Golang XUtil.Sync方法代碼示例

// compressMotionNotify takes a MotionNotify event, and inspects the event
// queue for any future MotionNotify events that can be received without
// blocking. The most recent MotionNotify event is then returned.
// Note that we need to make sure that the Event, Child, Detail, State, Root
// and SameScreen fields are the same to ensure the same window/action is
// generating events. That is, we are only compressing the RootX, RootY,
// EventX and EventY fields.
// This function is not thread safe, since Peek returns a *copy* of the
// event queue---which could be out of date by the time we dequeue events.
func compressMotionNotify(X *xgbutil.XUtil,
	ev xevent.MotionNotifyEvent) xevent.MotionNotifyEvent {

	// We force a round trip request so that we make sure to read all
	// available events.
	X.Sync()
	xevent.Read(X, false)

	// The most recent MotionNotify event that we'll end up returning.
	laste := ev

	// Look through each event in the queue. If it's an event and it matches
	// all the fields in 'ev' that are detailed above, then set it to 'laste'.
	// In which case, we'll also dequeue the event, otherwise it will be
	// processed twice!
	// N.B. If our only goal was to find the most recent relevant MotionNotify
	// event, we could traverse the event queue backwards and simply use
	// the first MotionNotify we see. However, this could potentially leave
	// other MotionNotify events in the queue, which we *don't* want to be
	// processed. So we stride along and just pick off MotionNotify events
	// until we don't see any more.
	for i, ee := range xevent.Peek(X) {
		if ee.Err != nil { // This is an error, skip it.
			continue
		}

		// Use type assertion to make sure this is a MotionNotify event.
		if mn, ok := ee.Event.(xproto.MotionNotifyEvent); ok {
			// Now make sure all appropriate fields are equivalent.
			if ev.Event == mn.Event && ev.Child == mn.Child &&
				ev.Detail == mn.Detail && ev.State == mn.State &&
				ev.Root == mn.Root && ev.SameScreen == mn.SameScreen {

				// Set the most recent/valid motion notify event.
				laste = xevent.MotionNotifyEvent{&mn}

				// We cheat and use the stack semantics of defer to dequeue
				// most recent motion notify events first, so that the indices
				// don't become invalid. (If we dequeued oldest first, we'd
				// have to account for all future events shifting to the left
				// by one.)
				defer func(i int) { xevent.DequeueAt(X, i) }(i)
			}
		}
	}

	// This isn't strictly necessary, but is correct. We should update
	// xgbutil's sense of time with the most recent event processed.
	// This is typically done in the main event loop, but since we are
	// subverting the main event loop, we should take care of it.
	X.TimeSet(laste.Time)

	return laste
}

// dragStep executes the "step" function registered for the current drag.
// It also compresses the MotionNotify events.
func dragStep(xu *xgbutil.XUtil, ev xevent.MotionNotifyEvent) {
	// If for whatever reason we don't have any *piece* of a grab,
	// we've gotta back out.
	if !mouseDrag(xu) || mouseDragStep(xu) == nil || mouseDragEnd(xu) == nil {
		dragUngrab(xu)
		mouseDragStepSet(xu, nil)
		mouseDragEndSet(xu, nil)
		return
	}

	// The most recent MotionNotify event that we'll end up returning.
	laste := ev

	// We force a round trip request so that we make sure to read all
	// available events.
	xu.Sync()
	xevent.Read(xu, false)

	// Compress MotionNotify events.
	for i, ee := range xevent.Peek(xu) {
		if ee.Err != nil { // This is an error, skip it.
			continue
		}

		// Use type assertion to make sure this is a MotionNotify event.
		if mn, ok := ee.Event.(xproto.MotionNotifyEvent); ok {
			// Now make sure all appropriate fields are equivalent.
			if ev.Event == mn.Event && ev.Child == mn.Child &&
				ev.Detail == mn.Detail && ev.State == mn.State &&
				ev.Root == mn.Root && ev.SameScreen == mn.SameScreen {

				// Set the most recent/valid motion notify event.
				laste = xevent.MotionNotifyEvent{&mn}

				// We cheat and use the stack semantics of defer to dequeue
				// most recent motion notify events first, so that the indices
				// don't become invalid. (If we dequeued oldest first, we'd
				// have to account for all future events shifting to the left
				// by one.)
				defer func(i int) { xevent.DequeueAt(xu, i) }(i)
			}
		}
	}
	xu.TimeSet(laste.Time)

	// now actually run the step
	mouseDragStep(xu)(xu, int(laste.RootX), int(laste.RootY),
		int(laste.EventX), int(laste.EventY))
}

// compressConfigureNotify "compresses" incoming ConfigureNotify events so that
// event processing never lags behind gradient drawing.
// This is necessary because drawing a gradient cannot keep up with the rate
// at which ConfigureNotify events are sent to us, thereby creating a "lag".
// Compression works by examining the "future" of the event queue, and skipping
// ahead to the most recent ConfigureNotify event and throwing away the rest.
//
// A more detailed treatment of event compression can be found in
// xgbutil/examples/compress-events.
func compressConfigureNotify(X *xgbutil.XUtil,
	ev xevent.ConfigureNotifyEvent) xevent.ConfigureNotifyEvent {

	// Catch up with all X events as much as we can.
	X.Sync()
	xevent.Read(X, false) // non-blocking

	laste := ev
	for i, ee := range xevent.Peek(X) {
		if ee.Err != nil {
			continue
		}
		if cn, ok := ee.Event.(xproto.ConfigureNotifyEvent); ok {
			// Only compress this ConfigureNotify if it matches the window
			// of the original event.
			if ev.Event == cn.Event && ev.Window == cn.Window {
				laste = xevent.ConfigureNotifyEvent{&cn}
				defer func(i int) { xevent.DequeueAt(X, i) }(i)
			}
		}
	}
	return laste
}