Add SkPngChunkReader.

This class allows a client of SkCodec to read chunks in the data
stream that are not recognized by libpng. This is used by Android
to specify ninepatch data.

Taken from SkImageDecoder::Peeker. Modify the name of the class
and its method to be more specific to their use. Make
SkImageDecoder::Peeker a subclass of the new class, to help stage
the change in Android.

Add a test to verify that it works.

BUG=skia:4574
BUG=skia:3257

Review URL: https://codereview.chromium.org/1040453002

3 files changed, 71 insertions, 19 deletions

diff --git a/include/codec/SkCodec.h b/include/codec/SkCodec.h
index d90fea8ced..dffab6b377 100644
--- a/include/codec/SkCodec.h
+++ b/include/codec/SkCodec.h
@@ -17,6 +17,7 @@
 #include "SkTypes.h"
 
 class SkData;
+class SkPngChunkReader;
 class SkSampler;
 
 /**
@@ -28,18 +29,24 @@ public:
      *  If this stream represents an encoded image that we know how to decode,
      *  return an SkCodec that can decode it. Otherwise return NULL.
      *
+     *  If SkPngChunkReader is not NULL, take a ref and pass it to libpng if
+     *  the image is a png.
+     *
      *  If NULL is returned, the stream is deleted immediately. Otherwise, the
      *  SkCodec takes ownership of it, and will delete it when done with it.
      */
-    static SkCodec* NewFromStream(SkStream*);
+    static SkCodec* NewFromStream(SkStream*, SkPngChunkReader* = NULL);
 
     /**
      *  If this data represents an encoded image that we know how to decode,
      *  return an SkCodec that can decode it. Otherwise return NULL.
      *
+     *  If SkPngChunkReader is not NULL, take a ref and pass it to libpng if
+     *  the image is a png.
+     *
      *  Will take a ref if it returns a codec, else will not affect the data.
      */
-    static SkCodec* NewFromData(SkData*);
+    static SkCodec* NewFromData(SkData*, SkPngChunkReader* = NULL);
 
     virtual ~SkCodec();
 
diff --git a/include/core/SkImageDecoder.h b/include/core/SkImageDecoder.h
index 144878c166..30323b59ee 100644
--- a/include/core/SkImageDecoder.h
+++ b/include/core/SkImageDecoder.h
@@ -10,11 +10,14 @@
 
 #include "SkBitmap.h"
 #include "SkImage.h"
+#include "SkPngChunkReader.h"
 #include "SkRect.h"
 #include "SkRefCnt.h"
 #include "SkTRegistry.h"
 #include "SkTypes.h"
 
+//#define SK_LEGACY_PEEKER
+
 class SkStream;
 class SkStreamRewindable;
 
@@ -126,23 +129,20 @@ public:
     */
     bool getRequireUnpremultipliedColors() const { return fRequireUnpremultipliedColors; }
 
-    /** \class Peeker
-
-        Base class for optional callbacks to retrieve meta/chunk data out of
-        an image as it is being decoded.
-    */
-    class Peeker : public SkRefCnt {
+#ifdef SK_LEGACY_PEEKER
+    // Android subclasses SkImageDecoder::Peeker, which has been changed into SkPngChunkReader.
+    // Temporarily use this class until Android can be updated to directly inherit from
+    // SkPngChunkReader.
+    class Peeker : public SkPngChunkReader {
     public:
-        /** Return true to continue decoding, or false to indicate an error, which
-            will cause the decoder to not return the image.
-        */
+        bool readChunk(const char tag[], const void* data, size_t length) final {
+            return this->peek(tag, data, length);
+        }
         virtual bool peek(const char tag[], const void* data, size_t length) = 0;
-    private:
-        typedef SkRefCnt INHERITED;
     };
-
-    Peeker* getPeeker() const { return fPeeker; }
-    Peeker* setPeeker(Peeker*);
+#endif
+    SkPngChunkReader* getPeeker() const { return fPeeker; }
+    SkPngChunkReader* setPeeker(SkPngChunkReader*);
 
     /**
      *  By default, the codec will try to comply with the "pref" colortype
@@ -229,8 +229,8 @@ public:
         to allocate the memory from a cache, volatile memory, or even from
         an existing bitmap's memory.
 
-        If a Peeker is installed via setPeeker, it may be used to peek into
-        meta data during the decode.
+        If an SkPngChunkReader is installed via setPeeker, it may be used to
+        peek into meta data during the decode.
     */
     Result decode(SkStream*, SkBitmap* bitmap, SkColorType pref, Mode);
     Result decode(SkStream* stream, SkBitmap* bitmap, Mode mode) {
@@ -350,7 +350,7 @@ protected:
     SkColorType getPrefColorType(SrcDepth, bool hasAlpha) const;
 
 private:
-    Peeker*                 fPeeker;
+    SkPngChunkReader*       fPeeker;
     SkBitmap::Allocator*    fAllocator;
     int                     fSampleSize;
     SkColorType             fDefaultPref;   // use if fUsePrefTable is false
diff --git a/include/core/SkPngChunkReader.h b/include/core/SkPngChunkReader.h
new file mode 100644
index 0000000000..f424dd8cfc
--- /dev/null
+++ b/include/core/SkPngChunkReader.h
@@ -0,0 +1,45 @@
+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkPngChunkReader_DEFINED
+#define SkPngChunkReader_DEFINED
+
+#include "SkTypes.h"
+#include "SkRefCnt.h"
+
+/**
+ *  SkPngChunkReader
+ *
+ *  Base class for optional callbacks to retrieve meta/chunk data out of a PNG
+ *  encoded image as it is being decoded.
+ *  Used by SkImageDecoder and SkCodec.
+ */
+class SkPngChunkReader : public SkRefCnt {
+public:
+    /**
+     *  This will be called by the decoder when it sees an unknown chunk.
+     *
+     *  Use by SkCodec:
+     *  Depending on the location of the unknown chunks, this callback may be
+     *  called by
+     *      - the factory (NewFromStream/NewFromData)
+     *      - getPixels
+     *      - startScanlineDecode
+     *      - the first call to getScanlines/skipScanlines
+     *  The callback may be called from a different thread (e.g. if the SkCodec
+     *  is passed to another thread), and it may be called multiple times, if
+     *  the SkCodec is used multiple times.
+     *
+     *  @param tag Name for this type of chunk.
+     *  @param data Data to be interpreted by the subclass.
+     *  @param length Number of bytes of data in the chunk.
+     *  @return true to continue decoding, or false to indicate an error, which
+     *      will cause the decoder to not return the image.
+     */
+    virtual bool readChunk(const char tag[], const void* data, size_t length) = 0;
+};
+#endif // SkPngChunkReader_DEFINED