Enable srcset support in HTMLImageElement

Source/core/html/parser/HTMLSrcsetParser.cpp

+/*
+ * Copyright (C) 2013 Google Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "config.h"
+#include "core/html/parser/HTMLSrcsetParser.h"
+
+#include "core/html/parser/HTMLParserIdioms.h"
+#include "core/platform/ParsingUtilities.h"
+
+namespace WebCore {
+
+static bool compareByScaleFactor(const ImageCandidate& first, const ImageCandidate& second)
+{
+    return first.scaleFactor() < second.scaleFactor();
+}
+
+// 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.
+        ++position;
+        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* qualifierStart = position;
+            if (position != attributeEnd && *position != ',') {
+                // This part differs from the spec as the current implementation only supports pixel density descriptors for now.
+                skipUntil<CharType, isHTMLSpaceOrComma<CharType> >(position, attributeEnd);
+                const CharType* qualifierEnd = position;
+                ASSERT(qualifierEnd > qualifierStart);
+                // Make sure there are no other descriptors
+                skipWhile<CharType, isHTMLSpace<CharType> >(position, attributeEnd);
+                // If the first non-html-space character after the scale modifier is not a comma,
+                // the current candidate is an invalid input.
+                if (position != attributeEnd && *position != ',') {
+                    skipUntil<CharType>(position, attributeEnd, ',');
+                    ++position;
+                    continue;
+                }
+                // If the current qualifier is not an 'x', the resource is ignored
+                if (*(qualifierEnd - 1) != 'x')
+                    continue;
+
+                bool validScaleFactor = false;
+                unsigned scaleFactorLengthWithoutUnit = qualifierEnd - qualifierStart - 1;
+                imgScaleFactor = charactersToFloat(qualifierStart, scaleFactorLengthWithoutUnit, &validScaleFactor);
+
+                if (!validScaleFactor)
+                    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;
+    }
+    return imageCandidates[i];
+}
+
+ImageCandidate bestFitSourceForSrcsetAttribute(float deviceScaleFactor, const String& srcsetAttribute)
+{
+    Vector<ImageCandidate> imageCandidates;
+
+    parseImageCandidatesFromSrcsetAttribute(srcsetAttribute, imageCandidates);
+
+    return pickBestImageCandidate(deviceScaleFactor, imageCandidates);
+}
+
+String bestFitSourceForImageAttributes(float deviceScaleFactor, const String& srcAttribute, const String& srcsetAttribute)
+{
+    if (srcsetAttribute.isNull())
+        return srcAttribute;
+
+    Vector<ImageCandidate> imageCandidates;
+
+    parseImageCandidatesFromSrcsetAttribute(srcsetAttribute, imageCandidates);
+
+    if (!srcAttribute.isEmpty())
+        imageCandidates.append(ImageCandidate(srcAttribute, 0, srcAttribute.length(), 1.0));
+
+    return pickBestImageCandidate(deviceScaleFactor, imageCandidates).toString();
+}
+
+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();
+}
+
+}