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 89 matching lines @@
     : m_client(client)
     , m_inScrollGesture(false)
     , m_momentumScrollInProgress(false)
     , m_ignoreMomentumScrolls(false)
     , m_lastMomentumScrollTimestamp(0)
     , m_startTime(0)
     , m_snapRubberbandTimerIsActive(false)
 {
 }
 
-bool ScrollElasticityController::handleWheelEvent(const PlatformWheelEvent& wheelEvent)
+// |canRubberbandLeft| and |canRubberbandRight| prevent the start of rubber-banding in their respective directions.
+// Once rubber banding has started, the two parameters have no effect.
+bool ScrollElasticityController::handleWheelEvent(const PlatformWheelEvent& wheelEvent, bool canRubberbandLeft, bool canRubberbandRight)
 {
     if (wheelEvent.phase() == PlatformWheelEventPhaseBegan) {
+        // Don't allow rubber banding to start in a direction that explicitly disallows rubberbanding.
+        if (!canRubberbandLeft && wheelEvent.deltaX() > 0) {
+          printf("cannot rubberband left");
+          return false;
+        }
+        if (!canRubberbandRight && wheelEvent.deltaX() < 0) {
+          printf("cannot rubberband right");
+          return false;
+        }
+
+
         // First, check if we should rubber-band at all.
         if (m_client->pinnedInDirection(FloatSize(-wheelEvent.deltaX(), 0)) &&
             !shouldRubberBandInHorizontalDirection(wheelEvent))

[Nico, 2014/03/14 17:51:46]

Should the checks be in shouldRubberBandInHorizontalDirection()?

[erikchen, 2014/03/20 18:04:26]

I've moved all the relevant logic into the method. I am also calling the method
before starting rubber-banding from a momentum event, which is a behavioral
change which I believe to be accurate.

             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)) {
+        // Momentum events should not trigger rubber banding in a disallowed direction.
+        if (!canRubberbandLeft && wheelEvent.deltaX() > 0) {
+          return false;
+        }
+        if (!canRubberbandRight && wheelEvent.deltaX() < 0) {
+          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 221 matching lines @@
         return m_client->shouldRubberBandInDirection(ScrollLeft);
     if (wheelEvent.deltaX() < 0)
         return m_client->shouldRubberBandInDirection(ScrollRight);
 
     return true;
 }
 
 } // namespace WebCore
 
 #endif // USE(RUBBER_BANDING)