String bestFitSourceForImageAttributes(float deviceScaleFactor, const String& srcAttribute, const String& srcsetAttribute)
{
ImageCandidates imageCandidates;
parseImagesWithScaleFromSrcsetAttribute(srcsetAttribute, imageCandidates);
if (!srcAttribute.isEmpty()) {
ImageWithScale image;
image.imageURL = srcAttribute;
image.scaleFactor = 1.0;
imageCandidates.append(image);
}
if (imageCandidates.isEmpty())
return String();
std::stable_sort(imageCandidates.begin(), imageCandidates.end(), compareByScaleFactor);
for (size_t i = 0; i < imageCandidates.size() - 1; ++i) {
if (imageCandidates[i].scaleFactor >= deviceScaleFactor)
return String(imageCandidates[i].imageURL);
}
return String(imageCandidates.last().imageURL);
}
String bestFitSourceForImageAttributes(float deviceScaleFactor, const String& srcAttribute, const String& srcsetAttribute)
{
ImageCandidates imageCandidates;
parseImagesWithScaleFromSrcsetAttribute(srcsetAttribute, imageCandidates);
if (!srcAttribute.isEmpty()) {
ImageWithScale srcPlaceholderImage;
imageCandidates.append(srcPlaceholderImage);
}
if (imageCandidates.isEmpty())
return String();
std::stable_sort(imageCandidates.begin(), imageCandidates.end(), compareByScaleFactor);
for (size_t i = 0; i < imageCandidates.size() - 1; ++i) {
if (imageCandidates[i].scaleFactor >= deviceScaleFactor)
return imageCandidates[i].hasImageURL() ? srcsetAttribute.substringSharingImpl(imageCandidates[i].imageURLStart, imageCandidates[i].imageURLLength) : srcAttribute;
}
const ImageWithScale& lastCandidate = imageCandidates.last();
return lastCandidate.hasImageURL() ? srcsetAttribute.substringSharingImpl(lastCandidate.imageURLStart, lastCandidate.imageURLLength) : srcAttribute;
}
// See the specifications for more details about the algorithm to follow.
// http://www.w3.org/TR/2013/WD-html-srcset-20130228/#processing-the-image-candidates.
static void parseImagesWithScaleFromSrcsetAttribute(const String& srcsetAttribute, ImageCandidates& imageCandidates)
{
ASSERT(imageCandidates.isEmpty());
size_t imageCandidateStart = 0;
unsigned srcsetAttributeLength = srcsetAttribute.length();
while (imageCandidateStart < srcsetAttributeLength) {
float imageScaleFactor = 1;
size_t separator;
// 4. Splitting loop: Skip whitespace.
size_t imageURLStart = srcsetAttribute.find(isNotHTMLSpace, imageCandidateStart);
if (imageURLStart == notFound)
break;
// If The current candidate is either totally empty or only contains space, skipping.
if (srcsetAttribute[imageURLStart] == ',') {
imageCandidateStart = imageURLStart + 1;
continue;
}
// 5. Collect a sequence of characters that are not space characters, and let that be url.
size_t imageURLEnd = srcsetAttribute.find(isHTMLSpace, imageURLStart + 1);
if (imageURLEnd == notFound) {
imageURLEnd = srcsetAttributeLength;
separator = srcsetAttributeLength;
} else if (srcsetAttribute[imageURLEnd - 1] == ',') {
--imageURLEnd;
separator = imageURLEnd;
} else {
// 7. Collect a sequence of characters that are not "," (U+002C) characters, and let that be descriptors.
size_t imageScaleStart = srcsetAttribute.find(isNotHTMLSpace, imageURLEnd + 1);
if (imageScaleStart == notFound)
separator = srcsetAttributeLength;
else if (srcsetAttribute[imageScaleStart] == ',')
separator = imageScaleStart;
else {
// This part differs from the spec as the current implementation only supports pixel density descriptors for now.
size_t imageScaleEnd = srcsetAttribute.find(isHTMLSpaceOrComma, imageScaleStart + 1);
imageScaleEnd = (imageScaleEnd == notFound) ? srcsetAttributeLength : imageScaleEnd;
size_t commaPosition = imageScaleEnd;
// Make sure there are no other descriptors.
while ((commaPosition < srcsetAttributeLength - 1) && isHTMLSpace(srcsetAttribute[commaPosition]))
++commaPosition;
// If the first not html space character after the scale modifier is not a comma,
// the current candidate is an invalid input.
if ((commaPosition < srcsetAttributeLength - 1) && srcsetAttribute[commaPosition] != ',') {
// Find the nearest comma and skip the input.
commaPosition = srcsetAttribute.find(',', commaPosition + 1);
if (commaPosition == notFound)
break;
imageCandidateStart = commaPosition + 1;
continue;
}
separator = commaPosition;
if (srcsetAttribute[imageScaleEnd - 1] != 'x') {
imageCandidateStart = separator + 1;
continue;
}
bool validScaleFactor = false;
size_t scaleFactorLengthWithoutUnit = imageScaleEnd - imageScaleStart - 1;
imageScaleFactor = charactersToFloat(srcsetAttribute.characters() + imageScaleStart, scaleFactorLengthWithoutUnit, &validScaleFactor);
if (!validScaleFactor) {
imageCandidateStart = separator + 1;
continue;
}
}
}
ImageWithScale image;
image.imageURL = String(srcsetAttribute.characters() + imageURLStart, imageURLEnd - imageURLStart);
image.scaleFactor = imageScaleFactor;
imageCandidates.append(image);
// 11. Return to the step labeled splitting loop.
imageCandidateStart = separator + 1;
}
}