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 0a0e8530776bffcb7df689bea0ff2b19e862f171..277ac747780e4c95464951122e4e7140273b8431 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;
@@ -574,11 +577,6 @@ public class AwContents implements SmartClipProvider,
         }
 
         @Override
-        public void onUnhandledFlingStartEvent(int velocityX, int velocityY) {
-            mScrollOffsetManager.onUnhandledFlingStartEvent(velocityX, velocityY);
-        }
-
-        @Override
         public void onScrollUpdateGestureConsumed() {
             mScrollAccessibilityHelper.postViewScrolledAccessibilityEventCallback();
         }
@@ -1881,7 +1879,7 @@ public class AwContents implements SmartClipProvider,
      */
     public void flingScroll(int velocityX, int velocityY) {
         if (TRACE) Log.d(TAG, "flingScroll");
-        mScrollOffsetManager.flingScroll(velocityX, velocityY);
+        mContentViewCore.fling(SystemClock.uptimeMillis(), 0, 0, -velocityX, -velocityY);

[hush (inactive), 2015/05/27 23:11:38]

Regarding the possibility of scrolling a scrollable sublayer instead of
scrolling just the root layer:

How about replacing 0, 0 with a magic number like -100, -100 so that the hit
test will always fall onto the root layer?
I tried -100, -100 with the test page you provided and flingScroll() correctly
scrolls the root layer.

[jdduke (slow), 2015/05/28 15:18:08]

That's a thought, though it might just be that it happens to work with that test
page. If you scrolled the page down/right by 100, in theory the hit test might
go back to the sublayer.

Another thought would be to make it explicit, so we add a bit to the
GestureScrollBegin (here
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...)
which says "targetRoot" or "targetViewport" or something like that. Then we just
set that bit for flings, and perhaps rename CVC.fling() to CVC.flingRoot()?

[hush (inactive), 2015/05/28 23:49:51]

Yeah... using -100, -100 was too brittle and too much of a hack. I agree with
adding a bit to WebInputEvent, scrollBegin

[bokan, 2015/05/29 19:32:49]

Sorry for late reply, "targetViewport" sgtm. "targetRoot" is ok but maybe a bit
misleading since the viewport may not actually be the root layer. (There's two
viewport scroll layers so they can't both be root, also, above even the top one
is the elastic overscroll layer...) 

     }
 
     /**
@@ -2492,8 +2490,8 @@ public class AwContents implements SmartClipProvider,
     }
 
     @CalledByNative
-    public boolean isFlingActive() {
-        return mScrollOffsetManager.isFlingActive();
+    public boolean isSmoothScrollingActive() {
+        return mScrollOffsetManager.isSmoothScrollingActive();
     }
 
     @CalledByNative
@@ -2513,15 +2511,24 @@ public class AwContents implements SmartClipProvider,
         client.init(mContentViewCore);
     }
 
+    @SuppressLint("NewApi")
     @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();
         }
     }
@@ -2925,7 +2932,13 @@ public class AwContents implements SmartClipProvider,
 
         @Override
         public void computeScroll() {
-            mScrollOffsetManager.computeScrollAndAbsorbGlow(mOverScrollGlow);
+            if (mScrollOffsetManager.willComputeScroll()) {
+                mScrollOffsetManager.computeScrollAndAbsorbGlow(mOverScrollGlow);
+            } else {
+                if (isDestroyed()) return;
+                nativeOnComputeScroll(
+                        mNativeAwContents, AnimationUtils.currentAnimationTimeMillis());
+            }
         }
     }
 
@@ -2962,6 +2975,8 @@ 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);