Add subsetting to SkScaledCodec

src/codec/SkSwizzler.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkSwizzler_DEFINED
 #define SkSwizzler_DEFINED
 
@@ skipping 101 matching lines @@
     static int BytesPerPixel(SrcConfig sc) {
         SkASSERT(SkIsAlign8(BitsPerPixel(sc)));
         return BitsPerPixel(sc) >> 3;
     }
 
     /**
      *  Create a new SkSwizzler.
      *  @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
      *
      * @param fillDst
      * The destination row to fill from.
      *
      * @param fillInfo
      * Contains the width of the rows to fill.
      * Contains the number of rows to fill.
      * Contains the color type of the rows to fill.
@@ skipping 44 matching lines @@
      *  @param offset The offset before the first pixel to sample.
                         Is in bytes or bits based on what deltaSrc is in.
      */
     typedef ResultAlpha (*RowProc)(void* SK_RESTRICT dstRow,
                                    const uint8_t* SK_RESTRICT src,
                                    int dstWidth, int bpp, int deltaSrc, int offset,
                                    const SkPMColor ctable[]);
 
     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