Do some minor pre cleanup work before converting all xfermodes to XPs.

include/core/SkXfermode.h

 
 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #ifndef SkXfermode_DEFINED
@@ skipping 172 matching lines @@
      *  not representable as a pair of Coeffs, return false and ignore the
      *  src and dst parameters.
      */
     static bool ModeAsCoeff(Mode mode, Coeff* src, Coeff* dst);
 
     SK_ATTR_DEPRECATED("use AsMode(...)")
     static bool IsMode(const SkXfermode* xfer, Mode* mode) {
         return AsMode(xfer, mode);
     }
 
     /** A subclass may implement this factory function to work with the GPU backend. It is legal

[bsalomon, 2015/01/14 15:18:12]

Let's clean this up a bit.

"Implemented by a subclass to support use as an image filter in the GPU backend.
When used as an image filter the xfer mode blends the source color against a
background texture rather than the destination. It is implemented as a fragment
processor. This can be called with both params set to NULL to query whether it
would succeed. Otherwise, both params are required. Upon success the function
returns true and the caller owns a ref to the fragment parameter. Upon failure
false is returned and the processor param is not written to."

         to call this with all params NULL to simply test the return value. If effect is non-NULL
         then the xfermode may optionally allocate an effect to return and the caller as *effect.
         The caller will install it and own a ref to it. Since the xfermode may or may not assign
         *effect, the caller should set *effect to NULL beforehand. background specifies the
         texture to use as the background for compositing, and should be accessed in the effect's
         fragment shader. If NULL, the effect should request access to destination color
         (setWillReadDstColor()), and use that in the fragment shader (builder->dstColor()).
      */
-    // TODO: Once all custom xp's have been created the background parameter will be required here.
-    //       We will always use the XPFactory if there is no background texture and the fragment if
-    //       there is one.
-    virtual bool asFragmentProcessor(GrFragmentProcessor**, GrTexture* background = NULL) const;
+    virtual bool asFragmentProcessor(GrFragmentProcessor**, GrTexture* background) const;
 
     /** A subclass may implement this factory function to work with the GPU backend. It is legal
         to call this with xpf NULL to simply test the return value. If xpf is non-NULL then the
         xfermode may optionally allocate a factory to return to the caller as *xpf. The caller
         will install it and own a ref to it. Since the xfermode may or may not assign *xpf, the
         caller should set *xpf to NULL beforehand. XP's cannot use a background texture since they
         have no coord transforms.
      */
     virtual bool asXPFactory(GrXPFactory** xpf) const;
 
@@ skipping 24 matching lines @@
 
 private:
     enum {
         kModeCount = kLastMode + 1
     };
 
     typedef SkFlattenable INHERITED;
 };
 
 #endif