Add scanline decoding to SkCodec.

Add an interface for decoding scanlines, and implement that interface
in the PNG decoder.

Use a separate method to determine whether an image that used a type
with alpha was actually opaque.

SkScanlineDecoder.h:
New interface for decoding scanlines.

SkCodec.h:
Add getScanlineDecoder.
Add a virtual function (with non-virtual caller) for determining
whether the image truly had alpha. The client can call this to
determine if the image was actually opaque if it reported having alpha.
Remove code to sneakily change the passed in alpha type.

SkCodec_libpng.*:
Split up code onGetPixels into helper functions that can be shared with
the scanline decoder.
Implement scanline decoding.
Implement onReallyHasAlpha.

SkSwizzler.*:
Add a new SrcConfig as a default, which is invalid.
Add a function for setting fDstRow directly.
Assert fDstRow is not NULL.

BUG=skia:3257

Review URL: https://codereview.chromium.org/1010903003

1 files changed, 24 insertions, 4 deletions

diff --git a/src/codec/SkCodec_libpng.h b/src/codec/SkCodec_libpng.h
index debb14b882..fa7b39d82f 100644
--- a/src/codec/SkCodec_libpng.h
+++ b/src/codec/SkCodec_libpng.h
@@ -6,15 +6,17 @@
  */
 
 #include "SkCodec.h"
+#include "SkColorTable.h"
 #include "SkEncodedFormat.h"
 #include "SkImageInfo.h"
+#include "SkRefCnt.h"
+#include "SkSwizzler.h"
 
 extern "C" {
-    // FIXME: I'd like to force all platforms to use the same decoder, but this
-    // means an extra dependency on Mac/Win.
     #include "png.h"
 }
 
+class SkScanlineDecoder;
 class SkStream;
 
 class SkPngCodec : public SkCodec {
@@ -26,12 +28,30 @@ protected:
     Result onGetPixels(const SkImageInfo&, void*, size_t, const Options&, SkPMColor*, int*)
             SK_OVERRIDE;
     SkEncodedFormat onGetEncodedFormat() const SK_OVERRIDE { return kPNG_SkEncodedFormat; }
+    SkScanlineDecoder* onGetScanlineDecoder(const SkImageInfo& dstInfo) SK_OVERRIDE;
+    bool onReallyHasAlpha() const SK_OVERRIDE { return fReallyHasAlpha; }
 private:
-    png_structp             fPng_ptr;
-    png_infop               fInfo_ptr;
+    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;
 
     SkPngCodec(const SkImageInfo&, SkStream*, png_structp, png_infop);
     ~SkPngCodec();
 
+    // Helper to set up swizzler and color table. Also calls png_read_update_info.
+    Result initializeSwizzler(const SkImageInfo& requestedInfo, void* dst,
+                              size_t rowBytes, const Options&);
+    bool decodePalette(bool premultiply);
+    void finish();
+
+    friend class SkPngScanlineDecoder;
+
     typedef SkCodec INHERITED;
 };