RampAnimator.java revision 4255869ac00e700395832ee73b2294603d4b6ece 
1/*
2 * Copyright (C) 2012 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.android.server.display;
18
19import android.animation.ValueAnimator;
20import android.util.IntProperty;
21import android.view.Choreographer;
22
23/**
24 * A custom animator that progressively updates a property value at
25 * a given variable rate until it reaches a particular target value.
26 */
27final class RampAnimator<T> {
28    private final T mObject;
29    private final IntProperty<T> mProperty;
30    private final Choreographer mChoreographer;
31
32    private int mCurrentValue;
33    private int mTargetValue;
34    private int mRate;
35
36    private boolean mAnimating;
37    private float mAnimatedValue; // higher precision copy of mCurrentValue
38    private long mLastFrameTimeNanos;
39
40    private boolean mFirstTime = true;
41
42    private Listener mListener;
43
44    public RampAnimator(T object, IntProperty<T> property) {
45        mObject = object;
46        mProperty = property;
47        mChoreographer = Choreographer.getInstance();
48    }
49
50    /**
51     * Starts animating towards the specified value.
52     *
53     * If this is the first time the property is being set, the value jumps
54     * directly to the target.
55     *
56     * @param target The target value.
57     * @param rate The convergence rate, in units per second.
58     * @return True if the target differs from the previous target.
59     */
60    public boolean animateTo(int target, int rate) {
61        // Immediately jump to the target the first time.
62        if (mFirstTime) {
63            mFirstTime = false;
64            mProperty.setValue(mObject, target);
65            mCurrentValue = target;
66            return true;
67        }
68
69        // Adjust the rate based on the closest target.
70        // If a faster rate is specified, then use the new rate so that we converge
71        // more rapidly based on the new request.
72        // If a slower rate is specified, then use the new rate only if the current
73        // value is somewhere in between the new and the old target meaning that
74        // we will be ramping in a different direction to get there.
75        // Otherwise, continue at the previous rate.
76        if (!mAnimating
77                || rate > mRate
78                || (target <= mCurrentValue && mCurrentValue <= mTargetValue)
79                || (mTargetValue <= mCurrentValue && mCurrentValue <= target)) {
80            mRate = rate;
81        }
82
83        final boolean changed = (mTargetValue != target);
84        mTargetValue = target;
85
86        // Start animating.
87        if (!mAnimating && target != mCurrentValue) {
88            mAnimating = true;
89            mAnimatedValue = mCurrentValue;
90            mLastFrameTimeNanos = System.nanoTime();
91            postCallback();
92        }
93
94        return changed;
95    }
96
97    /**
98     * Returns true if the animation is running.
99     */
100    public boolean isAnimating() {
101        return mAnimating;
102    }
103
104    /**
105     * Sets a listener to watch for animation events.
106     */
107    public void setListener(Listener listener) {
108        mListener = listener;
109    }
110
111    private void postCallback() {
112        mChoreographer.postCallback(Choreographer.CALLBACK_ANIMATION, mCallback, null);
113    }
114
115    private final Runnable mCallback = new Runnable() {
116        @Override // Choreographer callback
117        public void run() {
118            final long frameTimeNanos = mChoreographer.getFrameTimeNanos();
119            final float timeDelta = (frameTimeNanos - mLastFrameTimeNanos)
120                    * 0.000000001f;
121            mLastFrameTimeNanos = frameTimeNanos;
122
123            // Advance the animated value towards the target at the specified rate
124            // and clamp to the target. This gives us the new current value but
125            // we keep the animated value around to allow for fractional increments
126            // towards the target.
127            final float scale = ValueAnimator.getDurationScale();
128            if (scale == 0) {
129                // Animation off.
130                mAnimatedValue = mTargetValue;
131            } else {
132                final float amount = timeDelta * mRate / scale;
133                if (mTargetValue > mCurrentValue) {
134                    mAnimatedValue = Math.min(mAnimatedValue + amount, mTargetValue);
135                } else {
136                    mAnimatedValue = Math.max(mAnimatedValue - amount, mTargetValue);
137                }
138            }
139            final int oldCurrentValue = mCurrentValue;
140            mCurrentValue = Math.round(mAnimatedValue);
141
142            if (oldCurrentValue != mCurrentValue) {
143                mProperty.setValue(mObject, mCurrentValue);
144            }
145
146            if (mTargetValue != mCurrentValue) {
147                postCallback();
148            } else {
149                mAnimating = false;
150                if (mListener != null) {
151                    mListener.onAnimationEnd();
152                }
153            }
154        }
155    };
156
157    public interface Listener {
158        void onAnimationEnd();
159    }
160}
161