third_party/WebKit/Source/core/page/TouchDisambiguation.cpp

/*
 * Copyright (C) 2012 Google Inc. All rights reserved.
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 * modification, are permitted provided that the following conditions are
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 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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#include "core/page/TouchDisambiguation.h"

#include "core/HTMLNames.h"
#include "core/dom/Document.h"
#include "core/dom/Element.h"
#include "core/dom/NodeTraversal.h"
#include "core/frame/FrameView.h"
#include "core/frame/LocalFrame.h"
#include "core/html/HTMLHtmlElement.h"
#include "core/input/EventHandler.h"
#include "core/layout/HitTestResult.h"
#include "core/layout/LayoutBlock.h"
#include <algorithm>
#include <cmath>

namespace blink {

static IntRect boundingBoxForEventNodes(Node* eventNode) {
  if (!eventNode->document().view())
    return IntRect();

  IntRect result;
  Node* node = eventNode;
  while (node) {
    // Skip the whole sub-tree if the node doesn't propagate events.
    if (node != eventNode && node->willRespondToMouseClickEvents()) {
      node = NodeTraversal::nextSkippingChildren(*node, eventNode);
      continue;
    }
    result.unite(node->pixelSnappedBoundingBox());
    node = NodeTraversal::next(*node, eventNode);
  }
  return eventNode->document().view()->contentsToRootFrame(result);
}

static float scoreTouchTarget(IntPoint touchPoint,
                              int padding,
                              IntRect boundingBox) {
  if (boundingBox.isEmpty())
    return 0;

  float reciprocalPadding = 1.f / padding;
  float score = 1;

  IntSize distance = boundingBox.differenceToPoint(touchPoint);
  score *= std::max((padding - abs(distance.width())) * reciprocalPadding, 0.f);
  score *=
      std::max((padding - abs(distance.height())) * reciprocalPadding, 0.f);

  return score;
}

struct TouchTargetData {
  IntRect windowBoundingBox;
  float score;
};

void findGoodTouchTargets(const IntRect& touchBoxInRootFrame,
                          LocalFrame* mainFrame,
                          Vector<IntRect>& goodTargets,
                          HeapVector<Member<Node>>& highlightNodes) {
  goodTargets.clear();

  int touchPointPadding =
      ceil(std::max(touchBoxInRootFrame.width(), touchBoxInRootFrame.height()) *
           0.5);

  IntPoint touchPoint = touchBoxInRootFrame.center();
  IntPoint contentsPoint = mainFrame->view()->rootFrameToContents(touchPoint);

  HitTestResult result = mainFrame->eventHandler().hitTestResultAtPoint(
      contentsPoint, HitTestRequest::ReadOnly | HitTestRequest::Active |
                         HitTestRequest::ListBased,
      LayoutSize(touchPointPadding, touchPointPadding));
  const HeapListHashSet<Member<Node>>& hitResults =
      result.listBasedTestResult();

  // Blacklist nodes that are container of disambiguated nodes.
  // It is not uncommon to have a clickable <div> that contains other clickable
  // objects.  This heuristic avoids excessive disambiguation in that case.
  HeapHashSet<Member<Node>> blackList;
  for (const auto& hitResult : hitResults) {
    // Ignore any Nodes that can't be clicked on.
    LayoutObject* layoutObject = hitResult.get()->layoutObject();
    if (!layoutObject || !hitResult.get()->willRespondToMouseClickEvents())
      continue;

    // Blacklist all of the Node's containers.
    for (LayoutBlock* container = layoutObject->containingBlock(); container;
         container = container->containingBlock()) {
      Node* containerNode = container->node();
      if (!containerNode)
        continue;
      if (!blackList.add(containerNode).isNewEntry)
        break;
    }
  }

  HeapHashMap<Member<Node>, TouchTargetData> touchTargets;
  float bestScore = 0;
  for (const auto& hitResult : hitResults) {
    if (!hitResult)
      continue;
    for (Node& node : NodeTraversal::inclusiveAncestorsOf(*hitResult)) {
      if (blackList.contains(&node))
        continue;
      if (node.isDocumentNode() || isHTMLHtmlElement(node) ||
          isHTMLBodyElement(node))
        break;
      if (node.willRespondToMouseClickEvents()) {
        TouchTargetData& targetData =
            touchTargets.add(&node, TouchTargetData()).storedValue->value;
        targetData.windowBoundingBox = boundingBoxForEventNodes(&node);
        targetData.score = scoreTouchTarget(touchPoint, touchPointPadding,
                                            targetData.windowBoundingBox);
        bestScore = std::max(bestScore, targetData.score);
        break;
      }
    }
  }

  for (const auto& touchTarget : touchTargets) {
    // Currently the scoring function uses the overlap area with the fat point
    // as the score.  We ignore the candidates that has less than 1/2 overlap
    // (we consider not really ambiguous enough) than the best candidate to
    // avoid excessive popups.
    if (touchTarget.value.score < bestScore * 0.5)
      continue;
    goodTargets.append(touchTarget.value.windowBoundingBox);
    highlightNodes.append(touchTarget.key);
  }
}

}  // namespace blink