android/widget/OverScroller.java

/*
 * 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.util.FloatMath;
import android.view.animation.AnimationUtils;
import android.view.animation.Interpolator;
import android.widget.Scroller.MagneticScroller;

/**
 * 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 MagneticOverScroller mScrollerX;
    private MagneticOverScroller mScrollerY;

    private final Interpolator mInterpolator;

    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.
     * @param context
     */
    public OverScroller(Context context) {
        this(context, null);
    }

    /**
     * Creates an OverScroller with default edge bounce coefficients.
     * @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, MagneticOverScroller.DEFAULT_BOUNCE_COEFFICIENT,
                MagneticOverScroller.DEFAULT_BOUNCE_COEFFICIENT);
    }

    /**
     * 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) {
        mInterpolator = interpolator;
        mScrollerX = new MagneticOverScroller();
        mScrollerY = new MagneticOverScroller();
        MagneticScroller.initializeFromContext(context);

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

    /**
     *
     * 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 FloatMath.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.
     */
    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.
     */
    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.
     */
    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.
     */
    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;

                    if (mInterpolator == null)
                        q = Scroller.viscousFluid(q);
                    else
                        q = mInterpolator.getInterpolation(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) {
        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.
     */
    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);
    }

    static class MagneticOverScroller extends Scroller.MagneticScroller {
        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;

        // Duration in milliseconds to go back from edge to edge. Springback is half of it.
        private static final int OVERSCROLL_SPRINGBACK_DURATION = 200;

        // Oscillation period
        private static final float TIME_COEF =
            1000.0f * (float) Math.PI / OVERSCROLL_SPRINGBACK_DURATION;

        // 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;

        // Proportion of the velocity that is preserved when the edge is reached.
        private static final float DEFAULT_BOUNCE_COEFFICIENT = 0.16f;

        private float mBounceCoefficient = DEFAULT_BOUNCE_COEFFICIENT;

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

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

            mStart = start;
            mVelocity = 0;

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

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

            return !mFinished;
        }

        private void startSpringback(int start, int end, boolean positive) {
            mFinished = false;
            mState = TO_BOUNCE;
            mStart = mFinal = end;
            mDuration = OVERSCROLL_SPRINGBACK_DURATION;
            mStartTime -= OVERSCROLL_SPRINGBACK_DURATION / 2;
            mVelocity = (int) (Math.abs(end - start) * TIME_COEF * (positive ? 1.0 : -1.0f));
        }

        void fling(int start, int velocity, int min, int max, int over) {
            mState = TO_EDGE;
            mOver = over;

            super.fling(start, velocity, min, max);

            if (start > max) {
                if (start >= max + over) {
                    springback(max + over, min, max);
                } else {
                    if (velocity <= 0) {
                        springback(start, min, max);
                    } else {
                        long time = AnimationUtils.currentAnimationTimeMillis();
                        final double durationSinceEdge =
                            Math.atan((start-max) * TIME_COEF / velocity) / TIME_COEF;
                        mStartTime = (int) (time - 1000.0f * durationSinceEdge);

                        // Simulate a bounce that started from edge
                        mStart = max;

                        mVelocity = (int) (velocity / Math.cos(durationSinceEdge * TIME_COEF));

                        onEdgeReached();
                    }
                }
            } else {
                if (start < min) {
                    if (start <= min - over) {
                        springback(min - over, min, max);
                    } else {
                        if (velocity >= 0) {
                            springback(start, min, max);
                        } else {
                            long time = AnimationUtils.currentAnimationTimeMillis();
                            final double durationSinceEdge =
                                Math.atan((start-min) * TIME_COEF / velocity) / TIME_COEF;
                            mStartTime = (int) (time - 1000.0f * durationSinceEdge);

                            // Simulate a bounce that started from edge
                            mStart = min;

                            mVelocity = (int) (velocity / Math.cos(durationSinceEdge * TIME_COEF));

                            onEdgeReached();
                        }

                    }
                }
            }
        }

        void notifyEdgeReached(int start, int end, int over) {
            mDeceleration = getDeceleration(mVelocity);

            // Local time, used to compute edge crossing time.
            float timeCurrent = mCurrVelocity / mDeceleration;
            final int distance = end - start;
            float timeEdge = -(float) Math.sqrt((2.0f * distance / mDeceleration)
                    + (timeCurrent * timeCurrent));

            mVelocity = (int) (mDeceleration * timeEdge);

            // Simulate a symmetric bounce that started from edge
            mStart = end;

            mOver = over;

            long time = AnimationUtils.currentAnimationTimeMillis();
            mStartTime = (int) (time - 1000.0f * (timeCurrent - timeEdge));

            onEdgeReached();
        }

        private void onEdgeReached() {
            // mStart, mVelocity and mStartTime were adjusted to their values when edge was reached.
            final float distance = mVelocity / TIME_COEF;

            if (Math.abs(distance) < mOver) {
                // Spring force will bring us back to final position
                mState = TO_BOUNCE;
                mFinal = mStart;
                mDuration = OVERSCROLL_SPRINGBACK_DURATION;
            } 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) (1000.0f * Math.asin(over / distance) / TIME_COEF);
            }
        }

        @Override
        boolean continueWhenFinished() {
            switch (mState) {
                case TO_EDGE:
                    // Duration from start to null velocity
                    int duration = (int) (-1000.0f * mVelocity / mDeceleration);
                    if (mDuration < duration) {
                        // If the animation was clamped, we reached the edge
                        mStart = mFinal;
                        // Speed when edge was reached
                        mVelocity = (int) (mVelocity + mDeceleration * mDuration / 1000.0f);
                        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), mVelocity > 0);
                    break;
                case TO_BOUNCE:
                    //mVelocity = (int) (mVelocity * BOUNCE_COEFFICIENT);
                    mVelocity = (int) (mVelocity * mBounceCoefficient);
                    if (Math.abs(mVelocity) < MINIMUM_VELOCITY_FOR_BOUNCE) {
                        return false;
                    }
                    mStartTime += mDuration;
                    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.
         */
        @Override
        boolean update() {
            final long time = AnimationUtils.currentAnimationTimeMillis();
            final long duration = time - mStartTime;

            if (duration > mDuration) {
                return false;
            }

            double distance;
            final float t = duration / 1000.0f;
            if (mState == TO_EDGE) {
                mCurrVelocity = mVelocity + mDeceleration * t;
                distance = mVelocity * t + mDeceleration * t * t / 2.0f;
            } else {
                final float d = t * TIME_COEF;
                mCurrVelocity = mVelocity * (float)Math.cos(d);
                distance = mVelocity / TIME_COEF * Math.sin(d);
            }

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