Own canvas async work and thin NodeCanvas composite

src/legacy_canvas_draw_merge_services.h

@@ -175,6 +175,20 @@ struct LegacyCanvasDrawMergeFinalPlaneCompositeExecution {
     std::function<void()> unbind_merged_texture;
 };
 
+struct LegacyCanvasDrawMergeCacheToScreenCompositeUniforms {
+    LegacyCanvasDrawMergeCheckerboardUniforms checkerboard;
+    LegacyCanvasDrawMergeTextureUniforms texture;
+};
+
+struct LegacyCanvasDrawMergeCacheToScreenCompositeExecution {
+    std::function<void()> enable_blend;
+    std::function<void(const LegacyCanvasDrawMergeCheckerboardUniforms&, int)> draw_checkerboard_plane;
+    std::function<void()> bind_sampler;
+    std::function<void()> bind_cache_texture;
+    std::function<void()> draw_cache_texture;
+    std::function<void()> unbind_cache_texture;
+};
+
 struct LegacyCanvasDrawMergeDisplayResolveUniforms {
     LegacyCanvasDrawMergeTextureUniforms texture;
 };
@@ -447,6 +461,23 @@ inline void execute_legacy_canvas_draw_merge_final_plane_composite(
     execution.unbind_merged_texture();
 }
 
+inline void execute_legacy_canvas_draw_merge_cache_to_screen_composite(
+    const LegacyCanvasDrawMergeCacheToScreenCompositeUniforms& uniforms,
+    const LegacyCanvasDrawMergeCacheToScreenCompositeExecution& execution)
+{
+    execution.enable_blend();
+
+    for (int plane_index = 0; plane_index < 6; ++plane_index) {
+        execution.draw_checkerboard_plane(uniforms.checkerboard, plane_index);
+    }
+
+    execution.bind_sampler();
+    execution.bind_cache_texture();
+    setup_legacy_canvas_draw_merge_texture_shader(uniforms.texture);
+    execution.draw_cache_texture();
+    execution.unbind_cache_texture();
+}
+
 inline void execute_legacy_canvas_draw_merge_display_resolve(
     const LegacyCanvasDrawMergeDisplayResolveUniforms& uniforms,
     const LegacyCanvasDrawMergeDisplayResolveExecution& execution)