/*
 * Copyright (C) 2010 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.hardware.SensorManager;
import android.util.Log;
import android.view.ViewConfiguration;
import android.view.animation.AnimationUtils;
import android.view.animation.Interpolator;

This class encapsulates scrolling with the ability to overshoot the bounds of a scrolling operation. This class is a drop-in replacement for Scroller in most cases. /**
 * This class encapsulates scrolling with the ability to overshoot the bounds
 * of a scrolling operation. This class is a drop-in replacement for
 * {@link android.widget.Scroller} in most cases.
 */
public class OverScroller {
    private int mMode;

    private final SplineOverScroller mScrollerX;
    private final SplineOverScroller mScrollerY;

    private Interpolator mInterpolator;

    private final boolean mFlywheel;

    private static final int DEFAULT_DURATION = 250;
    private static final int SCROLL_MODE = 0;
    private static final int FLING_MODE = 1;

    
Creates an OverScroller with a viscous fluid scroll interpolator and flywheel.
Params:
context – /**
     * Creates an OverScroller with a viscous fluid scroll interpolator and flywheel.
     * @param context
     */
    public OverScroller(Context context) {
        this(context, null);
    }

    
Creates an OverScroller with flywheel enabled.
Params:
context – The context of this application.
interpolator – The scroll interpolator. If null, a default (viscous) interpolator will
be used./**
     * Creates an OverScroller with flywheel enabled.
     * @param context The context of this application.
     * @param interpolator The scroll interpolator. If null, a default (viscous) interpolator will
     * be used.
     */
    public OverScroller(Context context, Interpolator interpolator) {
        this(context, interpolator, true);
    }

    
Creates an OverScroller.
Params:
context – The context of this application.
interpolator – The scroll interpolator. If null, a default (viscous) interpolator will
be used.
flywheel – If true, successive fling motions will keep on increasing scroll speed.
@hide
/**
     * Creates an OverScroller.
     * @param context The context of this application.
     * @param interpolator The scroll interpolator. If null, a default (viscous) interpolator will
     * be used.
     * @param flywheel If true, successive fling motions will keep on increasing scroll speed.
     * @hide
     */
    public OverScroller(Context context, Interpolator interpolator, boolean flywheel) {
        if (interpolator == null) {
            mInterpolator = new Scroller.ViscousFluidInterpolator();
        } else {
            mInterpolator = interpolator;
        }
        mFlywheel = flywheel;
        mScrollerX = new SplineOverScroller(context);
        mScrollerY = new SplineOverScroller(context);
    }

    
Creates an OverScroller with flywheel enabled.
Params:
context – The context of this application.
interpolator – The scroll interpolator. If null, a default (viscous) interpolator will
be used.
bounceCoefficientX – A value between 0 and 1 that will determine the proportion of the
velocity which is preserved in the bounce when the horizontal edge is reached. A null value
means no bounce. This behavior is no longer supported and this coefficient has no effect.
bounceCoefficientY – Same as bounceCoefficientX but for the vertical direction. This
behavior is no longer supported and this coefficient has no effect.
Deprecated:
Use OverScroller(Context, Interpolator) instead./**
     * Creates an OverScroller with flywheel enabled.
     * @param context The context of this application.
     * @param interpolator The scroll interpolator. If null, a default (viscous) interpolator will
     * be used.
     * @param bounceCoefficientX A value between 0 and 1 that will determine the proportion of the
     * velocity which is preserved in the bounce when the horizontal edge is reached. A null value
     * means no bounce. This behavior is no longer supported and this coefficient has no effect.
     * @param bounceCoefficientY Same as bounceCoefficientX but for the vertical direction. This
     * behavior is no longer supported and this coefficient has no effect.
     * @deprecated Use {@link #OverScroller(Context, Interpolator)} instead.
     */
    @Deprecated
    public OverScroller(Context context, Interpolator interpolator,
            float bounceCoefficientX, float bounceCoefficientY) {
        this(context, interpolator, true);
    }

    
Creates an OverScroller.
Params:
context – The context of this application.
interpolator – The scroll interpolator. If null, a default (viscous) interpolator will
be used.
bounceCoefficientX – A value between 0 and 1 that will determine the proportion of the
velocity which is preserved in the bounce when the horizontal edge is reached. A null value
means no bounce. This behavior is no longer supported and this coefficient has no effect.
bounceCoefficientY – Same as bounceCoefficientX but for the vertical direction. This
behavior is no longer supported and this coefficient has no effect.
flywheel – If true, successive fling motions will keep on increasing scroll speed.
Deprecated:
Use OverScroller(Context, Interpolator) instead./**
     * Creates an OverScroller.
     * @param context The context of this application.
     * @param interpolator The scroll interpolator. If null, a default (viscous) interpolator will
     * be used.
     * @param bounceCoefficientX A value between 0 and 1 that will determine the proportion of the
     * velocity which is preserved in the bounce when the horizontal edge is reached. A null value
     * means no bounce. This behavior is no longer supported and this coefficient has no effect.
     * @param bounceCoefficientY Same as bounceCoefficientX but for the vertical direction. This
     * behavior is no longer supported and this coefficient has no effect.
     * @param flywheel If true, successive fling motions will keep on increasing scroll speed.
     * @deprecated Use {@link #OverScroller(Context, Interpolator)} instead.
     */
    @Deprecated
    public OverScroller(Context context, Interpolator interpolator,
            float bounceCoefficientX, float bounceCoefficientY, boolean flywheel) {
        this(context, interpolator, flywheel);
    }

    void setInterpolator(Interpolator interpolator) {
        if (interpolator == null) {
            mInterpolator = new Scroller.ViscousFluidInterpolator();
        } else {
            mInterpolator = interpolator;
        }
    }

    
The amount of friction applied to flings. The default value is ViewConfiguration.getScrollFriction. 
Params:
friction – A scalar dimension-less value representing the coefficient of
        friction./**
     * The amount of friction applied to flings. The default value
     * is {@link ViewConfiguration#getScrollFriction}.
     *
     * @param friction A scalar dimension-less value representing the coefficient of
     *         friction.
     */
    public final void setFriction(float friction) {
        mScrollerX.setFriction(friction);
        mScrollerY.setFriction(friction);
    }

    
Returns whether the scroller has finished scrolling.
Returns:
True if the scroller has finished scrolling, false otherwise./**
     *
     * Returns whether the scroller has finished scrolling.
     *
     * @return True if the scroller has finished scrolling, false otherwise.
     */
    public final boolean isFinished() {
        return mScrollerX.mFinished && mScrollerY.mFinished;
    }

    
Force the finished field to a particular value. Contrary to abortAnimation(), forcing the animation to finished does NOT cause the scroller to move to the final x and y position. 
Params:
finished – The new finished value./**
     * Force the finished field to a particular value. Contrary to
     * {@link #abortAnimation()}, forcing the animation to finished
     * does NOT cause the scroller to move to the final x and y
     * position.
     *
     * @param finished The new finished value.
     */
    public final void forceFinished(boolean finished) {
        mScrollerX.mFinished = mScrollerY.mFinished = finished;
    }

    
Returns the current X offset in the scroll.
Returns:
The new X offset as an absolute distance from the origin./**
     * 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 mScrollerX.mCurrentPosition;
    }

    
Returns the current Y offset in the scroll.
Returns:
The new Y offset as an absolute distance from the origin./**
     * 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 mScrollerY.mCurrentPosition;
    }

    
Returns the absolute value of the current velocity.
Returns:
The original velocity less the deceleration, norm of the X and Y velocity vector./**
     * Returns the absolute value of the current velocity.
     *
     * @return The original velocity less the deceleration, norm of the X and Y velocity vector.
     */
    public float getCurrVelocity() {
        return (float) Math.hypot(mScrollerX.mCurrVelocity, mScrollerY.mCurrVelocity);
    }

    
Returns the start X offset in the scroll.
Returns:
The start X offset as an absolute distance from the origin./**
     * 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 mScrollerX.mStart;
    }

    
Returns the start Y offset in the scroll.
Returns:
The start Y offset as an absolute distance from the origin./**
     * 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 mScrollerY.mStart;
    }

    
Returns where the scroll will end. Valid only for "fling" scrolls.
Returns:
The final X offset as an absolute distance from the origin./**
     * 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 mScrollerX.mFinal;
    }

    
Returns where the scroll will end. Valid only for "fling" scrolls.
Returns:
The final Y offset as an absolute distance from the origin./**
     * 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 mScrollerY.mFinal;
    }

    
Returns how long the scroll event will take, in milliseconds.
Returns:
The duration of the scroll in milliseconds.
@hide
Pending removal once nothing depends on it
Deprecated:
OverScrollers don't necessarily have a fixed duration.
            This function will lie to the best of its ability./**
     * Returns how long the scroll event will take, in milliseconds.
     *
     * @return The duration of the scroll in milliseconds.
     *
     * @hide Pending removal once nothing depends on it
     * @deprecated OverScrollers don't necessarily have a fixed duration.
     *             This function will lie to the best of its ability.
     */
    @Deprecated
    public final int getDuration() {
        return Math.max(mScrollerX.mDuration, mScrollerY.mDuration);
    }

    
Extend the scroll animation. This allows a running animation to scroll further and longer, when used with setFinalX(int) or setFinalY(int). 
Params:
extend – Additional time to scroll in milliseconds.
See Also:
setFinalX(int)
setFinalY(int)
@hide
Pending removal once nothing depends on it
Deprecated:
OverScrollers don't necessarily have a fixed duration.
            Instead of setting a new final position and extending
            the duration of an existing scroll, use startScroll
            to begin a new animation./**
     * Extend the scroll animation. This allows a running animation to scroll
     * further and longer, when used with {@link #setFinalX(int)} or {@link #setFinalY(int)}.
     *
     * @param extend Additional time to scroll in milliseconds.
     * @see #setFinalX(int)
     * @see #setFinalY(int)
     *
     * @hide Pending removal once nothing depends on it
     * @deprecated OverScrollers don't necessarily have a fixed duration.
     *             Instead of setting a new final position and extending
     *             the duration of an existing scroll, use startScroll
     *             to begin a new animation.
     */
    @Deprecated
    public void extendDuration(int extend) {
        mScrollerX.extendDuration(extend);
        mScrollerY.extendDuration(extend);
    }

    
Sets the final position (X) for this scroller.
Params:
newX – The new X offset as an absolute distance from the origin.
See Also:
extendDuration(int)
setFinalY(int)
@hide
Pending removal once nothing depends on it
Deprecated:
OverScroller's final position may change during an animation.
            Instead of setting a new final position and extending
            the duration of an existing scroll, use startScroll
            to begin a new animation./**
     * Sets the final position (X) for this scroller.
     *
     * @param newX The new X offset as an absolute distance from the origin.
     * @see #extendDuration(int)
     * @see #setFinalY(int)
     *
     * @hide Pending removal once nothing depends on it
     * @deprecated OverScroller's final position may change during an animation.
     *             Instead of setting a new final position and extending
     *             the duration of an existing scroll, use startScroll
     *             to begin a new animation.
     */
    @Deprecated
    public void setFinalX(int newX) {
        mScrollerX.setFinalPosition(newX);
    }

    
Sets the final position (Y) for this scroller.
Params:
newY – The new Y offset as an absolute distance from the origin.
See Also:
extendDuration(int)
setFinalX(int)
@hide
Pending removal once nothing depends on it
Deprecated:
OverScroller's final position may change during an animation.
            Instead of setting a new final position and extending
            the duration of an existing scroll, use startScroll
            to begin a new animation./**
     * Sets the final position (Y) for this scroller.
     *
     * @param newY The new Y offset as an absolute distance from the origin.
     * @see #extendDuration(int)
     * @see #setFinalX(int)
     *
     * @hide Pending removal once nothing depends on it
     * @deprecated OverScroller's final position may change during an animation.
     *             Instead of setting a new final position and extending
     *             the duration of an existing scroll, use startScroll
     *             to begin a new animation.
     */
    @Deprecated
    public void setFinalY(int newY) {
        mScrollerY.setFinalPosition(newY);
    }

    
Call this when you want to know the new location. If it returns true, the
animation is not yet finished.
/**
     * Call this when you want to know the new location. If it returns true, the
     * animation is not yet finished.
     */
    public boolean computeScrollOffset() {
        if (isFinished()) {
            return false;
        }

        switch (mMode) {
            case SCROLL_MODE:
                long time = AnimationUtils.currentAnimationTimeMillis();
                // Any scroller can be used for time, since they were started
                // together in scroll mode. We use X here.
                final long elapsedTime = time - mScrollerX.mStartTime;

                final int duration = mScrollerX.mDuration;
                if (elapsedTime < duration) {
                    final float q = mInterpolator.getInterpolation(elapsedTime / (float) duration);
                    mScrollerX.updateScroll(q);
                    mScrollerY.updateScroll(q);
                } else {
                    abortAnimation();
                }
                break;

            case FLING_MODE:
                if (!mScrollerX.mFinished) {
                    if (!mScrollerX.update()) {
                        if (!mScrollerX.continueWhenFinished()) {
                            mScrollerX.finish();
                        }
                    }
                }

                if (!mScrollerY.mFinished) {
                    if (!mScrollerY.update()) {
                        if (!mScrollerY.continueWhenFinished()) {
                            mScrollerY.finish();
                        }
                    }
                }

                break;
        }

        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.
Params:
startX – Starting horizontal scroll offset in pixels. Positive
       numbers will scroll the content to the left.
startY – Starting vertical scroll offset in pixels. Positive numbers
       will scroll the content up.
dx – Horizontal distance to travel. Positive numbers will scroll the
       content to the left.
dy – Vertical distance to travel. Positive numbers will scroll the
       content up./**
     * 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.
Params:
startX – Starting horizontal scroll offset in pixels. Positive
       numbers will scroll the content to the left.
startY – Starting vertical scroll offset in pixels. Positive numbers
       will scroll the content up.
dx – Horizontal distance to travel. Positive numbers will scroll the
       content to the left.
dy – Vertical distance to travel. Positive numbers will scroll the
       content up.
duration – Duration of the scroll in milliseconds./**
     * 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;
        mScrollerX.startScroll(startX, dx, duration);
        mScrollerY.startScroll(startY, dy, duration);
    }

    
Call this when you want to 'spring back' into a valid coordinate range.
Params:
startX – Starting X coordinate
startY – Starting Y coordinate
minX – Minimum valid X value
maxX – Maximum valid X value
minY – Minimum valid Y value
maxY – Minimum valid Y value
Returns:
true if a springback was initiated, false if startX and startY were
         already within the valid range./**
     * Call this when you want to 'spring back' into a valid coordinate range.
     *
     * @param startX Starting X coordinate
     * @param startY Starting Y coordinate
     * @param minX Minimum valid X value
     * @param maxX Maximum valid X value
     * @param minY Minimum valid Y value
     * @param maxY Minimum valid Y value
     * @return true if a springback was initiated, false if startX and startY were
     *          already within the valid range.
     */
    public boolean springBack(int startX, int startY, int minX, int maxX, int minY, int maxY) {
        mMode = FLING_MODE;

        // Make sure both methods are called.
        final boolean spingbackX = mScrollerX.springback(startX, minX, maxX);
        final boolean spingbackY = mScrollerY.springback(startY, minY, maxY);
        return spingbackX || spingbackY;
    }

    public void fling(int startX, int startY, int velocityX, int velocityY,
            int minX, int maxX, int minY, int maxY) {
        fling(startX, startY, velocityX, velocityY, minX, maxX, minY, maxY, 0, 0);
    }

    
Start scrolling based on a fling gesture. The distance traveled will
depend on the initial velocity of the fling.
Params:
startX – Starting point of the scroll (X)
startY – Starting point of the scroll (Y)
velocityX – Initial velocity of the fling (X) measured in pixels per
           second.
velocityY – Initial velocity of the fling (Y) measured in pixels per
           second
minX – Minimum X value. The scroller will not scroll past this point
           unless overX > 0. If overfling is allowed, it will use minX as
           a springback boundary.
maxX – Maximum X value. The scroller will not scroll past this point
           unless overX > 0. If overfling is allowed, it will use maxX as
           a springback boundary.
minY – Minimum Y value. The scroller will not scroll past this point
           unless overY > 0. If overfling is allowed, it will use minY as
           a springback boundary.
maxY – Maximum Y value. The scroller will not scroll past this point
           unless overY > 0. If overfling is allowed, it will use maxY as
           a springback boundary.
overX – Overfling range. If > 0, horizontal overfling in either
           direction will be possible.
overY – Overfling range. If > 0, vertical overfling in either
           direction will be possible./**
     * Start scrolling based on a fling gesture. The distance traveled 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
     *            unless overX > 0. If overfling is allowed, it will use minX as
     *            a springback boundary.
     * @param maxX Maximum X value. The scroller will not scroll past this point
     *            unless overX > 0. If overfling is allowed, it will use maxX as
     *            a springback boundary.
     * @param minY Minimum Y value. The scroller will not scroll past this point
     *            unless overY > 0. If overfling is allowed, it will use minY as
     *            a springback boundary.
     * @param maxY Maximum Y value. The scroller will not scroll past this point
     *            unless overY > 0. If overfling is allowed, it will use maxY as
     *            a springback boundary.
     * @param overX Overfling range. If > 0, horizontal overfling in either
     *            direction will be possible.
     * @param overY Overfling range. If > 0, vertical overfling in either
     *            direction will be possible.
     */
    public void fling(int startX, int startY, int velocityX, int velocityY,
            int minX, int maxX, int minY, int maxY, int overX, int overY) {
        // Continue a scroll or fling in progress
        if (mFlywheel && !isFinished()) {
            float oldVelocityX = mScrollerX.mCurrVelocity;
            float oldVelocityY = mScrollerY.mCurrVelocity;
            if (Math.signum(velocityX) == Math.signum(oldVelocityX) &&
                    Math.signum(velocityY) == Math.signum(oldVelocityY)) {
                velocityX += oldVelocityX;
                velocityY += oldVelocityY;
            }
        }

        mMode = FLING_MODE;
        mScrollerX.fling(startX, velocityX, minX, maxX, overX);
        mScrollerY.fling(startY, velocityY, minY, maxY, overY);
    }

    
Notify the scroller that we've reached a horizontal boundary.
Normally the information to handle this will already be known
when the animation is started, such as in a call to one of the
fling functions. However there are cases where this cannot be known
in advance. This function will transition the current motion and
animate from startX to finalX as appropriate.
Params:
startX – Starting/current X position
finalX – Desired final X position
overX – Magnitude of overscroll allowed. This should be the maximum
             desired distance from finalX. Absolute value - must be positive./**
     * Notify the scroller that we've reached a horizontal boundary.
     * Normally the information to handle this will already be known
     * when the animation is started, such as in a call to one of the
     * fling functions. However there are cases where this cannot be known
     * in advance. This function will transition the current motion and
     * animate from startX to finalX as appropriate.
     *
     * @param startX Starting/current X position
     * @param finalX Desired final X position
     * @param overX Magnitude of overscroll allowed. This should be the maximum
     *              desired distance from finalX. Absolute value - must be positive.
     */
    public void notifyHorizontalEdgeReached(int startX, int finalX, int overX) {
        mScrollerX.notifyEdgeReached(startX, finalX, overX);
    }

    
Notify the scroller that we've reached a vertical boundary.
Normally the information to handle this will already be known
when the animation is started, such as in a call to one of the
fling functions. However there are cases where this cannot be known
in advance. This function will animate a parabolic motion from
startY to finalY.
Params:
startY – Starting/current Y position
finalY – Desired final Y position
overY – Magnitude of overscroll allowed. This should be the maximum
             desired distance from finalY. Absolute value - must be positive./**
     * Notify the scroller that we've reached a vertical boundary.
     * Normally the information to handle this will already be known
     * when the animation is started, such as in a call to one of the
     * fling functions. However there are cases where this cannot be known
     * in advance. This function will animate a parabolic motion from
     * startY to finalY.
     *
     * @param startY Starting/current Y position
     * @param finalY Desired final Y position
     * @param overY Magnitude of overscroll allowed. This should be the maximum
     *              desired distance from finalY. Absolute value - must be positive.
     */
    public void notifyVerticalEdgeReached(int startY, int finalY, int overY) {
        mScrollerY.notifyEdgeReached(startY, finalY, overY);
    }

    
Returns whether the current Scroller is currently returning to a valid position. Valid bounds were provided by the fling(int, int, int, int, int, int, int, int, int, int) method. One should check this value before calling startScroll(int, int, int, int) as the interpolation currently in progress to restore a valid position will then be stopped. The caller has to take into account the fact that the started scroll will start from an overscrolled position. 
Returns:
true when the current position is overscrolled and in the process of
        interpolating back to a valid value./**
     * Returns whether the current Scroller is currently returning to a valid position.
     * Valid bounds were provided by the
     * {@link #fling(int, int, int, int, int, int, int, int, int, int)} method.
     *
     * One should check this value before calling
     * {@link #startScroll(int, int, int, int)} as the interpolation currently in progress
     * to restore a valid position will then be stopped. The caller has to take into account
     * the fact that the started scroll will start from an overscrolled position.
     *
     * @return true when the current position is overscrolled and in the process of
     *         interpolating back to a valid value.
     */
    public boolean isOverScrolled() {
        return ((!mScrollerX.mFinished &&
                mScrollerX.mState != SplineOverScroller.SPLINE) ||
                (!mScrollerY.mFinished &&
                        mScrollerY.mState != SplineOverScroller.SPLINE));
    }

    
Stops the animation. Contrary to forceFinished(boolean), aborting the animating causes the scroller to move to the final x and y positions. 
See Also:
forceFinished(boolean)/**
     * Stops the animation. Contrary to {@link #forceFinished(boolean)},
     * aborting the animating causes the scroller to move to the final x and y
     * positions.
     *
     * @see #forceFinished(boolean)
     */
    public void abortAnimation() {
        mScrollerX.finish();
        mScrollerY.finish();
    }

    
Returns the time elapsed since the beginning of the scrolling.
Returns:
The elapsed time in milliseconds.
@hide
/**
     * Returns the time elapsed since the beginning of the scrolling.
     *
     * @return The elapsed time in milliseconds.
     *
     * @hide
     */
    public int timePassed() {
        final long time = AnimationUtils.currentAnimationTimeMillis();
        final long startTime = Math.min(mScrollerX.mStartTime, mScrollerY.mStartTime);
        return (int) (time - startTime);
    }

    
@hide
/**
     * @hide
     */
    public boolean isScrollingInDirection(float xvel, float yvel) {
        final int dx = mScrollerX.mFinal - mScrollerX.mStart;
        final int dy = mScrollerY.mFinal - mScrollerY.mStart;
        return !isFinished() && Math.signum(xvel) == Math.signum(dx) &&
                Math.signum(yvel) == Math.signum(dy);
    }

    static class SplineOverScroller {
        // Initial position
        private int mStart;

        // Current position
        private int mCurrentPosition;

        // Final position
        private int mFinal;

        // Initial velocity
        private int mVelocity;

        // Current velocity
        private float mCurrVelocity;

        // Constant current deceleration
        private float mDeceleration;

        // Animation starting time, in system milliseconds
        private long mStartTime;

        // Animation duration, in milliseconds
        private int mDuration;

        // Duration to complete spline component of animation
        private int mSplineDuration;

        // Distance to travel along spline animation
        private int mSplineDistance;

        // Whether the animation is currently in progress
        private boolean mFinished;

        // The allowed overshot distance before boundary is reached.
        private int mOver;

        // Fling friction
        private float mFlingFriction = ViewConfiguration.getScrollFriction();

        // Current state of the animation.
        private int mState = SPLINE;

        // Constant gravity value, used in the deceleration phase.
        private static final float GRAVITY = 2000.0f;

        // A context-specific coefficient adjusted to physical values.
        private float mPhysicalCoeff;

        private static float DECELERATION_RATE = (float) (Math.log(0.78) / Math.log(0.9));
        private static final float INFLEXION = 0.35f; // Tension lines cross at (INFLEXION, 1)
        private static final float START_TENSION = 0.5f;
        private static final float END_TENSION = 1.0f;
        private static final float P1 = START_TENSION * INFLEXION;
        private static final float P2 = 1.0f - END_TENSION * (1.0f - INFLEXION);

        private static final int NB_SAMPLES = 100;
        private static final float[] SPLINE_POSITION = new float[NB_SAMPLES + 1];
        private static final float[] SPLINE_TIME = new float[NB_SAMPLES + 1];

        private static final int SPLINE = 0;
        private static final int CUBIC = 1;
        private static final int BALLISTIC = 2;

        static {
            float x_min = 0.0f;
            float y_min = 0.0f;
            for (int i = 0; i < NB_SAMPLES; i++) {
                final float alpha = (float) i / NB_SAMPLES;

                float x_max = 1.0f;
                float x, tx, coef;
                while (true) {
                    x = x_min + (x_max - x_min) / 2.0f;
                    coef = 3.0f * x * (1.0f - x);
                    tx = coef * ((1.0f - x) * P1 + x * P2) + x * x * x;
                    if (Math.abs(tx - alpha) < 1E-5) break;
                    if (tx > alpha) x_max = x;
                    else x_min = x;
                }
                SPLINE_POSITION[i] = coef * ((1.0f - x) * START_TENSION + x) + x * x * x;

                float y_max = 1.0f;
                float y, dy;
                while (true) {
                    y = y_min + (y_max - y_min) / 2.0f;
                    coef = 3.0f * y * (1.0f - y);
                    dy = coef * ((1.0f - y) * START_TENSION + y) + y * y * y;
                    if (Math.abs(dy - alpha) < 1E-5) break;
                    if (dy > alpha) y_max = y;
                    else y_min = y;
                }
                SPLINE_TIME[i] = coef * ((1.0f - y) * P1 + y * P2) + y * y * y;
            }
            SPLINE_POSITION[NB_SAMPLES] = SPLINE_TIME[NB_SAMPLES] = 1.0f;
        }

        void setFriction(float friction) {
            mFlingFriction = friction;
        }

        SplineOverScroller(Context context) {
            mFinished = true;
            final float ppi = context.getResources().getDisplayMetrics().density * 160.0f;
            mPhysicalCoeff = SensorManager.GRAVITY_EARTH // g (m/s^2)
                    * 39.37f // inch/meter
                    * ppi
                    * 0.84f; // look and feel tuning
        }

        void updateScroll(float q) {
            mCurrentPosition = mStart + Math.round(q * (mFinal - mStart));
        }

        /*
         * Get a signed deceleration that will reduce the velocity.
         */
        static private float getDeceleration(int velocity) {
            return velocity > 0 ? -GRAVITY : GRAVITY;
        }

        /*
         * Modifies mDuration to the duration it takes to get from start to newFinal using the
         * spline interpolation. The previous duration was needed to get to oldFinal.
         */
        private void adjustDuration(int start, int oldFinal, int newFinal) {
            final int oldDistance = oldFinal - start;
            final int newDistance = newFinal - start;
            final float x = Math.abs((float) newDistance / oldDistance);
            final int index = (int) (NB_SAMPLES * x);
            if (index < NB_SAMPLES) {
                final float x_inf = (float) index / NB_SAMPLES;
                final float x_sup = (float) (index + 1) / NB_SAMPLES;
                final float t_inf = SPLINE_TIME[index];
                final float t_sup = SPLINE_TIME[index + 1];
                final float timeCoef = t_inf + (x - x_inf) / (x_sup - x_inf) * (t_sup - t_inf);
                mDuration *= timeCoef;
            }
        }

        void startScroll(int start, int distance, int duration) {
            mFinished = false;

            mCurrentPosition = mStart = start;
            mFinal = start + distance;

            mStartTime = AnimationUtils.currentAnimationTimeMillis();
            mDuration = duration;

            // Unused
            mDeceleration = 0.0f;
            mVelocity = 0;
        }

        void finish() {
            mCurrentPosition = mFinal;
            // Not reset since WebView relies on this value for fast fling.
            // TODO: restore when WebView uses the fast fling implemented in this class.
            // mCurrVelocity = 0.0f;
            mFinished = true;
        }

        void setFinalPosition(int position) {
            mFinal = position;
            mFinished = false;
        }

        void extendDuration(int extend) {
            final long time = AnimationUtils.currentAnimationTimeMillis();
            final int elapsedTime = (int) (time - mStartTime);
            mDuration = elapsedTime + extend;
            mFinished = false;
        }

        boolean springback(int start, int min, int max) {
            mFinished = true;

            mCurrentPosition = mStart = mFinal = start;
            mVelocity = 0;

            mStartTime = AnimationUtils.currentAnimationTimeMillis();
            mDuration = 0;

            if (start < min) {
                startSpringback(start, min, 0);
            } else if (start > max) {
                startSpringback(start, max, 0);
            }

            return !mFinished;
        }

        private void startSpringback(int start, int end, int velocity) {
            // mStartTime has been set
            mFinished = false;
            mState = CUBIC;
            mCurrentPosition = mStart = start;
            mFinal = end;
            final int delta = start - end;
            mDeceleration = getDeceleration(delta);
            // TODO take velocity into account
            mVelocity = -delta; // only sign is used
            mOver = Math.abs(delta);
            mDuration = (int) (1000.0 * Math.sqrt(-2.0 * delta / mDeceleration));
        }

        void fling(int start, int velocity, int min, int max, int over) {
            mOver = over;
            mFinished = false;
            mCurrVelocity = mVelocity = velocity;
            mDuration = mSplineDuration = 0;
            mStartTime = AnimationUtils.currentAnimationTimeMillis();
            mCurrentPosition = mStart = start;

            if (start > max || start < min) {
                startAfterEdge(start, min, max, velocity);
                return;
            }

            mState = SPLINE;
            double totalDistance = 0.0;

            if (velocity != 0) {
                mDuration = mSplineDuration = getSplineFlingDuration(velocity);
                totalDistance = getSplineFlingDistance(velocity);
            }

            mSplineDistance = (int) (totalDistance * Math.signum(velocity));
            mFinal = start + mSplineDistance;

            // Clamp to a valid final position
            if (mFinal < min) {
                adjustDuration(mStart, mFinal, min);
                mFinal = min;
            }

            if (mFinal > max) {
                adjustDuration(mStart, mFinal, max);
                mFinal = max;
            }
        }

        private double getSplineDeceleration(int velocity) {
            return Math.log(INFLEXION * Math.abs(velocity) / (mFlingFriction * mPhysicalCoeff));
        }

        private double getSplineFlingDistance(int velocity) {
            final double l = getSplineDeceleration(velocity);
            final double decelMinusOne = DECELERATION_RATE - 1.0;
            return mFlingFriction * mPhysicalCoeff * Math.exp(DECELERATION_RATE / decelMinusOne * l);
        }

        /* Returns the duration, expressed in milliseconds */
        private int getSplineFlingDuration(int velocity) {
            final double l = getSplineDeceleration(velocity);
            final double decelMinusOne = DECELERATION_RATE - 1.0;
            return (int) (1000.0 * Math.exp(l / decelMinusOne));
        }

        private void fitOnBounceCurve(int start, int end, int velocity) {
            // Simulate a bounce that started from edge
            final float durationToApex = - velocity / mDeceleration;
            // The float cast below is necessary to avoid integer overflow.
            final float velocitySquared = (float) velocity * velocity;
            final float distanceToApex = velocitySquared / 2.0f / Math.abs(mDeceleration);
            final float distanceToEdge = Math.abs(end - start);
            final float totalDuration = (float) Math.sqrt(
                    2.0 * (distanceToApex + distanceToEdge) / Math.abs(mDeceleration));
            mStartTime -= (int) (1000.0f * (totalDuration - durationToApex));
            mCurrentPosition = mStart = end;
            mVelocity = (int) (- mDeceleration * totalDuration);
        }

        private void startBounceAfterEdge(int start, int end, int velocity) {
            mDeceleration = getDeceleration(velocity == 0 ? start - end : velocity);
            fitOnBounceCurve(start, end, velocity);
            onEdgeReached();
        }

        private void startAfterEdge(int start, int min, int max, int velocity) {
            if (start > min && start < max) {
                Log.e("OverScroller", "startAfterEdge called from a valid position");
                mFinished = true;
                return;
            }
            final boolean positive = start > max;
            final int edge = positive ? max : min;
            final int overDistance = start - edge;
            boolean keepIncreasing = overDistance * velocity >= 0;
            if (keepIncreasing) {
                // Will result in a bounce or a to_boundary depending on velocity.
                startBounceAfterEdge(start, edge, velocity);
            } else {
                final double totalDistance = getSplineFlingDistance(velocity);
                if (totalDistance > Math.abs(overDistance)) {
                    fling(start, velocity, positive ? min : start, positive ? start : max, mOver);
                } else {
                    startSpringback(start, edge, velocity);
                }
            }
        }

        void notifyEdgeReached(int start, int end, int over) {
            // mState is used to detect successive notifications 
            if (mState == SPLINE) {
                mOver = over;
                mStartTime = AnimationUtils.currentAnimationTimeMillis();
                // We were in fling/scroll mode before: current velocity is such that distance to
                // edge is increasing. This ensures that startAfterEdge will not start a new fling.
                startAfterEdge(start, end, end, (int) mCurrVelocity);
            }
        }

        private void onEdgeReached() {
            // mStart, mVelocity and mStartTime were adjusted to their values when edge was reached.
            // The float cast below is necessary to avoid integer overflow.
            final float velocitySquared = (float) mVelocity * mVelocity;
            float distance = velocitySquared / (2.0f * Math.abs(mDeceleration));
            final float sign = Math.signum(mVelocity);

            if (distance > mOver) {
                // Default deceleration is not sufficient to slow us down before boundary
                 mDeceleration = - sign * velocitySquared / (2.0f * mOver);
                 distance = mOver;
            }

            mOver = (int) distance;
            mState = BALLISTIC;
            mFinal = mStart + (int) (mVelocity > 0 ? distance : -distance);
            mDuration = - (int) (1000.0f * mVelocity / mDeceleration);
        }

        boolean continueWhenFinished() {
            switch (mState) {
                case SPLINE:
                    // Duration from start to null velocity
                    if (mDuration < mSplineDuration) {
                        // If the animation was clamped, we reached the edge
                        mCurrentPosition = mStart = mFinal;
                        // TODO Better compute speed when edge was reached
                        mVelocity = (int) mCurrVelocity;
                        mDeceleration = getDeceleration(mVelocity);
                        mStartTime += mDuration;
                        onEdgeReached();
                    } else {
                        // Normal stop, no need to continue
                        return false;
                    }
                    break;
                case BALLISTIC:
                    mStartTime += mDuration;
                    startSpringback(mFinal, mStart, 0);
                    break;
                case CUBIC:
                    return false;
            }

            update();
            return true;
        }

        /*
         * Update the current position and velocity for current time. Returns
         * true if update has been done and false if animation duration has been
         * reached.
         */
        boolean update() {
            final long time = AnimationUtils.currentAnimationTimeMillis();
            final long currentTime = time - mStartTime;

            if (currentTime == 0) {
                // Skip work but report that we're still going if we have a nonzero duration.
                return mDuration > 0;
            }
            if (currentTime > mDuration) {
                return false;
            }

            double distance = 0.0;
            switch (mState) {
                case SPLINE: {
                    final float t = (float) currentTime / mSplineDuration;
                    final int index = (int) (NB_SAMPLES * t);
                    float distanceCoef = 1.f;
                    float velocityCoef = 0.f;
                    if (index < NB_SAMPLES) {
                        final float t_inf = (float) index / NB_SAMPLES;
                        final float t_sup = (float) (index + 1) / NB_SAMPLES;
                        final float d_inf = SPLINE_POSITION[index];
                        final float d_sup = SPLINE_POSITION[index + 1];
                        velocityCoef = (d_sup - d_inf) / (t_sup - t_inf);
                        distanceCoef = d_inf + (t - t_inf) * velocityCoef;
                    }

                    distance = distanceCoef * mSplineDistance;
                    mCurrVelocity = velocityCoef * mSplineDistance / mSplineDuration * 1000.0f;
                    break;
                }

                case BALLISTIC: {
                    final float t = currentTime / 1000.0f;
                    mCurrVelocity = mVelocity + mDeceleration * t;
                    distance = mVelocity * t + mDeceleration * t * t / 2.0f;
                    break;
                }

                case CUBIC: {
                    final float t = (float) (currentTime) / mDuration;
                    final float t2 = t * t;
                    final float sign = Math.signum(mVelocity);
                    distance = sign * mOver * (3.0f * t2 - 2.0f * t * t2); 
                    mCurrVelocity = sign * mOver * 6.0f * (- t + t2); 
                    break;
                }
            }

            mCurrentPosition = mStart + (int) Math.round(distance);

            return true;
        }
    }
}