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* curNode) {
  Node* parentNode = FlatTreeTraversal::parent(*curNode);
  if (parentNode)
    return parentNode;

  if (curNode->isDocumentNode()) {
    const Document* doc = toDocument(curNode);
    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 effectiveTouchAction = TouchActionAuto;
  TouchAction handledTouchActions = TouchActionNone;
  for (const Node* curNode = &node; curNode;
       curNode = parentNodeAcrossFrames(curNode)) {
    if (LayoutObject* layoutObject = curNode->layoutObject()) {
      if (supportsTouchAction(*layoutObject)) {
        TouchAction action = layoutObject->style()->getTouchAction();
        action |= handledTouchActions;
        effectiveTouchAction &= action;
        if (effectiveTouchAction == TouchActionNone)
          break;
      }

      // If we've reached an ancestor that supports panning, stop allowing
      // panning to be disabled.
      if ((layoutObject->isBox() &&
           toLayoutBox(layoutObject)->scrollsOverflow()) ||
          layoutObject->isLayoutView())
        handledTouchActions |= TouchActionPan;
    }
  }
  return effectiveTouchAction;
}

}  // namespace TouchActionUtil
}  // namespace blink