complete open/save project including layer names, in layout bring canvas to background and use translucent UI on top, save computation on Android with lazy rendering on events only

engine/canvas.h

@@ -79,7 +79,7 @@ public:
     void stroke_draw();
     void stroke_end();
     void stroke_commit();
-    void clear(const glm::vec4& color = { 1, 1, 1, 1 });
+    void clear(const glm::vec4& color = { 1, 1, 1, 0 });
     void snapshot_save(std::string data_path);
     void snapshot_restore();
     void clear_context();