PicoGraphics: Implement RGB888 alpha blending.

pimoroni · Nov 21, 2024 · ad5120a · ad5120a
1 parent 18d3ed3
commit ad5120a
Showing 1 changed file with 23 additions and 7 deletions.
diff --git a/libraries/pico_graphics/pico_graphics_pen_rgb888.cpp b/libraries/pico_graphics/pico_graphics_pen_rgb888.cpp
@@ -38,19 +38,35 @@ namespace pimoroni {
     }
     bool PicoGraphics_PenRGB888::render_tile(const Tile *tile) {
         for(int y = 0; y < tile->h; y++) {
-            uint8_t *palpha = &tile->data[(y * tile->stride)];
-            uint32_t *pdest = &((uint32_t *)frame_buffer)[tile->x + ((tile->y + y) * bounds.w)];
+            uint8_t *p_alpha = &tile->data[(y * tile->stride)];
+            uint32_t *p_dest = &((uint32_t *)frame_buffer)[tile->x + ((tile->y + y) * bounds.w)];
             for(int x = 0; x < tile->w; x++) {
-                uint8_t alpha = *palpha;
+                uint16_t dest = *p_dest;
+                uint8_t alpha = *p_alpha;
 
                 // TODO: Alpha blending
-                if(alpha == 0) {
+                if(alpha == 255) {
+                  *p_dest = color;
+                }else if(alpha == 0) {
                 } else {
-                  *pdest = color;
+                    // blend tha pixel
+                    uint32_t sr = (color >> 16) & 0xff;
+                    uint32_t sg = (color >> 8) & 0xff;
+                    uint32_t sb = (color >> 0) & 0xff;
+
+                    uint32_t dr = (dest >> 16) & 0xff;
+                    uint32_t dg = (dest >> 8) & 0xff;
+                    uint32_t db = (dest >> 0) & 0xff;
+
+                    uint8_t r = ((sr * alpha) + (dr * (255 - alpha))) >> 8;
+                    uint8_t g = ((sg * alpha) + (dg * (255 - alpha))) >> 8;
+                    uint8_t b = ((sb * alpha) + (db * (255 - alpha))) >> 8;
+
+                    *p_dest = (r << 16) | (g << 8) | b;
                 }
 
-                pdest++;
-                palpha++;
+                p_dest++;
+                p_alpha++;
             }
         }