new background for main screen

src/graphics/effects/SpaceWarp.h

@@ -0,0 +1,69 @@
+#pragma once
+
+#include <SDL3/SDL.h>
+#include <random>
+#include <vector>
+
+struct SpaceWarpSettings {
+    float baseSpawnRange = 1.45f;        // logical radius for initial star positions
+    float warpFactorScale = 122.85f;       // scales perspective factor so stars spread faster or slower
+    float spawnMargin = 60.0f;          // how far offscreen a star can travel before respawn
+    float minShade = 0.85f;              // lower bound for per-star brightness multiplier
+    float maxShade = 1.15f;              // upper bound for per-star brightness multiplier
+    float minSpeed = 120.0f;             // slowest warp velocity (higher feels faster motion)
+    float maxSpeed = 280.0f;             // fastest warp velocity
+    float minDotSize = 2.5f;             // smallest star size in pixels
+    float maxDotSize = 4.5f;             // largest star size in pixels
+    float minAlpha = 70.0f;             // base opacity even for distant stars
+    float alphaDepthBoost = 160.0f;      // extra opacity applied as stars approach the camera
+    float minColor = 180.0f;             // clamp for minimum grayscale value
+    float maxColor = 205.0f;             // clamp for maximum grayscale value
+    float baseShadeScale = 0.75f;        // baseline multiplier applied to the sampled grayscale shade
+    float depthColorScale = 0.55f;       // how much depth affects the grayscale brightness
+    bool drawTrails = true;             // when true, also render streak lines for hyper-speed look
+    float trailAlphaScale = 0.75f;       // relative opacity for streak lines vs dots
+    float maxTrailLength = 36.0f;        // clamp length of each streak in pixels
+};
+
+class SpaceWarp {
+public:
+    SpaceWarp();
+    void init(int width, int height, int starCount = 320);
+    void resize(int width, int height);
+    void update(float deltaSeconds);
+    void draw(SDL_Renderer* renderer, float alphaScale = 1.0f);
+    void setSettings(const SpaceWarpSettings& newSettings);
+    const SpaceWarpSettings& getSettings() const { return settings; }
+
+private:
+    struct WarpStar {
+        float x = 0.0f;
+        float y = 0.0f;
+        float z = 0.0f;
+        float speed = 0.0f;
+        float prevScreenX = 0.0f;
+        float prevScreenY = 0.0f;
+        float screenX = 0.0f;
+        float screenY = 0.0f;
+        float shade = 1.0f;
+        Uint8 baseShade = 220;
+    };
+
+    void respawn(WarpStar& star, bool randomDepth = true);
+    bool project(const WarpStar& star, float& outX, float& outY) const;
+    float randomRange(float min, float max);
+
+    std::vector<WarpStar> stars;
+    std::mt19937 rng;
+
+    int width = 0;
+    int height = 0;
+    float centerX = 0.0f;
+    float centerY = 0.0f;
+    float warpFactor = 520.0f;
+
+    SpaceWarpSettings settings{};
+
+    float minDepth = 2.0f;
+    float maxDepth = 320.0f;
+};