Scanline decoding for gifs

include/codec/SkScanlineDecoder.h

Index: include/codec/SkScanlineDecoder.h
diff --git a/include/codec/SkScanlineDecoder.h b/include/codec/SkScanlineDecoder.h
index faf3e275324c1df58b813f559a91aeaf139c7b9f..2b2d76b147171d8af05542f679154a401611b719 100644
--- a/include/codec/SkScanlineDecoder.h
+++ b/include/codec/SkScanlineDecoder.h
@@ -202,7 +202,7 @@ public:
      *  kOutOfOrder_SkScanlineOrder and should be unnecessary in the case of
      *  kNone_SkScanlineOrder.
      */
-    int getY() const {
+    int getY() {
         SkASSERT(kNone_SkScanlineOrder != this->getScanlineOrder());
         return this->onGetY();
     }
@@ -231,7 +231,7 @@ protected:
     /**
      *  Most images will be kTopDown and will not need to override this function.
      */
-    virtual int onGetY() const { return fCurrScanline; }
+    virtual int onGetY() { return fCurrScanline; }

[msarett, 2015/08/24 23:20:12]

The current implementation of SkGifScanlineDecoder calls the gif iterator, so
this cannot be const.

A possible alternate solution would be to, instead of using an iterator, create
a function that takes a fCurrScanline and fHeight, and returns Y.  I'm not sure
of the difficulty/performance impact of this vs using the iterator.

[scroggo, 2015/08/27 16:35:49]

FWIW, it does seem a little odd that it is not const, but getScanlines is not
const, so the typical user will not have a const SkScanlineDecoder anyway.

[msarett, 2015/09/01 17:50:15]

Acknowledged.

 
     const SkImageInfo& dstInfo() const { return fDstInfo; }