/**
* Copyright (c) 2015-present, Facebook, Inc.
* All rights reserved.
*
* This source code is licensed under the BSD-style license found in the
* LICENSE file in the root directory of this source tree. An additional grant
* of patent rights can be found in the PATENTS file in the same directory.
*/
package com.facebook.react.animated;
import com.facebook.react.bridge.ReadableMap;
/**
* Implementation of {@link AnimationDriver} providing support for decay animations. The
* implementation is copied from the JS version in {@code AnimatedImplementation.js}.
*/
public class DecayAnimation extends AnimationDriver {
private final double mVelocity;
private final double mDeceleration;
private long mStartFrameTimeMillis = -1;
private double mFromValue;
private double mLastValue;
public DecayAnimation(ReadableMap config) {
mVelocity = config.getDouble("velocity");
mDeceleration = config.getDouble("deceleration");
}
@Override
public void runAnimationStep(long frameTimeNanos) {
long frameTimeMillis = frameTimeNanos / 1000000;
if (mStartFrameTimeMillis == -1) {
// since this is the first animation step, consider the start to be on the previous frame
mStartFrameTimeMillis = frameTimeMillis - 16;
mFromValue = mAnimatedValue.mValue;
mLastValue = mAnimatedValue.mValue;
}
final double value = mFromValue +
(mVelocity / (1 - mDeceleration)) *
(1 - Math.exp(-(1 - mDeceleration) * (frameTimeMillis - mStartFrameTimeMillis)));
if (Math.abs(mLastValue - value) < 0.1) {
mHasFinished = true;
return;
}
mLastValue = value;
mAnimatedValue.mValue = value;
}
}