transition effect when afvance level

src/main.cpp

@@ -108,15 +108,35 @@ static SDL_Texture* loadTextureFromImage(SDL_Renderer* renderer, const std::stri
     return texture;
 }
 
+enum class LevelBackgroundPhase { Idle, ZoomOut, ZoomIn };
+
 struct LevelBackgroundFader {
     SDL_Texture* currentTex = nullptr;
     SDL_Texture* nextTex = nullptr;
     int currentLevel = -1;
     int queuedLevel = -1;
-    float fadeElapsedMs = 0.0f;
+    float phaseElapsedMs = 0.0f;
+    float phaseDurationMs = 0.0f;
     float fadeDurationMs = Config::Gameplay::LEVEL_FADE_DURATION;
+    LevelBackgroundPhase phase = LevelBackgroundPhase::Idle;
 };
 
+static float getPhaseDurationMs(const LevelBackgroundFader& fader, LevelBackgroundPhase phase) {
+    const float total = std::max(1200.0f, fader.fadeDurationMs);
+    switch (phase) {
+        case LevelBackgroundPhase::ZoomOut: return total * 0.45f;
+        case LevelBackgroundPhase::ZoomIn:  return total * 0.45f;
+        case LevelBackgroundPhase::Idle:
+        default: return 0.0f;
+    }
+}
+
+static void setPhase(LevelBackgroundFader& fader, LevelBackgroundPhase nextPhase) {
+    fader.phase = nextPhase;
+    fader.phaseDurationMs = getPhaseDurationMs(fader, nextPhase);
+    fader.phaseElapsedMs = 0.0f;
+}
+
 static void destroyTexture(SDL_Texture*& tex) {
     if (tex) {
         SDL_DestroyTexture(tex);
@@ -146,32 +166,90 @@ static bool queueLevelBackground(LevelBackgroundFader& fader, SDL_Renderer* rend
     destroyTexture(fader.nextTex);
     fader.nextTex = newTexture;
     fader.queuedLevel = level;
-    fader.fadeElapsedMs = 0.0f;
 
     if (!fader.currentTex) {
+        // First background load happens instantly.
         fader.currentTex = fader.nextTex;
         fader.currentLevel = fader.queuedLevel;
         fader.nextTex = nullptr;
         fader.queuedLevel = -1;
+        fader.phase = LevelBackgroundPhase::Idle;
+        fader.phaseElapsedMs = 0.0f;
+        fader.phaseDurationMs = 0.0f;
+    } else if (fader.phase == LevelBackgroundPhase::Idle) {
+        // Kick off fancy transition.
+        setPhase(fader, LevelBackgroundPhase::ZoomOut);
     }
 
     return true;
 }
 
 static void updateLevelBackgroundFade(LevelBackgroundFader& fader, float frameMs) {
-    if (!fader.currentTex || !fader.nextTex) {
+    if (fader.phase == LevelBackgroundPhase::Idle) {
         return;
     }
 
-    fader.fadeElapsedMs += frameMs;
+    // Guard against missing textures
-    if (fader.fadeElapsedMs >= fader.fadeDurationMs) {
+    if (!fader.currentTex && !fader.nextTex) {
+        fader.phase = LevelBackgroundPhase::Idle;
+        return;
+    }
+
+    fader.phaseElapsedMs += frameMs;
+    if (fader.phaseElapsedMs < std::max(1.0f, fader.phaseDurationMs)) {
+        return;
+    }
+
+    switch (fader.phase) {
+        case LevelBackgroundPhase::ZoomOut:
+            // After zoom-out, swap textures then start zoom-in.
+            if (fader.nextTex) {
                 destroyTexture(fader.currentTex);
                 fader.currentTex = fader.nextTex;
                 fader.currentLevel = fader.queuedLevel;
                 fader.nextTex = nullptr;
                 fader.queuedLevel = -1;
-        fader.fadeElapsedMs = 0.0f;
             }
+            setPhase(fader, LevelBackgroundPhase::ZoomIn);
+            break;
+        case LevelBackgroundPhase::ZoomIn:
+            fader.phase = LevelBackgroundPhase::Idle;
+            fader.phaseElapsedMs = 0.0f;
+            fader.phaseDurationMs = 0.0f;
+            break;
+        case LevelBackgroundPhase::Idle:
+        default:
+            fader.phase = LevelBackgroundPhase::Idle;
+            break;
+    }
+}
+
+static void renderScaledBackground(SDL_Renderer* renderer, SDL_Texture* tex, int winW, int winH, float scale, Uint8 alpha = 255) {
+    if (!renderer || !tex) {
+        return;
+    }
+
+    scale = std::max(0.5f, scale);
+    SDL_FRect dest{
+        (winW - winW * scale) * 0.5f,
+        (winH - winH * scale) * 0.5f,
+        winW * scale,
+        winH * scale
+    };
+
+    SDL_SetTextureAlphaMod(tex, alpha);
+    SDL_RenderTexture(renderer, tex, nullptr, &dest);
+    SDL_SetTextureAlphaMod(tex, 255);
+}
+
+static void drawOverlay(SDL_Renderer* renderer, const SDL_FRect& rect, SDL_Color color, Uint8 alpha) {
+    if (!renderer || alpha == 0) {
+        return;
+    }
+    SDL_SetRenderDrawBlendMode(renderer, SDL_BLENDMODE_BLEND);
+    SDL_SetRenderDrawColor(renderer, color.r, color.g, color.b, alpha);
+    SDL_RenderFillRect(renderer, &rect);
+    SDL_SetRenderDrawBlendMode(renderer, SDL_BLENDMODE_NONE);
 }
 
 static void renderLevelBackgrounds(const LevelBackgroundFader& fader, SDL_Renderer* renderer, int winW, int winH) {
@@ -180,22 +258,36 @@ static void renderLevelBackgrounds(const LevelBackgroundFader& fader, SDL_Render
     }
 
     SDL_FRect fullRect{0.f, 0.f, static_cast<float>(winW), static_cast<float>(winH)};
+    const float duration = std::max(1.0f, fader.phaseDurationMs);
+    const float progress = (fader.phase == LevelBackgroundPhase::Idle) ? 0.0f : std::clamp(fader.phaseElapsedMs / duration, 0.0f, 1.0f);
 
-    if (fader.currentTex && fader.nextTex) {
+    switch (fader.phase) {
-        const float duration = std::max(1.0f, fader.fadeDurationMs);
+        case LevelBackgroundPhase::ZoomOut: {
-        const float alpha = std::clamp(fader.fadeElapsedMs / duration, 0.0f, 1.0f);
+            const float scale = 1.0f + progress * 0.15f;
-
+            if (fader.currentTex) {
-        SDL_SetTextureAlphaMod(fader.currentTex, Uint8((1.0f - alpha) * 255.0f));
+                renderScaledBackground(renderer, fader.currentTex, winW, winH, scale, Uint8((1.0f - progress * 0.4f) * 255.0f));
-        SDL_RenderTexture(renderer, fader.currentTex, nullptr, &fullRect);
+                drawOverlay(renderer, fullRect, SDL_Color{0, 0, 0, 255}, Uint8(progress * 200.0f));
-        SDL_SetTextureAlphaMod(fader.currentTex, 255);
+            }
-
+            break;
-        SDL_SetTextureAlphaMod(fader.nextTex, Uint8(alpha * 255.0f));
+        }
-        SDL_RenderTexture(renderer, fader.nextTex, nullptr, &fullRect);
+        case LevelBackgroundPhase::ZoomIn: {
-        SDL_SetTextureAlphaMod(fader.nextTex, 255);
+            const float scale = 1.10f - progress * 0.10f;
-    } else if (fader.currentTex) {
+            const Uint8 alpha = Uint8((0.4f + progress * 0.6f) * 255.0f);
-        SDL_RenderTexture(renderer, fader.currentTex, nullptr, &fullRect);
+            if (fader.currentTex) {
+                renderScaledBackground(renderer, fader.currentTex, winW, winH, scale, alpha);
+            }
+            break;
+        }
+        case LevelBackgroundPhase::Idle:
+        default:
+            if (fader.currentTex) {
+                renderScaledBackground(renderer, fader.currentTex, winW, winH, 1.0f, 255);
             } else if (fader.nextTex) {
-        SDL_RenderTexture(renderer, fader.nextTex, nullptr, &fullRect);
+                renderScaledBackground(renderer, fader.nextTex, winW, winH, 1.0f, 255);
+            } else {
+                drawOverlay(renderer, fullRect, SDL_Color{0, 0, 0, 255}, 255);
+            }
+            break;
     }
 }
 
@@ -204,7 +296,9 @@ static void resetLevelBackgrounds(LevelBackgroundFader& fader) {
     destroyTexture(fader.nextTex);
     fader.currentLevel = -1;
     fader.queuedLevel = -1;
-    fader.fadeElapsedMs = 0.0f;
+    fader.phaseElapsedMs = 0.0f;
+    fader.phaseDurationMs = 0.0f;
+    fader.phase = LevelBackgroundPhase::Idle;
 }
 
 // Hover state for level popup ( -1 = none, 0..19 = hovered level )