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/*
 * 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.shared.GWT;
import com.google.gwt.dom.client.Element;

/**
 * This class provides task scheduling for animations. Any exceptions thrown by
 * the command objects executed by the scheduler will be passed to the
 * {@link com.google.gwt.core.client.GWT.UncaughtExceptionHandler} if one is
 * installed.
 */
public abstract class AnimationScheduler {

  /**
   * Helper to detect native support for animations.
   * 

* Note: This class solely exists to provide opportunity for mocking frameworks to intercept * the native call. */ public static class AnimationSupportDetector { public native boolean isNativelySupported() /*-{ return !!$wnd.requestAnimationFrame && !!$wnd.cancelAnimationFrame; }-*/; } /** * The callback used when an animation frame becomes available. */ public interface AnimationCallback { /** * Invokes the command. * * @param timestamp the current timestamp */ void execute(double timestamp); } /** * A handle to the requested animation frame created by * {@link #requestAnimationFrame(AnimationCallback, Element)}. */ public abstract static class AnimationHandle { /** * Cancel the requested animation frame. If the animation frame is already * canceled, do nothing. */ public abstract void cancel(); } private static AnimationScheduler instance; /** * Returns the default implementation of the AnimationScheduler API. */ public static AnimationScheduler get() { if (instance == null) { AnimationSupportDetector supportDetector = GWT.create(AnimationSupportDetector.class); instance = (supportDetector != null && supportDetector.isNativelySupported()) ? new AnimationSchedulerImplStandard() : new AnimationSchedulerImplTimer(); } return instance; } /** * Schedule an animation, letting the browser decide when to trigger the next * step in the animation. * *

* NOTE: If you are animating an element, use * {@link #requestAnimationFrame(AnimationCallback, Element)} instead so the * browser can optimize for the specified element. *

* *

* Using this method instead of a timeout is preferred because the browser is * in the best position to decide how frequently to trigger the callback for * an animation of the specified element. The browser can balance multiple * animations and trigger callbacks at the optimal rate for smooth * performance. *

* * @param callback the callback to fire * @return a handle to the requested animation frame * @see #requestAnimationFrame(AnimationCallback, Element) */ public AnimationHandle requestAnimationFrame(AnimationCallback callback) { return requestAnimationFrame(callback, null); } /** * Schedule an animation, letting the browser decide when to trigger the next * step in the animation. * *

* Using this method instead of a timeout is preferred because the browser is * in the best position to decide how frequently to trigger the callback for * an animation of the specified element. The browser can balance multiple * animations and trigger callbacks at the optimal rate for smooth * performance. *

* * @param callback the callback to fire * @return a handle to the requested animation frame * @param element the element being animated */ public abstract AnimationHandle requestAnimationFrame(AnimationCallback callback, Element element); }




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