WIP: Implement APNG

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

Index: third_party/WebKit/Source/platform/image-decoders/png/PNGImageDecoder.h
diff --git a/third_party/WebKit/Source/platform/image-decoders/png/PNGImageDecoder.h b/third_party/WebKit/Source/platform/image-decoders/png/PNGImageDecoder.h
index dacc93828c0ce9879cd776667be3e5fb0c33aed2..d4d3e70fd165f9bd5c231aff3011ce1173095de0 100644
--- a/third_party/WebKit/Source/platform/image-decoders/png/PNGImageDecoder.h
+++ b/third_party/WebKit/Source/platform/image-decoders/png/PNGImageDecoder.h
@@ -44,26 +44,69 @@ class PLATFORM_EXPORT PNGImageDecoder final : public ImageDecoder {
                   size_t offset = 0);
   ~PNGImageDecoder() override;
 
+  enum class PNGParseQuery { PNGSizeQuery, PNGMetaDataQuery };
+
   // ImageDecoder:
   String filenameExtension() const override { return "png"; }
+  int repetitionCount() const override;
+  bool frameIsCompleteAtIndex(size_t) const override;
+  float frameDurationAtIndex(size_t) const override;
+  // Failures are handled differently, based on the image and state of the
+  // decoder:
+  //
+  // 1) When a non-animated PNG or the first frame of an animated PNG can't be
+  //    decoded or parsed, set the decoder to the failed state, because there
+  //    are no frames we can show to the client. Also set the state to failed if
+  //    a parse error occurs before any frames were received.
+  // 2) When a decoding failure occurs for non-first frames, we still want to
+  //    show earlier frames. This means the frame count needs to be adjusted.
+  // 3) When a parsing failure occurs, the frame count is adjusted to the number
+  //    of successfully parsed frames, since we can still show those.
+  //
+  // In cases 2 and 3, we have to prevent parse() from adjusting the frame
+  // count to pre-failure values by setting |m_failedWithCorrectFrames| to true.
+  bool setFailed() override;
 
   // Callbacks from libpng
   void headerAvailable();
   void rowAvailable(unsigned char* row, unsigned rowIndex, int);
   void complete();
 
+  // Additional methods used for APNG
+  void setRepetitionCount(size_t);
+
  private:
   // ImageDecoder:
-  void decodeSize() override { decode(true); }
-  void decode(size_t) override { decode(false); }
+  void decodeSize() override { parse(PNGParseQuery::PNGSizeQuery); }
+  void decode(size_t) override;
+  size_t decodeFrameCount() override;
+  void initializeNewFrame(size_t) override;
+  void clearFrameBuffer(size_t) override;
+
+  // Create an interlacing buffer when the frame is encoded with interlacing.
+  void onInitFrameBuffer(size_t) override;
 
-  // Decodes the image.  If |onlySize| is true, stops decoding after
-  // calculating the image size.  If decoding fails but there is no more
-  // data coming, sets the "decode failure" flag.
-  void decode(bool onlySize);
+  // When the disposal method of the frame is DisposeOverwritePrevious, the
+  // next frame will use the previous frame's buffer as its starting state, so
+  // we can't take over the data in that case. Before calling this method, the
+  // caller must verify that the frame exists.
+  bool canReusePreviousFrameBuffer(size_t index) const override;
+
+  void parse(PNGParseQuery);
 
   std::unique_ptr<PNGImageReader> m_reader;
-  const unsigned m_offset;
+  size_t m_frameCount;
+  size_t m_currentFrame;
+  // m_repetitionCount is set to cAnimationLoopOnce by default, so the
+  // DeferredImageDecoder takes into account that this may be an animated
+  // image, but we don't know for sure yet.
+  int m_repetitionCount;
+  bool m_hasAlphaChannel;
+  bool m_currentBufferSawAlpha;
+
+  // This flag is set to true while PNGImageReader is parsing. This is used by
+  // setFailed() to determine how to handle a failure.
+  bool m_isParsing;
 };
 
 }  // namespace blink