Scanline decoding for gifs

src/codec/SkCodec_libgif.h

Index: src/codec/SkCodec_libgif.h
diff --git a/src/codec/SkCodec_libgif.h b/src/codec/SkCodec_libgif.h
index 109020b5cf6c06c2f774fcd97f925e383cef4e6e..e918eb03d6a99ff4666b4846c7c807d2cf33c3b8 100644
--- a/src/codec/SkCodec_libgif.h
+++ b/src/codec/SkCodec_libgif.h
@@ -6,7 +6,10 @@
  */
 
 #include "SkCodec.h"
+#include "SkColorTable.h"
 #include "SkImageInfo.h"
+#include "SkScanlineDecoder.h"
+#include "SkSwizzler.h"
 
 #include "gif_lib.h"
 
@@ -30,6 +33,7 @@ public:
      */
     static SkCodec* NewFromStream(SkStream*);
     
+    static SkScanlineDecoder* NewSDFromStream(SkStream* stream);
 
 protected:
 
@@ -52,10 +56,11 @@ protected:
      * Ownership is unchanged when we returned a gifOut.
      *
      */
-    static bool ReadHeader(SkStream* stream, SkCodec** codecOut, GifFileType** gifOut);
+    static bool ReadHeader(SkStream* stream, SkCodec** codecOut,
+            GifFileType** gifOut);
 
     /*
-     * Initiates the gif decode
+     * Performs the full gif decode
      */
     Result onGetPixels(const SkImageInfo&, void*, size_t, const Options&,
             SkPMColor*, int32_t*) override;
@@ -69,6 +74,52 @@ protected:
 private:
 
     /*
+     * A gif can contain multiple image frames.  We will only decode the first
+     * frame.  This function reads up to the first image frame, processing
+     * transparency and/or animation information that comes before the image
+     * data.
+     *
+     * @param transIndex This call will set the transparent index based on the
+     *                   extension data.
+     */
+     SkCodec::Result readUpToFirstImage(uint32_t* transIndex);
+
+     /*
+      * A gif may contain many image frames, all of different sizes.
+      * This function checks if the frame dimensions are valid and corrects
+      * them if necessary.  It then sets fFrameDims to the corrected
+      * dimensions.
+      *
+      * @param desc The image frame descriptor
+      */
+     bool setFrameDimensions(const GifImageDesc& desc);
+
+    /*
+     * Initializes the color table that we will use for decoding.
+     * Sets inputColorCount to 256.  Since gifs always contain 8-bit indices,

[scroggo, 2015/08/27 16:35:50]

It seems weird that we always set this parameter to 256. Do we need that to be
in this function? I guess all places where we need to return this to the caller
share this function? In that case, maybe we should go all the way, and have this
function also call copy_color_table?

[msarett, 2015/09/01 18:03:59]

Sorry forgot this comment.  Moving copy_color_table into initializeColorTable,
which I think makes sense.

+     * we need a 256 entry color table to ensure that indexing is always in
+     * bounds.

[msarett, 2015/08/24 23:20:13]

Will improve this comment.

+     */
+    void initializeColorTable(int* inputColorCount, uint32_t transIndex);
+
+    /*
+     * Initializes the swizzler.
+     *
+     * @param dstInfo  Output image information.  Dimensions may have been
+     *                 adjusted if the image frame size does not match the size
+     *                 indicated in the header.
+     * @param zeroInit Indicates if destination memory is zero initialized.
+     */
+    SkCodec::Result initializeSwizzler(const SkImageInfo& dstInfo,
+            ZeroInitialized zeroInit);
+
+    /*
+     * @return kSuccess if the read is successful and kIncompleteInput is the

[scroggo, 2015/08/27 16:35:50]

if*

[msarett, 2015/09/01 17:50:16]

Done.

+     *         read fails.
+     */
+    SkCodec::Result readRow();
+
+    /*
      * This function cleans up the gif object after the decode completes
      * It is used in a SkAutoTCallIProc template
      */
@@ -92,6 +143,14 @@ private:
     SkGifCodec(const SkImageInfo& srcInfo, SkStream* stream, GifFileType* gif);
 
     SkAutoTCallVProc<GifFileType, CloseGif> fGif; // owned
+    SkIRect                                 fFrameDims;
+    uint32_t                                fFillIndex;
+    bool                                    fFrameIsSubset;
+    SkAutoTDelete<SkSwizzler>               fSwizzler;
+    SkAutoTUnref<SkColorTable>              fColorTable;
+    SkAutoTDeleteArray<uint8_t>             fSrcBuffer;
+
+    friend class SkGifScanlineDecoder;
 
     typedef SkCodec INHERITED;
 };