Add interface to SkXfermode to return a GrEffect and blend coeffs.

include/core/SkXfermode.h

Index: include/core/SkXfermode.h
===================================================================
--- include/core/SkXfermode.h	(revision 8410)
+++ include/core/SkXfermode.h	(working copy)
@@ -13,6 +13,8 @@
 #include "SkFlattenable.h"
 #include "SkColor.h"
 
+class GrContext;
+class GrEffectRef;
 class SkString;
 
 /** \class SkXfermode
@@ -74,7 +76,7 @@
 
     /**
      *  The same as calling xfermode->asCoeff(..), except that this also checks
-     *  if the xfermode is NULL, and if so, treats its as kSrcOver_Mode.
+     *  if the xfermode is NULL, and if so, treats it as kSrcOver_Mode.
      */
     static bool AsCoeff(const SkXfermode*, Coeff* src, Coeff* dst);
 
@@ -136,7 +138,7 @@
 
     /**
      *  The same as calling xfermode->asMode(mode), except that this also checks
-     *  if the xfermode is NULL, and if so, treats its as kSrcOver_Mode.
+     *  if the xfermode is NULL, and if so, treats it as kSrcOver_Mode.
      */
     static bool AsMode(const SkXfermode*, Mode* mode);
 
@@ -181,6 +183,21 @@
         return AsMode(xfer, mode);
     }
 
+    /** A subclass may implement this factory function to work with the GPU backend. It is legal

[robertphillips, 2013/03/27 18:12:09]

will -> with

[bsalomon, 2013/03/27 18:39:42]

Done.

+        to call this will all but the context param NULL to simply test the return value. effect,
+        src, and dst must all be NULL or all non-NULL. If effect is non-NULL before this function
+        is called then the xfermode may optionally allocate an effect to return and the caller will
+        install it and own a ref to it. If the function returns true then the src and dst coeffs
+        will be applied to the draw.
+     */
+    virtual bool asNewEffect(GrContext*, GrEffectRef** effect, Coeff* src, Coeff* dst) const;
+
+    /**
+     *  The same as calling xfermode->asNewEffect(...), except that this also checks if the xfermode
+     *  is NULL, and if so, treats it as kSrcOver_Mode.
+     */
+    static bool AsNewEffect(SkXfermode*, GrContext*, GrEffectRef** effect, Coeff* src, Coeff* dst);
+
     SkDEVCODE(virtual void toString(SkString* str) const = 0;)
     SK_DECLARE_FLATTENABLE_REGISTRAR_GROUP()
 protected: