/*
* Copyright (C) 2006 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 android.widget;
import android.content.Context;
import android.view.ViewConfiguration;
import android.view.animation.AnimationUtils;
import android.view.animation.Interpolator;
/**
* This class encapsulates scrolling. The duration of the scroll
* can be passed in the constructor and specifies the maximum time that
* the scrolling animation should take. Past this time, the scrolling is
* automatically moved to its final stage and computeScrollOffset()
* will always return false to indicate that scrolling is over.
*/
public class Scroller {
private int mMode;
private int mStartX;
private int mStartY;
private int mFinalX;
private int mFinalY;
private int mMinX;
private int mMaxX;
private int mMinY;
private int mMaxY;
private int mCurrX;
private int mCurrY;
private long mStartTime;
private int mDuration;
private float mDurationReciprocal;
private float mDeltaX;
private float mDeltaY;
private float mViscousFluidScale;
private float mViscousFluidNormalize;
private boolean mFinished;
private Interpolator mInterpolator;
private float mCoeffX = 0.0f;
private float mCoeffY = 1.0f;
private float mVelocity;
private static final int DEFAULT_DURATION = 250;
private static final int SCROLL_MODE = 0;
private static final int FLING_MODE = 1;
private final float mDeceleration;
/**
* Create a Scroller with the default duration and interpolator.
*/
public Scroller(Context context) {
this(context, null);
}
/**
* Create a Scroller with the specified interpolator. If the interpolator is
* null, the default (viscous) interpolator will be used.
*/
public Scroller(Context context, Interpolator interpolator) {
mFinished = true;
mInterpolator = interpolator;
float ppi = context.getResources().getDisplayMetrics().density * 160.0f;
mDeceleration = 9.8f // g (m/s^2)
* 39.37f // inch/meter
* ppi // pixels per inch
* ViewConfiguration.getScrollFriction();
}
/**
*
* Returns whether the scroller has finished scrolling.
*
* @return True if the scroller has finished scrolling, false otherwise.
*/
public final boolean isFinished() {
return mFinished;
}
/**
* Force the finished field to a particular value.
*
* @param finished The new finished value.
*/
public final void forceFinished(boolean finished) {
mFinished = finished;
}
/**
* Returns how long the scroll event will take, in milliseconds.
*
* @return The duration of the scroll in milliseconds.
*/
public final int getDuration() {
return mDuration;
}
/**
* Returns the current X offset in the scroll.
*
* @return The new X offset as an absolute distance from the origin.
*/
public final int getCurrX() {
return mCurrX;
}
/**
* Returns the current Y offset in the scroll.
*
* @return The new Y offset as an absolute distance from the origin.
*/
public final int getCurrY() {
return mCurrY;
}
/**
* Returns the start X offset in the scroll.
*
* @return The start X offset as an absolute distance from the origin.
*/
public final int getStartX() {
return mStartX;
}
/**
* Returns the start Y offset in the scroll.
*
* @return The start Y offset as an absolute distance from the origin.
*/
public final int getStartY() {
return mStartY;
}
/**
* Returns where the scroll will end. Valid only for "fling" scrolls.
*
* @return The final X offset as an absolute distance from the origin.
*/
public final int getFinalX() {
return mFinalX;
}
/**
* Returns where the scroll will end. Valid only for "fling" scrolls.
*
* @return The final Y offset as an absolute distance from the origin.
*/
public final int getFinalY() {
return mFinalY;
}
/**
* Call this when you want to know the new location. If it returns true,
* the animation is not yet finished. loc will be altered to provide the
* new location.
*/
public boolean computeScrollOffset() {
if (mFinished) {
return false;
}
int timePassed = (int)(AnimationUtils.currentAnimationTimeMillis() - mStartTime);
if (timePassed < mDuration) {
switch (mMode) {
case SCROLL_MODE:
float x = (float)timePassed * mDurationReciprocal;
if (mInterpolator == null)
x = viscousFluid(x);
else
x = mInterpolator.getInterpolation(x);
mCurrX = mStartX + Math.round(x * mDeltaX);
mCurrY = mStartY + Math.round(x * mDeltaY);
if ((mCurrX == mFinalX) && (mCurrY == mFinalY)) {
mFinished = true;
}
break;
case FLING_MODE:
float timePassedSeconds = timePassed / 1000.0f;
float distance = (mVelocity * timePassedSeconds)
- (mDeceleration * timePassedSeconds * timePassedSeconds / 2.0f);
mCurrX = mStartX + Math.round(distance * mCoeffX);
// Pin to mMinX <= mCurrX <= mMaxX
mCurrX = Math.min(mCurrX, mMaxX);
mCurrX = Math.max(mCurrX, mMinX);
mCurrY = mStartY + Math.round(distance * mCoeffY);
// Pin to mMinY <= mCurrY <= mMaxY
mCurrY = Math.min(mCurrY, mMaxY);
mCurrY = Math.max(mCurrY, mMinY);
if (mCurrX == mFinalX && mCurrY == mFinalY) {
mFinished = true;
}
break;
}
}
else {
mCurrX = mFinalX;
mCurrY = mFinalY;
mFinished = true;
}
return true;
}
/**
* Start scrolling by providing a starting point and the distance to travel.
* The scroll will use the default value of 250 milliseconds for the
* duration.
*
* @param startX Starting horizontal scroll offset in pixels. Positive
* numbers will scroll the content to the left.
* @param startY Starting vertical scroll offset in pixels. Positive numbers
* will scroll the content up.
* @param dx Horizontal distance to travel. Positive numbers will scroll the
* content to the left.
* @param dy Vertical distance to travel. Positive numbers will scroll the
* content up.
*/
public void startScroll(int startX, int startY, int dx, int dy) {
startScroll(startX, startY, dx, dy, DEFAULT_DURATION);
}
/**
* Start scrolling by providing a starting point and the distance to travel.
*
* @param startX Starting horizontal scroll offset in pixels. Positive
* numbers will scroll the content to the left.
* @param startY Starting vertical scroll offset in pixels. Positive numbers
* will scroll the content up.
* @param dx Horizontal distance to travel. Positive numbers will scroll the
* content to the left.
* @param dy Vertical distance to travel. Positive numbers will scroll the
* content up.
* @param duration Duration of the scroll in milliseconds.
*/
public void startScroll(int startX, int startY, int dx, int dy, int duration) {
mMode = SCROLL_MODE;
mFinished = false;
mDuration = duration;
mStartTime = AnimationUtils.currentAnimationTimeMillis();
mStartX = startX;
mStartY = startY;
mFinalX = startX + dx;
mFinalY = startY + dy;
mDeltaX = dx;
mDeltaY = dy;
mDurationReciprocal = 1.0f / (float) mDuration;
// This controls the viscous fluid effect (how much of it)
mViscousFluidScale = 8.0f;
// must be set to 1.0 (used in viscousFluid())
mViscousFluidNormalize = 1.0f;
mViscousFluidNormalize = 1.0f / viscousFluid(1.0f);
}
/**
* Start scrolling based on a fling gesture. The distance travelled will
* depend on the initial velocity of the fling.
*
* @param startX Starting point of the scroll (X)
* @param startY Starting point of the scroll (Y)
* @param velocityX Initial velocity of the fling (X) measured in pixels per
* second.
* @param velocityY Initial velocity of the fling (Y) measured in pixels per
* second
* @param minX Minimum X value. The scroller will not scroll past this
* point.
* @param maxX Maximum X value. The scroller will not scroll past this
* point.
* @param minY Minimum Y value. The scroller will not scroll past this
* point.
* @param maxY Maximum Y value. The scroller will not scroll past this
* point.
*/
public void fling(int startX, int startY, int velocityX, int velocityY,
int minX, int maxX, int minY, int maxY) {
mMode = FLING_MODE;
mFinished = false;
float velocity = (float)Math.hypot(velocityX, velocityY);
mVelocity = velocity;
mDuration = (int) (1000 * velocity / mDeceleration); // Duration is in
// milliseconds
mStartTime = AnimationUtils.currentAnimationTimeMillis();
mStartX = startX;
mStartY = startY;
mCoeffX = velocity == 0 ? 1.0f : velocityX / velocity;
mCoeffY = velocity == 0 ? 1.0f : velocityY / velocity;
int totalDistance = (int) ((velocity * velocity) / (2 * mDeceleration));
mMinX = minX;
mMaxX = maxX;
mMinY = minY;
mMaxY = maxY;
mFinalX = startX + Math.round(totalDistance * mCoeffX);
// Pin to mMinX <= mFinalX <= mMaxX
mFinalX = Math.min(mFinalX, mMaxX);
mFinalX = Math.max(mFinalX, mMinX);
mFinalY = startY + Math.round(totalDistance * mCoeffY);
// Pin to mMinY <= mFinalY <= mMaxY
mFinalY = Math.min(mFinalY, mMaxY);
mFinalY = Math.max(mFinalY, mMinY);
}
private float viscousFluid(float x)
{
x *= mViscousFluidScale;
if (x < 1.0f) {
x -= (1.0f - (float)Math.exp(-x));
} else {
float start = 0.36787944117f; // 1/e == exp(-1)
x = 1.0f - (float)Math.exp(1.0f - x);
x = start + x * (1.0f - start);
}
x *= mViscousFluidNormalize;
return x;
}
/**
*
*/
public void abortAnimation() {
mCurrX = mFinalX;
mCurrY = mFinalY;
mFinished = true;
}
/**
* Extend the scroll animation. This allows a running animation to
* scroll further and longer, when used with setFinalX() or setFinalY().
*
* @param extend Additional time to scroll in milliseconds.
*/
public void extendDuration(int extend) {
int passed = timePassed();
mDuration = passed + extend;
mDurationReciprocal = 1.0f / (float)mDuration;
mFinished = false;
}
public int timePassed() {
return (int)(AnimationUtils.currentAnimationTimeMillis() - mStartTime);
}
public void setFinalX(int newX) {
mFinalX = newX;
mDeltaX = mFinalX - mStartX;
mFinished = false;
}
public void setFinalY(int newY) {
mFinalY = newY;
mDeltaY = mFinalY - mStartY;
mFinished = false;
}
}
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