Mindy DelliCarpini
121 lines
3.5 KiB
Java
121 lines
3.5 KiB
Java
/*
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* Copyright (C) 2013 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.android.launcher3;
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import android.view.animation.AccelerateInterpolator;
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import android.view.animation.AnimationUtils;
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import android.view.animation.Interpolator;
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/**
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* Scroller that gradually reaches a target velocity.
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*/
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class RampUpScroller {
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private final Interpolator mInterpolator;
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private final long mRampUpTime;
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private long mStartTime;
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private long mDeltaTime;
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private float mTargetVelocityX;
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private float mTargetVelocityY;
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private int mDeltaX;
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private int mDeltaY;
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/**
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* Creates a new ramp-up scroller that reaches full velocity after a
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* specified duration.
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*
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* @param rampUpTime Duration before the scroller reaches target velocity.
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*/
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public RampUpScroller(long rampUpTime) {
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mInterpolator = new AccelerateInterpolator();
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mRampUpTime = rampUpTime;
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}
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/**
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* Starts the scroller at the current animation time.
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*/
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public void start() {
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mStartTime = AnimationUtils.currentAnimationTimeMillis();
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mDeltaTime = mStartTime;
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}
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/**
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* Computes the current scroll deltas. This usually only be called after
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* starting the scroller with {@link #start()}.
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*
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* @see #getDeltaX()
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* @see #getDeltaY()
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*/
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public void computeScrollDelta() {
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final long currentTime = AnimationUtils.currentAnimationTimeMillis();
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final long elapsedSinceStart = currentTime - mStartTime;
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final float scale;
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if (elapsedSinceStart < mRampUpTime) {
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scale = mInterpolator.getInterpolation((float) elapsedSinceStart / mRampUpTime);
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} else {
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scale = 1f;
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}
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final long elapsedSinceDelta = currentTime - mDeltaTime;
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mDeltaTime = currentTime;
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mDeltaX = (int) (elapsedSinceDelta * scale * mTargetVelocityX);
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mDeltaY = (int) (elapsedSinceDelta * scale * mTargetVelocityY);
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}
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/**
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* Sets the target velocity for this scroller.
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*
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* @param x The target X velocity in pixels per millisecond.
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* @param y The target Y velocity in pixels per millisecond.
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*/
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public void setTargetVelocity(float x, float y) {
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mTargetVelocityX = x;
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mTargetVelocityY = y;
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}
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/**
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* @return The target X velocity for this scroller.
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*/
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public float getTargetVelocityX() {
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return mTargetVelocityX;
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}
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/**
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* @return The target Y velocity for this scroller.
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*/
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public float getTargetVelocityY() {
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return mTargetVelocityY;
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}
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/**
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* The distance traveled in the X-coordinate computed by the last call to
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* {@link #computeScrollDelta()}.
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*/
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public int getDeltaX() {
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return mDeltaX;
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}
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/**
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* The distance traveled in the Y-coordinate computed by the last call to
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* {@link #computeScrollDelta()}.
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*/
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public int getDeltaY() {
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return mDeltaY;
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}
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}
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