[497679] Ensure UI is updated while processing events.

org.eclipse.gef4.fx.swt/src/org/eclipse/gef4/fx/swt/canvas/FXCanvasEx.java

@@ -15,6 +15,8 @@
 package org.eclipse.gef4.fx.swt.canvas;
 
 import java.lang.reflect.Method;
+import java.util.ArrayList;
+import java.util.List;
 
 import org.eclipse.gef4.common.reflect.ReflectionUtils;
 import org.eclipse.gef4.fx.swt.gestures.SWT2FXEventConverter;
@@ -24,11 +26,15 @@
 import org.eclipse.swt.graphics.ImageData;
 import org.eclipse.swt.widgets.Canvas;
 import org.eclipse.swt.widgets.Composite;
+import org.eclipse.swt.widgets.Display;
 
 import javafx.beans.value.ChangeListener;
 import javafx.beans.value.ObservableValue;
 import javafx.embed.swt.FXCanvas;
 import javafx.embed.swt.SWTFXUtils;
+import javafx.event.Event;
+import javafx.event.EventDispatchChain;
+import javafx.event.EventDispatcher;
 import javafx.scene.Cursor;
 import javafx.scene.ImageCursor;
 import javafx.scene.Scene;
@@ -50,6 +56,47 @@
 public class FXCanvasEx extends FXCanvas {
 
 	private SWT2FXEventConverter gestureConverter;
+	private EventDispatcher initialEventDispatcher;
+	private boolean wasUpdated = true;
+	private List<Event> deferredEvents = new ArrayList<>();
+
+	private EventDispatcher deferringEventDispatcher = new EventDispatcher() {
+		@Override
+		public Event dispatchEvent(final Event event,
+				final EventDispatchChain tail) {
+			// defer event if display was not updated since the last
+			// event was processed
+			if (!wasUpdated) {
+				deferredEvents.add(event);
+				return event;
+			}
+			// schedule runnable
+			wasUpdated = false;
+			Display.getDefault().asyncExec(new Runnable() {
+				@Override
+				public void run() {
+					wasUpdated = true;
+					if (!deferredEvents.isEmpty()) {
+						// dispatch deferred events
+						for (Event e : deferredEvents) {
+							initialEventDispatcher.dispatchEvent(e, tail);
+						}
+						// clear deferred events
+						deferredEvents.clear();
+					}
+					// update UI
+					while (Display.getDefault().readAndDispatch()) {
+						;
+					}
+				}
+			});
+			// dispatch the most recent event
+			Event returnedEvent = initialEventDispatcher.dispatchEvent(event,
+					tail);
+			// return dispatched event
+			return returnedEvent;
+		}
+	};
 
 	private ChangeListener<Cursor> cursorChangeListener = new ChangeListener<Cursor>() {
 		@Override
@@ -143,10 +190,13 @@ public Window getStage() {
 	public void setScene(Scene newScene) {
 		Scene oldScene = getScene();
 		if (oldScene != null) {
+			oldScene.setEventDispatcher(initialEventDispatcher);
 			oldScene.cursorProperty().removeListener(cursorChangeListener);
 		}
 		super.setScene(newScene);
 		if (newScene != null) {
+			initialEventDispatcher = newScene.getEventDispatcher();
+			newScene.setEventDispatcher(deferringEventDispatcher);
 			newScene.cursorProperty().addListener(cursorChangeListener);
 		}
 	}