Add scanline decoding to SkCodec.

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
 
 #include "SkTypes.h"
 #include "SkColor.h"
 #include "SkImageInfo.h"
 
 class SkSwizzler : public SkNoncopyable {
 public:
     /**
      *  Enum describing the config of the source data.
      */
     enum SrcConfig {
+        kUnknown,  // Invalid type.
         kGray,  // 1 byte per pixel
         kIndex, // 1 byte per pixel
         kRGB,   // 3 bytes per pixel
         kRGBX,  // 4 byes per pixel (ignore 4th)
         kRGBA,  // 4 bytes per pixel
         kRGB_565 // 2 bytes per pixel
     };
 
     static int BytesPerPixel(SrcConfig sc) {
         switch (sc) {
@@ skipping 26 matching lines @@
      */
     static SkSwizzler* CreateSwizzler(SrcConfig sc, const SkPMColor* ctable,
                                       const SkImageInfo& info, void* dst,
                                       size_t dstRowBytes, bool skipZeroes);
     /**
      *  Swizzle the next line. Call height times, once for each row of source.
      *  @param src The next row of the source data.
      *  @return Whether the row had non-opaque alpha.
      */
     bool next(const uint8_t* SK_RESTRICT src);
+
+    /**
+     *  Update the destination row.
+     *
+     *  Typically this is done by next, but for a client that wants to manually
+     *  modify the destination row (for example, for decoding scanline one at a
+     *  time) they can call this before each call to next.
+     *  TODO: Maybe replace this with a version of next which allows supplying the
+     *  destination?
+     */
+    void setDstRow(void* dst) { fDstRow = dst; }
 private:
     /**
      *  Method for converting raw data to Skia pixels.
      *  @param dstRow Row in which to write the resulting pixels.
      *  @param src Row of src data, in format specified by SrcConfig
      *  @param width Width in pixels
      *  @param bpp bytes per pixel of the source.
      *  @param y Line of source.
      *  @param ctable Colors (used for kIndex source).
      */
     typedef bool (*RowProc)(void* SK_RESTRICT dstRow,
                             const uint8_t* SK_RESTRICT src,
                             int width, int bpp, int y,
                             const SkPMColor ctable[]);
 
     const RowProc       fRowProc;
     const SkPMColor*    fColorTable;    // Unowned pointer
     const int           fSrcPixelSize;
     const SkImageInfo   fDstInfo;
     void*               fDstRow;
     const size_t        fDstRowBytes;
     int                 fCurrY;
 
     SkSwizzler(RowProc proc, const SkPMColor* ctable, int srcBpp,
                const SkImageInfo& info, void* dst, size_t rowBytes);
 
 };
 #endif // SkSwizzler_DEFINED