Enable gesture events handling on Android.

content/public/android/java/src/org/chromium/content/browser/ContentViewGestureHandler.java

+// Copyright (c) 2012 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.content.browser;
+
+import android.content.Context;
+import android.os.Bundle;
+import android.util.Log;
+import android.util.Pair;
+import android.view.GestureDetector;
+import android.view.GestureDetector.OnGestureListener;
+import android.view.MotionEvent;
+import android.view.ViewConfiguration;
+
+import org.chromium.content.browser.LongPressDetector.LongPressDelegate;
+import org.chromium.content.common.TraceEvent;
+
+import java.util.ArrayDeque;
+import java.util.Deque;
+
+/**
+ * This class handles all MotionEvent handling done in ContentViewCore including the gesture
+ * recognition. It sends all related native calls through the interface MotionEventDelegate.
+ */
+class ContentViewGestureHandler implements LongPressDelegate {
+
+    private static final String TAG = ContentViewGestureHandler.class.toString();
+    /**
+     * Used for GESTURE_FLING_START x velocity
+     */
+    static final String VELOCITY_X = "Velocity X";
+    /**
+     * Used for GESTURE_FLING_START y velocity
+     */
+    static final String VELOCITY_Y = "Velocity Y";
+    /**
+     * Used in GESTURE_SINGLE_TAP_CONFIRMED to check whether ShowPress has been called before.
+     */
+    static final String SHOW_PRESS = "ShowPress";
+    /**
+     * Used for GESTURE_PINCH_BY delta
+     */
+    static final String DELTA = "Delta";
+
+    private final Bundle mExtraParamBundle;
+    private GestureDetector mGestureDetector;
+    private final ZoomManager mZoomManager;
+    private LongPressDetector mLongPressDetector;
+    private OnGestureListener mListener;
+    private MotionEvent mCurrentDownEvent;
+    private final MotionEventDelegate mMotionEventDelegate;
+
+    // Queue of motion events. If the boolean value is true, it means
+    // that the event has been offered to the native side but not yet acknowledged. If the
+    // value is false, it means the touch event has not been offered
+    // to the native side and can be immediately processed.
+    private final Deque<Pair<MotionEvent, Boolean>> mPendingMotionEvents =
+            new ArrayDeque<Pair<MotionEvent, Boolean>>();
+
+    // Has WebKit told us the current page requires touch events.
+    private boolean mNeedTouchEvents = false;
+
+    // Remember whether onShowPress() is called. If it is not, in onSingleTapConfirmed()
+    // we will first show the press state, then trigger the click.
+    private boolean mShowPressIsCalled;
+
+    // TODO(klobag): this is to avoid a bug in GestureDetector. With multi-touch,
+    // mAlwaysInTapRegion is not reset. So when the last finger is up, onSingleTapUp()
+    // will be mistakenly fired.
+    private boolean mIgnoreSingleTap;
+
+    // Does native think we are scrolling?  True from right before we
+    // send the first scroll event until the last finger is raised, or
+    // until after the follow-up fling has finished.  Call
+    // nativeScrollBegin() when setting this to true, and use
+    // tellNativeScrollingHasEnded() to set it to false.
+    private boolean mNativeScrolling;
+
+    private boolean mPinchInProgress = false;
+
+    // Tracks whether a touch cancel event has been sent as a result of switching
+    // into scrolling or pinching mode.
+    private boolean mTouchCancelEventSent = false;
+
+    private static final int DOUBLE_TAP_TIMEOUT = ViewConfiguration.getDoubleTapTimeout();
+
+    //On single tap this will store the x, y coordinates of the touch.
+    private int mSingleTapX;
+    private int mSingleTapY;
+
+    // Used to track the last rawX/Y coordinates for moves.  This gives absolute scroll distance.
+    // Useful for full screen tracking.
+    private float mLastRawX = 0;
+    private float mLastRawY = 0;
+
+    // Cache of square of the scaled touch slop so we don't have to calculate it on every touch.
+    private int mScaledTouchSlopSquare;
+
+    // Used to track the accumulated scroll error over time. This is used to remove the
+    // rounding error we introduced by passing integers to webkit.
+    private float mAccumulatedScrollErrorX = 0;
+    private float mAccumulatedScrollErrorY = 0;
+
+    private static final int SNAP_NONE = 0;
+    private static final int SNAP_HORIZ = 1;
+    private static final int SNAP_VERT = 2;
+    private int mSnapScrollMode = SNAP_NONE;
+    private float mAverageAngle;
+    private boolean mSeenFirstScroll;
+
+    /*
+     * Here is the snap align logic:
+     * 1. If it starts nearly horizontally or vertically, snap align;
+     * 2. If there is a dramatic direction change, let it go;
+     *
+     * Adjustable parameters. Angle is the radians on a unit circle, limited
+     * to quadrant 1. Values range from 0f (horizontal) to PI/2 (vertical)
+     */
+    private static final float HSLOPE_TO_START_SNAP = .25f;
+    private static final float HSLOPE_TO_BREAK_SNAP = .6f;
+    private static final float VSLOPE_TO_START_SNAP = 1.25f;
+    private static final float VSLOPE_TO_BREAK_SNAP = .6f;
+
+    /*
+     * These values are used to influence the average angle when entering
+     * snap mode. If it is the first movement entering snap, we set the average
+     * to the appropriate ideal. If the user is entering into snap after the
+     * first movement, then we average the average angle with these values.
+     */
+    private static final float ANGLE_VERT = (float)(Math.PI / 2.0);
+    private static final float ANGLE_HORIZ = 0f;
+
+    /*
+     *  The modified moving average weight.
+     *  Formula: MAV[t]=MAV[t-1] + (P[t]-MAV[t-1])/n
+     */
+    private static final float MMA_WEIGHT_N = 5;
+
+    static final int GESTURE_SHOW_PRESSED_STATE = 0;
+    static final int GESTURE_DOUBLE_TAP = 1;
+    static final int GESTURE_SINGLE_TAP_UP = 2;
+    static final int GESTURE_SINGLE_TAP_CONFIRMED = 3;
+    static final int GESTURE_LONG_PRESS = 4;
+    static final int GESTURE_SCROLL_START = 5;
+    static final int GESTURE_SCROLL_BY = 6;
+    static final int GESTURE_SCROLL_END = 7;
+    static final int GESTURE_FLING_START = 8;
+    static final int GESTURE_FLING_CANCEL = 9;
+    static final int GESTURE_PINCH_BEGIN = 10;
+    static final int GESTURE_PINCH_BY = 11;
+    static final int GESTURE_PINCH_END = 12;
+
+    /**
+     * This is an interface to handle MotionEvent related communication with the native side also
+     * access some ContentView specific parameters.
+     */
+    public interface MotionEventDelegate {
+        /**
+         * Send a raw {@link MotionEvent} to the native side
+         * @param timeMs Time of the event in ms.
+         * @param action The action type for the event.
+         * @param pts The TouchPoint array to be sent for the event.
+         * @return Whether the event was sent to the native side successfully or not.
+         */
+        public boolean sendTouchEvent(long timeMs, int action, TouchPoint[] pts);
+
+        /**
+         * Send a gesture event to the native side.
+         * @param type The type of the gesture event.
+         * @param timeMs The time the gesture event occurred at.
+         * @param x The x location for the gesture event.
+         * @param y The y location for the gesture event.
+         * @param extraParams A bundle that holds specific extra parameters for certain gestures.
+         * Refer to gesture type definition for more information.
+         * @return Whether the gesture was sent successfully.
+         */
+        boolean sendGesture(
+                int type, long timeMs, int x, int y, Bundle extraParams);
+
+        /**
+         * Gives the UI the chance to override each scroll event.
+         * @param x The amount scrolled in the X direction.
+         * @param y The amount scrolled in the Y direction.
+         * @return Whether or not the UI consumed and handled this event.
+         */
+        boolean didUIStealScroll(float x, float y);
+
+        /**
+         * Show the zoom picker UI.
+         */
+        public void invokeZoomPicker();
+    }
+
+    ContentViewGestureHandler(
+            Context context, MotionEventDelegate delegate, ZoomManager zoomManager) {
+        mExtraParamBundle = new Bundle();
+        mLongPressDetector = new LongPressDetector(context, this);
+        mMotionEventDelegate = delegate;
+        mZoomManager = zoomManager;
+        initGestureDetectors(context);
+    }
+
+    /**
+     * Used to override the default long press detector, gesture detector and listener.
+     * This is used for testing only.
+     * @param longPressDetector The new LongPressDetector to be assigned.
+     * @param gestureDetector The new GestureDetector to be assigned.
+     * @param listener The new onGestureListener to be assigned.
+     */
+    void setTestDependencies(
+            LongPressDetector longPressDetector, GestureDetector gestureDetector,
+            OnGestureListener listener) {
+        mLongPressDetector = longPressDetector;
+        mGestureDetector = gestureDetector;
+        mListener = listener;
+    }
+
+    private void initGestureDetectors(final Context context) {
+        int scaledTouchSlop = ViewConfiguration.get(context).getScaledTouchSlop();
+        mScaledTouchSlopSquare = scaledTouchSlop * scaledTouchSlop;
+        try {
+            TraceEvent.begin();
+            GestureDetector.SimpleOnGestureListener listener =
+                new GestureDetector.SimpleOnGestureListener() {
+                    @Override
+                    public boolean onDown(MotionEvent e) {
+                        mShowPressIsCalled = false;
+                        mIgnoreSingleTap = false;
+                        mSeenFirstScroll = false;
+                        mNativeScrolling = false;
+                        mSnapScrollMode = SNAP_NONE;
+                        mLastRawX = e.getRawX();
+                        mLastRawY = e.getRawY();
+                        mAccumulatedScrollErrorX = 0;
+                        mAccumulatedScrollErrorY = 0;
+                        // Return true to indicate that we want to handle touch
+                        return true;
+                    }
+
+                    @Override
+                    public boolean onScroll(MotionEvent e1, MotionEvent e2,
+                            float distanceX, float distanceY) {
+                        // Scroll snapping
+                        if (!mSeenFirstScroll) {
+                            mAverageAngle = calculateDragAngle(distanceX, distanceY);
+                            // Initial scroll event
+                            if (!mZoomManager.isScaleGestureDetectionInProgress()) {
+                                // if it starts nearly horizontal or vertical, enforce it
+                                if (mAverageAngle < HSLOPE_TO_START_SNAP) {
+                                    mSnapScrollMode = SNAP_HORIZ;
+                                    mAverageAngle = ANGLE_HORIZ;
+                                } else if (mAverageAngle > VSLOPE_TO_START_SNAP) {
+                                    mSnapScrollMode = SNAP_VERT;
+                                    mAverageAngle = ANGLE_VERT;
+                                }
+                            }
+                            mSeenFirstScroll = true;
+                            // Ignore the first scroll delta to avoid a visible jump.
+                            return true;
+                        } else {
+                            mAverageAngle +=
+                                (calculateDragAngle(distanceX, distanceY) - mAverageAngle)
+                                / MMA_WEIGHT_N;
+                            if (mSnapScrollMode != SNAP_NONE) {
+                                if ((mSnapScrollMode == SNAP_VERT
+                                        && mAverageAngle < VSLOPE_TO_BREAK_SNAP)
+                                        || (mSnapScrollMode == SNAP_HORIZ
+                                                && mAverageAngle > HSLOPE_TO_BREAK_SNAP)) {
+                                    // radical change means getting out of snap mode
+                                    mSnapScrollMode = SNAP_NONE;
+                                }
+                            } else {
+                                if (!mZoomManager.isScaleGestureDetectionInProgress()) {
+                                    if (mAverageAngle < HSLOPE_TO_START_SNAP) {
+                                        mSnapScrollMode = SNAP_HORIZ;
+                                        mAverageAngle = (mAverageAngle + ANGLE_HORIZ) / 2;
+                                    } else if (mAverageAngle > VSLOPE_TO_START_SNAP) {
+                                        mSnapScrollMode = SNAP_VERT;
+                                        mAverageAngle = (mAverageAngle + ANGLE_VERT) / 2;
+                                    }
+                                }
+                            }
+                        }
+
+                        if (mSnapScrollMode != SNAP_NONE) {
+                            if (mSnapScrollMode == SNAP_HORIZ) {
+                                distanceY = 0;
+                            } else {
+                                distanceX = 0;
+                            }
+                        }
+
+                        boolean didUIStealScroll = mMotionEventDelegate.didUIStealScroll(
+                                e2.getRawX() - mLastRawX, e2.getRawY() - mLastRawY);
+
+                        mLastRawX = e2.getRawX();
+                        mLastRawY = e2.getRawY();
+                        if (didUIStealScroll) return true;
+                        if (!mNativeScrolling && mMotionEventDelegate.sendGesture(
+                                GESTURE_SCROLL_START, e1.getEventTime(),
+                                        (int) e1.getX(), (int) e1.getY(), null)) {
+                            mNativeScrolling = true;
+
+                        }
+                        // distanceX and distanceY is the scrolling offset since last onScroll.
+                        // Because we are passing integers to webkit, this could introduce
+                        // rounding errors. The rounding errors will accumulate overtime.
+                        // To solve this, we should adding back the rounding errors each time
+                        // when we calculate the new offset.
+                        int dx = (int) (distanceX + mAccumulatedScrollErrorX);
+                        int dy = (int) (distanceY + mAccumulatedScrollErrorY);
+                        mAccumulatedScrollErrorX = distanceX + mAccumulatedScrollErrorX - dx;
+                        mAccumulatedScrollErrorY = distanceY + mAccumulatedScrollErrorY - dy;
+                        if ((dx | dy) != 0) {
+                            mMotionEventDelegate.sendGesture(GESTURE_SCROLL_BY,
+                                    e2.getEventTime(), dx, dy, null);
+                        }
+
+                        mMotionEventDelegate.invokeZoomPicker();
+
+                        return true;
+                    }
+
+                    @Override
+                    public boolean onFling(MotionEvent e1, MotionEvent e2,
+                            float velocityX, float velocityY) {
+                        if (mSnapScrollMode == SNAP_NONE) {
+                            float flingAngle = calculateDragAngle(velocityX, velocityY);
+                            if (flingAngle < HSLOPE_TO_START_SNAP) {
+                                mSnapScrollMode = SNAP_HORIZ;
+                                mAverageAngle = ANGLE_HORIZ;
+                            } else if (flingAngle > VSLOPE_TO_START_SNAP) {
+                                mSnapScrollMode = SNAP_VERT;
+                                mAverageAngle = ANGLE_VERT;
+                            }
+                        }
+
+                        if (mSnapScrollMode != SNAP_NONE) {
+                            if (mSnapScrollMode == SNAP_HORIZ) {
+                                velocityY = 0;
+                            } else {
+                                velocityX = 0;
+                            }
+                        }
+
+                        fling(e1.getEventTime(),(int) e1.getX(0), (int) e1.getY(0),
+                                        (int) velocityX, (int) velocityY);
+                        return true;
+                    }
+
+                    @Override
+                    public void onShowPress(MotionEvent e) {
+                        mShowPressIsCalled = true;
+                        mMotionEventDelegate.sendGesture(GESTURE_SHOW_PRESSED_STATE,
+                                e.getEventTime(), (int) e.getX(), (int) e.getY(), null);
+                    }
+
+                    @Override
+                    public boolean onSingleTapUp(MotionEvent e) {
+                        if (isDistanceBetweenDownAndUpTooLong(e.getRawX(), e.getRawY())) {
+                            mIgnoreSingleTap = true;
+                            return true;
+                        }
+                        // This is a hack to address the issue where user hovers
+                        // over a link for longer than DOUBLE_TAP_TIMEOUT, then
+                        // onSingleTapConfirmed() is not triggered. But we still
+                        // want to trigger the tap event at UP. So we override
+                        // onSingleTapUp() in this case. This assumes singleTapUp
+                        // gets always called before singleTapConfirmed.
+                        if (!mIgnoreSingleTap && !mLongPressDetector.isInLongPress() &&
+                                (e.getEventTime() - e.getDownTime() > DOUBLE_TAP_TIMEOUT)) {
+                            float x = e.getX();
+                            float y = e.getY();
+                            if (mMotionEventDelegate.sendGesture(GESTURE_SINGLE_TAP_UP,
+                                    e.getEventTime(), (int) x, (int) y, null)) {
+                                mIgnoreSingleTap = true;
+                            }
+                            setClickXAndY((int) x, (int) y);
+                            return true;
+                        }
+                        return false;
+                    }
+
+                    @Override
+                    public boolean onSingleTapConfirmed(MotionEvent e) {
+                        // Long taps in the edges of the screen have their events delayed by
+                        // ChromeViewHolder for tab swipe operations. As a consequence of the delay
+                        // this method might be called after receiving the up event.
+                        // These corner cases should be ignored.
+                        if (mLongPressDetector.isInLongPress() || mIgnoreSingleTap) return true;
+
+                        int x = (int) e.getX();
+                        int y = (int) e.getY();
+                        mExtraParamBundle.clear();
+                        mExtraParamBundle.putBoolean(SHOW_PRESS, mShowPressIsCalled);
+                        mMotionEventDelegate.sendGesture(GESTURE_SINGLE_TAP_CONFIRMED,
+                                e.getEventTime(), x, y, mExtraParamBundle);
+                        setClickXAndY(x, y);
+                        return true;
+                    }
+
+                    @Override
+                    public boolean onDoubleTap(MotionEvent e) {
+                        mMotionEventDelegate.sendGesture(GESTURE_DOUBLE_TAP,
+                                e.getEventTime(), (int) e.getX(), (int) e.getY(), null);
+                        return true;
+                    }
+
+                    @Override
+                    public void onLongPress(MotionEvent e) {
+                        if (!mZoomManager.isScaleGestureDetectionInProgress()) {
+                            mMotionEventDelegate.sendGesture(GESTURE_LONG_PRESS,
+                                    e.getEventTime(), (int) e.getX(), (int) e.getY(), null);
+                        }
+                    }
+
+                    /**
+                     * This method inspects the distance between where the user started touching
+                     * the surface, and where she released. If the points are too far apart, we
+                     * should assume that the web page has consumed the scroll-events in-between,
+                     * and as such, this should not be considered a single-tap.
+                     *
+                     * We use the Android frameworks notion of how far a touch can wander before
+                     * we think the user is scrolling.
+                     *
+                     * @param x the new x coordinate
+                     * @param y the new y coordinate
+                     * @return true if the distance is too long to be considered a single tap
+                     */
+                    private boolean isDistanceBetweenDownAndUpTooLong(float x, float y) {
+                        double deltaX = mLastRawX - x;
+                        double deltaY = mLastRawY - y;
+                        return deltaX * deltaX + deltaY * deltaY > mScaledTouchSlopSquare;
+                    }
+                };
+                mListener = listener;
+                mGestureDetector = new GestureDetector(context, listener);
+                mGestureDetector.setIsLongpressEnabled(false);
+        } finally {
+            TraceEvent.end();
+        }
+    }
+
+    /**
+     * @return LongPressDetector handling setting up timers for and canceling LongPress gestures.
+     */
+    LongPressDetector getLongPressDetector() {
+        return mLongPressDetector;
+    }
+
+    /**
+     * @param event Start a LongPress gesture event from the listener.
+     */
+    @Override
+    public void onLongPress(MotionEvent event) {
+        mListener.onLongPress(event);
+    }
+
+    /**
+     * Cancels any ongoing LongPress timers.
+     */
+    void cancelLongPress() {
+        mLongPressDetector.cancelLongPress();
+    }
+
+    /**
+     * Fling the ContentView from the current position.
+     * @param x Fling touch starting position
+     * @param y Fling touch starting position
+     * @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.
+     */
+    void fling(long timeMs, int x, int y, int velocityX, int velocityY) {
+        endFling(timeMs);
+        mExtraParamBundle.clear();
+        mExtraParamBundle.putInt(VELOCITY_X, velocityX);
+        mExtraParamBundle.putInt(VELOCITY_Y, velocityY);
+        mMotionEventDelegate.sendGesture(GESTURE_FLING_START,
+                timeMs, x, y, mExtraParamBundle);
+    }
+
+    /**
+     * Send a FlingCancel gesture event and also cancel scrolling if it is active.
+     * @param timeMs The time in ms for the event initiating this gesture.
+     */
+    void endFling(long timeMs) {
+        mMotionEventDelegate.sendGesture(GESTURE_FLING_CANCEL, timeMs, 0, 0, null);
+        tellNativeScrollingHasEnded(timeMs);
+    }
+
+    // If native thinks scrolling (or fling-scrolling) is going on, tell native
+    // it has ended.
+    private void tellNativeScrollingHasEnded(long timeMs) {
+        if (mNativeScrolling) {
+            mNativeScrolling = false;
+            mMotionEventDelegate.sendGesture(GESTURE_SCROLL_END, timeMs, 0, 0, null);
+        }
+    }
+
+    /**
+     * Starts a pinch gesture.
+     * @param timeMs The time in ms for the event initiating this gesture.
+     * @param x The x coordinate for the event initiating this gesture.
+     * @param y The x coordinate for the event initiating this gesture.
+     */
+    void pinchBegin(long timeMs, int x, int y) {
+        mMotionEventDelegate.sendGesture(GESTURE_PINCH_BEGIN, timeMs, x, y, null);
+    }
+
+    /**
+     * Pinch by a given percentage.
+     * @param timeMs The time in ms for the event initiating this gesture.
+     * @param anchorX The x coordinate for the anchor point to be used in pinch.
+     * @param anchorY The y coordinate for the anchor point to be used in pinch.
+     * @param delta The percentage to pinch by.
+     */
+    void pinchBy(long timeMs, int anchorX, int anchorY, float delta) {
+        mExtraParamBundle.clear();
+        mExtraParamBundle.putFloat(DELTA, delta);
+        mMotionEventDelegate.sendGesture(GESTURE_PINCH_BY,
+                timeMs, anchorX, anchorY, mExtraParamBundle);
+        mPinchInProgress = true;
+    }
+
+    /**
+     * End a pinch gesture.
+     * @param timeMs The time in ms for the event initiating this gesture.
+     */
+    void pinchEnd(long timeMs) {
+        mMotionEventDelegate.sendGesture(GESTURE_PINCH_END, timeMs, 0, 0, null);
+        mPinchInProgress = false;
+    }
+
+    /**
+     * Ignore singleTap gestures.
+     */
+    void setIgnoreSingleTap(boolean value) {
+        mIgnoreSingleTap = value;
+    }
+
+    private float calculateDragAngle(float dx, float dy) {
+        dx = Math.abs(dx);
+        dy = Math.abs(dy);
+        return (float) Math.atan2(dy, dx);
+    }
+
+    private void setClickXAndY(int x, int y) {
+        mSingleTapX = x;
+        mSingleTapY = y;
+    }
+
+    /**
+     * @return The x coordinate for the last point that a singleTap gesture was initiated from.
+     */
+    public int getSingleTapX()  {
+        return mSingleTapX;
+    }
+
+    /**
+     * @return The y coordinate for the last point that a singleTap gesture was initiated from.
+     */
+    public int getSingleTapY()  {
+        return mSingleTapY;
+    }
+
+    /**
+     * Handle the incoming MotionEvent.
+     * @return Whether the event was handled.
+     */
+    boolean onTouchEvent(MotionEvent event) {
+        TraceEvent.begin("onTouchEvent");
+        mLongPressDetector.cancelLongPressIfNeeded(event);
+        // Notify native that scrolling has stopped whenever a down action is processed prior to
+        // passing the event to native as it will drop them as an optimization if scrolling is
+        // enabled.  Ending the fling ensures scrolling has stopped as well as terminating the
+        // current fling if applicable.
+        if (event.getActionMasked() == MotionEvent.ACTION_DOWN) {
+            endFling(event.getEventTime());
+        }
+
+        if (offerTouchEventToJavaScript(event)) {
+            // offerTouchEventToJavaScript returns true to indicate the event was sent
+            // to the render process. If it is not subsequently handled, it will
+            // be returned via confirmTouchEvent(false) and eventually passed to
+            // processTouchEvent asynchronously.
+            TraceEvent.end("onTouchEvent");
+            return true;
+        }
+        return processTouchEvent(event);
+    }
+
+    /**
+     * Sets the flag indicating that the content has registered listeners for touch events.
+     */
+    void didSetNeedTouchEvents(boolean needTouchEvents) {
+        mNeedTouchEvents = needTouchEvents;
+        // When mainframe is loading, FrameLoader::transitionToCommitted will
+        // call this method to set mNeedTouchEvents to false. We use this as
+        // an indicator to clear the pending motion events so that events from
+        // the previous page will not be carried over to the new page.
+        if (!mNeedTouchEvents) mPendingMotionEvents.clear();
+    }
+
+    private boolean offerTouchEventToJavaScript(MotionEvent event) {
+        mLongPressDetector.onOfferTouchEventToJavaScript(event);
+
+        if (!mNeedTouchEvents) return false;
+
+        if (event.getActionMasked() == MotionEvent.ACTION_MOVE) {
+            // Only send move events if the move has exceeded the slop threshold.
+            if (!mLongPressDetector.confirmOfferMoveEventToJavaScript(event)) {
+                return true;
+            }
+            // Avoid flooding the renderer process with move events: if the previous pending
+            // command is also a move (common case), skip sending this event to the webkit
+            // side and collapse it into the pending event.
+            Pair<MotionEvent, Boolean> previousEvent = mPendingMotionEvents.peekLast();
+            if (previousEvent != null && previousEvent.second == true
+                    && previousEvent.first.getActionMasked() == MotionEvent.ACTION_MOVE
+                    && previousEvent.first.getPointerCount() == event.getPointerCount()) {
+                MotionEvent.PointerCoords[] coords =
+                    new MotionEvent.PointerCoords[event.getPointerCount()];
+                for (int i = 0; i < coords.length; ++i) {
+                    coords[i] = new MotionEvent.PointerCoords();
+                    event.getPointerCoords(i, coords[i]);
+                }
+                previousEvent.first.addBatch(event.getEventTime(), coords, event.getMetaState());
+                return true;
+            }
+        }
+
+        TouchPoint[] pts = new TouchPoint[event.getPointerCount()];
+        int type = TouchPoint.createTouchPoints(event, pts);
+
+        boolean forwarded = false;
+        if (type != TouchPoint.CONVERSION_ERROR && !mNativeScrolling && !mPinchInProgress) {
+            mTouchCancelEventSent = false;
+            forwarded = mMotionEventDelegate.sendTouchEvent(event.getEventTime(), type, pts);
+        } else if ((mNativeScrolling || mPinchInProgress) && !mTouchCancelEventSent) {
+            forwarded = mMotionEventDelegate.sendTouchEvent(event.getEventTime(),
+                    TouchPoint.TOUCH_EVENT_TYPE_CANCEL, pts);
+            mTouchCancelEventSent = true;
+        }
+        if (forwarded || !mPendingMotionEvents.isEmpty()) {
+            // Copy the event, as the original may get mutated after this method returns.
+            mPendingMotionEvents.add(Pair.create(MotionEvent.obtain(event), forwarded));
+            // TODO(joth): If needed, start a watchdog timer to pump mPendingMotionEvents
+            // in the case of the WebKit renderer / JS being unresponsive.
+            return true;
+        }
+        return false;
+    }
+
+    private boolean processTouchEvent(MotionEvent event) {
+        boolean handled = false;
+        // The last "finger up" is an end to scrolling but may not be
+        // an end to movement (e.g. fling scroll).  We do not tell
+        // native code to end scrolling until we are sure we did not
+        // fling.
+        boolean possiblyEndMovement = false;
+
+        // "Last finger raised" could be an end to movement.  However,
+        // give the mSimpleTouchDetector a chance to continue
+        // scrolling with a fling.
+        if ((event.getAction() == MotionEvent.ACTION_UP) &&
+            (event.getPointerCount() == 1)) {
+            if (mNativeScrolling) {
+                possiblyEndMovement = true;
+            }
+        }
+
+        mLongPressDetector.startLongPressTimerIfNeeded(event);
+
+        // Use the framework's GestureDetector to detect pans and zooms not already
+        // handled by the WebKit touch events gesture manager.
+        if (canHandle(event)) {
+            handled |= mGestureDetector.onTouchEvent(event);
+            if (event.getAction() == MotionEvent.ACTION_DOWN) mCurrentDownEvent = event;
+        }
+
+        handled |= mZoomManager.processTouchEvent(event);
+
+        if (possiblyEndMovement && !handled) {
+            tellNativeScrollingHasEnded(event.getEventTime());
+        }
+
+        return handled;
+    }
+
+    /**
+     * Respond to a MotionEvent being returned from the native side.
+     * @param handled Whether the MotionEvent was handled on the native side.
+     */
+    void confirmTouchEvent(boolean handled) {
+        MotionEvent eventToPassThrough = null;
+        if (mPendingMotionEvents.isEmpty()) {
+            Log.w(TAG, "confirmTouchEvent with Empty pending list!");
+            return;
+        }
+        TraceEvent.begin();
+        Pair<MotionEvent, Boolean> event = mPendingMotionEvents.removeFirst();
+        if (!handled) {
+            if (!processTouchEvent(event.first)) {
+                // TODO(joth): If the Java side gesture handler also fails to consume
+                // this deferred event, should it be bubbled up to the parent view?
+                Log.w(TAG, "Unhandled deferred touch event");
+            }
+        } else {
+            mZoomManager.passTouchEventThrough(event.first);
+        }
+
+        // Now process all events that are in the queue but not sent to the native.
+        Pair<MotionEvent, Boolean> nextEvent = mPendingMotionEvents.peekFirst();
+        while (nextEvent != null && nextEvent.second == false) {
+            processTouchEvent(nextEvent.first);
+            mPendingMotionEvents.removeFirst();
+            nextEvent.first.recycle();
+            nextEvent = mPendingMotionEvents.peekFirst();
+        }
+
+        // We may have pending events that could cancel the timers:
+        // For instance, if we received an UP before the DOWN completed
+        // its roundtrip (so it didn't cancel the timer during onTouchEvent()).
+        mLongPressDetector.cancelLongPressIfNeeded(mPendingMotionEvents.iterator());
+        event.first.recycle();
+        TraceEvent.end();
+    }
+
+    /**
+     * @return Whether the ContentViewGestureHandler can handle a MotionEvent right now. True only
+     * if it's the start of a new stream (ACTION_DOWN), or a continuation of the current stream.
+     */
+    boolean canHandle(MotionEvent ev) {
+        return ev.getAction() == MotionEvent.ACTION_DOWN ||
+                (mCurrentDownEvent != null && mCurrentDownEvent.getDownTime() == ev.getDownTime());
+    }
+
+}