Upstream oodles of Chrome for Android code into Chromium.

chrome/android/java_staging/src/org/chromium/chrome/browser/compositor/layouts/phone/stack/StackScroller.java

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.chrome.browser.compositor.layouts.phone.stack;
+
+import android.content.Context;
+import android.hardware.SensorManager;
+import android.util.Log;
+import android.view.ViewConfiguration;
+
+/**
+ * This class is vastly copied from {@link android.widget.OverScroller} but decouples the time
+ * from the app time so it can be specified manually.
+ */
+public class StackScroller {
+    private int mMode;
+
+    private final SplineStackScroller mScrollerX;
+    private final SplineStackScroller mScrollerY;
+
+    private final boolean mFlywheel;
+
+    private static final int SCROLL_MODE = 0;
+    private static final int FLING_MODE = 1;
+
+    private static float sViscousFluidScale;
+    private static float sViscousFluidNormalize;
+
+    /**
+     * Creates an StackScroller with a viscous fluid scroll interpolator and flywheel.
+     * @param context
+     */
+    public StackScroller(Context context) {
+        mFlywheel = true;
+        mScrollerX = new SplineStackScroller(context);
+        mScrollerY = new SplineStackScroller(context);
+        initContants();
+    }
+
+    private static void initContants() {
+        // This controls the viscous fluid effect (how much of it)
+        sViscousFluidScale = 8.0f;
+        // must be set to 1.0 (used in viscousFluid())
+        sViscousFluidNormalize = 1.0f;
+        sViscousFluidNormalize = 1.0f / viscousFluid(1.0f);
+    }
+
+    /**
+     *
+     * 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;
+    }
+
+    /**
+     * 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;
+    }
+
+    /**
+     * Sets where the scroll will end.  Valid only for "fling" scrolls.
+     *
+     * @param x The final X offset as an absolute distance from the origin.
+     */
+    public final void setFinalX(int x) {
+        mScrollerX.setFinalPosition(x);
+    }
+
+    private static float viscousFluid(float x) {
+        x *= sViscousFluidScale;
+        if (x < 1.0f) {
+            x -= (1.0f - (float) Math.exp(-x));
+        } else {
+            float start = 0.36787944117f; // 1/e == exp(-1)
+            x = 1.0f - (float) Math.exp(1.0f - x);
+            x = start + x * (1.0f - start);
+        }
+        x *= sViscousFluidNormalize;
+        return x;
+    }
+
+    /**
+     * Call this when you want to know the new location. If it returns true, the
+     * animation is not yet finished.
+     */
+    public boolean computeScrollOffset(long time) {
+        if (isFinished()) {
+            return false;
+        }
+
+        switch (mMode) {
+            case SCROLL_MODE:
+                // 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 = viscousFluid(q);
+                    mScrollerX.updateScroll(q);
+                    mScrollerY.updateScroll(q);
+                } else {
+                    abortAnimation();
+                }
+                break;
+
+            case FLING_MODE:
+                if (!mScrollerX.mFinished) {
+                    if (!mScrollerX.update(time)) {
+                        if (!mScrollerX.continueWhenFinished(time)) {
+                            mScrollerX.finish();
+                        }
+                    }
+                }
+
+                if (!mScrollerY.mFinished) {
+                    if (!mScrollerY.update(time)) {
+                        if (!mScrollerY.continueWhenFinished(time)) {
+                            mScrollerY.finish();
+                        }
+                    }
+                }
+
+                break;
+
+            default:
+                break;
+        }
+
+        return true;
+    }
+
+    /**
+     * 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, long startTime, int duration) {
+        mMode = SCROLL_MODE;
+        mScrollerX.startScroll(startX, dx, startTime, duration);
+        mScrollerY.startScroll(startY, dy, startTime, 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, long time) {
+        mMode = FLING_MODE;
+
+        // Make sure both methods are called.
+        final boolean spingbackX = mScrollerX.springback(startX, minX, maxX, time);
+        final boolean spingbackY = mScrollerY.springback(startY, minY, maxY, time);
+        return spingbackX || spingbackY;
+    }
+
+    /**
+     * 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, long time) {
+        // 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, time);
+        mScrollerY.fling(startY, velocityY, minY, maxY, overY, time);
+    }
+
+    /**
+     * 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();
+    }
+
+    static class SplineStackScroller {
+        // 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 final 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 final float mPhysicalCoeff;
+
+        private static final 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 xMin = 0.0f;
+            float yMin = 0.0f;
+            for (int i = 0; i < NB_SAMPLES; i++) {
+                final float alpha = (float) i / NB_SAMPLES;
+
+                float xMax = 1.0f;
+                float x, tx, coef;
+                while (true) {
+                    x = xMin + (xMax - xMin) / 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) {
+                        xMax = x;
+                    } else {
+                        xMin = x;
+                    }
+                }
+                SPLINE_POSITION[i] = coef * ((1.0f - x) * START_TENSION + x) + x * x * x;
+
+                float yMax = 1.0f;
+                float y, dy;
+                while (true) {
+                    y = yMin + (yMax - yMin) / 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) {
+                        yMax = y;
+                    } else {
+                        yMin = y;
+                    }
+                }
+                SPLINE_TIME[i] = coef * ((1.0f - y) * P1 + y * P2) + y * y * y;
+            }
+            SPLINE_POSITION[NB_SAMPLES] = SPLINE_TIME[NB_SAMPLES] = 1.0f;
+        }
+
+        SplineStackScroller(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.
+         */
+        private static 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 xInf = (float) index / NB_SAMPLES;
+                final float xSup = (float) (index + 1) / NB_SAMPLES;
+                final float tInf = SPLINE_TIME[index];
+                final float tSup = SPLINE_TIME[index + 1];
+                final float timeCoef = tInf + (x - xInf) / (xSup - xInf) * (tSup - tInf);
+                mDuration *= timeCoef;
+            }
+        }
+
+        void startScroll(int start, int distance, long startTime, int duration) {
+            mFinished = false;
+
+            mStart = start;
+            mFinal = start + distance;
+
+            mStartTime = startTime;
+            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;
+        }
+
+        boolean springback(int start, int min, int max, long time) {
+            mFinished = true;
+
+            mStart = mFinal = start;
+            mVelocity = 0;
+
+            mStartTime = time;
+            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;
+            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, long time) {
+            mOver = over;
+            mFinished = false;
+            mCurrVelocity = mVelocity = velocity;
+            mDuration = mSplineDuration = 0;
+            mStartTime = time;
+            mCurrentPosition = mStart = start;
+
+            if (start > max || start < min) {
+                startAfterEdge(start, min, max, velocity, time);
+                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;
+            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, long time) {
+            if (start > min && start < max) {
+                Log.e("StackScroller", "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,
+                            time);
+                } else {
+                    startSpringback(start, edge, velocity);
+                }
+            }
+        }
+
+        private void onEdgeReached() {
+            // mStart, mVelocity and mStartTime were adjusted to their values when edge was reached.
+            float distance = mVelocity * mVelocity / (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 * mVelocity * mVelocity / (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(long time) {
+            switch (mState) {
+                case SPLINE:
+                    // Duration from start to null velocity
+                    if (mDuration < mSplineDuration) {
+                        // If the animation was clamped, we reached the edge
+                        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(time);
+            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(long time) {
+            final long currentTime = time - mStartTime;
+
+            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 tInf = (float) index / NB_SAMPLES;
+                        final float tSup = (float) (index + 1) / NB_SAMPLES;
+                        final float dInf = SPLINE_POSITION[index];
+                        final float dSup = SPLINE_POSITION[index + 1];
+                        velocityCoef = (dSup - dInf) / (tSup - tInf);
+                        distanceCoef = dInf + (t - tInf) * 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;
+        }
+    }
+}