Merge SkCodec with SkScanlineDecoder

src/codec/SkCodec_libpng.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 "SkEncodedFormat.h"
@@ skipping 18 matching lines @@
     static SkCodec* NewFromStream(SkStream*);
     static SkScanlineDecoder* NewSDFromStream(SkStream*);
 
     virtual ~SkPngCodec();
 
 protected:
     Result onGetPixels(const SkImageInfo&, void*, size_t, const Options&, SkPMColor*, int*)
             override;
     SkEncodedFormat onGetEncodedFormat() const override { return kPNG_SkEncodedFormat; }
     bool onRewind() override;
-    bool onReallyHasAlpha() const override { return fReallyHasAlpha; }
+    bool onReallyHasAlpha() const final;
+
+    // Helper to set up swizzler and color table. Also calls png_read_update_info.
+    Result initializeSwizzler(const SkImageInfo& requestedInfo, const Options&,
+                              SkPMColor*, int* ctableCount);
+
+    SkPngCodec(const SkImageInfo&, SkStream*, png_structp, png_infop, int, int);
+
+    png_structp png_ptr() { return fPng_ptr; }
+    // FIXME: I think the subclass does not need this.
+    //png_infop info_ptr() { return fInfo_ptr; }

[scroggo, 2015/09/25 16:07:50]

Will remove in next patch set.

+    SkSwizzler* swizzler() { return fSwizzler; }
+    SkSwizzler::SrcConfig srcConfig() const { return fSrcConfig; }
+    int numberPasses() const { return fNumberPasses; }
+
+    enum AlphaState {

[msarett, 2015/09/28 14:48:50]

I think this is good.

Not in this CL, but maybe in the future, we will want to consider sharing this
with other codecs that might benefit this optimization.

[scroggo, 2015/09/28 16:01:52]

Yeah, no other codecs currently do any checking, but I agree it would make sense
for them to share if and when they do.

+        // This class has done no decoding, or threw away its knowledge (in
+        // scanline decodes).
+        kUnknown_AlphaState,
+        // This class found the image (possibly partial, in the case of a
+        // scanline decode) to be opaque.
+        kOpaque_AlphaState,
+        // Ths class found the image to have alpha.
+        kHasAlpha_AlphaState,
+    };
+
+    virtual AlphaState alphaInScanlineDecode() const = 0;
 
 private:
     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;
-    int                         fNumberPasses;
-    bool                        fReallyHasAlpha;
+    const int                   fNumberPasses;
     int                         fBitDepth;
 
-    SkPngCodec(const SkImageInfo&, SkStream*, png_structp, png_infop, int);
-
-    // Helper to set up swizzler and color table. Also calls png_read_update_info.
-    Result initializeSwizzler(const SkImageInfo& requestedInfo, const Options&,
-                              SkPMColor*, int* ctableCount);
+    AlphaState                  fAlphaState;
 
     bool decodePalette(bool premultiply, int* ctableCount);
     void destroyReadStruct();
 
-    friend class SkPngScanlineDecoder;
-    friend class SkPngInterlacedScanlineDecoder;
-
     typedef SkCodec INHERITED;
 };