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/*
* Copyright (C) 2013 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.launcher3;
import android.view.animation.AccelerateInterpolator;
import android.view.animation.AnimationUtils;
import android.view.animation.Interpolator;
/**
* Scroller that gradually reaches a target velocity.
*/
class RampUpScroller {
private final Interpolator mInterpolator;
private final long mRampUpTime;
private long mStartTime;
private long mDeltaTime;
private float mTargetVelocityX;
private float mTargetVelocityY;
private int mDeltaX;
private int mDeltaY;
/**
* Creates a new ramp-up scroller that reaches full velocity after a
* specified duration.
*
* @param rampUpTime Duration before the scroller reaches target velocity.
*/
public RampUpScroller(long rampUpTime) {
mInterpolator = new AccelerateInterpolator();
mRampUpTime = rampUpTime;
}
/**
* Starts the scroller at the current animation time.
*/
public void start() {
mStartTime = AnimationUtils.currentAnimationTimeMillis();
mDeltaTime = mStartTime;
}
/**
* Computes the current scroll deltas. This usually only be called after
* starting the scroller with {@link #start()}.
*
* @see #getDeltaX()
* @see #getDeltaY()
*/
public void computeScrollDelta() {
final long currentTime = AnimationUtils.currentAnimationTimeMillis();
final long elapsedSinceStart = currentTime - mStartTime;
final float scale;
if (elapsedSinceStart < mRampUpTime) {
scale = mInterpolator.getInterpolation((float) elapsedSinceStart / mRampUpTime);
} else {
scale = 1f;
}
final long elapsedSinceDelta = currentTime - mDeltaTime;
mDeltaTime = currentTime;
mDeltaX = (int) (elapsedSinceDelta * scale * mTargetVelocityX);
mDeltaY = (int) (elapsedSinceDelta * scale * mTargetVelocityY);
}
/**
* Sets the target velocity for this scroller.
*
* @param x The target X velocity in pixels per millisecond.
* @param y The target Y velocity in pixels per millisecond.
*/
public void setTargetVelocity(float x, float y) {
mTargetVelocityX = x;
mTargetVelocityY = y;
}
/**
* @return The target X velocity for this scroller.
*/
public float getTargetVelocityX() {
return mTargetVelocityX;
}
/**
* @return The target Y velocity for this scroller.
*/
public float getTargetVelocityY() {
return mTargetVelocityY;
}
/**
* The distance traveled in the X-coordinate computed by the last call to
* {@link #computeScrollDelta()}.
*/
public int getDeltaX() {
return mDeltaX;
}
/**
* The distance traveled in the Y-coordinate computed by the last call to
* {@link #computeScrollDelta()}.
*/
public int getDeltaY() {
return mDeltaY;
}
}
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