root/Source/core/html/parser/HTMLSrcsetParser.cpp

DEFINITIONS

1. compareByScaleFactor
2. isComma
3. parseDescriptors
4. parseImageCandidatesFromSrcsetAttribute
5. parseImageCandidatesFromSrcsetAttribute
6. pickBestImageCandidate
7. bestFitSourceForSrcsetAttribute
8. bestFitSourceForImageAttributes
9. bestFitSourceForImageAttributes

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#include "config.h"
#include "core/html/parser/HTMLSrcsetParser.h"

#include "core/html/parser/HTMLParserIdioms.h"
#include "platform/ParsingUtilities.h"

namespace WebCore {

static bool compareByScaleFactor(const ImageCandidate& first, const ImageCandidate& second)
{
    return first.scaleFactor() < second.scaleFactor();
}

template<typename CharType>
inline bool isComma(CharType character)
{
    return character == ',';
}

template<typename CharType>
static bool parseDescriptors(const CharType* descriptorsStart, const CharType* descriptorsEnd, float& imgScaleFactor)
{
    const CharType* position = descriptorsStart;
    bool isValid = false;
    bool isFoundScaleFactor = false;
    bool isEmptyDescriptor = !(descriptorsEnd > descriptorsStart);
    while (position < descriptorsEnd) {
        // 13.1. Let descriptor list be the result of splitting unparsed descriptors on spaces.
        skipWhile<CharType, isHTMLSpace<CharType> >(position, descriptorsEnd);
        const CharType* currentDescriptorStart = position;
        skipWhile<CharType, isNotHTMLSpace<CharType> >(position, descriptorsEnd);
        const CharType* currentDescriptorEnd = position;

        ++position;
        ASSERT(currentDescriptorEnd > currentDescriptorStart);
        --currentDescriptorEnd;
        unsigned descriptorLength = currentDescriptorEnd - currentDescriptorStart;
        if (*currentDescriptorEnd == 'x') {
            if (isFoundScaleFactor)
                return false;
            imgScaleFactor = charactersToFloat(currentDescriptorStart, descriptorLength, &isValid);
            isFoundScaleFactor = true;
        } else {
            continue;
        }
    }
    return isEmptyDescriptor || isValid;
}

// http://www.whatwg.org/specs/web-apps/current-work/multipage/embedded-content-1.html#processing-the-image-candidates
template<typename CharType>
static void parseImageCandidatesFromSrcsetAttribute(const String& attribute, const CharType* attributeStart, unsigned length, Vector<ImageCandidate>& imageCandidates)
{
    const CharType* position = attributeStart;
    const CharType* attributeEnd = position + length;

    while (position < attributeEnd) {
        float imgScaleFactor = 1.0;

        // 4. Splitting loop: Skip whitespace.
        skipWhile<CharType, isHTMLSpace<CharType> >(position, attributeEnd);
        if (position == attributeEnd)
            break;
        const CharType* imageURLStart = position;

        // If The current candidate is either totally empty or only contains space, skipping.
        if (*position == ',') {
            ++position;
            continue;
        }

        // 5. Collect a sequence of characters that are not space characters, and let that be url.
        skipUntil<CharType, isHTMLSpace<CharType> >(position, attributeEnd);
        const CharType* imageURLEnd = position;

        if (position != attributeEnd && *(position - 1) == ',') {
            --imageURLEnd;
        } else {
            // 7. Collect a sequence of characters that are not "," (U+002C) characters, and let that be descriptors.
            skipWhile<CharType, isHTMLSpace<CharType> >(position, attributeEnd);
            const CharType* descriptorsStart = position;
            skipUntil<CharType, isComma<CharType> >(position, attributeEnd);
            const CharType* descriptorsEnd = position;
            if (!parseDescriptors(descriptorsStart, descriptorsEnd, imgScaleFactor))
                continue;
        }

        imageCandidates.append(ImageCandidate(attribute, imageURLStart - attributeStart, imageURLEnd - imageURLStart, imgScaleFactor));
        // 11. Return to the step labeled splitting loop.
    }
}

static void parseImageCandidatesFromSrcsetAttribute(const String& attribute, Vector<ImageCandidate>& imageCandidates)
{
    if (attribute.isNull())
        return;

    if (attribute.is8Bit())
        parseImageCandidatesFromSrcsetAttribute<LChar>(attribute, attribute.characters8(), attribute.length(), imageCandidates);
    else
        parseImageCandidatesFromSrcsetAttribute<UChar>(attribute, attribute.characters16(), attribute.length(), imageCandidates);
}

static ImageCandidate pickBestImageCandidate(float deviceScaleFactor, Vector<ImageCandidate>& imageCandidates)
{
    if (imageCandidates.isEmpty())
        return ImageCandidate();

    std::stable_sort(imageCandidates.begin(), imageCandidates.end(), compareByScaleFactor);

    unsigned i;
    for (i = 0; i < imageCandidates.size() - 1; ++i)
        if (imageCandidates[i].scaleFactor() >= deviceScaleFactor)
            break;

    float winningScaleFactor = imageCandidates[i].scaleFactor();
    unsigned winner = i;
    // 16. If an entry b in candidates has the same associated ... pixel density as an earlier entry a in candidates,
    // then remove entry b
    while ((i > 0) && (imageCandidates[--i].scaleFactor() == winningScaleFactor))
        winner = i;

    return imageCandidates[winner];
}

ImageCandidate bestFitSourceForSrcsetAttribute(float deviceScaleFactor, const String& srcsetAttribute)
{
    Vector<ImageCandidate> imageCandidates;

    parseImageCandidatesFromSrcsetAttribute(srcsetAttribute, imageCandidates);

    return pickBestImageCandidate(deviceScaleFactor, imageCandidates);
}

ImageCandidate bestFitSourceForImageAttributes(float deviceScaleFactor, const String& srcAttribute, const String& srcsetAttribute)
{
    if (srcsetAttribute.isNull()) {
        if (srcAttribute.isNull())
            return ImageCandidate();
        return ImageCandidate(srcAttribute, 0, srcAttribute.length(), 1);
    }

    Vector<ImageCandidate> imageCandidates;

    parseImageCandidatesFromSrcsetAttribute(srcsetAttribute, imageCandidates);

    if (!srcAttribute.isEmpty())
        imageCandidates.append(ImageCandidate(srcAttribute, 0, srcAttribute.length(), 1.0));

    return pickBestImageCandidate(deviceScaleFactor, imageCandidates);
}

String bestFitSourceForImageAttributes(float deviceScaleFactor, const String& srcAttribute, ImageCandidate& srcsetImageCandidate)
{
    if (srcsetImageCandidate.isEmpty())
        return srcAttribute;

    Vector<ImageCandidate> imageCandidates;
    imageCandidates.append(srcsetImageCandidate);

    if (!srcAttribute.isEmpty())
        imageCandidates.append(ImageCandidate(srcAttribute, 0, srcAttribute.length(), 1.0));

    return pickBestImageCandidate(deviceScaleFactor, imageCandidates).toString();
}

}