compress file when saving, using bbox, dirty flags and PNG compression

engine/app.cpp

@@ -580,7 +580,7 @@ void App::initLayout()
             button->on_click = [this,button](Node*) {
                 if (canvas)
                 {
-                    canvas->m_canvas->save(data_path);
+                    canvas->m_canvas->export_equirectangular(data_path);
                 }
             };
         }