Extract Canvas draw_merge plane setup helper

src/legacy_canvas_draw_merge_services.h

@@ -87,6 +87,19 @@ struct LegacyCanvasDrawMergeLayerTextureExecution {
     std::function<void()> unbind_layer_texture;
 };
 
+struct LegacyCanvasDrawMergePlaneSetupUniforms {
+    LegacyCanvasDrawMergeCheckerboardUniforms checkerboard;
+    bool use_blend = false;
+    bool draw_checkerboard = false;
+};
+
+struct LegacyCanvasDrawMergePlaneSetupExecution {
+    std::function<void()> clear_plane;
+    std::function<void()> disable_blend;
+    std::function<void()> enable_blend;
+    std::function<void()> draw;
+};
+
 struct LegacyCanvasDrawMergeFinalPlaneCompositeUniforms {
     LegacyCanvasDrawMergeCheckerboardUniforms checkerboard;
     LegacyCanvasDrawMergeTextureUniforms texture;
@@ -291,6 +304,26 @@ inline void execute_legacy_canvas_draw_merge_layer_texture(
     execution.unbind_layer_texture();
 }
 
+inline void execute_legacy_canvas_draw_merge_plane_setup(
+    const LegacyCanvasDrawMergePlaneSetupUniforms& uniforms,
+    const LegacyCanvasDrawMergePlaneSetupExecution& execution)
+{
+    execution.clear_plane();
+
+    if (uniforms.use_blend) {
+        execution.disable_blend();
+        execution.clear_plane();
+        return;
+    }
+
+    if (uniforms.draw_checkerboard) {
+        setup_legacy_canvas_draw_merge_checkerboard_shader(uniforms.checkerboard);
+        execution.draw();
+    }
+
+    execution.enable_blend();
+}
+
 inline void execute_legacy_canvas_draw_merge_final_plane_composite(
     const LegacyCanvasDrawMergeFinalPlaneCompositeUniforms& uniforms,
     const LegacyCanvasDrawMergeFinalPlaneCompositeExecution& execution)