Unify Android Webview and Chrome's fling

android_webview/java/src/org/chromium/android_webview/AwContents.java

Index: android_webview/java/src/org/chromium/android_webview/AwContents.java
diff --git a/android_webview/java/src/org/chromium/android_webview/AwContents.java b/android_webview/java/src/org/chromium/android_webview/AwContents.java
index 9060c091319daeb93e497aee886b4e3450569c6e..aee90089e5c682eb84c246513acd1c36b8f64cf0 100644
--- a/android_webview/java/src/org/chromium/android_webview/AwContents.java
+++ b/android_webview/java/src/org/chromium/android_webview/AwContents.java
@@ -22,8 +22,10 @@ import android.os.Build;
 import android.os.Bundle;
 import android.os.Handler;
 import android.os.Message;
+import android.os.SystemClock;
 import android.text.TextUtils;
 import android.util.Base64;
+import android.util.FloatMath;
 import android.util.Log;
 import android.util.Pair;
 import android.view.KeyEvent;
@@ -33,6 +35,7 @@ import android.view.ViewGroup;
 import android.view.accessibility.AccessibilityEvent;
 import android.view.accessibility.AccessibilityNodeInfo;
 import android.view.accessibility.AccessibilityNodeProvider;
+import android.view.animation.AnimationUtils;
 import android.view.inputmethod.EditorInfo;
 import android.view.inputmethod.InputConnection;
 import android.webkit.GeolocationPermissions;
@@ -579,11 +582,6 @@ public class AwContents implements SmartClipProvider,
         }
 
         @Override
-        public void onUnhandledFlingStartEvent(int velocityX, int velocityY) {
-            mScrollOffsetManager.onUnhandledFlingStartEvent(velocityX, velocityY);
-        }
-
-        @Override
         public void onScrollUpdateGestureConsumed() {
             mScrollAccessibilityHelper.postViewScrolledAccessibilityEventCallback();
         }
@@ -1936,7 +1934,12 @@ public class AwContents implements SmartClipProvider,
      */
     public void flingScroll(int velocityX, int velocityY) {
         if (TRACE) Log.d(TAG, "flingScroll");
-        mScrollOffsetManager.flingScroll(velocityX, velocityY);
+        // TODO(hush): crbug.com/493765. A hit test at 0, 0 may not
+        // target the scroll at root scrolling layer.  Instead, we
+        // should add a method flingRootLayer to ContentViewCore
+        // and call it here to specifically target the scroll at
+        // the root layer.
+        mContentViewCore.fling(SystemClock.uptimeMillis(), 0, 0, -velocityX, -velocityY);
     }
 
     /**
@@ -2549,8 +2552,8 @@ public class AwContents implements SmartClipProvider,
     }
 
     @CalledByNative
-    public boolean isFlingActive() {
-        return mScrollOffsetManager.isFlingActive();
+    public boolean isSmoothScrollingActive() {
+        return mScrollOffsetManager.isSmoothScrollingActive();
     }
 
     @CalledByNative
@@ -2570,15 +2573,24 @@ public class AwContents implements SmartClipProvider,
         client.init(mContentViewCore);
     }
 
+    @SuppressLint("NewApi")

[boliu, 2015/05/29 19:42:47]

Add a comment which api

[hush (inactive), 2015/06/05 21:47:21]

Done.

     @CalledByNative
-    private void didOverscroll(int deltaX, int deltaY) {
-        if (mOverScrollGlow != null) {
-            mOverScrollGlow.setOverScrollDeltas(deltaX, deltaY);
-        }
-
+    private void didOverscroll(int deltaX, int deltaY, float velocityX, float velocityY) {
         mScrollOffsetManager.overScrollBy(deltaX, deltaY);
 
-        if (mOverScrollGlow != null && mOverScrollGlow.isAnimating()) {
+        if (mOverScrollGlow == null) return;
+
+        mOverScrollGlow.setOverScrollDeltas(deltaX, deltaY);
+        final int oldX = mContainerView.getScrollX();
+        final int oldY = mContainerView.getScrollY();
+        final int x = oldX + deltaX;
+        final int y = oldY + deltaY;
+        final int scrollRangeX = mScrollOffsetManager.computeMaximumHorizontalScrollOffset();
+        final int scrollRangeY = mScrollOffsetManager.computeMaximumVerticalScrollOffset();
+        mOverScrollGlow.absorbGlow(x, y, oldX, oldY, scrollRangeX, scrollRangeY,
+                FloatMath.hypot(velocityX, velocityY));
+
+        if (mOverScrollGlow.isAnimating()) {
             postInvalidateOnAnimation();
         }
     }
@@ -2987,7 +2999,13 @@ public class AwContents implements SmartClipProvider,
 
         @Override
         public void computeScroll() {
-            mScrollOffsetManager.computeScrollAndAbsorbGlow(mOverScrollGlow);
+            if (mScrollOffsetManager.willComputeScroll()) {

[boliu, 2015/05/29 19:42:47]

What does it mean when this is true, but compositor also wants updates via
BVR::OnComputeScroll?

[hush (inactive), 2015/06/05 21:47:21]

That's a good observation.
This means "pending_fling_animation_" in BVR will stay not null until
mScrollOffsetManager.willComputeScroll() returns false.
So LTHI::AnimateInput will not be called, which means InputHandlerProxy::Animate
won't be called.
From inspecting the code of these mentioned functions, I don't think there is
anything waiting on InputHandlerProxy::Animate to be called eventually. 

That is the case until the current smooth scrolling (caused by pageUp, pageDown)
finishes.
I've found a problem here:
Suppose there is a fling that lasts for 10 seconds and scrolls the webview by
1000 pixels intercepted by a pageDown that scrolls the webview by 100 pixels and
lasts for 1 second. Right after pageDown finishes and scrolls the webview to its
location,mScrollOffsetManager.willComputeScroll will return false, the fling
curve takes over to update the scroll offset of webview. This will probably make
the WebView's scroll position "teleport" to a different position as calculated
by the fling curve.

I think the correct behavior (and it is also the behavior before this CL) should
be the in-flight fling will be canceled instead of being temporarily ignored, if
there comes another smooth scroll. Jared, sorry about not getting this right
when you first commented about it..

+                mScrollOffsetManager.computeScrollAndAbsorbGlow(mOverScrollGlow);
+            } else {
+                if (isDestroyed()) return;
+                nativeOnComputeScroll(
+                        mNativeAwContents, AnimationUtils.currentAnimationTimeMillis());
+            }
         }
     }
 
@@ -3026,6 +3044,8 @@ public class AwContents implements SmartClipProvider,
             long nativeAwContents, String path, ValueCallback<String> callback);
 
     private native void nativeAddVisitedLinks(long nativeAwContents, String[] visitedLinks);
+    private native void nativeOnComputeScroll(
+            long nativeAwContents, long currentAnimationTimeMillis);
     private native boolean nativeOnDraw(long nativeAwContents, Canvas canvas,
             boolean isHardwareAccelerated, int scrollX, int scrollY,
             int visibleLeft, int visibleTop, int visibleRight, int visibleBottom);