Add a SkPixelSerializer SkImage encode variant

include/core/SkImage.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkImage_DEFINED
 #define SkImage_DEFINED
 
 #include "SkFilterQuality.h"
 #include "SkImageInfo.h"
 #include "SkImageEncoder.h"
 #include "SkRefCnt.h"
 #include "SkScalar.h"
 #include "SkShader.h"
 
 class SkData;
 class SkCanvas;
 class SkColorTable;
 class SkImageGenerator;
 class SkPaint;
 class SkPicture;
+class SkPixelSerializer;
 class SkString;
 class SkSurface;
 class SkSurfaceProps;
 class GrContext;
 class GrTexture;
 
 /**
  *  SkImage is an abstraction for drawing a rectagle of pixels, though the
  *  particular type of image could be actually storing its data on the GPU, or
  *  as drawing commands (picture or PDF or otherwise), ready to be played back
@@ skipping 175 matching lines @@
      *  - If srcR does not intersect the image bounds.
      *  - If the requested colortype/alphatype cannot be converted from the image's types.
      */
     bool readPixels(const SkImageInfo& dstInfo, void* dstPixels, size_t dstRowBytes,
                     int srcX, int srcY) const;
 
     bool readPixels(const SkPixmap& dst, int srcX, int srcY) const;
 
     /**
      *  Encode the image's pixels and return the result as a new SkData, which
      *  the caller must manage (i.e. call unref() when they are done).

[reed1, 2015/09/03 02:36:13]

// Note: this will attempt to encode the image's pixels in the specified format,
even if the image returns a data from refEncoded(). That data will be ignored.

[f(malita), 2015/09/03 14:10:27]

Done.

      *
      *  If the image type cannot be encoded, or the requested encoder type is
      *  not supported, this will return NULL.
      */
     SkData* encode(SkImageEncoder::Type, int quality) const;
 
-    SkData* encode() const {
-        return this->encode(SkImageEncoder::kPNG_Type, 100);
-    }
+    /**
+     *  Encode the image's pixels using an optional SkPixelSerializer, and return the result
+     *  as a caller-managed SkData.
+     *
+     *  If the serializer is NULL, a default PNG encoder (with quality == 100) will be used.

[reed1, 2015/09/03 02:36:13]

How about this as a way to organize this wackiness:

- This attempts to return the image as an encoded (compressed) data.
- If the image already has itself in that form (i.e. refEncoded() returns a
data), we return that.
- Else we try to encode the image into PNG.

However, if the caller passes a pixel-serializer, then it can change this
behavior:
- if the image returns data from refEncoded(), that is passed to the serializer,
which can reject it (e.g. that format may not be supported by the intended
recipient).
- if we need to encode/compress the raw pixels, the serializer may perform that,
and return the data in any format it chooses.

Actually I think mine is also confusing. Anyway, I do want us to be explicit
about the contract (e.g. order of what we check when), but wording it is clearly
hard.

If there is a serializer, we completely defer to it. If it fails, we will fail
(return null).

If there is no 

[f(malita), 2015/09/03 14:10:27]

(this looks truncated, did you have more text which didn't post?)

Yeah, describing the behavior seems tricky.  Always a bad sign :)

How about we focus on the serializer-present flow, and then describe the
default-serializer (instead of a separate serializer-missing flow)?

Updated, but don't feel strongly and at this point I'll just past whatever you
prefer.

+     *
+     *  This method may return exising encoded data (from refEncoded) if it passes the
+     *  serializer's useEncodedData() test, or the serializer itself is NULL.
+     */
+    SkData* encode(SkPixelSerializer* = nullptr) const;
 
     /**
      *  If the image already has its contents in encoded form (e.g. PNG or JPEG), return a ref
      *  to that data (which the caller must call unref() on). The caller is responsible for calling
      *  unref on the data when they are done.
      *
      *  If the image does not already has its contents in encoded form, return NULL.
      *
      *  Note: to force the image to return its contents as encoded data, try calling encode(...).
      */
@@ skipping 60 matching lines @@
 
 private:
     const int       fWidth;
     const int       fHeight;
     const uint32_t  fUniqueID;
 
     typedef SkRefCnt INHERITED;
 };
 
 #endif