Unify Android Webview and Chrome's fling

android_webview/java/src/org/chromium/android_webview/AwScrollOffsetManager.java

Index: android_webview/java/src/org/chromium/android_webview/AwScrollOffsetManager.java
diff --git a/android_webview/java/src/org/chromium/android_webview/AwScrollOffsetManager.java b/android_webview/java/src/org/chromium/android_webview/AwScrollOffsetManager.java
index 9ed9a14ff6f0d1ddf05cca819f81b9a858cee1eb..d5babc41b5f1c974851f268d818621b06c8cad51 100644
--- a/android_webview/java/src/org/chromium/android_webview/AwScrollOffsetManager.java
+++ b/android_webview/java/src/org/chromium/android_webview/AwScrollOffsetManager.java
@@ -46,6 +46,8 @@ public class AwScrollOffsetManager {
         int getContainerViewScrollY();
 
         void invalidate();
+
+        void cancelFling();
     }
 
     private final Delegate mDelegate;
@@ -65,9 +67,6 @@ public class AwScrollOffsetManager {
     // Whether we're in the middle of processing a touch event.
     private boolean mProcessingTouchEvent;
 
-    // Don't skip computeScrollAndAbsorbGlow just because isFling is called in between.
-    private boolean mWasFlinging;
-
     // Whether (and to what value) to update the native side scroll offset after we've finished
     // processing a touch event.
     private boolean mApplyDeferredNativeScroll;
@@ -163,10 +162,10 @@ public class AwScrollOffsetManager {
                 scrollRangeX, scrollRangeY, mProcessingTouchEvent);
     }
 
-    public boolean isFlingActive() {
-        boolean flinging = mScroller.computeScrollOffset();
-        mWasFlinging |= flinging;
-        return flinging;
+    // This is used temporarily until animateScrollTo path of Android WebView (pageUp, pageDown)
+    // is unified with Chrome smooth scrolling.
+    public boolean isSmoothScrollingActive() {
+        return mScroller.computeScrollOffset();
     }
 
     // Called by the native side to over-scroll the container view.
@@ -252,39 +251,14 @@ public class AwScrollOffsetManager {
     }
 
     // Called whenever some other touch interaction requires the fling gesture to be canceled.
-    public void onFlingCancelGesture() {
+    public void finishScroll() {
         // TODO(mkosiba): Support speeding up a fling by flinging again.
         // http://crbug.com/265841
         mScroller.forceFinished(true);
     }
 
-    // Called when a fling gesture is not handled by the renderer.
-    // We explicitly ask the renderer not to handle fling gestures targeted at the root
-    // scroll layer.
-    public void onUnhandledFlingStartEvent(int velocityX, int velocityY) {
-        flingScroll(-velocityX, -velocityY);
-    }
-
-    // Starts the fling animation. Called both as a response to a fling gesture and as via the
-    // public WebView#flingScroll(int, int) API.
-    public void flingScroll(int velocityX, int velocityY) {
-        final int scrollX = mDelegate.getContainerViewScrollX();
-        final int scrollY = mDelegate.getContainerViewScrollY();
-        final int scrollRangeX = computeMaximumHorizontalScrollOffset();
-        final int scrollRangeY = computeMaximumVerticalScrollOffset();
-
-        mScroller.fling(scrollX, scrollY, velocityX, velocityY,
-                0, scrollRangeX, 0, scrollRangeY);
-        mDelegate.invalidate();
-    }
-
     // Called immediately before the draw to update the scroll offset.
     public void computeScrollAndAbsorbGlow(OverScrollGlow overScrollGlow) {

[boliu, 2015/06/08 16:54:52]

safe to assert isSmoothScrollingActive? It's not a clear no-op though

[hush (inactive), 2015/06/09 19:11:34]

Yes, it is safe to assert so, because this function is only called inside the if
statement.
By the way, I decide to change isSmoothScrollingActive to returning
!mScroller.isFinished() which is lighter weight and only call
mScroller.computeScrollOffset() here.
The source code of OverScroller.java shows that "isFinished" and
"computeScrollOffset" always return the opposite values while the latter does
some computations and changes the "finished" state.

-        if (!mScroller.computeScrollOffset() && !mWasFlinging) {
-            return;
-        }
-        mWasFlinging = false;
-
         final int oldX = mDelegate.getContainerViewScrollX();
         final int oldY = mDelegate.getContainerViewScrollY();
         int x = mScroller.getCurrX();
@@ -323,6 +297,9 @@ public class AwScrollOffsetManager {
 
         if (dx == 0 && dy == 0) return false;
 
+        // The scroll will be handled by AwScrollOffsetManager instead of the compositor.
+        // So stop the current fling (either by flingScroll() or by user finger).
+        mDelegate.cancelFling();
         mScroller.startScroll(scrollX, scrollY, dx, dy, computeDurationInMilliSec(dx, dy));
         mDelegate.invalidate();