Add subsetting to SkScaledCodec

src/codec/SkBmpCodec.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 SkBmpCodec_DEFINED
 #define SkBmpCodec_DEFINED
 
 #include "SkCodec.h"
@@ skipping 71 matching lines @@
 
     /*
      * Compute the number of colors in the color table
      */
     uint32_t computeNumColors(uint32_t numColors);
 
     /*
      * Accessors used by subclasses
      */
     uint16_t bitsPerPixel() const { return fBitsPerPixel; }
+
+    int subsetLeft() const { return fSubsetLeft; }
+    int subsetWidth() const {return fSubsetWidth; }
+
+private:
+
     SkScanlineOrder onGetScanlineOrder() const override { return fRowOrder; }
 
     /*
      * To be overriden by bmp subclasses, which provide unique implementations.
      * Performs subclass specific setup.
      *
      * @param dstInfo         Contains output information.  Height specifies
      *                        the total number of rows that will be decoded.
      * @param options         Additonal options to pass to the decoder.
      * @param inputColorPtr   Client-provided memory for a color table.  Must
      *                        be enough for 256 colors.  This will be
      *                        populated with colors if the encoded image uses
      *                        a color table.
      * @param inputColorCount If the encoded image uses a color table, this
      *                        will be set to the number of colors in the
      *                        color table.
      */
     virtual SkCodec::Result prepareToDecode(const SkImageInfo& dstInfo,
             const SkCodec::Options& options, SkPMColor inputColorPtr[],
             int* inputColorCount) = 0;
 
-private:
-
     /*
      * Creates a bmp decoder
      * Reads enough of the stream to determine the image format
      */
     static SkCodec* NewFromStream(SkStream*, bool inIco);
 
     /*
      * Decodes the next dstInfo.height() lines.
      *
      * onGetPixels() uses this for full image decodes.
      * SkScaledCodec::onGetPixels() uses the scanline decoder to call this with
      * dstInfo.height() = 1, in order to implement sampling.
      * A potential future use is to allow the caller to decode a subset of the
      * lines in the image.
      *
      * @param dstInfo     Contains output information.  Height specifies the
      *                    number of rows to decode at this time.
      * @param dst         Memory location to store output pixels
      * @param dstRowBytes Bytes in a row of the destination
      * @return            Number of rows successfully decoded
      */
     virtual int decodeRows(const SkImageInfo& dstInfo, void* dst, size_t dstRowBytes,
             const Options& opts) = 0;
 
     Result onStartScanlineDecode(const SkImageInfo& dstInfo, const SkCodec::Options&,
-            SkPMColor inputColorPtr[], int* inputColorCount) override;
+            SkPMColor inputColorPtr[], int* inputColorCount, int subsetLeft, int subsetWidth)
+            override;
 
     int onGetScanlines(void* dst, int count, size_t rowBytes) override;
 
     // TODO(msarett): Override default skipping with something more clever.
 
     const uint16_t          fBitsPerPixel;
+    int                     fSubsetLeft;
+    int                     fSubsetWidth;
     const SkScanlineOrder   fRowOrder;
 
     typedef SkCodec INHERITED;
 };
 
 #endif