Scanline decoding for gifs

src/codec/SkCodecPriv.h

Index: src/codec/SkCodecPriv.h
diff --git a/src/codec/SkCodecPriv.h b/src/codec/SkCodecPriv.h
index 726074195daf23d787c0187520baa9a4a97e1e86..2769cec1cd4025f15611d4c9e5d53e65cb2eb47b 100644
--- a/src/codec/SkCodecPriv.h
+++ b/src/codec/SkCodecPriv.h
@@ -31,6 +31,17 @@
     SkSwizzler::GetResult(zeroAlpha, maxAlpha);
 
 /*
+ * returns a scaled dimension based on the original dimension and the sampleSize
+ * NOTE: we round down here for scaled dimension to match the behavior of SkImageDecoder
+ */
+static int get_scaled_dimension(int srcDimension, int sampleSize) {

[scroggo, 2015/09/02 22:45:48]

It seems weird to me that we need this for gif, but did not need it for others.
Any idea why?

[msarett, 2015/09/03 17:13:30]

We need it for gif because each image frame in a gif may have different
dimensions than the image size specified in the header.  And we need to know the
scaled size of the "image frame".

We actually know the frameDims in ReadHeader (now that I have moved
DGifGetImageDesc() to the header), but I don't think it makes sense to make it
visible outside of SkGifCodec.

+    if (sampleSize > srcDimension) {
+        return 1;
+    }
+    return srcDimension / sampleSize;
+}
+
+/*
  * Returns the first coordinate that we will keep during a scaled decode.
  * The output can be interpreted as an x-coordinate or a y-coordinate.
  *
@@ -137,7 +148,7 @@ static inline void copy_color_table(const SkImageInfo& dstInfo, SkColorTable* co
         SkASSERT(nullptr != inputColorPtr);
         SkASSERT(nullptr != inputColorCount);
         SkASSERT(nullptr != colorTable);
-        memcpy(inputColorPtr, colorTable->readColors(), *inputColorCount * 4);
+        memcpy(inputColorPtr, colorTable->readColors(), *inputColorCount * sizeof(SkPMColor));
     }
 }