Make swizzler optional for SkPngCodec, refactor xforms

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 "SkColorSpaceXform.h"
 #include "SkColorTable.h"
@@ skipping 28 matching lines @@
         void* fPtr;
     };
 
     Result onGetPixels(const SkImageInfo&, void*, size_t, const Options&, SkPMColor*, int*, int*)
             override;
     SkEncodedFormat onGetEncodedFormat() const override { return kPNG_SkEncodedFormat; }
     bool onRewind() override;
     uint32_t onGetFillValue(SkColorType) const override;
 
     // Helper to set up swizzler, color xforms, and color table. Also calls png_read_update_info.
-    bool initializeXforms(const SkImageInfo& requestedInfo, const Options&, SkPMColor* colorPtr,
+    bool initializeXforms(const SkImageInfo& dstInfo, const Options&, SkPMColor* colorPtr,
                           int* colorCount);
-    SkSampler* getSampler(bool createIfNecessary) override {
-        SkASSERT(fSwizzler);
-        return fSwizzler;
-    }
-    void allocateStorage();
+    void initializeSwizzler(const SkImageInfo& dstInfo, const Options&);
+    SkSampler* getSampler(bool createIfNecessary) override;
+    void allocateStorage(const SkImageInfo& dstInfo);
+    void applyXformRow(void* dst, const void* src, SkColorType, SkAlphaType, int width);
 
     virtual int readRows(const SkImageInfo& dstInfo, void* dst, size_t rowBytes, int count,
                          int startRow) = 0;
 
     SkPngCodec(const SkEncodedInfo&, const SkImageInfo&, SkStream*, SkPngChunkReader*,
                void* png_ptr, void* info_ptr, int, int);
 
     SkAutoTUnref<SkPngChunkReader> fPngChunkReader;
     voidp                          fPng_ptr;
     voidp                          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;
     std::unique_ptr<SkColorSpaceXform> fColorXform;
     SkAutoTMalloc<uint8_t>             fStorage;
     uint8_t*                           fSwizzlerSrcRow;
     uint32_t*                          fColorXformSrcRow;
     size_t                             fSrcRowBytes;
 
     const int                          fNumberPasses;
     int                                fBitDepth;
 
 private:
+
+    enum XformMode {
+        // Requires only a swizzle pass.
+        kSwizzleOnly_XformMode,
+
+        // Requires only a color xform pass.
+        kColorOnly_XformMode,
+
+        // Requires a swizzle and a color xform.
+        kSwizzleColor_XformMode,
+    };
+
     bool createColorTable(const SkImageInfo& dstInfo, int* ctableCount);
     void destroyReadStruct();
 
+    XformMode fXformMode;
+
     typedef SkCodec INHERITED;
 };