feat(editor): brush amb preview snap-to-grid i pintura per clic

source/game/map/tilemap.cpp

@@ -127,6 +127,30 @@ void Tilemap::setTileAt(int col, int row, int index) {
 auto Tilemap::save(const std::string& yaml_path) const -> bool {
     return TilemapWriter::saveDataBlock(yaml_path, data_);
 }
+
+void Tilemap::renderTilePreview(int canvas_x, int canvas_y, int tile_index) const {
+    if (tile_index < 0) { return; }
+    const auto TILESET = Resource::Cache::get().getSurface(tileset_path_);
+    if (TILESET == nullptr) { return; }
+    auto& screen = Screen::get();
+    auto* buf = screen.getCanvasArgb();
+    const int CW = screen.getCanvasWidth();
+    const int CH = screen.getCanvasHeight();
+    const auto TRANSPARENT = TILESET->getTransparentColor();
+    const int SX0 = (tile_index % tileset_cols_) * tile_size_;
+    const int SY0 = (tile_index / tileset_cols_) * tile_size_;
+    for (int y = 0; y < tile_size_; ++y) {
+        const int DY = canvas_y + y;
+        if (DY < 0 || DY >= CH) { continue; }
+        for (int x = 0; x < tile_size_; ++x) {
+            const int DX = canvas_x + x;
+            if (DX < 0 || DX >= CW) { continue; }
+            const auto IDX = TILESET->getPixel(SX0 + x, SY0 + y);
+            if (IDX == TRANSPARENT) { continue; }
+            buf[(static_cast<std::size_t>(DY) * static_cast<std::size_t>(CW)) + static_cast<std::size_t>(DX)] = TILESET->getPaletteColor(IDX);
+        }
+    }
+}
 #endif
 
 void Tilemap::render() const {

source/game/map/tilemap.hpp

@@ -50,6 +50,13 @@ class Tilemap {
     // només toca el bloc `data:` i preserva la resta byte a byte.
     void setTileAt(int col, int row, int index);
     [[nodiscard]] auto save(const std::string& yaml_path) const -> bool;
+
+    // Pinta un únic tile del tileset sobre el canvas del Screen a la
+    // posició (canvas_x, canvas_y). Els píxels transparents del tileset
+    // es respecten (deixen visible el que hi ha sota). Usat per l'editor
+    // com a preview del brush sota el cursor, sense tocar `pixels_` ni
+    // `data_` fins que l'usuari fa click.
+    void renderTilePreview(int canvas_x, int canvas_y, int tile_index) const;
 #endif
 
    private: