canvas pan/zoom, project into canvas using inverse transform, implement eraser (early prototype)

engine/layout.cpp

@@ -69,6 +69,8 @@ kEventResult Node::on_event(Event* e)
             }
             break;
         default:
+            if (handle_event(e) == kEventResult::Consumed)
+                return kEventResult::Consumed;
             break;
         }
         break;