fix rtt copy/move

src/canvas.h

@@ -175,6 +175,7 @@ public:
     void destroy();
     bool create(int width, int height);
     void resize(int width, int height);
+    Layer& layer() { return *m_layers[m_current_layer_idx]; }
     void layer_remove(int idx);
     void layer_add(std::string name, std::shared_ptr<Layer> layer = nullptr, int index = 0);
     void layer_order(int idx, int pos);