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 c0c9ca872b0ab94e8fb7bf03370a5c2441ca247f..43de7ca502148bf013193432a0fff5d1b8a51125 100644
--- a/third_party/WebKit/Source/platform/image-decoders/png/PNGImageDecoder.h
+++ b/third_party/WebKit/Source/platform/image-decoders/png/PNGImageDecoder.h
@@ -39,26 +39,38 @@ public:
     PNGImageDecoder(AlphaOption, GammaAndColorProfileOption, size_t maxDecodedBytes, size_t offset = 0);
     ~PNGImageDecoder() override;
 
+    enum class PNGParseQuery { PNGSizeQuery, PNGMetaDataQuery };
+
     // ImageDecoder:
     String filenameExtension() const override { return "png"; }
+    int repetitionCount() const 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);
+    // This is called by PNGImageReader when it encounters the IEND chunk
+    // while parsing PNGMetaDataQuery. If m_metaDataDecoded is true, the decoder
+    // does not need to query for meta data again.
+    void setMetaDataDecoded() { m_metaDataDecoded = true; };

[cblume, 2016/10/15 00:30:50]

These two methods are public because they get called by PNGImageReader I am
guessing?

I assume the client is not calling these.

If that is the case, maybe we can make them private and make PNGImageReader a
friend?

[scroggo_chromium, 2016/10/17 13:24:00]

A similar suggestion came up crrev.com/2045293002 (specifically here [1]). My
preference would be to leave these as public, for the following reasons:

1. Most real clients of this class don't know they have a PNGImageDecoder - they
just know it's an ImageDecoder. (I suppose they could call the public
constructor, or cast an ImageDecoder to this class, but I think that already
goes against the spirit of ImageDecoder. An exception is ICOImageDecoder, which
creates a PNGImageDecoder directly.)

2. Making the PNGImageReader a friend allows it to access *all* the internals of
PNGImageDecoder. Weighed against 1, this seems more dangerous to me.

FWIW, Google's C++ style guide [2] suggests that "friend" classes should be in
the same file. Otherwise, I don't think it pushes us strongly in one direction
or another.

[1]
https://codereview.chromium.org/2045293002/diff/260001/src/codec/SkGifCodec.h...
[2]
https://engdoc.corp.google.com/eng/doc/devguide/cpp/styleguide.shtml?cl=head#...

[cblume, 2016/10/17 17:08:16]

Okay, I agree.

I definitely agree that I dislike granting access to *all* private things. And I
like what you are saying about it not being part of the ImageDecoder interface.
Works for me. :)

+    
 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;
 
-    // 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);
+    void parse(PNGParseQuery);
 
     std::unique_ptr<PNGImageReader> m_reader;
     const unsigned m_offset;
+    bool m_metaDataDecoded;
+    size_t m_frameCount;
+    int m_repetitionCount;
 };
 
 } // namespace blink