examples/renderer/20-blending: Note when a blend mode is unsupported.

examples/renderer/20-blending/blending.c

@@ -211,14 +211,25 @@ SDL_AppResult SDL_AppIterate(void *appstate)
         SDL_FRect blue_dst  = { panels[i].x + BLUE_OFFSET,  panels[i].y + BLUE_OFFSET,  RECT_SIZE, RECT_SIZE };
 
         /* Apply the current blend mode */
-        SDL_SetTextureBlendMode(red_rect_texture,   blend_modes[i]);
+        const bool supported = SDL_SetTextureBlendMode(red_rect_texture, blend_modes[i]);  /* just make sure the renderer supports this blend mode */
         SDL_SetTextureBlendMode(green_rect_texture, blend_modes[i]);
-        SDL_SetTextureBlendMode(blue_rect_texture,  blend_modes[i]);
+        SDL_SetTextureBlendMode(blue_rect_texture, blend_modes[i]);
 
         /* Render textures */
         SDL_RenderTexture(renderer, red_rect_texture,   NULL, &red_dst);
         SDL_RenderTexture(renderer, green_rect_texture, NULL, &green_dst);
         SDL_RenderTexture(renderer, blue_rect_texture,  NULL, &blue_dst);
+
+        /* Not all renderers support all blend modes. The renderer will try to pick something close in this case,
+           but it should be noted that the results might be unexpected, so we add "[UNSUPPORTED]" to this panel. */
+        if (!supported) {
+            const float textwidth = 104.0f;
+            const SDL_FRect dst = { panels[i].x + ((panels[i].w - textwidth) / 2.0f), panels[i].y + (panels[i].h - 8), textwidth, 8 };
+            SDL_SetRenderDrawColor(renderer, 0, 0, 0, SDL_ALPHA_OPAQUE);
+            SDL_RenderFillRect(renderer, &dst);
+            SDL_SetRenderDrawColor(renderer, 255, 255, 255, SDL_ALPHA_OPAQUE);
+            SDL_RenderDebugText(renderer, dst.x, dst.y, "[UNSUPPORTED]");
+        }
     }
 
     SDL_RenderPresent(renderer);