Selectively disable rubber banding on mac.

Source/platform/mac/ScrollElasticityController.mm

 /*
  * Copyright (C) 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 92 matching lines @@
     , m_ignoreMomentumScrolls(false)
     , m_lastMomentumScrollTimestamp(0)
     , m_startTime(0)
     , m_snapRubberbandTimerIsActive(false)
 {
 }
 
 bool ScrollElasticityController::handleWheelEvent(const PlatformWheelEvent& wheelEvent)
 {
     if (wheelEvent.phase() == PlatformWheelEventPhaseBegan) {
-        // First, check if we should rubber-band at all.
-        if (m_client->pinnedInDirection(FloatSize(-wheelEvent.deltaX(), 0)) &&
-            !shouldRubberBandInHorizontalDirection(wheelEvent))
+        if (!shouldStartRubberBanding(wheelEvent))
             return false;
 
         m_inScrollGesture = true;
         m_momentumScrollInProgress = false;
         m_ignoreMomentumScrolls = false;
         m_lastMomentumScrollTimestamp = 0;
         m_momentumVelocity = FloatSize();
 
         IntSize stretchAmount = m_client->stretchAmount();
         m_stretchScrollForce.setWidth(reboundDeltaForElasticDelta(stretchAmount.width()));
@@ skipping 52 matching lines @@
         deltaX = 0;
     else
         deltaY = 0;
 
     bool shouldStretch = false;
 
     PlatformWheelEventPhase momentumPhase = wheelEvent.momentumPhase();
 
     // If we are starting momentum scrolling then do some setup.
     if (!m_momentumScrollInProgress && (momentumPhase == PlatformWheelEventPhaseBegan || momentumPhase == PlatformWheelEventPhaseChanged)) {
+        if (!shouldStartRubberBanding(wheelEvent))
+            return false;
+
         m_momentumScrollInProgress = true;
         // Start the snap rubber band timer if it's not running. This is needed to
         // snap back from the over scroll caused by momentum events.
         if (!m_snapRubberbandTimerIsActive && m_startTime == 0)
             snapRubberBand();
     }
 
     CFTimeInterval timeDelta = wheelEvent.timestamp() - m_lastMomentumScrollTimestamp;
     if (m_inScrollGesture || m_momentumScrollInProgress) {
         if (m_lastMomentumScrollTimestamp && timeDelta > 0 && timeDelta < scrollVelocityZeroingTimeout) {
@@ skipping 208 matching lines @@
         m_startTime = 0;
         m_stretchScrollForce = FloatSize();
         return;
     }
 
     m_startTime = [NSDate timeIntervalSinceReferenceDate];
     m_client->startSnapRubberbandTimer();
     m_snapRubberbandTimerIsActive = true;
 }
 
-bool ScrollElasticityController::shouldRubberBandInHorizontalDirection(const PlatformWheelEvent& wheelEvent)
+bool ScrollElasticityController::shouldStartRubberBanding(const PlatformWheelEvent& wheelEvent)
 {
-    if (wheelEvent.deltaX() > 0)
-        return m_client->shouldRubberBandInDirection(ScrollLeft);
-    if (wheelEvent.deltaX() < 0)
-        return m_client->shouldRubberBandInDirection(ScrollRight);
+    if (wheelEvent.deltaX() > 0) {
+        if (!wheelEvent.canRubberbandLeft())
+            return false;
+        if (m_client->pinnedInDirection(FloatSize(-wheelEvent.deltaX(), 0)) && !m_client->shouldRubberBandInDirection(ScrollLeft))

[Alexei Svitkine (slow), 2014/03/20 18:38:09]

Could the pinnedInDirection() check be made inside
m_client->shouldRubberBandInDirection() so two calls aren't required here?

[erikchen, 2014/03/24 22:12:04]

I've reworked the logic of this method to be much simpler.
m_client->shouldRubberBandInDirection() is no longer used - see my comment in
the header file and the CL description.

+            return false;
+        return true;
+    }
+    if (wheelEvent.deltaX() < 0) {
+        if (!wheelEvent.canRubberbandRight())
+            return false;
+        if (m_client->pinnedInDirection(FloatSize(-wheelEvent.deltaX(), 0)) && !m_client->shouldRubberBandInDirection(ScrollRight))
+            return false;
+        return true;
+    }
 
     return true;
 }
 
 } // namespace WebCore
 
 #endif // USE(RUBBER_BANDING)