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/*
* Copyright (C) 2014 The Android Open Source Project
*
* 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.android.systemui.statusbar;
import android.animation.ValueAnimator;
import android.content.Context;
import android.view.animation.AnimationUtils;
import android.view.animation.Interpolator;
import android.view.animation.PathInterpolator;
/**
* Utility class to calculate general fling animation when the finger is released.
*/
public class FlingAnimationUtils {
private static final float LINEAR_OUT_SLOW_IN_Y2 = 0.35f;
private static final float MAX_LENGTH_SECONDS = 0.4f;
private static final float MIN_VELOCITY_DP_PER_SECOND = 250;
/**
* Crazy math. http://en.wikipedia.org/wiki/B%C3%A9zier_curve
*/
private static final float LINEAR_OUT_SLOW_IN_START_GRADIENT = 1/LINEAR_OUT_SLOW_IN_Y2;
private Interpolator mLinearOutSlowIn;
private Interpolator mFastOutSlowIn;
private float mMinVelocityPxPerSecond;
public FlingAnimationUtils(Context ctx) {
mLinearOutSlowIn = new PathInterpolator(0, 0, LINEAR_OUT_SLOW_IN_Y2, 1);
mFastOutSlowIn
= AnimationUtils.loadInterpolator(ctx, android.R.interpolator.fast_out_slow_in);
mMinVelocityPxPerSecond
= MIN_VELOCITY_DP_PER_SECOND * ctx.getResources().getDisplayMetrics().density;
}
/**
* Applies the interpolator and length to the animator, such that the fling animation is
* consistent with the finger motion.
*
* @param animator the animator to apply
* @param currValue the current value
* @param endValue the end value of the animator
* @param velocity the current velocity of the motion
*/
public void apply(ValueAnimator animator, float currValue, float endValue, float velocity) {
float diff = Math.abs(endValue - currValue);
float velAbs = Math.abs(velocity);
float durationSeconds = LINEAR_OUT_SLOW_IN_START_GRADIENT * diff / velAbs;
if (durationSeconds <= MAX_LENGTH_SECONDS) {
animator.setInterpolator(mLinearOutSlowIn);
} else if (velAbs >= mMinVelocityPxPerSecond) {
// Cross fade between fast-out-slow-in and linear interpolator with current velocity.
durationSeconds = MAX_LENGTH_SECONDS;
VelocityInterpolator velocityInterpolator
= new VelocityInterpolator(durationSeconds, velAbs, diff);
InterpolatorInterpolator superInterpolator = new InterpolatorInterpolator(
velocityInterpolator, mLinearOutSlowIn, mLinearOutSlowIn);
animator.setInterpolator(superInterpolator);
} else {
// Just use a normal interpolator which doesn't take the velocity into account.
durationSeconds = MAX_LENGTH_SECONDS;
animator.setInterpolator(mFastOutSlowIn);
}
animator.setDuration((long) (durationSeconds * 1000));
}
/**
* An interpolator which interpolates two interpolators with an interpolator.
*/
private static final class InterpolatorInterpolator implements Interpolator {
private Interpolator mInterpolator1;
private Interpolator mInterpolator2;
private Interpolator mCrossfader;
InterpolatorInterpolator(Interpolator interpolator1, Interpolator interpolator2,
Interpolator crossfader) {
mInterpolator1 = interpolator1;
mInterpolator2 = interpolator2;
mCrossfader = crossfader;
}
@Override
public float getInterpolation(float input) {
float t = mCrossfader.getInterpolation(input);
return (1 - t) * mInterpolator1.getInterpolation(input)
+ t * mInterpolator2.getInterpolation(input);
}
}
/**
* An interpolator which interpolates with a fixed velocity.
*/
private static final class VelocityInterpolator implements Interpolator {
private float mDurationSeconds;
private float mVelocity;
private float mDiff;
private VelocityInterpolator(float durationSeconds, float velocity, float diff) {
mDurationSeconds = durationSeconds;
mVelocity = velocity;
mDiff = diff;
}
@Override
public float getInterpolation(float input) {
float time = input * mDurationSeconds;
return time * mVelocity / mDiff;
}
}
}
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