Implement touch-action pan-x/pan-y handling on the main thread

Source/core/page/EventHandler.cpp

Index: Source/core/page/EventHandler.cpp
diff --git a/Source/core/page/EventHandler.cpp b/Source/core/page/EventHandler.cpp
old mode 100644
new mode 100755
index c0466e38edf8f049f52f8cc888c43ae3f00f1842..08894ef41568cf8413482137d9f7f7e435d99cbc
--- a/Source/core/page/EventHandler.cpp
+++ b/Source/core/page/EventHandler.cpp
@@ -3979,13 +3979,35 @@ TouchAction EventHandler::computeEffectiveTouchAction(const Node& node)
     // the target node up to the nearest scrollable ancestor and exclude any
     // prohibited actions. For now this is trivial, but when we add more types
     // of actions it'll get a little more complex.
+    TouchAction effectiveTouchAction = TouchActionAuto;
     for (const Node* curNode = &node; curNode; curNode = NodeRenderingTraversal::parent(curNode)) {
         // The spec says only block and SVG elements get touch-action.
         // FIXME(rbyers): Add correct support for SVG, crbug.com/247396.
         if (RenderObject* renderer = curNode->renderer()) {
             if (renderer->isRenderBlockFlow()) {
-                if (renderer->style()->touchAction() == TouchActionNone)
-                    return TouchActionNone;
+                TouchAction action = renderer->style()->touchAction();
+                if (action == TouchActionNone) {
+                    effectiveTouchAction = action;

[Rick Byers, 2013/12/12 20:47:24]

As esprehn pointed out reviewing my CL for this, we should immediately return
whenever effectiveTouchAction becomes None.  Perhaps just add a test and 'break'
for this at the bottom.

[gnana, 2013/12/13 16:52:53]

Done.

+                } else if (action == TouchActionPanX) {

[Rick Byers, 2013/12/12 20:47:24]

This seems correct, but it's pretty verbose and hard to scale as we add more
flags.   I think this could be simplified and made more general by writing a
helper function like:

TouchAction intersectTouchAction(TouchAction ta1, TouchAction ta2)
{
  if (ta1 == None || ta2 == None)
    return None;
  if (ta1 == Auto)
    return ta2;
  if (ta2 == Auto)
    return ta1;
  if (!(ta1 & ta2))
    return None;
  return ta1 & ta2;
}

This logic could be slightly simpler if we renumbered None to be 0 and Auto to
be 1 (instead of the other way around as it is currently), but I don't think it
really matters (and having the default be value 0 is kind of nice).

[gnana, 2013/12/13 16:52:53]

Done.

+                    if (effectiveTouchAction == TouchActionPanY) {
+                        effectiveTouchAction = TouchActionNone;
+                    } else if (effectiveTouchAction == TouchActionAuto || effectiveTouchAction == (TouchActionPanX | TouchActionPanY)) {
+                        effectiveTouchAction = TouchActionPanX;
+                    }
+                } else if (action == TouchActionPanY) {
+                    if (effectiveTouchAction == TouchActionPanX) {
+                        effectiveTouchAction = TouchActionNone;
+                    } else if (effectiveTouchAction == TouchActionAuto || effectiveTouchAction == (TouchActionPanX | TouchActionPanY)) {
+                        effectiveTouchAction = TouchActionPanY;
+                    }
+                } else if (action == (TouchActionPanX | TouchActionPanY)) {
+                    if (effectiveTouchAction == TouchActionPanX)
+                        effectiveTouchAction = TouchActionPanX;
+                    else if (effectiveTouchAction == TouchActionPanY)
+                        effectiveTouchAction = TouchActionPanY;
+                    else if (effectiveTouchAction == TouchActionAuto)
+                        effectiveTouchAction = TouchActionPanX | TouchActionPanY;
+                }
             }
 
             // If we've reached an ancestor that supports a touch action, search no further.
@@ -3993,7 +4015,7 @@ TouchAction EventHandler::computeEffectiveTouchAction(const Node& node)
                 break;
         }
     }
-    return TouchActionAuto;
+    return effectiveTouchAction;
 }
 
 void EventHandler::setLastKnownMousePosition(const PlatformMouseEvent& event)