Bug 497679

Description Matthias Wienand 2016-07-11 09:40:51 EDT

Currently, when embedding a JavaFX application into an SWT application using FXCanvas, the UI is not always updated while processing events. This is especially noticeable when the event processing is slow, i.e. multiple events are queued while an event is being processed. This results in a UI freeze until the events are fully processed and the UI thread is free to update itself.

The FXCanvasEx should ensure that the UI is always updated while processing events. This can be done by deferring the processing of incoming events while waiting for a UI update, as follows:

Scene scene = getCanvas().getScene();
final EventDispatcher eventDispatcher = scene.getEventDispatcher();
final boolean[] updated = new boolean[] { true };
final List<Event>[] deferred = new List[] { new ArrayList<Event>() };
scene.setEventDispatcher(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 (!updated[0]) {
			deferred[0].add(event);
			return event;
		}
		// schedule runnable
		updated[0] = false;
		Display.getDefault().asyncExec(new Runnable() {
			@Override
			public void run() {
				updated[0] = true;
				// dispatch deferred events
				if (!deferred[0].isEmpty()) {
					for (Event e : deferred[0]) {
						eventDispatcher.dispatchEvent(e, tail);
					}
					deferred[0].clear();
				}
				// update UI
				while (Display.getDefault().readAndDispatch()) {
					;
				}
			}
		});
		// dispatch the most recent event
		Event returnedEvent = eventDispatcher.dispatchEvent(event, tail);
		// return dispatched event
		return returnedEvent;
	}
});