sky/engine/core/css/resolver/SharedStyleFinder.cpp

/*
 * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
 *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
 * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
 * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc. All rights reserved.
 * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
 * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
 * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
 * Copyright (c) 2011, Code Aurora Forum. All rights reserved.
 * Copyright (C) Research In Motion Limited 2011. All rights reserved.
 * Copyright (C) 2013 Google Inc. All rights reserved.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public License
 * along with this library; see the file COPYING.LIB.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 */

#include "sky/engine/core/css/resolver/SharedStyleFinder.h"

#include "gen/sky/core/HTMLNames.h"
#include "sky/engine/core/css/resolver/StyleResolver.h"
#include "sky/engine/core/css/resolver/StyleResolverStats.h"
#include "sky/engine/core/dom/ContainerNode.h"
#include "sky/engine/core/dom/Document.h"
#include "sky/engine/core/dom/ElementTraversal.h"
#include "sky/engine/core/dom/Node.h"
#include "sky/engine/core/dom/NodeRenderStyle.h"
#include "sky/engine/core/dom/QualifiedName.h"
#include "sky/engine/core/dom/SpaceSplitString.h"
#include "sky/engine/core/html/HTMLElement.h"
#include "sky/engine/core/rendering/style/RenderStyle.h"
#include "sky/engine/wtf/HashSet.h"
#include "sky/engine/wtf/text/AtomicString.h"

namespace blink {

bool SharedStyleFinder::classNamesAffectedByRules(const Element& element) const
{
    const SpaceSplitString& classNames = element.classNames();
    unsigned count = classNames.size();
    for (unsigned i = 0; i < count; ++i) {
        if (element.affectedByClassSelector(classNames[i]))
            return true;
    }
    return false;
}

bool SharedStyleFinder::attributesAffectedByRules(const Element& element) const
{
    for (auto& attribute : element.attributesWithoutUpdate()) {
        if (element.affectedByAttributeSelector(attribute.localName()))
            return true;
    }
    return false;
}

bool SharedStyleFinder::sharingCandidateHasIdenticalStyleAffectingAttributes(Element& candidate) const
{
    if (element().sharesSameElementData(candidate))
        return true;
    if (element().getAttribute(HTMLNames::langAttr) != candidate.getAttribute(HTMLNames::langAttr))
        return false;

    if (!m_elementAffectedByClassRules) {
        if (candidate.hasClass() && classNamesAffectedByRules(candidate))
            return false;
    } else if (candidate.hasClass()) {
        if (element().classNames() != candidate.classNames())
            return false;
    } else {
        return false;
    }

    return true;
}

bool SharedStyleFinder::sharingCandidateCanShareHostStyles(Element& candidate) const
{
    return true;
}

bool SharedStyleFinder::canShareStyleWithElement(Element& candidate) const
{
    ASSERT(candidate.supportsStyleSharing());

    if (element() == candidate)
        return false;
    if (candidate.tagQName() != element().tagQName())
        return false;
    if (candidate.needsStyleRecalc())
        return false;
    RenderStyle* style = candidate.renderStyle();
    if (!style)
        return false;
    if (!style->isSharable())
        return false;
    ContainerNode* parent = candidate.parentNode();
    if (!parent)
        return false;
    RenderStyle* parentStyle = parent->renderStyle();
    if (!parentStyle)
        return false;
    // The StyleAdjuster will change the display of the renderer depending
    // on it's parent's display.
    if (parentStyle->requiresOnlyBlockChildren() !=
        m_renderingParent->renderStyle()->requiresOnlyBlockChildren())
        return false;
    if (m_renderingParent->renderStyle()->inheritedNotEqual(parentStyle))
        return false;
    if (!sharingCandidateHasIdenticalStyleAffectingAttributes(candidate))
        return false;
    if (!sharingCandidateCanShareHostStyles(candidate))
        return false;
    if (!candidate.treeScope().hasSameStyles(element().treeScope()))
        return false;
    return true;
}

bool SharedStyleFinder::documentContainsValidCandidate() const
{
    for (Element* element = ElementTraversal::firstChild(document()); element; element = ElementTraversal::next(*element)) {
        if (element->supportsStyleSharing() && canShareStyleWithElement(*element))
            return true;
    }
    return false;
}

inline Element* SharedStyleFinder::findElementForStyleSharing() const
{
    StyleSharingList& styleSharingList = m_styleResolver.styleSharingList();
    for (StyleSharingList::iterator it = styleSharingList.begin(); it != styleSharingList.end(); ++it) {
        Element& candidate = **it;
        // We shouldn't have elements in the style sharing list that don't
        // support style sharing.
        if (!canShareStyleWithElement(candidate))
            continue;
        if (it != styleSharingList.begin()) {
            // Move the element to the front of the LRU
            styleSharingList.remove(it);
            styleSharingList.prepend(&candidate);
        }
        return &candidate;
    }
    m_styleResolver.addToStyleSharingList(element());
    return 0;
}

RenderStyle* SharedStyleFinder::findSharedStyle()
{
    INCREMENT_STYLE_STATS_COUNTER(m_styleResolver, sharedStyleLookups);

    if (!element().supportsStyleSharing())
        return 0;

    if (attributesAffectedByRules(element())) {
        INCREMENT_STYLE_STATS_COUNTER(m_styleResolver, sharedStyleRejectedByAttributeRules);
        return 0;
    }

    // Cache whether context.element() is affected by any known class selectors.
    m_elementAffectedByClassRules = element().hasClass() && classNamesAffectedByRules(element());
    m_renderingParent = element().parentNode();

    Element* shareElement = findElementForStyleSharing();

    if (!shareElement) {
        if (m_styleResolver.stats() && m_styleResolver.stats()->printMissedCandidateCount && documentContainsValidCandidate())
            INCREMENT_STYLE_STATS_COUNTER(m_styleResolver, sharedStyleMissed);
        return 0;
    }

    INCREMENT_STYLE_STATS_COUNTER(m_styleResolver, sharedStyleFound);

    return shareElement->renderStyle();
}

}