WIP: Implement APNG

third_party/WebKit/Source/platform/image-decoders/png/PNGImageDecoder.cpp

Index: third_party/WebKit/Source/platform/image-decoders/png/PNGImageDecoder.cpp
diff --git a/third_party/WebKit/Source/platform/image-decoders/png/PNGImageDecoder.cpp b/third_party/WebKit/Source/platform/image-decoders/png/PNGImageDecoder.cpp
index 2ef4182cbe85b28b4158c7acf551d76c72a85a91..85f08c4bd17734043dc4c65102e0a862da749a1e 100644
--- a/third_party/WebKit/Source/platform/image-decoders/png/PNGImageDecoder.cpp
+++ b/third_party/WebKit/Source/platform/image-decoders/png/PNGImageDecoder.cpp
@@ -38,8 +38,8 @@
 
 #include "platform/image-decoders/png/PNGImageDecoder.h"
 
+#include "platform/image-decoders/png/PNGImageReader.h"
 #include "png.h"
-#include "wtf/PtrUtil.h"
 #include <memory>
 
 #if !defined(PNG_LIBPNG_VER_MAJOR) || !defined(PNG_LIBPNG_VER_MINOR)
@@ -53,115 +53,260 @@
 #define JMPBUF(png_ptr) png_ptr->jmpbuf
 #endif
 
-namespace {
+namespace blink {
+
+PNGImageDecoder::PNGImageDecoder(AlphaOption alphaOption,
+                                 ColorSpaceOption colorOptions,
+                                 size_t maxDecodedBytes,
+                                 size_t offset)
+    : ImageDecoder(alphaOption, colorOptions, maxDecodedBytes),
+      m_offset(offset),
+      m_frameCount(0),
+      m_currentFrame(0),
+      m_repetitionCount(cAnimationLoopOnce) {}
 
-inline blink::PNGImageDecoder* imageDecoder(png_structp png) {
-  return static_cast<blink::PNGImageDecoder*>(png_get_progressive_ptr(png));
+PNGImageDecoder::~PNGImageDecoder() {}
+
+size_t PNGImageDecoder::decodeFrameCount() {
+  parse(PNGParseQuery::PNGMetaDataQuery);
+  return m_frameCount;
 }
 
-void PNGAPI pngHeaderAvailable(png_structp png, png_infop) {
-  imageDecoder(png)->headerAvailable();
+void PNGImageDecoder::decode(size_t index) {
+  parse(PNGParseQuery::PNGMetaDataQuery);
+
+  // @TODO(joostouwerling): show complete frames even if a later frame fails.
+  if (failed())
+    return;
+
+  updateAggressivePurging(index);
+
+  Vector<size_t> framesToDecode;
+  size_t frameToDecode = index;
+
+  // This method is only called by ImageDecoder::frameBufferAtIndex if the frame
+  // status of frame |index| is not ImageFrame::FrameComplete. Therefore, it is
+  // OK that the do-while loop always appends |index| to |m_framesToDecode|,
+  // without checking for its status.
+  //
+  // The requiredPreviousFrameIndex for each frame is set in
+  // PNGImageDecoder::initializeNewFrame().
+  do {
+    framesToDecode.append(frameToDecode);
+    frameToDecode =
+        m_frameBufferCache[frameToDecode].requiredPreviousFrameIndex();
+  } while (frameToDecode != kNotFound &&
+           m_frameBufferCache[frameToDecode].getStatus() !=
+               ImageFrame::FrameComplete);
+
+  for (auto i = framesToDecode.rbegin(); i != framesToDecode.rend(); i++) {
+    m_currentFrame = *i;
+    m_reader->decode(*m_data, *i);
+    if (failed())
+      return;
+
+    // If the frame is not yet complete, we need more data to continue.
+    if (m_frameBufferCache[*i].getStatus() != ImageFrame::FrameComplete)
+      break;
+
+    if (m_purgeAggressively)
+      clearCacheExceptFrame(*i);
+  }
 }
 
-void PNGAPI pngRowAvailable(png_structp png,
-                            png_bytep row,
-                            png_uint_32 rowIndex,
-                            int state) {
-  imageDecoder(png)->rowAvailable(row, rowIndex, state);
+// @TODO(joostouwerling) Consolidate this with a proposed change in
+//                       ImageDecoder::clearCacheExceptFrame. See
+//                       crrev.com/2468233002
+size_t PNGImageDecoder::clearCacheExceptFrame(size_t clearExceptFrame) {
+  // As per the comments at ImageDecoder::clearCacheExceptFrame
+  if (m_frameBufferCache.size() <= 1)
+    return 0;
+
+  // We expect that after this call, we'll be asked to decode frames after
+  // this one.  So we want to avoid clearing frames such that those requests
+  // would force re-decoding from the beginning of the image.
+  //
+  // When |clearExceptFrame| is e.g. DisposeKeep, simply not clearing that
+  // frame is sufficient, as the next frame will be based on it, and in
+  // general future frames can't be based on anything previous.
+  //
+  // However, if this frame is DisposeOverwritePrevious, then subsequent
+  // frames will depend on this frame's required previous frame.  In this
+  // case, we need to preserve both this frame and that one.
+  size_t clearExceptFrame2 = kNotFound;
+  if (clearExceptFrame < m_frameBufferCache.size()) {
+    const ImageFrame& frame = m_frameBufferCache[clearExceptFrame];
+    if (frame.getStatus() != ImageFrame::FrameEmpty &&
+        frame.getDisposalMethod() == ImageFrame::DisposeOverwritePrevious) {
+      clearExceptFrame2 = clearExceptFrame;
+      clearExceptFrame = frame.requiredPreviousFrameIndex();
+    }
+  }
+
+  // Now |clearExceptFrame| indicates the frame that future frames will
+  // depend on.  But if decoding is skipping forward past intermediate frames,
+  // this frame may be FrameEmpty.  So we need to keep traversing back through
+  // the required previous frames until we find the nearest non-empty
+  // ancestor.  Preserving that will minimize the amount of future decoding
+  // needed.
+  while (clearExceptFrame < m_frameBufferCache.size() &&
+         m_frameBufferCache[clearExceptFrame].getStatus() ==
+             ImageFrame::FrameEmpty)
+    clearExceptFrame =
+        m_frameBufferCache[clearExceptFrame].requiredPreviousFrameIndex();
+
+  return clearCacheExceptTwoFrames(clearExceptFrame, clearExceptFrame2);
 }
 
-void PNGAPI pngComplete(png_structp png, png_infop) {
-  imageDecoder(png)->complete();
+size_t PNGImageDecoder::clearCacheExceptTwoFrames(size_t clearExceptFrame1,
+                                                  size_t clearExceptFrame2) {
+  size_t frameBytesCleared = 0;
+  for (size_t i = 0; i < m_frameBufferCache.size(); ++i) {
+    if (m_frameBufferCache[i].getStatus() != ImageFrame::FrameEmpty &&
+        i != clearExceptFrame1 && i != clearExceptFrame2) {
+      frameBytesCleared += frameBytesAtIndex(i);
+      clearFrameBuffer(i);
+    }
+  }
+  return frameBytesCleared;
 }
 
-void PNGAPI pngFailed(png_structp png, png_const_charp) {
-  longjmp(JMPBUF(png), 1);
+void PNGImageDecoder::clearFrameBuffer(size_t frameIndex) {
+  if (m_frameBufferCache[frameIndex].getStatus() == ImageFrame::FramePartial)
+    m_reader->clearDecodeState(frameIndex);
+
+  m_frameBufferCache[frameIndex].clearPixelData();
 }
 
-}  // namespace
+void PNGImageDecoder::parse(PNGParseQuery query) {
+  if (failed())
+    return;
 
-namespace blink {
+  if (!m_reader)
+    m_reader = wrapUnique(new PNGImageReader(this, m_offset));
 
-class PNGImageReader final {
-  USING_FAST_MALLOC(PNGImageReader);
-  WTF_MAKE_NONCOPYABLE(PNGImageReader);
-
- public:
-  PNGImageReader(PNGImageDecoder* decoder, size_t readOffset)
-      : m_decoder(decoder),
-        m_readOffset(readOffset),
-        m_currentBufferSize(0),
-        m_decodingSizeOnly(false),
-        m_hasAlpha(false) {
-    m_png = png_create_read_struct(PNG_LIBPNG_VER_STRING, 0, pngFailed, 0);
-    m_info = png_create_info_struct(m_png);
-    png_set_progressive_read_fn(m_png, m_decoder, pngHeaderAvailable,
-                                pngRowAvailable, pngComplete);
-  }
+  if (!m_reader->parse(*m_data, query) && isAllDataReceived())
+    setFailed();
 
-  ~PNGImageReader() {
-    png_destroy_read_struct(m_png ? &m_png : 0, m_info ? &m_info : 0, 0);
-    ASSERT(!m_png && !m_info);
+  if (query == PNGParseQuery::PNGMetaDataQuery)
+    m_frameCount = m_reader->frameCount();
+}
 
-    m_readOffset = 0;
-  }
+void PNGImageDecoder::setRepetitionCount(size_t repetitionCount) {
+  m_repetitionCount =
+      (repetitionCount == 0) ? cAnimationLoopInfinite : repetitionCount;
+}
 
-  bool decode(const SegmentReader& data, bool sizeOnly) {
-    m_decodingSizeOnly = sizeOnly;
-
-    // We need to do the setjmp here. Otherwise bad things will happen.
-    if (setjmp(JMPBUF(m_png)))
-      return m_decoder->setFailed();
-
-    const char* segment;
-    while (size_t segmentLength = data.getSomeData(segment, m_readOffset)) {
-      m_readOffset += segmentLength;
-      m_currentBufferSize = m_readOffset;
-      png_process_data(m_png, m_info,
-                       reinterpret_cast<png_bytep>(const_cast<char*>(segment)),
-                       segmentLength);
-      if (sizeOnly ? m_decoder->isDecodedSizeAvailable()
-                   : m_decoder->frameIsCompleteAtIndex(0))
-        return true;
-    }
+// This matches the existing behavior to loop once if decoding fails, but this
+// should be changed to stick with m_repetitionCount to match other browsers.
+// See crbug.com/267883
+int PNGImageDecoder::repetitionCount() const {
+  if (m_reader->parseCompleted() && isAllDataReceived() &&
+      m_reader->frameCount() == 1)
+    return cAnimationNone;
+  return failed() ? cAnimationLoopOnce : m_repetitionCount;
+}
 
-    return false;
+// These are mapped according to:
+// https://wiki.mozilla.org/APNG_Specification#.60fcTL.60:_The_Frame_Control_Chunk
+static inline ImageFrame::DisposalMethod getDisposalMethod(
+    uint8_t disposalMethod) {
+  switch (disposalMethod) {
+    case 0:
+      return ImageFrame::DisposalMethod::DisposeKeep;
+    case 1:
+      return ImageFrame::DisposalMethod::DisposeOverwriteBgcolor;
+    case 2:
+      return ImageFrame::DisposalMethod::DisposeOverwritePrevious;
+    default:
+      return ImageFrame::DisposalMethod::DisposeNotSpecified;
   }
+}
+
+// These are mapped according to:
+// https://wiki.mozilla.org/APNG_Specification#.60fcTL.60:_The_Frame_Control_Chunk
+static inline ImageFrame::AlphaBlendSource getAlphaBlend(uint8_t alphaBlend) {
+  if (alphaBlend == 1)
+    return ImageFrame::AlphaBlendSource::BlendAtopPreviousFrame;
+  return ImageFrame::AlphaBlendSource::BlendAtopBgcolor;
+}
+
+void PNGImageDecoder::initializeNewFrame(size_t index) {
+  const PNGImageReader::FrameInfo& frameInfo = m_reader->frameInfo(index);
+  ImageFrame* buffer = &m_frameBufferCache[index];
+
+  IntRect frameRectWithinSize =
+      intersection(frameInfo.frameRect, {IntPoint(), size()});
+  buffer->setOriginalFrameRect(frameRectWithinSize);
+  buffer->setDuration(frameInfo.duration);
+  buffer->setDisposalMethod(getDisposalMethod(frameInfo.disposalMethod));
+  buffer->setAlphaBlendSource(getAlphaBlend(frameInfo.alphaBlend));
+  buffer->setRequiredPreviousFrameIndex(
+      findRequiredPreviousFrame(index, false));
+}
 
-  png_structp pngPtr() const { return m_png; }
-  png_infop infoPtr() const { return m_info; }
+// Initialize the frame buffer before decoding. The returned boolean indicates
+// whether initialisation succeeded when it is true, false otherwise.
+bool PNGImageDecoder::initFrameBuffer(size_t index) {
+  ImageFrame* const buffer = &m_frameBufferCache[index];
 
-  size_t getReadOffset() const { return m_readOffset; }
-  void setReadOffset(size_t offset) { m_readOffset = offset; }
-  size_t currentBufferSize() const { return m_currentBufferSize; }
-  bool decodingSizeOnly() const { return m_decodingSizeOnly; }
-  void setHasAlpha(bool hasAlpha) { m_hasAlpha = hasAlpha; }
-  bool hasAlpha() const { return m_hasAlpha; }
+  // Return true if the frame is already initialised.
+  if (buffer->getStatus() != ImageFrame::FrameEmpty)
+    return true;
 
-  png_bytep interlaceBuffer() const { return m_interlaceBuffer.get(); }
-  void createInterlaceBuffer(int size) {
-    m_interlaceBuffer = wrapArrayUnique(new png_byte[size]);
+  if (!buffer->setSizeAndColorSpace(size().width(), size().height(),
+                                    colorSpace()))
+    return false;
+
+  // Create the image buffer if:
+  // A) The image is encoded with interlacing, or
+  // B) frameShouldBeDecodedIncrementally(m_frameBufferCache) == false. In this
+  //    case, the image buffer is used to store the row data, so it can be
+  //    written to the frame buffer at once in PNGImageDecoder::complete().
+  //    This prevents partially overwriting the content of previous frames.
+  unsigned colorChannels = m_reader->hasAlpha() ? 4 : 3;
+  png_structp png = m_reader->pngPtr();
+  if (PNG_INTERLACE_ADAM7 == png_get_interlace_type(png, m_reader->infoPtr()) ||
+      !frameShouldBeDecodedIncrementally(m_currentFrame)) {
+    m_reader->createImageBuffer(colorChannels * size().width() *
+                                size().height());
+    if (!m_reader->imageBuffer())
+      return false;
   }
 
- private:
-  png_structp m_png;
-  png_infop m_info;
-  PNGImageDecoder* m_decoder;
-  size_t m_readOffset;
-  size_t m_currentBufferSize;
-  bool m_decodingSizeOnly;
-  bool m_hasAlpha;
-  std::unique_ptr<png_byte[]> m_interlaceBuffer;
-};
+  buffer->setHasAlpha(false);
+  size_t requiredPreviousFrameIndex = buffer->requiredPreviousFrameIndex();
 
-PNGImageDecoder::PNGImageDecoder(AlphaOption alphaOption,
-                                 ColorSpaceOption colorOptions,
-                                 size_t maxDecodedBytes,
-                                 size_t offset)
-    : ImageDecoder(alphaOption, colorOptions, maxDecodedBytes),
-      m_offset(offset) {}
+  // If frame |index| does not depend on any other frame, ensure the frame is
+  // fully transparent black after initialisation.
+  if (requiredPreviousFrameIndex == kNotFound) {
+    buffer->zeroFillPixelData();
+  } else {
+    ImageFrame* prevBuffer = &m_frameBufferCache[requiredPreviousFrameIndex];
+    ASSERT(prevBuffer->getStatus() == ImageFrame::FrameComplete);
+
+    // We try to reuse |prevBuffer| as starting state to avoid copying.
+    // For DisposeOverwritePrevious, the next frame will also use
+    // |prevBuffer| as its starting state, so we can't take over its image
+    // data using takeBitmapDataIfWritable.  Copy the data instead.
+    if ((buffer->getDisposalMethod() == ImageFrame::DisposeOverwritePrevious ||
+         !buffer->takeBitmapDataIfWritable(prevBuffer)) &&
+        !buffer->copyBitmapData(*prevBuffer))
+      return false;
+
+    // We want to clear the previous frame to transparent, without affecting
+    // pixels in the image outside of the frame.
+    if (prevBuffer->getDisposalMethod() ==
+        ImageFrame::DisposeOverwriteBgcolor) {
+      const IntRect& prevRect = prevBuffer->originalFrameRect();
+      ASSERT(!prevRect.contains(IntRect(IntPoint(), size())));
+      buffer->zeroFillFrameRect(prevRect);
+    }
+  }
 
-PNGImageDecoder::~PNGImageDecoder() {}
+  buffer->setStatus(ImageFrame::FramePartial);
+  return true;
+}
 
 inline float pngFixedToFloat(png_fixed_point x) {
   return ((float)x) * 0.00001f;
@@ -223,17 +368,21 @@ void PNGImageDecoder::headerAvailable() {
   png_uint_32 width = png_get_image_width(png, info);
   png_uint_32 height = png_get_image_height(png, info);
 
-  // Protect against large PNGs. See http://bugzil.la/251381 for more details.
-  const unsigned long maxPNGSize = 1000000UL;
-  if (width > maxPNGSize || height > maxPNGSize) {
-    longjmp(JMPBUF(png), 1);
-    return;
-  }
+  // Only set the size of the image once. Since single frames also use this
+  // method, we don't want them to override the size to their frame rect.
+  if (!isDecodedSizeAvailable()) {
+    // Protect against large PNGs. See http://bugzil.la/251381 for more details.
+    const unsigned long maxPNGSize = 1000000UL;
+    if (width > maxPNGSize || height > maxPNGSize) {
+      longjmp(JMPBUF(png), 1);
+      return;
+    }
 
-  // Set the image size now that the image header is available.
-  if (!setSize(width, height)) {
-    longjmp(JMPBUF(png), 1);
-    return;
+    // Set the image size now that the image header is available.
+    if (!setSize(width, height)) {
+      longjmp(JMPBUF(png), 1);
+      return;
+    }
   }
 
   int bitDepth, colorType, interlaceType, compressionType, filterType, channels;
@@ -299,7 +448,9 @@ void PNGImageDecoder::headerAvailable() {
     }
   }
 
-  // Tell libpng to send us rows for interlaced pngs.
+  // Tell libpng to send us rows for interlaced pngs. Make sure the interlace

[scroggo_chromium, 2016/11/09 13:42:50]

image* buffer

[joostouwerling, 2016/11/11 20:22:18]

In the revisited patch, this is correct.

+  // buffer is cleared before decoding.
+  m_reader->clearImageBuffer();
   if (interlaceType == PNG_INTERLACE_ADAM7)
     png_set_interlace_handling(png);
 
@@ -309,19 +460,6 @@ void PNGImageDecoder::headerAvailable() {
   ASSERT(channels == 3 || channels == 4);
 
   m_reader->setHasAlpha(channels == 4);
-
-  if (m_reader->decodingSizeOnly()) {
-// If we only needed the size, halt the reader.
-#if PNG_LIBPNG_VER_MAJOR > 1 || \
-    (PNG_LIBPNG_VER_MAJOR == 1 && PNG_LIBPNG_VER_MINOR >= 5)
-    // Passing '0' tells png_process_data_pause() not to cache unprocessed data.
-    m_reader->setReadOffset(m_reader->currentBufferSize() -
-                            png_process_data_pause(png, 0));
-#else
-    m_reader->setReadOffset(m_reader->currentBufferSize() - png->buffer_size);
-    png->buffer_size = 0;
-#endif
-  }
 }
 
 void PNGImageDecoder::rowAvailable(unsigned char* rowBuffer,
@@ -330,88 +468,77 @@ void PNGImageDecoder::rowAvailable(unsigned char* rowBuffer,
   if (m_frameBufferCache.isEmpty())
     return;
 
-  // Initialize the framebuffer if needed.
-  ImageFrame& buffer = m_frameBufferCache[0];
-  if (buffer.getStatus() == ImageFrame::FrameEmpty) {
-    png_structp png = m_reader->pngPtr();
-    if (!buffer.setSizeAndColorSpace(size().width(), size().height(),
-                                     colorSpace())) {
-      longjmp(JMPBUF(png), 1);
-      return;
-    }
-
-    unsigned colorChannels = m_reader->hasAlpha() ? 4 : 3;
-    if (PNG_INTERLACE_ADAM7 ==
-        png_get_interlace_type(png, m_reader->infoPtr())) {
-      m_reader->createInterlaceBuffer(colorChannels * size().width() *
-                                      size().height());
-      if (!m_reader->interlaceBuffer()) {
-        longjmp(JMPBUF(png), 1);
-        return;
-      }
-    }
-
-    buffer.setStatus(ImageFrame::FramePartial);
-    buffer.setHasAlpha(false);
-
-    // For PNGs, the frame always fills the entire image.
-    buffer.setOriginalFrameRect(IntRect(IntPoint(), size()));
+  ImageFrame& buffer = m_frameBufferCache[m_currentFrame];
+  if (!initFrameBuffer(m_currentFrame)) {
+    setFailed();
+    return;
   }
 
+  // This frameRect is already clipped, so that it fits within the size of the
+  // image. This is done in initializeNewFrame() after a frameCount() call.
+  const IntRect& frameRect = buffer.originalFrameRect();
+
   /* libpng comments (here to explain what follows).
-     *
-     * this function is called for every row in the image. If the
-     * image is interlacing, and you turned on the interlace handler,
-     * this function will be called for every row in every pass.
-     * Some of these rows will not be changed from the previous pass.
-     * When the row is not changed, the new_row variable will be NULL.
-     * The rows and passes are called in order, so you don't really
-     * need the row_num and pass, but I'm supplying them because it
-     * may make your life easier.
-     */
+   *
+   * this function is called for every row in the image. If the
+   * image is interlacing, and you turned on the interlace handler,
+   * this function will be called for every row in every pass.
+   * Some of these rows will not be changed from the previous pass.
+   * When the row is not changed, the new_row variable will be NULL.
+   * The rows and passes are called in order, so you don't really
+   * need the row_num and pass, but I'm supplying them because it
+   * may make your life easier.
+   */
 
   // Nothing to do if the row is unchanged, or the row is outside
   // the image bounds: libpng may send extra rows, ignore them to
   // make our lives easier.
   if (!rowBuffer)
     return;
-  int y = rowIndex;
-  if (y < 0 || y >= size().height())
+  int y = rowIndex + frameRect.y();
+  ASSERT(y >= 0);
+  if (y >= size().height())
     return;
 
   /* libpng comments (continued).
-     *
-     * For the non-NULL rows of interlaced images, you must call
-     * png_progressive_combine_row() passing in the row and the
-     * old row.  You can call this function for NULL rows (it will
-     * just return) and for non-interlaced images (it just does the
-     * memcpy for you) if it will make the code easier. Thus, you
-     * can just do this for all cases:
-     *
-     *    png_progressive_combine_row(png_ptr, old_row, new_row);
-     *
-     * where old_row is what was displayed for previous rows. Note
-     * that the first pass (pass == 0 really) will completely cover
-     * the old row, so the rows do not have to be initialized. After
-     * the first pass (and only for interlaced images), you will have
-     * to pass the current row, and the function will combine the
-     * old row and the new row.
-     */
+   *
+   * For the non-NULL rows of interlaced images, you must call
+   * png_progressive_combine_row() passing in the row and the
+   * old row.  You can call this function for NULL rows (it will
+   * just return) and for non-interlaced images (it just does the
+   * memcpy for you) if it will make the code easier. Thus, you
+   * can just do this for all cases:
+   *
+   *    png_progressive_combine_row(png_ptr, old_row, new_row);
+   *
+   * where old_row is what was displayed for previous rows. Note
+   * that the first pass (pass == 0 really) will completely cover
+   * the old row, so the rows do not have to be initialized. After
+   * the first pass (and only for interlaced images), you will have
+   * to pass the current row, and the function will combine the
+   * old row and the new row.
+   */
 
   bool hasAlpha = m_reader->hasAlpha();
   png_bytep row = rowBuffer;
 
-  if (png_bytep interlaceBuffer = m_reader->interlaceBuffer()) {
+  if (png_bytep imageBuffer = m_reader->imageBuffer()) {
     unsigned colorChannels = hasAlpha ? 4 : 3;
-    row = interlaceBuffer + (rowIndex * colorChannels * size().width());
+    row = imageBuffer + (rowIndex * colorChannels * size().width());
     png_progressive_combine_row(m_reader->pngPtr(), row, rowBuffer);
   }
 
+  // For non-first frames, don't write rows incrementally to the buffer, since

[scroggo_chromium, 2016/11/09 13:42:50]

This comment is no longer correct. This now applies to frames that depend on
other frames.

[joostouwerling, 2016/11/11 20:22:18]

This is now removed in the revisited patch.

+  // this may result in partial frames being displayed. Instead, write the
+  // rows in the complete() callback.
+  if (!frameShouldBeDecodedIncrementally(m_currentFrame))
+    return;
+
   // Write the decoded row pixels to the frame buffer. The repetitive
   // form of the row write loops is for speed.
-  ImageFrame::PixelData* const dstRow = buffer.getAddr(0, y);
+  ImageFrame::PixelData* const dstRow = buffer.getAddr(frameRect.x(), y);
   unsigned alphaMask = 255;
-  int width = size().width();
+  int width = frameRect.width();
 
   png_bytep srcPtr = row;
   if (hasAlpha) {
@@ -468,32 +595,120 @@ void PNGImageDecoder::rowAvailable(unsigned char* rowBuffer,
   buffer.setPixelsChanged(true);
 }
 
+bool PNGImageDecoder::frameIsCompleteAtIndex(size_t index) const {
+  // @TODO(joostouwerling): show complete frames even if a later frame fails.
+  if (failed())
+    return false;
+  if (index == 0)
+    return ImageDecoder::frameIsCompleteAtIndex(index);
+
+  // For non-first frames, the frame is considered complete if all frame data
+  // has been received. Non-first frames are reported by |m_reader| once it has
+  // parsed all data for that frame, so we can simply return if the index
+  // exists in |m_frameBufferCache| here.
+  return (index < m_frameBufferCache.size());
+}
+
+float PNGImageDecoder::frameDurationAtIndex(size_t index) const {
+  return (index < m_frameBufferCache.size()
+              ? m_frameBufferCache[index].duration()
+              : 0);
+}
+
 void PNGImageDecoder::complete() {
   if (m_frameBufferCache.isEmpty())
     return;
 
-  m_frameBufferCache[0].setStatus(ImageFrame::FrameComplete);
-}
+  // @TODO(joostouwerling) if necessary, do a check if all expected data has
+  //                       been received. This is because the IEND chunk is sent
+  //                       artificially. The necessity of this check depends on
+  //                       how libpng handles in- and overcomplete frame data.
+  ImageFrame* buffer = &m_frameBufferCache[m_currentFrame];
+
+  // The pixels for the first frame or any non-first frame with no required
+  // previous frame are already written to the framebuffer in rowAvailable.
+  if (frameShouldBeDecodedIncrementally(m_currentFrame)) {
+    m_reader->clearImageBuffer();
+    buffer->setStatus(ImageFrame::FrameComplete);
+    return;
+  }
 
-inline bool isComplete(const PNGImageDecoder* decoder) {
-  return decoder->frameIsCompleteAtIndex(0);
-}
+  // For non-first frames, the frame data was written to the image buffer in
+  // rowAvailable. Write the decoded pixels from the the image buffer to the
+  // the frame buffer.
+  png_bytep image = m_reader->imageBuffer();
 
-void PNGImageDecoder::decode(bool onlySize) {
-  if (failed())
-    return;
+  IntRect frameRect = buffer->originalFrameRect();
+  bool hasAlpha = m_reader->hasAlpha();
+  unsigned colorChannels = hasAlpha ? 4 : 3;
+  unsigned alphaMask = 255;
 
-  if (!m_reader)
-    m_reader = wrapUnique(new PNGImageReader(this, m_offset));
+  // TODO(joostouwerling): for now, this is a straight copy of the code in
+  //                       rowAvailable, except for writing multiple rows. Alpha
+  //                       blending and possible code sharing need to be added.
+  for (int y = frameRect.y(); y < frameRect.maxY();
+       ++y, image += colorChannels * size().width()) {
+    ImageFrame::PixelData* const dstRow = buffer->getAddr(frameRect.x(), y);
+    unsigned alphaMask = 255;
+    int width = frameRect.width();
+
+    png_bytep srcPtr = image;
+    if (hasAlpha) {
+      // Here we apply the color space transformation to the dst space.
+      // It does not really make sense to transform to a gamma-encoded
+      // space and then immediately after, perform a linear premultiply.
+      // Ideally we would pass kPremul_SkAlphaType to xform->apply(),
+      // instructing SkColorSpaceXform to perform the linear premultiply
+      // while the pixels are a linear space.
+      // We cannot do this because when we apply the gamma encoding after
+      // the premultiply, we will very likely end up with valid pixels
+      // where R, G, and/or B are greater than A.  The legacy drawing
+      // pipeline does not know how to handle this.
+      if (SkColorSpaceXform* xform = colorTransform()) {
+        SkColorSpaceXform::ColorFormat colorFormat =
+            SkColorSpaceXform::kRGBA_8888_ColorFormat;
+        xform->apply(colorFormat, dstRow, colorFormat, srcPtr, size().width(),
+                     kUnpremul_SkAlphaType);
+        srcPtr = (png_bytep)dstRow;
+      }
 
-  // If we couldn't decode the image but have received all the data, decoding
-  // has failed.
-  if (!m_reader->decode(*m_data, onlySize) && isAllDataReceived())
-    setFailed();
+      if (buffer->premultiplyAlpha()) {
+        for (auto *dstPixel = dstRow; dstPixel < dstRow + width;
+             dstPixel++, srcPtr += 4) {
+          buffer->setRGBAPremultiply(dstPixel, srcPtr[0], srcPtr[1], srcPtr[2],
+                                     srcPtr[3]);
+          alphaMask &= srcPtr[3];
+        }
+      } else {
+        for (auto *dstPixel = dstRow; dstPixel < dstRow + width;
+             dstPixel++, srcPtr += 4) {
+          buffer->setRGBARaw(dstPixel, srcPtr[0], srcPtr[1], srcPtr[2],
+                             srcPtr[3]);
+          alphaMask &= srcPtr[3];
+        }
+      }
+    } else {
+      for (auto *dstPixel = dstRow; dstPixel < dstRow + width;
+           dstPixel++, srcPtr += 3) {
+        buffer->setRGBARaw(dstPixel, srcPtr[0], srcPtr[1], srcPtr[2], 255);
+      }
+
+      // We'll apply the color space xform to opaque pixels after they have been
+      // written to the ImageFrame, purely because SkColorSpaceXform supports
+      // RGBA (and not RGB).
+      if (SkColorSpaceXform* xform = colorTransform()) {
+        xform->apply(xformColorFormat(), dstRow, xformColorFormat(), dstRow,
+                     size().width(), kOpaque_SkAlphaType);
+      }
+    }
+  }
+
+  if (alphaMask != 255 && !buffer->hasAlpha())
+    buffer->setHasAlpha(true);
 
-  // If decoding is done or failed, we don't need the PNGImageReader anymore.
-  if (isComplete(this) || failed())
-    m_reader.reset();
+  m_reader->clearImageBuffer();
+  buffer->setPixelsChanged(true);
+  buffer->setStatus(ImageFrame::FrameComplete);
 }
 
 }  // namespace blink