SkPngCodec: voidp instead of forward-declares for png.h types.

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"
 #include "SkPngChunkReader.h"
 #include "SkEncodedFormat.h"
 #include "SkImageInfo.h"
 #include "SkRefCnt.h"
 #include "SkSwizzler.h"
 
-// Instead of including png.h here, forward declare the few types we refer to.
-struct png_struct_def;
-struct png_info_def;
-typedef png_struct_def png_struct;
-typedef png_info_def png_info;
-
 class SkStream;
 
 class SkPngCodec : public SkCodec {
 public:
     static bool IsPng(const char*, size_t);
 
     // Assume IsPng was called and returned true.
     static SkCodec* NewFromStream(SkStream*, SkPngChunkReader* = NULL);
 
     virtual ~SkPngCodec();
 
 protected:
+    // We hold the png_ptr and info_ptr as voidp to avoid having to include png.h
+    // or forward declare their types here.  voidp auto-casts to the real pointer types.
+    struct voidp {
+        voidp(void* ptr) : fPtr(ptr) {}
+
+        template <typename T>
+        operator T*() const { return (T*)fPtr; }
+
+        explicit operator bool() const { return fPtr != nullptr; }
+
+        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,
                           int* colorCount);
     SkSampler* getSampler(bool createIfNecessary) override {
         SkASSERT(fSwizzler);
         return fSwizzler;
     }
     void allocateStorage();
 
     virtual int readRows(const SkImageInfo& dstInfo, void* dst, size_t rowBytes, int count,
                          int startRow) = 0;
 
     SkPngCodec(const SkEncodedInfo&, const SkImageInfo&, SkStream*, SkPngChunkReader*,
-               png_struct*, png_info*, int, int);
+               void* png_ptr, void* info_ptr, int, int);
 
-    SkAutoTUnref<SkPngChunkReader>     fPngChunkReader;
-    png_struct*                        fPng_ptr;
-    png_info*                          fInfo_ptr;
+    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:
     bool createColorTable(const SkImageInfo& dstInfo, int* ctableCount);
     void destroyReadStruct();
 
     typedef SkCodec INHERITED;
 };