android/widget/OverScroller.java

/*
 * 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.graphics.Interpolator;
import android.view.ViewConfiguration;
import android.view.animation.AnimationUtils;

/**
 * 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 {
    int mMode;

    private final MagneticOverScroller mScrollerX;
    private final MagneticOverScroller mScrollerY;

    private float mDeceleration;
    private final float mPpi;
    private final boolean mFlywheel;

    private static float DECELERATION_RATE = (float) (Math.log(0.75) / Math.log(0.9));
    private static float ALPHA = 800; // pixels / seconds
    private static float START_TENSION = 0.4f; // Tension at start: (0.4 * total T, 1.0 * Distance)
    private static float END_TENSION = 1.0f - START_TENSION;
    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 DEFAULT_DURATION = 250;
    private static final int SCROLL_MODE = 0;
    private static final int FLING_MODE = 1;

    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) * START_TENSION + x * END_TENSION) + 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 + x * x * x;
            }

            {
                float y_max = 1.0f;
                float y, dy, coef;
                while (true) {
                    y = y_min + (y_max - y_min) / 2.0f;
                    coef = 3.0f * y * (1.0f - y);
                    dy = coef + 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) * START_TENSION + y * END_TENSION) + y * y * y;
            }
        }
        SPLINE_POSITION[NB_SAMPLES] = SPLINE_TIME[NB_SAMPLES] = 1.0f;
    }

    public OverScroller(Context context) {
        this(context, null, 0.f, 0.f, true);
    }

    /**
     * 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.
     * @param bounceCoefficientY Same as bounceCoefficientX but for the vertical direction.
     */
    public OverScroller(Context context, Interpolator interpolator,
            float bounceCoefficientX, float bounceCoefficientY, boolean flywheel) {
        mFlywheel = flywheel;
        mPpi = context.getResources().getDisplayMetrics().density * 160.0f;
        mDeceleration = computeDeceleration(ViewConfiguration.getScrollFriction());
        mScrollerX = new MagneticOverScroller();
        mScrollerY = new MagneticOverScroller();

        mScrollerX.setBounceCoefficient(bounceCoefficientX);
        mScrollerY.setBounceCoefficient(bounceCoefficientY);
    }


    /**
     * 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) {
        mDeceleration = computeDeceleration(friction);
    }

    private float computeDeceleration(float friction) {
        return 9.81f   // g (m/s^2)
        * 39.37f               // inch/meter
        * mPpi                 // pixels per inch
        * friction;
    }

    /**
     *
     * 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
     * {@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.
     *
     * @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.
     *
     * @return The new Y offset as an absolute distance from the origin.
     */
    public final int getCurrY() {
        return mScrollerY.mCurrentPosition;
    }

    /**
     * @hide
     * Returns the current velocity.
     *
     * @return The original velocity less the deceleration, norm of the X and Y velocity vector.
     */
    public float getCurrVelocity() {
        float squaredNorm = mScrollerX.mCurrVelocity * mScrollerX.mCurrVelocity;
        squaredNorm += mScrollerY.mCurrVelocity * mScrollerY.mCurrVelocity;
        return (float) Math.sqrt(squaredNorm);
    }

    /**
     * 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.
     *
     * @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.
     *
     * @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.
     *
     * @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.
     *
     * @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 {@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.
     *
     * @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.
     *
     * @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.
     */
    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) {
                    float q = (float) (elapsedTime) / duration;

                    q = Scroller.viscousFluid(q);

                    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.
     *
     * @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;
        mScrollerX.startScroll(startX, dx, duration);
        mScrollerY.startScroll(startY, dy, duration);
    }

    /**
     * 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.
     *
     * @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.
     *
     * @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.
     *
     * @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
     * {@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 != MagneticOverScroller.TO_EDGE) ||
                (!mScrollerY.mFinished &&
                        mScrollerY.mState != MagneticOverScroller.TO_EDGE));
    }

    /**
     * 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.
     *
     * @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
     */
    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);
    }

    class MagneticOverScroller {
        // Initial position
        int mStart;

        // Current position
        int mCurrentPosition;

        // Final position
        int mFinal;

        // Initial velocity
        int mVelocity;

        // Current velocity
        float mCurrVelocity;

        // Constant current deceleration
        float mDeceleration;

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

        // Animation duration, in milliseconds
        int mDuration;

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

        // Distance to travel along spline animation
        int mSplineDistance;

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

        private static final int TO_EDGE = 0;
        private static final int TO_BOUNDARY = 1;
        private static final int TO_BOUNCE = 2;

        private int mState = TO_EDGE;

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

        // If the velocity is smaller than this value, no bounce is triggered
        // when the edge limits are reached (would result in a zero pixels
        // displacement anyway).
        private static final float MINIMUM_VELOCITY_FOR_BOUNCE = 140.0f; //Float.MAX_VALUE;//140.0f;

        // Proportion of the velocity that is preserved when the edge is reached.
        private static final float DEFAULT_BOUNCE_COEFFICIENT = 0.36f;

        private float mBounceCoefficient = DEFAULT_BOUNCE_COEFFICIENT;

        MagneticOverScroller() {
            mFinished = true;
        }

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

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

        /*
         * 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.
         */
        void adjustDuration(int start, int oldFinal, int newFinal) {
            final int oldDistance = oldFinal - start;
            final int newDistance = newFinal - start;
            final float x = (float) 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;

            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;
        }

        void setBounceCoefficient(float coefficient) {
            mBounceCoefficient = coefficient;
        }

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

            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) {
            mFinished = false;
            mState = TO_BOUNCE;
            mStart = mFinal = end;
            final float velocitySign = Math.signum(start - end);
            mDeceleration = getDeceleration((int) velocitySign);
            fitOnBounceCurve(start, end, velocity);
            mDuration = - (int) (2000.0f * mVelocity / 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();
            mStart = start;

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

            mState = TO_EDGE;
            double totalDistance = 0.0;

            if (velocity != 0) {
                final double l = Math.log(START_TENSION * Math.abs(velocity) / ALPHA);
                // Duration are expressed in milliseconds
                mDuration = mSplineDuration = (int) (1000.0 * Math.exp(l / (DECELERATION_RATE - 1.0)));
                totalDistance = (ALPHA * Math.exp(DECELERATION_RATE / (DECELERATION_RATE - 1.0) * l));
            }

            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 void fitOnBounceCurve(int start, int end, int velocity) {
            // Simulate a bounce that started from edge
            final float durationToApex = - velocity / mDeceleration;
            final float distanceToApex = velocity * velocity / 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));
            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) {
                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 l = Math.log(START_TENSION * Math.abs(velocity) / ALPHA);
                final double totalDistance =
                    (ALPHA * Math.exp(DECELERATION_RATE / (DECELERATION_RATE - 1.0) * l));
                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) {
            mOver = over;
            mStartTime = AnimationUtils.currentAnimationTimeMillis();
            // We were in fling/scroll mode before: current velocity is such that distance to edge
            // is increasing. 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.
            final float distance = - mVelocity * mVelocity / (2.0f * mDeceleration);

            if (Math.abs(distance) < mOver) {
                // Spring force will bring us back to final position
                mState = TO_BOUNCE;
                mFinal = mStart;
                mDuration = - (int) (2000.0f * mVelocity / mDeceleration);
            } else {
                // Velocity is too high, we will hit the boundary limit
                mState = TO_BOUNDARY;
                int over = mVelocity > 0 ? mOver : -mOver;
                mFinal = mStart + over;
                mDuration = (int) (1000.0 * Math.PI * over / 2.0 / mVelocity);
            }
        }

        boolean continueWhenFinished() {
            switch (mState) {
                case TO_EDGE:
                    // Duration from start to null velocity
                    if (mDuration < mSplineDuration) {
                        // If the animation was clamped, we reached the edge
                        mStart = mFinal;
                        // 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 TO_BOUNDARY:
                    mStartTime += mDuration;
                    startSpringback(mFinal, mFinal - (mVelocity > 0 ? mOver:-mOver), 0);
                    break;
                case TO_BOUNCE:
                    mVelocity = (int) (mVelocity * mBounceCoefficient);
                    if (Math.abs(mVelocity) < MINIMUM_VELOCITY_FOR_BOUNCE) {
                        return false;
                    }
                    mStartTime += mDuration;
                    mDuration = - (int) (mVelocity / mDeceleration);
                    break;
            }

            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 > mDuration) {
                return false;
            }

            double distance = 0.0;
            switch (mState) {
                case TO_EDGE: {
                    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;
                    break;
                }

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

                case TO_BOUNDARY: {
                    final float t = currentTime / 1000.0f;
                    final float d = t * Math.abs(mVelocity) / mOver;
                    mCurrVelocity = mVelocity * (float) Math.cos(d);
                    distance = (mVelocity > 0 ? mOver : -mOver) * Math.sin(d);
                    break;
                }
            }

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