Compute effective touch action in StyleAdjuster.

third_party/WebKit/Source/core/input/TouchActionUtil.cpp

 // Copyright 2015 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 "core/input/TouchActionUtil.h"
 
 #include "core/dom/Node.h"
 #include "core/html/HTMLFrameOwnerElement.h"
 #include "core/layout/LayoutBox.h"
 #include "core/layout/LayoutObject.h"
 
 namespace blink {
 namespace TouchActionUtil {
 
 namespace {
 
-// touch-action applies to all elements with both width AND height properties.
-// According to the CSS Box Model Spec
-// (http://dev.w3.org/csswg/css-box/#the-width-and-height-properties)
-// width applies to all elements but non-replaced inline elements, table rows,
-// and row groups and height applies to all elements but non-replaced inline
-// elements, table columns, and column groups.
-bool SupportsTouchAction(const LayoutObject& object) {
-  if (object.IsInline() && !object.IsAtomicInlineLevel())
-    return false;
-  if (object.IsTableRow() || object.IsLayoutTableCol())
-    return false;
-
-  return true;
-}
-
 const Node* ParentNodeAcrossFrames(const Node* cur_node) {
   Node* parent_node = FlatTreeTraversal::Parent(*cur_node);
   if (parent_node)
     return parent_node;
 
   if (cur_node->IsDocumentNode()) {
     const Document* doc = ToDocument(cur_node);
     return doc->LocalOwner();
   }
 
   return nullptr;
 }
 
 }  // namespace
 
 TouchAction ComputeEffectiveTouchAction(const Node& node) {
-  // Start by permitting all actions, then walk the elements supporting
-  // touch-action from the target node up to root document, exclude any
-  // prohibited actions at or below the element that supports them.
-  // I.e. pan-related actions are considered up to the nearest scroller,
-  // and zoom related actions are considered up to the root.
   TouchAction effective_touch_action = TouchAction::kTouchActionAuto;
-  TouchAction handled_touch_actions = TouchAction::kTouchActionNone;
   for (const Node* cur_node = &node; cur_node;
        cur_node = ParentNodeAcrossFrames(cur_node)) {
-    if (LayoutObject* layout_object = cur_node->GetLayoutObject()) {
-      if (SupportsTouchAction(*layout_object)) {
-        TouchAction action = layout_object->Style()->GetTouchAction();
-        action |= handled_touch_actions;
-        effective_touch_action &= action;
-        if (effective_touch_action == TouchAction::kTouchActionNone)
-          break;
-      }
-
-      // If we've reached an ancestor that supports panning, stop allowing
-      // panning to be disabled.
-      if ((layout_object->IsBox() &&
-           ToLayoutBox(layout_object)->ScrollsOverflow()) ||
-          layout_object->IsLayoutView())
-        handled_touch_actions |= TouchAction::kTouchActionPan;
+    if (cur_node->GetLayoutObject()) {

[flackr, 2017/06/07 18:21:47]

I wonder if we can use Node::GetComputedStyle? What are the cases we get a Node
without a layout object?

[sunxd, 2017/06/08 19:08:12]

There are cases where the function is called with a non-element node and we do
not have styles calculated for those nodes.

I vaguely remember that sometimes the node does not have a layout object. I need
to double check it. I think there are cases like this:

+-node (with layout object)
+---node (without element or layout object)
+-----node (without element or layout object)

[flackr, 2017/06/08 19:35:21]

Acknowledged.

+      effective_touch_action =
+          cur_node->GetLayoutObject()->Style()->GetEffectiveTouchAction();
+      break;
     }
   }
   return effective_touch_action;
 }
 
 }  // namespace TouchActionUtil
 }  // namespace blink