/*
* Copyright 2011 Google Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not
* use this file except in compliance with the License. You may obtain a copy of
* the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations under
* the License.
*/
package com.google.gwt.animation.client;
import com.google.gwt.core.client.Duration;
import com.google.gwt.dom.client.Element;
import com.google.gwt.user.client.Timer;
import java.util.ArrayList;
import java.util.List;
/**
* Implementation using a timer for browsers that do not support animation
* frames.
*/
class AnimationSchedulerImplTimer extends AnimationScheduler {
/**
* Timer based implementation of {@link AnimationScheduler.AnimationHandle}.
*/
private class AnimationHandleImpl extends AnimationHandle {
private final AnimationCallback callback;
public AnimationHandleImpl(AnimationCallback callback) {
this.callback = callback;
}
@Override
public void cancel() {
cancelAnimationFrame(this);
}
public AnimationCallback getCallback() {
return callback;
}
}
/**
* The default time in milliseconds between frames. 60 fps == 16.67 ms.
*/
private static final int DEFAULT_FRAME_DELAY = 16;
/**
* The minimum delay in milliseconds between frames. The minimum delay is
* imposed to prevent freezing the UI.
*/
private static final int MIN_FRAME_DELAY = 5;
/**
* The list of animations that are currently running.
*/
private final List<AnimationHandleImpl> animationRequests = new ArrayList<AnimationHandleImpl>();
/**
* The singleton timer that updates all animations.
*/
private final Timer timer = new Timer() {
@Override
public void run() {
updateAnimations();
}
};
@Override
public AnimationHandle requestAnimationFrame(final AnimationCallback callback, Element element) {
// Save the animation frame request.
AnimationHandleImpl requestId = new AnimationHandleImpl(callback);
animationRequests.add(requestId);
// Start the timer if it isn't started.
if (animationRequests.size() == 1) {
timer.schedule(DEFAULT_FRAME_DELAY);
}
// Return the request id.
return requestId;
}
private void cancelAnimationFrame(AnimationHandle requestId) {
// Remove the request from the list.
animationRequests.remove(requestId);
// Stop the timer if there are no more requests.
if (animationRequests.size() == 0) {
timer.cancel();
}
}
/**
* Iterate over all animations and update them.
*/
private void updateAnimations() {
// Copy the animation requests to avoid concurrent modifications.
AnimationHandleImpl[] curAnimations = new AnimationHandleImpl[animationRequests.size()];
curAnimations = animationRequests.toArray(curAnimations);
// Iterate over the animation requests.
Duration duration = new Duration();
for (AnimationHandleImpl requestId : curAnimations) {
// Remove the current request.
animationRequests.remove(requestId);
// Execute the callback.
requestId.getCallback().execute(duration.getStartMillis());
}
// Reschedule the timer if there are more animation requests.
if (animationRequests.size() > 0) {
/*
* In order to achieve as close to 60fps as possible, we calculate the new
* delay based on the execution time of this method. The delay will be
* less than 16ms, assuming this method takes more than 1ms to complete.
*/
timer.schedule(Math.max(MIN_FRAME_DELAY, DEFAULT_FRAME_DELAY - duration.elapsedMillis()));
}
}
}