Skip memcpy() swizzles in SkPngCodec

src/codec/SkPngCodec.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.
  */
 
 #include "SkCodec.h"
 #include "SkColorTable.h"
 #include "SkPngChunkReader.h"
@@ skipping 20 matching lines @@
             override;
     SkEncodedFormat onGetEncodedFormat() const override { return kPNG_SkEncodedFormat; }
     bool onRewind() override;
     uint32_t onGetFillValue(SkColorType) const override;
 
     // Helper to set up swizzler and color table. Also calls png_read_update_info.
     Result initializeSwizzler(const SkImageInfo& requestedInfo, const Options&,
                               SkPMColor*, int* ctableCount);
     SkSampler* getSampler(bool createIfNecessary) override {
         SkASSERT(fSwizzler);
+        fInPlaceSwizzle = false;

[msarett, 2016/02/05 20:48:18]

Problem:

Here we assume that the client is calling getSampler() in order to call
setSampleSize() next (in which case we can't swizzle in place).

This is weird and unnecessarily pessimistic.

         return fSwizzler;
     }
 
     SkPngCodec(const SkImageInfo&, SkStream*, SkPngChunkReader*, png_structp, png_infop, int, int);
 
     png_structp png_ptr() { return fPng_ptr; }
     SkSwizzler* swizzler() { return fSwizzler; }
     SkSwizzler::SrcConfig srcConfig() const { return fSrcConfig; }
     int numberPasses() const { return fNumberPasses; }
+    bool inPlaceSwizzle() { return fInPlaceSwizzle; }
 
 private:
     SkAutoTUnref<SkPngChunkReader>  fPngChunkReader;
     png_structp                     fPng_ptr;
     png_infop                       fInfo_ptr;
 
     // These are stored here so they can be used both by normal decoding and scanline decoding.
     SkAutoTUnref<SkColorTable>      fColorTable;    // May be unpremul.
     SkAutoTDelete<SkSwizzler>       fSwizzler;
 
     SkSwizzler::SrcConfig           fSrcConfig;
     const int                       fNumberPasses;
     int                             fBitDepth;
+    bool                            fInPlaceSwizzle;
 
     bool decodePalette(bool premultiply, int* ctableCount);
     void destroyReadStruct();
 
     typedef SkCodec INHERITED;
 };