Initial touch-action main thread implementation

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
index 80ec34a263280ef5c0ca41ef5bdebec929461e9c..a5e2a885a6bd8d8d1ebbd03917c4d2cc6bb09571 100644
--- a/Source/core/page/EventHandler.cpp
+++ b/Source/core/page/EventHandler.cpp
@@ -60,6 +60,7 @@
 #include "core/page/AutoscrollController.h"
 #include "core/page/BackForwardClient.h"
 #include "core/page/Chrome.h"
+#include "core/page/ChromeClient.h"
 #include "core/page/DragController.h"
 #include "core/page/DragState.h"
 #include "core/page/EditorClient.h"
@@ -85,6 +86,7 @@
 #include "core/rendering/RenderView.h"
 #include "core/rendering/RenderWidget.h"
 #include "core/rendering/style/CursorList.h"
+#include "core/rendering/style/RenderStyle.h"
 #include "core/svg/SVGDocument.h"
 #include "core/svg/SVGElementInstance.h"
 #include "core/svg/SVGUseElement.h"
@@ -3616,6 +3618,12 @@ bool EventHandler::handleTouchEvent(const PlatformTouchEvent& event)
                 continue;
             m_originatingTouchPointTargets.set(touchPointTargetKey, node);
             touchTarget = node;
+
+            // FIXME(rbyers): Should really be doing a second hit test that ignores inline elements - crbug.com/319479.
+            TouchAction effectiveTouchAction = computeEffectiveTouchAction(node);
+            if (effectiveTouchAction != TouchActionAuto)
+                m_frame->page()->chrome().client().setTouchAction(effectiveTouchAction);
+
         } else if (pointState == PlatformTouchPoint::TouchReleased || pointState == PlatformTouchPoint::TouchCancelled) {
             // The target should be the original target for this touch, so get it from the hashmap. As it's a release or cancel
             // we also remove it from the map.
@@ -3827,6 +3835,39 @@ bool EventHandler::handleWheelEventAsEmulatedGesture(const PlatformWheelEvent& e
     return true;
 }
 
+TouchAction EventHandler::computeEffectiveTouchAction(Node* node)
+{
+    // Optimization to minimize risk of this new feature (behavior should be identical
+    // since there's no way to get non-default touch-action values).
+    if (!RuntimeEnabledFeatures::cssTouchActionEnabled())
+        return TouchActionAuto;
+
+    // Start by permitting all actions, then walk the block level elements from
+    // 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;
+
+    while (node) {
+        // The spec says only block and SVG elements get touch-action.
+        // FIXME(rbyers): Add correct support for SVG, crbug.com/247396.
+        if (node->isBlockFlowElement()) {
+            if (RenderObject* renderer = node->renderer()) {

[esprehn, 2013/11/21 16:26:29]

This loop checks for renderer() repeatedly (isBlockFlowElement, renderer here
and then below.). Instead you should just abort before the loop if there's no
renderer for the argument |node|. If you have a renderer than all your ancestors
do.

[Rick Byers, 2013/11/21 22:09:29]

Thanks.  I could have sworn I've seen situations where a node had a renderer but
it's parent node didn't, but looking back at some examples it seems I was
probably wrong.  I've added a comment to Node::renderer() to document this
invariant.

However, I don't want to abort if the provided node has no renderer - I want to
walk up the DOM until I find one that does.  So how is this?  It still tests for
renderer inside the loop, but it's simpler to read than having one loop to walk
up until we find a renderer then another to keep walking up accessing renderers
(but not checking them for null).  Note that this is not a hot path here - it's
called only when a touch point goes down.

+                TouchAction action = renderer->style()->touchAction();
+                if (action == TouchActionNone)
+                    effectiveTouchAction = action;
+            }
+        }
+
+        // If we've reached an ancestor that supports a touch action, search no further.
+        if (node->renderBox() && node->renderBox()->scrollsOverflow())
+            break;
+
+        node = node->parentNode();

[esprehn, 2013/11/21 16:26:29]

This doesn't appear correct, Shadow DOM means parentNode() can be null, and you
probably want to traverse up through projections?

[Rick Byers, 2013/11/21 22:09:29]

Yes, thank you!  I've fixed this to traverse up through projections, and I've
added a few shadow DOM test cases.

+    }
+    return effectiveTouchAction;
+}
+
 void EventHandler::setLastKnownMousePosition(const PlatformMouseEvent& event)
 {
     m_mousePositionIsUnknown = false;