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 7ce6aa0faf83c7c6d2ece1ce6cc94ea5d07f7427..141540931e38004948f7807d187f25c89d363595 100644
--- a/third_party/WebKit/Source/platform/image-decoders/png/PNGImageDecoder.h
+++ b/third_party/WebKit/Source/platform/image-decoders/png/PNGImageDecoder.h
@@ -43,26 +43,74 @@ 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;
+  size_t clearCacheExceptFrame(size_t) 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

[scroggo_chromium, 2016/11/29 16:30:52]

nit: these commas are unnecessary

[joostouwerling, 2016/12/02 16:08:42]

Done.

+  //    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

[scroggo_chromium, 2016/11/29 16:30:52]

For a partial first frame (or partial only frame, for non-animated), we *could*
show what we've decoded so far, but I think showing nothing matches the current
behavior?

[joostouwerling, 2016/12/02 16:08:42]

Yes, the current behavior is that any failure invalidates the decoder. You can
stretch your idea even further and show *any* partial frame, but I think it is
safer to not do this. I would guess web authors never intend to show partial
frames, and we can only guess why the image decoding failed, so I would err on
the safe side and not show any frame that can't be completely decoded.

+  //    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;
 
-  // 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);
+  bool initFrameBuffer(size_t);
+  void parse(PNGParseQuery);
+  // Used by clearCacheExceptFrame if two frames need to be kept in cache.
+  size_t clearCacheExceptTwoFrames(size_t, size_t);
 
   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;
+  // This flag is set to true if the color space has been set. This is used to
+  // prevent setting the color space in each frame, which is unnecessary since
+  // frames don't have their own color space.
+  bool m_colorSpaceSet;
+  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;
+  // This flag is set to true when a failure has occured, but there are earlier
+  // frames that can still be shown. In that case, the frame count is lowered.
+  // This flag prevents from calling parse() again, which could change the frame
+  // count back to the pre-failure value.
+  bool m_failedWithCorrectFrames;
 };
 
 }  // namespace blink