b/3307761 Tuning two fingers pan.

User reports jumpy when trying two fingers pan. This change keeps
track of the previous movements of the fingers' middle point,
compares to the change of the fingers' distance, and decides
to pan or zoom or do both.

Change-Id: I8a6a8e9259db85b0e820b6e25ba0822ed289fb45

diff --git a/core/java/android/webkit/ZoomManager.java b/core/java/android/webkit/ZoomManager.java
index f27ced8..942425a 100644 (file)
--- a/core/java/android/webkit/ZoomManager.java
+++ b/core/java/android/webkit/ZoomManager.java
@@ -16,6 +16,9 @@
 
 package android.webkit;
 
+import java.util.LinkedList;
+import java.util.Queue;
+
 import android.content.Context;
 import android.content.pm.PackageManager;
 import android.graphics.Canvas;
@@ -23,6 +26,7 @@ import android.graphics.Point;
 import android.graphics.Rect;
 import android.os.Bundle;
 import android.os.SystemClock;
+import android.util.FloatMath;
 import android.util.Log;
 import android.view.ScaleGestureDetector;
 import android.view.View;
@@ -112,6 +116,24 @@ class ZoomManager {
     private float mZoomCenterY;
 
     /*
+     * Similar to mZoomCenterX(Y), these track the focus point of the scale
+     * gesture. The difference is these get updated every time when onScale is
+     * invoked no matter if a zooming really happens.
+     */
+    private float mFocusX;
+    private float mFocusY;
+
+    /*
+     * mFocusMovement keeps track of the total movement that the focus point
+     * has been through. Comparing to the difference of mCurrlen and mPrevLen,
+     * it determines if the gesture is for panning or zooming or both.
+     */
+    private static final int FOCUS_QUEUE_SIZE = 5;
+    private float mFocusMovementSum;
+    private Queue<Float> mFocusMovementQueue;
+
+
+    /*
      * These values represent the point around which the screen should be
      * centered after zooming. In other words it is used to determine the center
      * point of the visible document after the page has finished zooming. This
@@ -196,6 +218,8 @@ class ZoomManager {
          * viewport size is.
          */
         setZoomOverviewWidth(WebView.DEFAULT_VIEWPORT_WIDTH);
+
+        mFocusMovementQueue = new LinkedList<Float>();
     }
 
     /**
@@ -715,10 +739,11 @@ class ZoomManager {
     }
 
     private class ScaleDetectorListener implements ScaleGestureDetector.OnScaleGestureListener {
-
         public boolean onScaleBegin(ScaleGestureDetector detector) {
             mInitialZoomOverview = false;
             dismissZoomPicker();
+            mFocusMovementSum = 0;
+            mFocusMovementQueue.clear();
             mWebView.mViewManager.startZoom();
             mWebView.onPinchToZoomAnimationStart();
             return true;
@@ -729,6 +754,29 @@ class ZoomManager {
             float scale = Math.max(
                     computeScaleWithLimits(detector.getScaleFactor() * mActualScale),
                     getZoomOverviewScale());
+
+            float prevFocusX = mFocusX;
+            float prevFocusY = mFocusY;
+            mFocusX = detector.getFocusX();
+            mFocusY = detector.getFocusY();
+            float focusDelta = (prevFocusX == 0 && prevFocusY == 0) ? 0 :
+                    FloatMath.sqrt((mFocusX - prevFocusX) * (mFocusX - prevFocusX)
+                                   + (mFocusY - prevFocusY) * (mFocusY - prevFocusY));
+            mFocusMovementSum += focusDelta;
+            mFocusMovementQueue.add(focusDelta);
+            if (mFocusMovementQueue.size() > FOCUS_QUEUE_SIZE) {
+                mFocusMovementSum -= mFocusMovementQueue.remove();
+            }
+            float deltaSpan = Math.abs(detector.getCurrentSpan() - detector.getPreviousSpan());
+
+            // If the user moves the fingers but keeps the same distance between them,
+            // we should do panning only.
+            if (mFocusMovementSum > deltaSpan) {
+                mFocusMovementSum = 0;
+                mFocusMovementQueue.clear();
+                return true;
+            }
+
             if (mPinchToZoomAnimating || willScaleTriggerZoom(scale)) {
                 mPinchToZoomAnimating = true;
                 // limit the scale change per step