Report accurate Overscroll on handleWheel.

Source/core/input/EventHandler.cpp

Index: Source/core/input/EventHandler.cpp
diff --git a/Source/core/input/EventHandler.cpp b/Source/core/input/EventHandler.cpp
index ed72ddf7134747ec0f7302532c2da5e16c164a68..37487d57003f0b8440a8db08288fb6d00ba5f2b7 100644
--- a/Source/core/input/EventHandler.cpp
+++ b/Source/core/input/EventHandler.cpp
@@ -1782,7 +1782,10 @@ bool EventHandler::handleWheelEvent(const PlatformWheelEvent& event)
     if (!view)
         return false;
 
-    if (view->scrollableArea()->handleWheel(event).didScroll())
+    ScrollResult scrollResult = view->scrollableArea()->handleWheel(event);
+    if (m_frame->settings() && m_frame->settings()->elasticOverscrollEnabled())
+        handleOverscroll(scrollResult);
+    if (scrollResult.didScroll())
         RETURN_WHEEL_EVENT_HANDLED();
 
     return false;
@@ -2255,17 +2258,23 @@ void EventHandler::resetOverscroll(bool didScrollX, bool didScrollY)
         m_accumulatedRootOverscroll.setHeight(0);
 }
 
-void EventHandler::handleOverscroll(const ScrollResult& scrollResult, const PlatformGestureEvent& gestureEvent)
+void EventHandler::handleOverscroll(const ScrollResult& scrollResult, const FloatPoint& position, const FloatSize& velocity)
 {
     if (m_frame->isMainFrame() && m_frame->view() && m_frame->view()->scrollableArea()) {
         ScrollableArea* scrollablearea = m_frame->view()->scrollableArea();
-        // Set unusedDelta if axis is scrollable, else set 0 to ensure overflow is not reported on non-scrollable axes.
-        FloatSize unusedDelta(scrollablearea->scrollSize(HorizontalScrollbar) ? scrollResult.unusedScrollDeltaX : 0, scrollablearea->scrollSize(VerticalScrollbar) ? scrollResult.unusedScrollDeltaY : 0);
+        FloatSize unusedDelta;
+        if (m_frame->settings() && m_frame->settings()->elasticOverscrollEnabled()) {
+            // ElasticOverscroll should be applied even on non-Scrollable axis.

[bokan, 2015/06/25 17:50:31]

This distinction seems strange to me, we shouldn't have a difference at the
Blink level here. If we don't want to have an overscroll effect on unscrollable
axes, that should be done at the implementation - Blink should pass all the
overscroll information along anyway.

Could we move the scrollability check in the Android block to CC? That would
obviously have to be done in a separate patch (chromium side). For now the
simplest thing might just be to move the zeroing out of unscrollable delta for
Android to handleGestureScrollUpdate so it's not dependent on this flag.

[MuVen, 2015/06/26 09:55:44]

Done.

+            unusedDelta.setWidth(scrollResult.unusedScrollDeltaX);
+            unusedDelta.setHeight(scrollResult.unusedScrollDeltaY);
+        } else {
+            // In Case of android set unusedDelta if axis is scrollable, else set 0 to ensure overflow is not reported on non-scrollable axes.
+            unusedDelta.setWidth(scrollablearea->scrollSize(HorizontalScrollbar) ? scrollResult.unusedScrollDeltaX : 0);
+            unusedDelta.setHeight(scrollablearea->scrollSize(VerticalScrollbar) ? scrollResult.unusedScrollDeltaY : 0);
+        }
         resetOverscroll(scrollResult.didScrollX, scrollResult.didScrollY);
         if (unusedDelta != FloatSize()) {
             m_accumulatedRootOverscroll += unusedDelta;
-            FloatPoint position = FloatPoint(gestureEvent.position().x(), gestureEvent.position().y());
-            FloatSize velocity = FloatSize(gestureEvent.velocityX(), gestureEvent.velocityY());
             m_frame->chromeClient().didOverscroll(unusedDelta, m_accumulatedRootOverscroll, position, velocity);
         }
     }
@@ -2354,7 +2363,9 @@ bool EventHandler::handleGestureScrollUpdate(const PlatformGestureEvent& gesture
 
     // Try to scroll the frame view.
     ScrollResult scrollResult = m_frame->applyScrollDelta(delta, false);
-    handleOverscroll(scrollResult, gestureEvent);
+    FloatPoint position = FloatPoint(gestureEvent.position().x(), gestureEvent.position().y());
+    FloatSize velocity = FloatSize(gestureEvent.velocityX(), gestureEvent.velocityY());
+    handleOverscroll(scrollResult, position, velocity);
     if (scrollResult.didScroll()) {
         setFrameWasScrolledByUser();
         return true;