Add canvas clear service boundary

src/app_core/document_canvas.h

@@ -17,6 +17,13 @@ struct DocumentCanvasClearPlan {
     bool no_op = true;
 };
 
+class DocumentCanvasClearServices {
+public:
+    virtual ~DocumentCanvasClearServices() = default;
+
+    virtual void clear_current_canvas(float r, float g, float b, float a) = 0;
+};
+
 [[nodiscard]] inline pp::foundation::Status validate_clear_color_channel(float value) noexcept
 {
     if (!std::isfinite(value)) {
@@ -55,4 +62,24 @@ struct DocumentCanvasClearPlan {
     return pp::foundation::Result<DocumentCanvasClearPlan>::success(plan);
 }
 
+[[nodiscard]] inline pp::foundation::Status execute_document_canvas_clear_plan(
+    const DocumentCanvasClearPlan& plan,
+    DocumentCanvasClearServices& services)
+{
+    const float channels[] { plan.r, plan.g, plan.b, plan.a };
+    for (const float channel : channels) {
+        const auto status = validate_clear_color_channel(channel);
+        if (!status.ok()) {
+            return status;
+        }
+    }
+
+    if (plan.no_op || !plan.clears_canvas) {
+        return pp::foundation::Status::success();
+    }
+
+    services.clear_current_canvas(plan.r, plan.g, plan.b, plan.a);
+    return pp::foundation::Status::success();
+}
+
 } // namespace pp::app