added clear line effect

src/gameplay/effects/LineEffect.cpp

@@ -188,10 +188,11 @@ 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) {
     if (rows.empty()) return;
     
     clearingRows = rows;
+    effectGridCols = std::max(1, gridCols);
     state = AnimationState::FLASH_WHITE;
     timer = 0.0f;
     dropProgress = 0.0f;
@@ -228,7 +229,7 @@ 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;
         SDL_Color tint = pickFireColor();
         spawnGlowPulse(centerX, centerY, static_cast<float>(blockSize), tint);
@@ -386,7 +387,7 @@ void LineEffect::renderFlash(int gridX, int gridY, int blockSize) {
         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 + 8),
             static_cast<float>(blockSize + 8)
         };
         SDL_RenderFillRect(renderer, &flashRect);

src/gameplay/effects/LineEffect.h

@@ -69,7 +69,7 @@ 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);
     
     // Update and render the effect
     bool update(float deltaTime); // Returns true if effect is complete
@@ -120,4 +120,5 @@ private:
     std::array<float, Game::ROWS> rowDropTargets{};
     float dropProgress = 0.0f;
     int dropBlockSize = 0;
+    int effectGridCols = Game::COLS;
 };

src/graphics/renderers/GameRenderer.cpp

@@ -1926,12 +1926,18 @@ void GameRenderer::renderCoopPlayingState(
     // Handle line clearing effects (defer to LineEffect like single-player)
     if (game->hasCompletedLines() && lineEffect && !lineEffect->isActive()) {
         auto completedLines = game->getCompletedLines();
-        lineEffect->startLineClear(completedLines, static_cast<int>(gridX), static_cast<int>(gridY), static_cast<int>(finalBlockSize));
+        lineEffect->startLineClear(completedLines, static_cast<int>(gridX), static_cast<int>(gridY), static_cast<int>(finalBlockSize), CoopGame::COLS);
         if (completedLines.size() == 4) {
             AppFireworks::spawn(gridX + GRID_W * 0.5f, gridY + GRID_H * 0.5f);
         }
     }
 
+    // Precompute row drop offsets (line collapse effect)
+    std::array<float, CoopGame::ROWS> rowDropOffsets{};
+    for (int y = 0; y < CoopGame::ROWS; ++y) {
+        rowDropOffsets[y] = (lineEffect ? lineEffect->getRowDropOffset(y) : 0.0f);
+    }
+
     // Grid backdrop and border
     drawRectWithOffset(gridX - 3 - contentOffsetX, gridY - 3 - contentOffsetY, GRID_W + 6, GRID_H + 6, {100, 120, 200, 255});
     drawRectWithOffset(gridX - contentOffsetX, gridY - contentOffsetY, GRID_W, GRID_H, {20, 25, 35, 255});
@@ -1980,11 +1986,12 @@ void GameRenderer::renderCoopPlayingState(
     // Draw settled blocks
     const auto& board = game->boardRef();
     for (int y = 0; y < CoopGame::ROWS; ++y) {
+        float dropOffset = rowDropOffsets[y];
         for (int x = 0; x < CoopGame::COLS; ++x) {
             const auto& cell = board[y * CoopGame::COLS + x];
             if (!cell.occupied || cell.value <= 0) continue;
             float px = gridX + x * finalBlockSize;
-            float py = gridY + y * finalBlockSize;
+            float py = gridY + y * finalBlockSize + dropOffset;
             drawBlockTexturePublic(renderer, blocksTex, px, py, finalBlockSize, cell.value - 1);
         }
     }
@@ -2012,7 +2019,20 @@ void GameRenderer::renderCoopPlayingState(
                 sf.tileSize = finalBlockSize;
                 // Target to first visible row (row 0)
                 sf.targetX = gridX + static_cast<float>(sf.piece.x) * finalBlockSize;
-                sf.targetY = gridY + 0.0f * finalBlockSize;
+                // IMPORTANT: In classic mode, pieces can spawn with their first filled
+                // cell not at cy=0 within the 4x4. To avoid appearing one row too low
+                // (and then jumping up), align the topmost filled cell to row 0.
+                int minCy = 4;
+                for (int cy = 0; cy < 4; ++cy) {
+                    for (int cx = 0; cx < 4; ++cx) {
+                        if (!CoopGame::cellFilled(sf.piece, cx, cy)) continue;
+                        minCy = std::min(minCy, cy);
+                    }
+                }
+                if (minCy == 4) {
+                    minCy = 0;
+                }
+                sf.targetY = gridY - static_cast<float>(minCy) * finalBlockSize;
             } else {
                 // Reuse exact horizontal smoothing from single-player
                 constexpr float HORIZONTAL_SMOOTH_MS = 55.0f;
@@ -2177,6 +2197,11 @@ void GameRenderer::renderCoopPlayingState(
         drawPiece(game->current(CoopGame::PlayerSide::Right), rightOffsets, false);
     }
 
+    // Draw line clearing effects above pieces (matches single-player)
+    if (lineEffect && lineEffect->isActive()) {
+        lineEffect->render(renderer, blocksTex, static_cast<int>(gridX), static_cast<int>(gridY), static_cast<int>(finalBlockSize));
+    }
+
     // Next panels (two)
     const float nextPanelPad = 12.0f;
     const float nextPanelW = (GRID_W * 0.5f) - finalBlockSize * 1.5f;