Added intro video

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;
+};