Add subsetting to SkScaledCodec

src/codec/SkSwizzler.h

Index: src/codec/SkSwizzler.h
diff --git a/src/codec/SkSwizzler.h b/src/codec/SkSwizzler.h
index 9cd1d2092e15fb3dae89a21348bcbb5b2a1e4769..90da06549c2d1baa5eda9cb4d3bd41e29982255a 100644
--- a/src/codec/SkSwizzler.h
+++ b/src/codec/SkSwizzler.h
@@ -119,20 +119,22 @@ public:
      *  @param SrcConfig Description of the format of the source.
      *  @param dstInfo describes the destination.
      *  @param ZeroInitialized Whether dst is zero-initialized. The
-                               implementation may choose to skip writing zeroes
+     *                         implementation may choose to skip writing zeroes
      *                         if set to kYes_ZeroInitialized.
      *  @param srcInfo is the info of the source. Used to calculate the width samplesize.
-     *                  Width sampling is supported by the swizzler, by skipping pixels when 
-                        swizzling the row. Height sampling is not supported by the swizzler, 
-                        but is implemented in SkScaledCodec.
-                        Sampling in Y can be done by a client with a scanline decoder, 
-                        but sampling in X allows the swizzler to skip swizzling pixels and
-                        reading from and writing to memory.
+     *                  Width sampling is supported by the swizzler, by skipping pixels when
+     *                  swizzling the row. Height sampling is not supported by the swizzler,
+     *                  but is implemented in SkScaledCodec.
+     *                  Sampling in Y can be done by a client with a scanline decoder,
+     *                  but sampling in X allows the swizzler to skip swizzling pixels and
+     *                  reading from and writing to memory.
+     *  @param subsetLeft the left offset on the src for each row swizzle.
+     *  @param subsetWidth the width of each swizzle in destination pixels.
      *  @return A new SkSwizzler or nullptr on failure.
      */
     static SkSwizzler* CreateSwizzler(SrcConfig, const SkPMColor* ctable,
                                       const SkImageInfo& dstInfo, SkCodec::ZeroInitialized, 
-                                      const SkImageInfo& srcInfo);
+                                      const SkImageInfo& srcInfo, int subsetLeft, int subsetWidth);
     /**
      * Fill the remainder of the destination with a single color
      *
@@ -197,16 +199,14 @@ private:
 
     const RowProc       fRowProc;
     const SkPMColor*    fColorTable;      // Unowned pointer
-    const int           fDeltaSrc;        // if bitsPerPixel % 8 == 0
-                                          //     deltaSrc is bytesPerPixel
+    const int           fLeft;
+    const int           fWidth;
+    const int           fBPP;             // if bitsPerPixel % 8 == 0
+                                          //     fBPP is bytesPerPixel
                                           // else
-                                          //     deltaSrc is bitsPerPixel
-    const SkImageInfo   fDstInfo;
-    int                 fCurrY;
-    const int           fX0;              // first X coord to sample
-    const int           fSampleX;         // step between X samples
+                                          //     fBPP is bitsPerPixel
+    const int           fDeltaSrc;        // fBPP * sampleX
 
-    SkSwizzler(RowProc proc, const SkPMColor* ctable, int deltaSrc, const SkImageInfo& info, 
-               int sampleX);
+    SkSwizzler(RowProc proc, const SkPMColor* ctable, int left, int width, int bpp, int deltaSrc);
 };
 #endif // SkSwizzler_DEFINED