change pixel-serializer to support reencoding existing data

include/core/SkPixelSerializer.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkPixelSerializer_DEFINED
 #define SkPixelSerializer_DEFINED
 
+#include "SkData.h"
+#include "SkPixmap.h"
 #include "SkRefCnt.h"
 
-class SkData;
 struct SkImageInfo;
 
 /**
  *  Interface for serializing pixels, e.g. SkBitmaps in an SkPicture.
  */
 class SkPixelSerializer : public SkRefCnt {
 public:
-    virtual ~SkPixelSerializer() {}
-
     /**
-     *  Call to determine if the client wants to serialize the encoded data. If
-     *  false, serialize another version (e.g. the result of encodePixels).
+     *  Call to determine if the client wants to serialize the encoded data.
+     *
+     *  If the encoded data is can be re-encoded (or taken as is), this returns a ref to a data
+     *  with the result, which the caller must unref() when they are through. The returned
+     *  data may be the same as the input, or it may be different, but either way the caller is
+     *  responsible for calling unref() on it.
+     *
+     *  If the encoded data is not acceptable to this pixel serializer, this returns NULL.
      */
-    bool useEncodedData(const void* data, size_t len) {
-        return this->onUseEncodedData(data, len);
-    }
+    SkData* reencodeData(SkData* encoded);
 
     /**
      *  Call to get the client's version of encoding these pixels. If it
      *  returns NULL, serialize the raw pixels.
      */
-    SkData* encodePixels(const SkImageInfo& info, const void* pixels, size_t rowBytes) {
-        return this->onEncodePixels(info, pixels, rowBytes);
+    SkData* encodePixels(const SkImageInfo& info, const void* pixels, size_t rowBytes);
+
+    /**
+     *  Call to get the client's version of encoding these pixels. If it
+     *  returns NULL, serialize the raw pixels.
+     */
+    SkData* encodePixels(const SkPixmap& pixmap);
+    
+protected:
+    // DEPRECATED -- this is no longer called, so remove from your subclasses!
+    virtual bool onUseEncodedData(const void*, size_t) { return true; }
+
+    virtual SkData* onReencodeData(SkData* encoded) {
+        return SkRef(encoded);
     }
 
-protected:
-    /**
-     *  Return true if you want to serialize the encoded data, false if you want
-     *  another version serialized (e.g. the result of encodePixels).
-     */
-    virtual bool onUseEncodedData(const void* data, size_t len) = 0;
-
-    /**
-     *  If you want to encode these pixels, return the encoded data as an SkData
-     *  Return null if you want to serialize the raw pixels.
-     */
     virtual SkData* onEncodePixels(const SkImageInfo&, const void* pixels, size_t rowBytes) = 0;
 };
 #endif // SkPixelSerializer_DEFINED