ? SDL_Color{255, 230, 180, 255} : SDL_Color{255, 224, 130, 255};
+        float scale = 0.75f;
+        int tw = 0, th = 0;
+        ctx.pixelFont->measure(text, scale, tw, th);
+
+        SDL_BlendMode prevBlend = SDL_BLENDMODE_NONE;
+        SDL_GetRenderDrawBlendMode(renderer, &prevBlend);
+        SDL_SetRenderDrawBlendMode(renderer, SDL_BLENDMODE_BLEND);
+
+        const float pad = 8.0f;
+        const float x = 18.0f;
+        const float y = 14.0f;
+        SDL_FRect bg{ x - pad, y - pad, (float)tw + pad * 2.0f, (float)th + pad * 2.0f };
+        SDL_SetRenderDrawColor(renderer, 0, 0, 0, 160);
+        SDL_RenderFillRect(renderer, &bg);
+        ctx.pixelFont->draw(renderer, x, y, text, scale, textColor);
+
+        SDL_SetRenderDrawBlendMode(renderer, prevBlend);
+    };
+
     if (shouldBlur && m_renderTarget) {
         // Render game to texture
         SDL_SetRenderTarget(renderer, m_renderTarget);
@@ -244,26 +420,45 @@ void PlayingState::render(SDL_Renderer* renderer, float logicalScale, SDL_Rect l
         // Render game content (no overlays)
         // If a transport effect was requested due to a recent spawn, start it here so
         // the renderer has the correct layout and renderer context to compute coords.
-        if (s_pendingTransport) {
+        if (!coopActive && s_pendingTransport) {
             GameRenderer::startTransportEffectForGame(ctx.game, ctx.blocksTex, 1200.0f, 1000.0f, logicalScale, (float)winW, (float)winH, 0.4f);
             s_pendingTransport = false;
         }
 
-        GameRenderer::renderPlayingState(
-            renderer,
-            ctx.game,
-            ctx.pixelFont,
-            ctx.lineEffect,
-            ctx.blocksTex,
-            ctx.asteroidsTex,
-            ctx.statisticsPanelTex,
-            ctx.scorePanelTex,
-            ctx.nextPanelTex,
-            ctx.holdPanelTex,
-            countdown,
-            1200.0f, // LOGICAL_W
-            1000.0f, // LOGICAL_H
-            logicalScale,
+        if (coopActive && ctx.coopGame) {
+            GameRenderer::renderCoopPlayingState(
+                renderer,
+                ctx.coopGame,
+                ctx.pixelFont,
+                ctx.lineEffect,
+                ctx.blocksTex,
+                ctx.statisticsPanelTex,
+                ctx.scorePanelTex,
+                ctx.nextPanelTex,
+                ctx.holdPanelTex,
+                paused,
+                1200.0f,
+                1000.0f,
+                logicalScale,
+                (float)winW,
+                (float)winH
+            );
+        } else {
+            GameRenderer::renderPlayingState(
+                renderer,
+                ctx.game,
+                ctx.pixelFont,
+                ctx.lineEffect,
+                ctx.blocksTex,
+                ctx.asteroidsTex,
+                ctx.statisticsPanelTex,
+                ctx.scorePanelTex,
+                ctx.nextPanelTex,
+                ctx.holdPanelTex,
+                countdown,
+                1200.0f, // LOGICAL_W
+                1000.0f, // LOGICAL_H
+                logicalScale,
                 (float)winW,
                 (float)winH,
                 challengeClearFx,
@@ -272,7 +467,8 @@ void PlayingState::render(SDL_Renderer* renderer, float logicalScale, SDL_Rect l
                 challengeClearDuration,
                 countdown ? nullptr : ctx.challengeStoryText,
                 countdown ? 0.0f : (ctx.challengeStoryAlpha ? *ctx.challengeStoryAlpha : 0.0f)
-        );
+            );
+        }
 
         // Reset to screen
         SDL_SetRenderTarget(renderer, nullptr);
@@ -319,6 +515,9 @@ void PlayingState::render(SDL_Renderer* renderer, float logicalScale, SDL_Rect l
         SDL_SetRenderViewport(renderer, &oldVP);
         SDL_SetRenderScale(renderer, oldSX, oldSY);
 
+        // Net overlay (on top of blurred game, under pause/exit overlays)
+        renderNetOverlay();
+
         // Draw overlays
         if (exitPopup) {
             GameRenderer::renderExitPopup(
@@ -341,33 +540,57 @@ void PlayingState::render(SDL_Renderer* renderer, float logicalScale, SDL_Rect l
         
     } else {
         // Render normally directly to screen
-        if (s_pendingTransport) {
+        if (!coopActive && s_pendingTransport) {
             GameRenderer::startTransportEffectForGame(ctx.game, ctx.blocksTex, 1200.0f, 1000.0f, logicalScale, (float)winW, (float)winH, 0.4f);
             s_pendingTransport = false;
         }
-        GameRenderer::renderPlayingState(
-            renderer,
-            ctx.game,
-            ctx.pixelFont,
-            ctx.lineEffect,
-            ctx.blocksTex,
-            ctx.asteroidsTex,
-            ctx.statisticsPanelTex,
-            ctx.scorePanelTex,
-            ctx.nextPanelTex,
-            ctx.holdPanelTex,
-            countdown,
-            1200.0f,
-            1000.0f,
-            logicalScale,
-            (float)winW,
-            (float)winH,
-            challengeClearFx,
-            challengeClearOrder,
-            challengeClearElapsed,
-            challengeClearDuration,
-            countdown ? nullptr : ctx.challengeStoryText,
-            countdown ? 0.0f : (ctx.challengeStoryAlpha ? *ctx.challengeStoryAlpha : 0.0f)
-        );
+
+        if (coopActive && ctx.coopGame) {
+            GameRenderer::renderCoopPlayingState(
+                renderer,
+                ctx.coopGame,
+                ctx.pixelFont,
+                ctx.lineEffect,
+                ctx.blocksTex,
+                ctx.statisticsPanelTex,
+                ctx.scorePanelTex,
+                ctx.nextPanelTex,
+                ctx.holdPanelTex,
+                paused,
+                1200.0f,
+                1000.0f,
+                logicalScale,
+                (float)winW,
+                (float)winH
+            );
+
+            // Net overlay (on top of coop HUD)
+            renderNetOverlay();
+        } else {
+            GameRenderer::renderPlayingState(
+                renderer,
+                ctx.game,
+                ctx.pixelFont,
+                ctx.lineEffect,
+                ctx.blocksTex,
+                ctx.asteroidsTex,
+                ctx.statisticsPanelTex,
+                ctx.scorePanelTex,
+                ctx.nextPanelTex,
+                ctx.holdPanelTex,
+                countdown,
+                1200.0f,
+                1000.0f,
+                logicalScale,
+                (float)winW,
+                (float)winH,
+                challengeClearFx,
+                challengeClearOrder,
+                challengeClearElapsed,
+                challengeClearDuration,
+                countdown ? nullptr : ctx.challengeStoryText,
+                countdown ? 0.0f : (ctx.challengeStoryAlpha ? *ctx.challengeStoryAlpha : 0.0f)
+            );
+        }
     }
 }

src/states/State.h

@@ -6,9 +6,13 @@
 #include <functional>
 #include <string>
 #include <array>
+#include <cstdint>
+
+#include "../network/NetSession.h"
 
 // Forward declarations for frequently used types
 class Game;
+class CoopGame;
 class ScoreManager;
 class Starfield;
 class Starfield3D;
@@ -24,6 +28,7 @@ class StateManager;
 struct StateContext {
     // Core subsystems (may be null if not available)
     Game* game = nullptr;
+    CoopGame* coopGame = nullptr;
     ScoreManager* scores = nullptr;
     Starfield* starfield = nullptr;
     Starfield3D* starfield3D = nullptr;
@@ -77,12 +82,33 @@ struct StateContext {
     int* challengeStoryLevel = nullptr; // Cached level for the current story line
     float* challengeStoryAlpha = nullptr; // Current render alpha for story text fade
     std::string* playerName = nullptr; // Shared player name buffer for highscores/options
+    // Coop setting: when true, COOPERATE runs with a computer-controlled right player.
+    bool* coopVsAI = nullptr;
+
+    // COOPERATE (network) --------------------------------------------------
+    // These fields are only meaningful when `coopNetEnabled` is true.
+    bool coopNetEnabled = false;
+    bool coopNetIsHost = false;
+    bool coopNetLocalIsLeft = true; // host = left (WASD), client = right (arrows)
+    uint32_t coopNetRngSeed = 0;
+    uint32_t coopNetTick = 0;
+    uint8_t coopNetPendingButtons = 0; // one-shot actions captured from keydown (rotate/hold/harddrop)
+    bool coopNetStalled = false; // true when waiting for remote input for current tick
+    bool coopNetDesyncDetected = false;
+    std::string coopNetUiStatusText; // transient status shown in menu after net abort
+    double coopNetUiStatusRemainingMs = 0.0;
+    std::unique_ptr<NetSession> coopNetSession;
     bool* fullscreenFlag = nullptr; // Tracks current fullscreen state when available
     std::function<void(bool)> applyFullscreen; // Allows states to request fullscreen changes
     std::function<bool()> queryFullscreen; // Optional callback if fullscreenFlag is not reliable
     std::function<void()> requestQuit; // Allows menu/option states to close the app gracefully
     std::function<void()> startPlayTransition; // Optional fade hook when transitioning from menu to gameplay
     std::function<void(AppState)> requestFadeTransition; // Generic state fade requests (menu/options/level)
+
+    // Startup transition fade (used for intro video -> main).
+    // When active, the app should render a black overlay with alpha = startupFadeAlpha*255.
+    bool* startupFadeActive = nullptr;
+    float* startupFadeAlpha = nullptr;
     // Pointer to the application's StateManager so states can request transitions
     StateManager* stateManager = nullptr;
     // Optional explicit per-button coordinates (logical coordinates). When

src/states/VideoState.cpp

@@ -0,0 +1,390 @@
+// VideoState.cpp
+#include "VideoState.h"
+
+#include "../video/VideoPlayer.h"
+#include "../audio/Audio.h"
+#include "../audio/AudioManager.h"
+#include "../core/state/StateManager.h"
+
+#include <SDL3/SDL.h>
+
+#include <algorithm>
+#include <cmath>
+#include <cstring>
+#include <cstdint>
+
+extern "C" {
+#include <libavformat/avformat.h>
+#include <libavcodec/avcodec.h>
+#include <libavutil/avutil.h>
+#include <libavutil/channel_layout.h>
+#include <libswresample/swresample.h>
+}
+
+VideoState::VideoState(StateContext& ctx)
+    : State(ctx)
+    , m_player(std::make_unique<VideoPlayer>())
+{
+}
+
+VideoState::~VideoState() {
+    onExit();
+}
+
+bool VideoState::begin(SDL_Renderer* renderer, const std::string& path) {
+    m_path = path;
+
+    if (!m_player) {
+        m_player = std::make_unique<VideoPlayer>();
+    }
+
+    if (!m_player->open(m_path, renderer)) {
+        SDL_LogWarn(SDL_LOG_CATEGORY_APPLICATION, "[VideoState] Failed to open intro video: %s", m_path.c_str());
+        return false;
+    }
+
+    if (!m_player->decodeFirstFrame()) {
+        SDL_LogWarn(SDL_LOG_CATEGORY_APPLICATION, "[VideoState] Failed to decode first frame: %s", m_path.c_str());
+        // Still allow entering; we will likely render black.
+    }
+
+    return true;
+}
+
+void VideoState::onEnter() {
+    m_phase = Phase::FadeInFirstFrame;
+    m_phaseClockMs = 0.0;
+    m_blackOverlayAlpha = 1.0f;
+
+    m_audioDecoded.store(false);
+    m_audioDecodeFailed.store(false);
+    m_audioStarted = false;
+    m_audioPcm.clear();
+    m_audioRate = 44100;
+    m_audioChannels = 2;
+
+    // Decode audio in the background during fade-in.
+    m_audioThread = std::make_unique<std::jthread>([this](std::stop_token st) {
+        (void)st;
+        std::vector<int16_t> pcm;
+        int rate = 44100;
+        int channels = 2;
+
+        const bool ok = decodeAudioPcm16Stereo44100(m_path, pcm, rate, channels);
+        if (!ok) {
+            m_audioDecodeFailed.store(true);
+            m_audioDecoded.store(true, std::memory_order_release);
+            return;
+        }
+
+        // Transfer results.
+        m_audioRate = rate;
+        m_audioChannels = channels;
+        m_audioPcm = std::move(pcm);
+        m_audioDecoded.store(true, std::memory_order_release);
+    });
+}
+
+void VideoState::onExit() {
+    stopAudio();
+
+    if (m_audioThread) {
+        // Request stop and join.
+        m_audioThread.reset();
+    }
+}
+
+void VideoState::handleEvent(const SDL_Event& e) {
+    (void)e;
+}
+
+void VideoState::startAudioIfReady() {
+    if (m_audioStarted) return;
+    if (!m_audioDecoded.load(std::memory_order_acquire)) return;
+    if (m_audioDecodeFailed.load()) return;
+    if (m_audioPcm.empty()) return;
+
+    // Use the existing audio output path (same device as music/SFX).
+    if (auto sys = AudioManager::get()) sys->playSfx(m_audioPcm, m_audioChannels, m_audioRate, 1.0f);
+    m_audioStarted = true;
+}
+
+void VideoState::stopAudio() {
+    // We currently feed intro audio as an SFX buffer into the mixer.
+    // It will naturally end; no explicit stop is required.
+}
+
+void VideoState::update(double frameMs) {
+    switch (m_phase) {
+        case Phase::FadeInFirstFrame: {
+            m_phaseClockMs += frameMs;
+            const float t = (FADE_IN_MS > 0.0) ? float(std::clamp(m_phaseClockMs / FADE_IN_MS, 0.0, 1.0)) : 1.0f;
+            m_blackOverlayAlpha = 1.0f - t;
+
+            if (t >= 1.0f) {
+                m_phase = Phase::Playing;
+                m_phaseClockMs = 0.0;
+                if (m_player) {
+                    m_player->start();
+                }
+                startAudioIfReady();
+            }
+            break;
+        }
+        case Phase::Playing: {
+            startAudioIfReady();
+            if (m_player) {
+                m_player->update(frameMs);
+                if (m_player->isFinished()) {
+                    m_phase = Phase::FadeOutToBlack;
+                    m_phaseClockMs = 0.0;
+                    m_blackOverlayAlpha = 0.0f;
+                }
+            } else {
+                m_phase = Phase::FadeOutToBlack;
+                m_phaseClockMs = 0.0;
+                m_blackOverlayAlpha = 0.0f;
+            }
+            break;
+        }
+        case Phase::FadeOutToBlack: {
+            m_phaseClockMs += frameMs;
+            const float t = (FADE_OUT_MS > 0.0) ? float(std::clamp(m_phaseClockMs / FADE_OUT_MS, 0.0, 1.0)) : 1.0f;
+            m_blackOverlayAlpha = t;
+            if (t >= 1.0f) {
+                // Switch to MAIN (Menu) with a fade-in from black.
+                if (ctx.startupFadeAlpha) {
+                    *ctx.startupFadeAlpha = 1.0f;
+                }
+                if (ctx.startupFadeActive) {
+                    *ctx.startupFadeActive = true;
+                }
+                if (ctx.stateManager) {
+                    ctx.stateManager->setState(AppState::Menu);
+                }
+                m_phase = Phase::Done;
+            }
+            break;
+        }
+        case Phase::Done:
+        default:
+            break;
+     }
+ }
+
+ void VideoState::render(SDL_Renderer* renderer, float logicalScale, SDL_Rect logicalVP) {
+    (void)logicalScale;
+    (void)logicalVP;
+
+    if (!renderer) return;
+
+    int winW = 0, winH = 0;
+    SDL_GetRenderOutputSize(renderer, &winW, &winH);
+
+    // Draw video fullscreen if available.
+    if (m_player && m_player->isTextureReady()) {
+        SDL_SetRenderViewport(renderer, nullptr);
+        SDL_SetRenderScale(renderer, 1.0f, 1.0f);
+        m_player->render(renderer, winW, winH);
+    } else {
+        SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
+        SDL_FRect r{0.f, 0.f, (float)winW, (float)winH};
+        SDL_RenderFillRect(renderer, &r);
+    }
+
+    // Apply fade overlay (black).
+    if (m_blackOverlayAlpha > 0.0f) {
+        const Uint8 a = (Uint8)std::clamp((int)std::lround(m_blackOverlayAlpha * 255.0f), 0, 255);
+        SDL_SetRenderDrawBlendMode(renderer, SDL_BLENDMODE_BLEND);
+        SDL_SetRenderDrawColor(renderer, 0, 0, 0, a);
+        SDL_FRect full{0.f, 0.f, (float)winW, (float)winH};
+        SDL_RenderFillRect(renderer, &full);
+    }
+ }
+
+bool VideoState::decodeAudioPcm16Stereo44100(
+    const std::string& path,
+    std::vector<int16_t>& outPcm,
+    int& outRate,
+    int& outChannels
+) {
+    outPcm.clear();
+    outRate = 44100;
+    outChannels = 2;
+
+    AVFormatContext* fmt = nullptr;
+    if (avformat_open_input(&fmt, path.c_str(), nullptr, nullptr) != 0) {
+        return false;
+    }
+
+    if (avformat_find_stream_info(fmt, nullptr) < 0) {
+        avformat_close_input(&fmt);
+        return false;
+    }
+
+    int audioStream = -1;
+    for (unsigned i = 0; i < fmt->nb_streams; ++i) {
+        if (fmt->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_AUDIO) {
+            audioStream = (int)i;
+            break;
+        }
+    }
+    if (audioStream < 0) {
+        avformat_close_input(&fmt);
+        return false;
+    }
+
+    AVCodecParameters* codecpar = fmt->streams[audioStream]->codecpar;
+    const AVCodec* codec = avcodec_find_decoder(codecpar->codec_id);
+    if (!codec) {
+        avformat_close_input(&fmt);
+        return false;
+    }
+
+    AVCodecContext* dec = avcodec_alloc_context3(codec);
+    if (!dec) {
+        avformat_close_input(&fmt);
+        return false;
+    }
+
+    if (avcodec_parameters_to_context(dec, codecpar) < 0) {
+        avcodec_free_context(&dec);
+        avformat_close_input(&fmt);
+        return false;
+    }
+
+    if (avcodec_open2(dec, codec, nullptr) < 0) {
+        avcodec_free_context(&dec);
+        avformat_close_input(&fmt);
+        return false;
+    }
+
+    AVChannelLayout outLayout{};
+    av_channel_layout_default(&outLayout, 2);
+
+    AVChannelLayout inLayout{};
+    if (av_channel_layout_copy(&inLayout, &dec->ch_layout) < 0 || inLayout.nb_channels <= 0) {
+        av_channel_layout_uninit(&inLayout);
+        av_channel_layout_default(&inLayout, 2);
+    }
+
+    SwrContext* swr = nullptr;
+    if (swr_alloc_set_opts2(
+            &swr,
+            &outLayout,
+            AV_SAMPLE_FMT_S16,
+            44100,
+            &inLayout,
+            dec->sample_fmt,
+            dec->sample_rate,
+            0,
+            nullptr
+        ) < 0) {
+        av_channel_layout_uninit(&inLayout);
+        av_channel_layout_uninit(&outLayout);
+        avcodec_free_context(&dec);
+        avformat_close_input(&fmt);
+        return false;
+    }
+
+    if (swr_init(swr) < 0) {
+        swr_free(&swr);
+        av_channel_layout_uninit(&inLayout);
+        av_channel_layout_uninit(&outLayout);
+        avcodec_free_context(&dec);
+        avformat_close_input(&fmt);
+        return false;
+    }
+
+    AVPacket* pkt = av_packet_alloc();
+    AVFrame* frame = av_frame_alloc();
+    if (!pkt || !frame) {
+        if (pkt) av_packet_free(&pkt);
+        if (frame) av_frame_free(&frame);
+        swr_free(&swr);
+        av_channel_layout_uninit(&inLayout);
+        av_channel_layout_uninit(&outLayout);
+        avcodec_free_context(&dec);
+        avformat_close_input(&fmt);
+        return false;
+    }
+
+    const int outRateConst = 44100;
+    const int outCh = 2;
+
+    while (av_read_frame(fmt, pkt) >= 0) {
+        if (pkt->stream_index != audioStream) {
+            av_packet_unref(pkt);
+            continue;
+        }
+
+        if (avcodec_send_packet(dec, pkt) < 0) {
+            av_packet_unref(pkt);
+            continue;
+        }
+        av_packet_unref(pkt);
+
+        while (true) {
+            const int rr = avcodec_receive_frame(dec, frame);
+            if (rr == AVERROR(EAGAIN) || rr == AVERROR_EOF) {
+                break;
+            }
+            if (rr < 0) {
+                break;
+            }
+
+            const int64_t delay = swr_get_delay(swr, dec->sample_rate);
+            const int dstNbSamples = (int)av_rescale_rnd(delay + frame->nb_samples, outRateConst, dec->sample_rate, AV_ROUND_UP);
+
+            std::vector<uint8_t> outBytes;
+            outBytes.resize((size_t)dstNbSamples * (size_t)outCh * sizeof(int16_t));
+
+            uint8_t* outData[1] = { outBytes.data() };
+            const uint8_t** inData = (const uint8_t**)frame->data;
+
+            const int converted = swr_convert(swr, outData, dstNbSamples, inData, frame->nb_samples);
+            if (converted > 0) {
+                const size_t samplesOut = (size_t)converted * (size_t)outCh;
+                const int16_t* asS16 = (const int16_t*)outBytes.data();
+                const size_t oldSize = outPcm.size();
+                outPcm.resize(oldSize + samplesOut);
+                std::memcpy(outPcm.data() + oldSize, asS16, samplesOut * sizeof(int16_t));
+            }
+
+            av_frame_unref(frame);
+        }
+    }
+
+    // Flush decoder
+    avcodec_send_packet(dec, nullptr);
+    while (avcodec_receive_frame(dec, frame) >= 0) {
+        const int64_t delay = swr_get_delay(swr, dec->sample_rate);
+        const int dstNbSamples = (int)av_rescale_rnd(delay + frame->nb_samples, outRateConst, dec->sample_rate, AV_ROUND_UP);
+        std::vector<uint8_t> outBytes;
+        outBytes.resize((size_t)dstNbSamples * (size_t)outCh * sizeof(int16_t));
+        uint8_t* outData[1] = { outBytes.data() };
+        const uint8_t** inData = (const uint8_t**)frame->data;
+        const int converted = swr_convert(swr, outData, dstNbSamples, inData, frame->nb_samples);
+        if (converted > 0) {
+            const size_t samplesOut = (size_t)converted * (size_t)outCh;
+            const int16_t* asS16 = (const int16_t*)outBytes.data();
+            const size_t oldSize = outPcm.size();
+            outPcm.resize(oldSize + samplesOut);
+            std::memcpy(outPcm.data() + oldSize, asS16, samplesOut * sizeof(int16_t));
+        }
+        av_frame_unref(frame);
+    }
+
+    av_frame_free(&frame);
+    av_packet_free(&pkt);
+    swr_free(&swr);
+    av_channel_layout_uninit(&inLayout);
+    av_channel_layout_uninit(&outLayout);
+    avcodec_free_context(&dec);
+    avformat_close_input(&fmt);
+
+    outRate = outRateConst;
+    outChannels = outCh;
+
+    return !outPcm.empty();
+}

src/states/VideoState.h

@@ -0,0 +1,67 @@
+// VideoState.h
+#pragma once
+
+#include "State.h"
+
+#include <atomic>
+#include <memory>
+#include <string>
+#include <thread>
+#include <vector>
+
+class VideoPlayer;
+
+class VideoState : public State {
+public:
+    explicit VideoState(StateContext& ctx);
+    ~VideoState() override;
+
+    void onEnter() override;
+    void onExit() override;
+    void handleEvent(const SDL_Event& e) override;
+    void update(double frameMs) override;
+    void render(SDL_Renderer* renderer, float logicalScale, SDL_Rect logicalVP) override;
+
+    // Called from the App's on-enter hook so we can create textures.
+    bool begin(SDL_Renderer* renderer, const std::string& path);
+
+private:
+    enum class Phase {
+        FadeInFirstFrame,
+        Playing,
+        FadeOutToBlack,
+        Done
+    };
+
+    void startAudioIfReady();
+    void stopAudio();
+
+    static bool decodeAudioPcm16Stereo44100(
+        const std::string& path,
+        std::vector<int16_t>& outPcm,
+        int& outRate,
+        int& outChannels
+    );
+
+    std::unique_ptr<VideoPlayer> m_player;
+    std::string m_path;
+
+    Phase m_phase = Phase::FadeInFirstFrame;
+    double m_phaseClockMs = 0.0;
+
+    static constexpr double FADE_IN_MS = 900.0;
+    static constexpr double FADE_OUT_MS = 450.0;
+
+    // Audio decoding runs in the background while we fade in.
+    std::atomic<bool> m_audioDecoded{false};
+    std::atomic<bool> m_audioDecodeFailed{false};
+    std::vector<int16_t> m_audioPcm;
+    int m_audioRate = 44100;
+    int m_audioChannels = 2;
+    bool m_audioStarted = false;
+
+    std::unique_ptr<std::jthread> m_audioThread;
+
+    // Render-time overlay alpha (0..1) for fade stages.
+    float m_blackOverlayAlpha = 1.0f;
+};

src/ui/BottomMenu.cpp

@@ -13,7 +13,7 @@ static bool pointInRect(const SDL_FRect& r, float x, float y) {
     return x >= r.x && x <= (r.x + r.w) && y >= r.y && y <= (r.y + r.h);
 }
 
-BottomMenu buildBottomMenu(const MenuLayoutParams& params, int startLevel) {
+BottomMenu buildBottomMenu(const MenuLayoutParams& params, int startLevel, bool coopVsAI) {
     BottomMenu menu{};
 
     auto rects = computeMenuButtonRects(params);
@@ -22,12 +22,14 @@ BottomMenu buildBottomMenu(const MenuLayoutParams& params, int startLevel) {
     std::snprintf(levelBtnText, sizeof(levelBtnText), "LEVEL %d", startLevel);
 
     menu.buttons[0] = Button{ BottomMenuItem::Play, rects[0], "PLAY", false };
-    menu.buttons[1] = Button{ BottomMenuItem::Challenge, rects[1], "CHALLENGE", false };
-    menu.buttons[2] = Button{ BottomMenuItem::Level, rects[2], levelBtnText, true };
-    menu.buttons[3] = Button{ BottomMenuItem::Options, rects[3], "OPTIONS", true };
-    menu.buttons[4] = Button{ BottomMenuItem::Help, rects[4], "HELP", true };
-    menu.buttons[5] = Button{ BottomMenuItem::About, rects[5], "ABOUT", true };
-    menu.buttons[6] = Button{ BottomMenuItem::Exit, rects[6], "EXIT", true };
+    // Always show a neutral "COOPERATE" label (remove per-mode suffixes)
+    menu.buttons[1] = Button{ BottomMenuItem::Cooperate, rects[1], "COOPERATE", false };
+    menu.buttons[2] = Button{ BottomMenuItem::Challenge, rects[2], "CHALLENGE", false };
+    menu.buttons[3] = Button{ BottomMenuItem::Level, rects[3], levelBtnText, true };
+    menu.buttons[4] = Button{ BottomMenuItem::Options, rects[4], "OPTIONS", true };
+    menu.buttons[5] = Button{ BottomMenuItem::Help, rects[5], "HELP", true };
+    menu.buttons[6] = Button{ BottomMenuItem::About, rects[6], "ABOUT", true };
+    menu.buttons[7] = Button{ BottomMenuItem::Exit, rects[7], "EXIT", true };
 
     return menu;
 }
@@ -62,10 +64,15 @@ void renderBottomMenu(SDL_Renderer* renderer,
 
         if (!b.textOnly) {
             const bool isPlay = (i == 0);
-            const bool isChallenge = (i == 1);
+            const bool isCoop = (i == 1);
+            const bool isChallenge = (i == 2);
             SDL_Color bgCol{ 18, 22, 28, static_cast<Uint8>(std::round(180.0 * aMul)) };
             SDL_Color bdCol{ 255, 200, 70, static_cast<Uint8>(std::round(220.0 * aMul)) };
-            if (isChallenge) {
+            if (isCoop) {
+                // Cooperative mode gets a cyan/magenta accent to separate from Endless/Challenge
+                bgCol = SDL_Color{ 22, 30, 40, static_cast<Uint8>(std::round(190.0 * aMul)) };
+                bdCol = SDL_Color{ 160, 210, 255, static_cast<Uint8>(std::round(230.0 * aMul)) };
+            } else if (isChallenge) {
                 // Give Challenge a teal accent to distinguish from Play
                 bgCol = SDL_Color{ 18, 36, 36, static_cast<Uint8>(std::round(190.0 * aMul)) };
                 bdCol = SDL_Color{ 120, 255, 220, static_cast<Uint8>(std::round(230.0 * aMul)) };
@@ -82,14 +89,14 @@ void renderBottomMenu(SDL_Renderer* renderer,
         }
     }
 
-    // '+' separators between the bottom HUD buttons (indices 2..last)
+    // '+' separators between the bottom HUD buttons (indices 3..last)
     {
         SDL_BlendMode prevBlend = SDL_BLENDMODE_NONE;
         SDL_GetRenderDrawBlendMode(renderer, &prevBlend);
         SDL_SetRenderDrawBlendMode(renderer, SDL_BLENDMODE_BLEND);
         SDL_SetRenderDrawColor(renderer, 120, 220, 255, static_cast<Uint8>(std::round(180.0 * baseMul)));
 
-        const int firstSmall = 2;
+        const int firstSmall = 3;
         const int lastSmall = MENU_BTN_COUNT - 1;
         float y = menu.buttons[firstSmall].rect.y + menu.buttons[firstSmall].rect.h * 0.5f;
         for (int i = firstSmall; i < lastSmall; ++i) {

src/ui/BottomMenu.h

@@ -15,12 +15,13 @@ namespace ui {
 
 enum class BottomMenuItem : int {
     Play = 0,
-    Challenge = 1,
-    Level = 2,
-    Options = 3,
-    Help = 4,
-    About = 5,
-    Exit = 6,
+    Cooperate = 1,
+    Challenge = 2,
+    Level = 3,
+    Options = 4,
+    Help = 5,
+    About = 6,
+    Exit = 7,
 };
 
 struct Button {
@@ -34,11 +35,11 @@ struct BottomMenu {
     std::array<Button, MENU_BTN_COUNT> buttons{};
 };
 
-BottomMenu buildBottomMenu(const MenuLayoutParams& params, int startLevel);
+BottomMenu buildBottomMenu(const MenuLayoutParams& params, int startLevel, bool coopVsAI);
 
 // Draws the cockpit HUD menu (PLAY + 4 bottom items) using existing UIRenderer primitives.
-// hoveredIndex: -1..5
-// selectedIndex: 0..5 (keyboard selection)
+// hoveredIndex: -1..7
+// selectedIndex: 0..7 (keyboard selection)
 // alphaMul: 0..1 (overall group alpha)
 void renderBottomMenu(SDL_Renderer* renderer,
                       FontAtlas* font,

src/ui/MenuLayout.cpp

@@ -1,7 +1,8 @@
 #include "ui/MenuLayout.h"
 #include "ui/UIConstants.h"
-#include <cmath>
+#include <algorithm>
 #include <array>
+#include <cmath>
 
 namespace ui {
 
@@ -12,7 +13,7 @@ std::array<SDL_FRect, MENU_BTN_COUNT> computeMenuButtonRects(const MenuLayoutPar
     float contentOffsetY = (p.winH - LOGICAL_H * p.logicalScale) * 0.5f / p.logicalScale;
 
     // Cockpit HUD layout (matches main_screen art):
-    //  - Top row: PLAY and CHALLENGE (big buttons)
+    //  - Top row: PLAY / COOPERATE / CHALLENGE (big buttons)
     //  - Second row: LEVEL / OPTIONS / HELP / ABOUT / EXIT (smaller buttons)
     const float marginX = std::max(24.0f, LOGICAL_W * 0.03f);
     const float marginBottom = std::max(26.0f, LOGICAL_H * 0.03f);
@@ -26,9 +27,10 @@ std::array<SDL_FRect, MENU_BTN_COUNT> computeMenuButtonRects(const MenuLayoutPar
     float smallSpacing = 26.0f;
 
     // Scale down for narrow windows so nothing goes offscreen.
-    const int smallCount = MENU_BTN_COUNT - 2;
-    float smallTotal = smallW * static_cast<float>(smallCount) + smallSpacing * static_cast<float>(smallCount - 1);
-    float topRowTotal = playW * 2.0f + bigGap;
+    const int bigCount = 3;
+    const int smallCount = MENU_BTN_COUNT - bigCount;
+    float smallTotal = smallW * static_cast<float>(smallCount) + smallSpacing * static_cast<float>(std::max(smallCount - 1, 0));
+    float topRowTotal = playW * static_cast<float>(bigCount) + bigGap * static_cast<float>(bigCount - 1);
     if (smallTotal > availableW || topRowTotal > availableW) {
         float s = availableW / std::max(std::max(smallTotal, topRowTotal), 1.0f);
         smallW *= s;
@@ -48,11 +50,13 @@ std::array<SDL_FRect, MENU_BTN_COUNT> computeMenuButtonRects(const MenuLayoutPar
     float playCY = smallCY - smallH * 0.5f - rowGap - playH * 0.5f;
 
     std::array<SDL_FRect, MENU_BTN_COUNT> rects{};
-    // Top row big buttons
-    float playLeft = centerX - (playW + bigGap * 0.5f);
-    float challengeLeft = centerX + bigGap * 0.5f;
-    rects[0] = SDL_FRect{ playLeft, playCY - playH * 0.5f, playW, playH };
-    rects[1] = SDL_FRect{ challengeLeft, playCY - playH * 0.5f, playW, playH };
+    // Top row big buttons (PLAY / COOPERATE / CHALLENGE)
+    float bigRowW = playW * static_cast<float>(bigCount) + bigGap * static_cast<float>(bigCount - 1);
+    float leftBig = centerX - bigRowW * 0.5f;
+    for (int i = 0; i < bigCount; ++i) {
+        float x = leftBig + i * (playW + bigGap);
+        rects[i] = SDL_FRect{ x, playCY - playH * 0.5f, playW, playH };
+    }
 
     float rowW = smallW * static_cast<float>(smallCount) + smallSpacing * static_cast<float>(smallCount - 1);
     float left = centerX - rowW * 0.5f;
@@ -63,7 +67,7 @@ std::array<SDL_FRect, MENU_BTN_COUNT> computeMenuButtonRects(const MenuLayoutPar
 
     for (int i = 0; i < smallCount; ++i) {
         float x = left + i * (smallW + smallSpacing);
-        rects[i + 2] = SDL_FRect{ x, smallCY - smallH * 0.5f, smallW, smallH };
+        rects[i + bigCount] = SDL_FRect{ x, smallCY - smallH * 0.5f, smallW, smallH };
     }
     return rects;
 }

src/ui/MenuLayout.h

@@ -17,7 +17,7 @@ struct MenuLayoutParams {
 std::array<SDL_FRect, MENU_BTN_COUNT> computeMenuButtonRects(const MenuLayoutParams& p);
 
 // Hit test a point given in logical content-local coordinates against menu buttons
-// Returns index 0..4 or -1 if none
+// Returns index 0..(MENU_BTN_COUNT-1) or -1 if none
 int hitTestMenuButtons(const MenuLayoutParams& p, float localX, float localY);
 
 // Return settings button rect (logical coords)

src/ui/MenuWrappers.cpp

@@ -83,6 +83,6 @@ void menu_drawSettingsPopup(SDL_Renderer* renderer, FontAtlas& font, bool musicE
     bool sfxOn = true;
     font.draw(renderer, popupX + 140, popupY + 100, sfxOn ? "ON" : "OFF", 1.5f, sfxOn ? SDL_Color{0,255,0,255} : SDL_Color{255,0,0,255});
     font.draw(renderer, popupX + 20, popupY + 150, "M = TOGGLE MUSIC", 1.0f, SDL_Color{200,200,220,255});
-    font.draw(renderer, popupX + 20, popupY + 170, "S = TOGGLE SOUND FX", 1.0f, SDL_Color{200,200,220,255});
+    font.draw(renderer, popupX + 20, popupY + 170, "K = TOGGLE SOUND FX", 1.0f, SDL_Color{200,200,220,255});
     font.draw(renderer, popupX + 20, popupY + 190, "ESC = CLOSE", 1.0f, SDL_Color{200,200,220,255});
 }

src/ui/UIConstants.h

@@ -1,6 +1,6 @@
 #pragma once
 
-static constexpr int MENU_BTN_COUNT = 7;
+static constexpr int MENU_BTN_COUNT = 8;
 static constexpr float MENU_SMALL_THRESHOLD = 700.0f;
 static constexpr float MENU_BTN_WIDTH_LARGE = 300.0f;
 static constexpr float MENU_BTN_WIDTH_SMALL_FACTOR = 0.4f; // multiplied by LOGICAL_W

src/video/VideoPlayer.cpp

@@ -0,0 +1,172 @@
+#include "VideoPlayer.h"
+
+#include <iostream>
+#include <chrono>
+
+extern "C" {
+#include <libavformat/avformat.h>
+#include <libavcodec/avcodec.h>
+#include <libswscale/swscale.h>
+#include <libavutil/imgutils.h>
+}
+
+VideoPlayer::VideoPlayer() {}
+
+VideoPlayer::~VideoPlayer() {
+    if (m_texture) SDL_DestroyTexture(m_texture);
+    if (m_rgbBuffer) av_free(m_rgbBuffer);
+    if (m_frame) av_frame_free(&m_frame);
+    if (m_sws) sws_freeContext(m_sws);
+    if (m_dec) avcodec_free_context(&m_dec);
+    if (m_fmt) avformat_close_input(&m_fmt);
+}
+
+bool VideoPlayer::open(const std::string& path, SDL_Renderer* renderer) {
+    m_path = path;
+    avformat_network_init();
+    if (avformat_open_input(&m_fmt, path.c_str(), nullptr, nullptr) != 0) {
+        std::cerr << "VideoPlayer: failed to open " << path << "\n";
+        return false;
+    }
+    if (avformat_find_stream_info(m_fmt, nullptr) < 0) {
+        std::cerr << "VideoPlayer: failed to find stream info\n";
+        return false;
+    }
+    // Find video stream
+    m_videoStream = -1;
+    for (unsigned i = 0; i < m_fmt->nb_streams; ++i) {
+        if (m_fmt->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) { m_videoStream = (int)i; break; }
+    }
+    if (m_videoStream < 0) { std::cerr << "VideoPlayer: no video stream\n"; return false; }
+
+    AVCodecParameters* codecpar = m_fmt->streams[m_videoStream]->codecpar;
+    const AVCodec* codec = avcodec_find_decoder(codecpar->codec_id);
+    if (!codec) { std::cerr << "VideoPlayer: decoder not found\n"; return false; }
+    m_dec = avcodec_alloc_context3(codec);
+    if (!m_dec) { std::cerr << "VideoPlayer: failed to alloc codec ctx\n"; return false; }
+    if (avcodec_parameters_to_context(m_dec, codecpar) < 0) { std::cerr << "VideoPlayer: param to ctx failed\n"; return false; }
+    if (avcodec_open2(m_dec, codec, nullptr) < 0) { std::cerr << "VideoPlayer: open codec failed\n"; return false; }
+
+    m_width = m_dec->width;
+    m_height = m_dec->height;
+    m_frame = av_frame_alloc();
+    m_sws = sws_getContext(m_width, m_height, m_dec->pix_fmt, m_width, m_height, AV_PIX_FMT_RGBA, SWS_BILINEAR, nullptr, nullptr, nullptr);
+    m_rgbBufferSize = av_image_get_buffer_size(AV_PIX_FMT_RGBA, m_width, m_height, 1);
+    m_rgbBuffer = (uint8_t*)av_malloc(m_rgbBufferSize);
+
+    if (renderer) {
+        m_texture = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_RGBA32, SDL_TEXTUREACCESS_STREAMING, m_width, m_height);
+        if (!m_texture) { std::cerr << "VideoPlayer: failed create texture\n"; }
+    }
+
+    m_finished = false;
+    m_textureReady = false;
+    m_started = false;
+    m_frameAccumulatorMs = 0.0;
+
+    // Estimate frame interval.
+    m_frameIntervalMs = 33.333;
+    if (m_fmt && m_videoStream >= 0) {
+        AVRational fr = m_fmt->streams[m_videoStream]->avg_frame_rate;
+        if (fr.num > 0 && fr.den > 0) {
+            const double fps = av_q2d(fr);
+            if (fps > 1.0) {
+                m_frameIntervalMs = 1000.0 / fps;
+            }
+        }
+    }
+
+    // Seek to start
+    av_seek_frame(m_fmt, m_videoStream, 0, AVSEEK_FLAG_BACKWARD);
+    if (m_dec) avcodec_flush_buffers(m_dec);
+    return true;
+}
+
+bool VideoPlayer::decodeOneFrame() {
+    if (m_finished || !m_fmt) return false;
+
+    AVPacket* pkt = av_packet_alloc();
+    if (!pkt) {
+        m_finished = true;
+        return false;
+    }
+
+    int ret = 0;
+    while (av_read_frame(m_fmt, pkt) >= 0) {
+        if (pkt->stream_index == m_videoStream) {
+            ret = avcodec_send_packet(m_dec, pkt);
+            if (ret < 0) {
+                av_packet_unref(pkt);
+                continue;
+            }
+
+            while (ret >= 0) {
+                ret = avcodec_receive_frame(m_dec, m_frame);
+                if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) break;
+                if (ret < 0) break;
+
+                uint8_t* dstData[4] = { m_rgbBuffer, nullptr, nullptr, nullptr };
+                int dstLinesize[4] = { m_width * 4, 0, 0, 0 };
+                sws_scale(m_sws, m_frame->data, m_frame->linesize, 0, m_height, dstData, dstLinesize);
+                m_textureReady = true;
+                if (m_texture) {
+                    SDL_UpdateTexture(m_texture, nullptr, m_rgbBuffer, dstLinesize[0]);
+                }
+                av_frame_unref(m_frame);
+
+                av_packet_unref(pkt);
+                av_packet_free(&pkt);
+                return true;
+            }
+        }
+        av_packet_unref(pkt);
+    }
+
+    av_packet_free(&pkt);
+    m_finished = true;
+    return false;
+}
+
+bool VideoPlayer::decodeFirstFrame() {
+    if (!m_fmt || m_finished) return false;
+    if (m_textureReady) return true;
+    // Ensure we are at the beginning.
+    av_seek_frame(m_fmt, m_videoStream, 0, AVSEEK_FLAG_BACKWARD);
+    if (m_dec) avcodec_flush_buffers(m_dec);
+    return decodeOneFrame();
+}
+
+void VideoPlayer::start() {
+    m_started = true;
+}
+
+bool VideoPlayer::update(double deltaMs) {
+    if (m_finished || !m_fmt) return false;
+    if (!m_started) return true;
+
+    m_frameAccumulatorMs += deltaMs;
+
+    // Decode at most a small burst per frame to avoid spiral-of-death.
+    int framesDecoded = 0;
+    const int maxFramesPerTick = 4;
+    while (m_frameAccumulatorMs >= m_frameIntervalMs && framesDecoded < maxFramesPerTick) {
+        m_frameAccumulatorMs -= m_frameIntervalMs;
+        if (!decodeOneFrame()) {
+            return false;
+        }
+        ++framesDecoded;
+    }
+    return !m_finished;
+}
+
+bool VideoPlayer::update() {
+    // Legacy behavior: decode exactly one frame.
+    return decodeOneFrame();
+}
+
+void VideoPlayer::render(SDL_Renderer* renderer, int winW, int winH) {
+    if (!m_textureReady || !m_texture || !renderer) return;
+    if (winW <= 0 || winH <= 0) return;
+    SDL_FRect dst = { 0.0f, 0.0f, (float)winW, (float)winH };
+    SDL_RenderTexture(renderer, m_texture, nullptr, &dst);
+}

src/video/VideoPlayer.h

@@ -0,0 +1,59 @@
+// Minimal FFmpeg-based video player (video) that decodes into an SDL texture.
+// Audio for the intro is currently handled outside this class.
+#pragma once
+
+#include <string>
+#include <SDL3/SDL.h>
+
+struct AVFormatContext;
+struct AVCodecContext;
+struct SwsContext;
+struct AVFrame;
+
+class VideoPlayer {
+public:
+    VideoPlayer();
+    ~VideoPlayer();
+
+    // Open video file and attach to SDL_Renderer for texture creation
+    bool open(const std::string& path, SDL_Renderer* renderer);
+    // Decode the first frame immediately so it can be used for fade-in.
+    bool decodeFirstFrame();
+
+    // Start time-based playback.
+    void start();
+
+    // Update playback using elapsed time in milliseconds.
+    // Returns false if finished or error.
+    bool update(double deltaMs);
+
+    // Compatibility: advance by one decoded frame.
+    bool update();
+
+    // Render video frame fullscreen to the given renderer using provided output size.
+    void render(SDL_Renderer* renderer, int winW, int winH);
+    bool isFinished() const { return m_finished; }
+    bool isTextureReady() const { return m_textureReady; }
+
+    double getFrameIntervalMs() const { return m_frameIntervalMs; }
+    bool isStarted() const { return m_started; }
+
+private:
+    bool decodeOneFrame();
+
+    AVFormatContext* m_fmt = nullptr;
+    AVCodecContext* m_dec = nullptr;
+    SwsContext* m_sws = nullptr;
+    AVFrame* m_frame = nullptr;
+    int m_videoStream = -1;
+    double m_frameIntervalMs = 33.333;
+    double m_frameAccumulatorMs = 0.0;
+    bool m_started = false;
+    int m_width = 0, m_height = 0;
+    SDL_Texture* m_texture = nullptr;
+    uint8_t* m_rgbBuffer = nullptr;
+    int m_rgbBufferSize = 0;
+    bool m_textureReady = false;
+    bool m_finished = true;
+    std::string m_path;
+};

tests/test_board.cpp

@@ -0,0 +1,38 @@
+#include "../src/logic/Board.h"
+#include <gtest/gtest.h>
+
+using logic::Board;
+
+TEST(BoardTests, InitiallyEmpty)
+{
+    Board b;
+    for (int y = 0; y < Board::Height; ++y)
+        for (int x = 0; x < Board::Width; ++x)
+            EXPECT_EQ(b.at(x, y), Board::Cell::Empty);
+}
+
+TEST(BoardTests, ClearSingleFullLine)
+{
+    Board b;
+    int y = Board::Height - 1;
+    for (int x = 0; x < Board::Width; ++x) b.set(x, y, Board::Cell::Filled);
+    int cleared = b.clearFullLines();
+    EXPECT_EQ(cleared, 1);
+    for (int x = 0; x < Board::Width; ++x) EXPECT_EQ(b.at(x, Board::Height - 1), Board::Cell::Empty);
+}
+
+TEST(BoardTests, ClearTwoNonAdjacentLines)
+{
+    Board b;
+    int y1 = Board::Height - 1;
+    int y2 = Board::Height - 3;
+    for (int x = 0; x < Board::Width; ++x) { b.set(x, y1, Board::Cell::Filled); b.set(x, y2, Board::Cell::Filled); }
+    int cleared = b.clearFullLines();
+    EXPECT_EQ(cleared, 2);
+}
+
+int main(int argc, char** argv)
+{
+    ::testing::InitGoogleTest(&argc, argv);
+    return RUN_ALL_TESTS();
+}

vcpkg.json

@@ -6,8 +6,11 @@
 			"name": "sdl3-image",
 			"features": ["jpeg", "png", "webp"]
 		},
+		"enet",
 		"catch2",
+		"gtest",
 		"cpr",
-		"nlohmann-json"
+		"nlohmann-json",
+		"ffmpeg"
 	]
 }