Add a bit to not bubble scrolls to parent scrolling layers

cc/layer_tree_host_impl.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/layer_tree_host_impl.h"
 
 #include <algorithm>
 
 #include "base/basictypes.h"
 #include "base/debug/trace_event.h"
@@ skipping 114 matching lines @@
 }
 
 scoped_ptr<LayerTreeHostImpl> LayerTreeHostImpl::create(const LayerTreeSettings& settings, LayerTreeHostImplClient* client, Proxy* proxy)
 {
     return make_scoped_ptr(new LayerTreeHostImpl(settings, client, proxy));
 }
 
 LayerTreeHostImpl::LayerTreeHostImpl(const LayerTreeSettings& settings, LayerTreeHostImplClient* client, Proxy* proxy)
     : m_client(client)
     , m_proxy(proxy)
+    , m_didScrollOnce(false)
+    , m_shouldBubbleScrolls(false)
     , m_scrollDeltaIsInViewportSpace(false)
     , m_settings(settings)
     , m_debugState(settings.initialDebugState)
     , m_deviceScaleFactor(1)
     , m_visible(true)
     , m_managedMemoryPolicy(PrioritizedResourceManager::defaultMemoryAllocationLimit(),
                             ManagedMemoryPolicy::CUTOFF_ALLOW_EVERYTHING,
                             0,
                             ManagedMemoryPolicy::CUTOFF_ALLOW_NOTHING)
     , m_pinchGestureActive(false)
@@ skipping 1051 matching lines @@
 
 InputHandlerClient::ScrollStatus LayerTreeHostImpl::scrollBegin(gfx::Point viewportPoint, InputHandlerClient::ScrollInputType type)
 {
     TRACE_EVENT0("cc", "LayerTreeHostImpl::scrollBegin");
 
     if (m_topControlsManager)
         m_topControlsManager->ScrollBegin();
 
     DCHECK(!currentlyScrollingLayer());
     clearCurrentlyScrollingLayer();
+    m_didScrollOnce = false;

[Sami, 2013/01/30 19:28:31]

Better do this in clearCurrentlyScrollingLayer().

[Yusuf, 2013/01/30 21:01:02]

Done.

 
     if (!ensureRenderSurfaceLayerList())
         return ScrollIgnored;
 
     gfx::PointF deviceViewportPoint = gfx::ScalePoint(viewportPoint, m_deviceScaleFactor);
 
     // First find out which layer was hit from the saved list of visible layers
     // in the most recent frame.
     LayerImpl* layerImpl = LayerTreeHostCommon::findLayerThatIsHitByPoint(deviceViewportPoint, activeTree()->RenderSurfaceLayerList());
 
@@ skipping 17 matching lines @@
             m_numMainThreadScrolls++;
             return ScrollOnMainThread;
         }
 
         if (status == ScrollStarted && !potentiallyScrollingLayerImpl)
             potentiallyScrollingLayerImpl = scrollLayerImpl;
     }
 
     if (potentiallyScrollingLayerImpl) {
         m_activeTree->set_currently_scrolling_layer(potentiallyScrollingLayerImpl);
+        m_shouldBubbleScrolls = (type != NonBubblingGesture);
         // Gesture events need to be transformed from viewport coordinates to local layer coordinates
         // so that the scrolling contents exactly follow the user's finger. In contrast, wheel
         // events are already in local layer coordinates so we can just apply them directly.
         m_scrollDeltaIsInViewportSpace = (type == Gesture);
         m_numImplThreadScrolls++;
         m_client->renewTreePriority();
         return ScrollStarted;
     }
     return ScrollIgnored;
 }
@@ skipping 81 matching lines @@
             pendingDelta = m_topControlsManager->ScrollBy(pendingDelta);
 
         if (m_scrollDeltaIsInViewportSpace) {
             float scaleFromViewportToScreenSpace = m_deviceScaleFactor;
             appliedDelta = scrollLayerWithViewportSpaceDelta(layerImpl, scaleFromViewportToScreenSpace, viewportPoint, pendingDelta);
         } else
             appliedDelta = scrollLayerWithLocalDelta(*layerImpl, pendingDelta);
 
         // If the layer wasn't able to move, try the next one in the hierarchy.
         float moveThresholdSquared = 0.1f * 0.1f;
-        if (appliedDelta.LengthSquared() < moveThresholdSquared)
-            continue;
+        if (appliedDelta.LengthSquared() < moveThresholdSquared) {
+            if (m_shouldBubbleScrolls || !m_didScrollOnce)
+                continue;
+            else
+              break;

[Sami, 2013/01/30 19:28:31]

Indent?

[Yusuf, 2013/01/30 21:01:02]

Done.

[Yusuf, 2013/01/30 21:01:02]

Done.

+        }
+        if (!m_shouldBubbleScrolls) m_activeTree->set_currently_scrolling_layer(layerImpl);

[Sami, 2013/01/30 19:28:31]

You could also break here since there's no need to continue recursing, but only
after updating didScroll and m_didScrollOnce.

[Yusuf, 2013/01/30 21:01:02]

Done.

         didScroll = true;
+        m_didScrollOnce = true;
 
         // If the applied delta is within 45 degrees of the input delta, bail out to make it easier
         // to scroll just one layer in one direction without affecting any of its parents.
         float angleThreshold = 45;
         if (MathUtil::smallestAngleBetweenVectors(appliedDelta, pendingDelta) < angleThreshold) {
             pendingDelta = gfx::Vector2d();
             break;
         }
 
         // Allow further movement only on an axis perpendicular to the direction in which the layer
@@ skipping 385 matching lines @@
     LayerImpl* layer = getNonCompositedContentLayerRecursive(tree->RootLayer());
     return layer ? layer->getPicture() : skia::RefPtr<SkPicture>();
 }
 
 void LayerTreeHostImpl::savePaintTime(const base::TimeDelta& totalPaintTime)
 {
     m_paintTimeCounter->SavePaintTime(totalPaintTime);
 }
 
 }  // namespace cc