Bug 1421384 - Inherit touch-action flags down in the compositor hit-test infos. r=miko

Per the touch-action spec, the effective touch-action on an element includes
touch-action restrictions from ancestor elements up to and including the
element that has the "default action". This patch implements that behaviour
so that WebRender gets correct touch-action values on its display items.

MozReview-Commit-ID: Cw5uqAsE9qm

--HG--
extra : rebase_source : ef6e24a66385e097d50b3a03c06091464b1bb5b9

Author: staktrace

gfx/layers/apz/test/mochitest/mochitest.ini

@@ -69,7 +69,7 @@
 [test_group_pointerevents.html]
   skip-if = os == 'win' && os_version == '10.0' # Bug 1404836
 [test_group_touchevents.html]
-  skip-if = webrender || (verify && debug && (os == 'win')) # bug 1424752
+  skip-if = (verify && debug && (os == 'win'))
 [test_group_wheelevents.html]
   skip-if = (toolkit == 'android') # wheel events not supported on mobile
 [test_group_zoom.html]

layout/generic/nsFrame.cpp

@@ -11263,10 +11263,31 @@ nsIFrame::GetCompositorHitTestInfo(nsDisplayListBuilder* aBuilder)
     }
   }
 
+  // Inherit the touch-action flags from the parent, if there is one. We do this
+  // because of how the touch-action on a frame combines the touch-action from
+  // ancestor DOM elements. Refer to the documentation in TouchActionHelper.cpp
+  // for details; this code is meant to be equivalent to that code, but woven
+  // into the top-down recursive display list building process.
+  CompositorHitTestInfo inheritedTouchAction = CompositorHitTestInfo::eInvisibleToHitTest;
+  if (nsDisplayCompositorHitTestInfo* parentInfo = aBuilder->GetCompositorHitTestInfo()) {
+    inheritedTouchAction = (parentInfo->HitTestInfo() & CompositorHitTestInfo::eTouchActionMask);
+  }
+
   nsIFrame* touchActionFrame = this;
   if (nsIScrollableFrame* scrollFrame = nsLayoutUtils::GetScrollableFrameFor(this)) {
     touchActionFrame = do_QueryFrame(scrollFrame);
+    // On scrollframes, stop inheriting the pan-x and pan-y flags; instead,
+    // reset them back to zero to allow panning on the scrollframe unless we
+    // encounter an element that disables it that's inside the scrollframe.
+    // This is equivalent to the |considerPanning| variable in
+    // TouchActionHelper.cpp, but for a top-down traversal.
+    CompositorHitTestInfo panMask = CompositorHitTestInfo::eTouchActionPanXDisabled
+                                  | CompositorHitTestInfo::eTouchActionPanYDisabled;
+    inheritedTouchAction &= ~panMask;
   }
+
+  result |= inheritedTouchAction;
+
   const uint32_t touchAction = nsLayoutUtils::GetTouchActionFromFrame(touchActionFrame);
   // The CSS allows the syntax auto | none | [pan-x || pan-y] | manipulation
   // so we can eliminate some combinations of things.

layout/painting/nsDisplayList.h

@@ -734,6 +734,10 @@ class nsDisplayListBuilder {
   {
     mCompositorHitTestInfo = aHitTestInfo;
   }
+  nsDisplayCompositorHitTestInfo* GetCompositorHitTestInfo() const
+  {
+    return mCompositorHitTestInfo;
+  }
 
   /**
    * Builds a new nsDisplayCompositorHitTestInfo for the frame |aFrame| if