TouchDisambiguation.cpp   [plain text]

/*
 * Copyright (C) 2012 Google Inc. All rights reserved.
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#include "config.h"

#include "TouchDisambiguation.h"

#include "Document.h"
#include "Element.h"
#include "Frame.h"
#include "FrameView.h"
#include "HTMLNames.h"
#include "HitTestResult.h"
#include "NodeTraversal.h"
#include "RenderBlock.h"
#include <algorithm>
#include <cmath>

using namespace std;

namespace WebCore {

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()->contentsToWindow(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 *= max((padding - abs(distance.width())) * reciprocalPadding, 0.f);
    score *= max((padding - abs(distance.height())) * reciprocalPadding, 0.f);

    return score;
}

struct TouchTargetData {
    IntRect windowBoundingBox;
    float score;
};

void findGoodTouchTargets(const IntRect& touchBox, Frame* mainFrame, Vector<IntRect>& goodTargets)
{
    goodTargets.clear();

    int touchPointPadding = ceil(max(touchBox.width(), touchBox.height()) * 0.5);
    // FIXME: Rect-based hit test doesn't transform the touch point size.
    //        We have to pre-apply frame scale factor here.
    int padding = ceil(touchPointPadding / mainFrame->frameScaleFactor());

    IntPoint touchPoint = touchBox.center();
    IntPoint contentsPoint = mainFrame->view()->windowToContents(touchPoint);

    HitTestResult result = mainFrame->eventHandler()->hitTestResultAtPoint(contentsPoint, HitTestRequest::ReadOnly | HitTestRequest::Active | HitTestRequest::DisallowShadowContent, IntSize(padding, padding));
    const ListHashSet<RefPtr<Node> >& hitResults = result.rectBasedTestResult();

    // 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.
    HashSet<Node*> blackList;
    for (ListHashSet<RefPtr<Node> >::const_iterator it = hitResults.begin(); it != hitResults.end(); ++it) {
        // Ignore any Nodes that can't be clicked on.
        RenderObject* renderer = it->get()->renderer();
        if (!renderer || !it->get()->willRespondToMouseClickEvents())
            continue;

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

    HashMap<Node*, TouchTargetData> touchTargets;
    float bestScore = 0;
    for (ListHashSet<RefPtr<Node> >::const_iterator it = hitResults.begin(); it != hitResults.end(); ++it) {
        for (Node* node = it->get(); node; node = node->parentNode()) {
            if (blackList.contains(node))
                continue;
            if (node->isDocumentNode() || node->hasTagName(HTMLNames::htmlTag) || node->hasTagName(HTMLNames::bodyTag))
                break;
            if (node->willRespondToMouseClickEvents()) {
                TouchTargetData& targetData = touchTargets.add(node, TouchTargetData()).iterator->value;
                targetData.windowBoundingBox = boundingBoxForEventNodes(node);
                targetData.score = scoreTouchTarget(touchPoint, touchPointPadding, targetData.windowBoundingBox);
                bestScore = max(bestScore, targetData.score);
                break;
            }
        }
    }

    for (HashMap<Node*, TouchTargetData>::iterator it = touchTargets.begin(); it != touchTargets.end(); ++it) {
        // 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 (it->value.score < bestScore * 0.5)
            continue;
        goodTargets.append(it->value.windowBoundingBox);
    }
}

} // namespace WebCore