Add XferProcessor factory in GrPaint and GrDrawState.

include/core/SkXfermode.h

Index: include/core/SkXfermode.h
diff --git a/include/core/SkXfermode.h b/include/core/SkXfermode.h
index bedcc2456976713cdd7159d3dac16782f038ada9..6db7119973e2eb7feda126fef7e217d9b4165e4f 100644
--- a/include/core/SkXfermode.h
+++ b/include/core/SkXfermode.h
@@ -15,6 +15,7 @@
 
 class GrFragmentProcessor;
 class GrTexture;
+class GrXPFactory;
 class SkString;
 
 /** \class SkXfermode
@@ -200,14 +201,24 @@ public:
      */
     virtual bool asFragmentProcessor(GrFragmentProcessor**, GrTexture* background = NULL) const;
 
-    /** Returns true if the xfermode can be expressed as coeffs (src, dst), or as an effect
-        (effect). This helper calls the asCoeff() and asFragmentProcessor() virtuals. If the
-        xfermode is NULL, it is treated as kSrcOver_Mode. It is legal to call this with all params
-        NULL to simply test the return value.  effect, src, and dst must all be NULL or all
-        non-NULL.
+    /** 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 effect is non-NULL

[bsalomon, 2014/11/26 21:02:44]

Use "factory" instead of "effect"? I don't really follow the comment.

[egdaniel, 2014/12/01 18:18:24]

Done.

+        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. XP's cannot use a background
+        texture since they have no coord transforms.
+     */
+    virtual bool asXPFactory(GrXPFactory** xpf) const;
+
+    /** Returns true if the xfermode can be expressed as coeffs (src, dst), a xfer processor
+        (returned as xpFactory), or a fragment processor. This helper calls the asCoeff(),
+        asXPFactor(), and asFragmentProcessor() virtuals. If the xfermode is NULL, it is treated
+        as kSrcOver_Mode. It is legal to call this with all params NULL to simply test the return
+        value.  effect, src, and dst must all be NULL or all non-NULL.
      */
-    static bool asFragmentProcessorOrCoeff(SkXfermode*, GrFragmentProcessor**, Coeff* src,
-                                           Coeff* dst, GrTexture* background = NULL);
+    static bool asFragmentProcessorOrXPFactoryOrCoeff(SkXfermode*, GrFragmentProcessor**,

[bsalomon, 2014/11/26 21:02:44]

Yikes! I guess its just temporary. Do we really need coeff if we have
porter-duff xpf?

static member functions are capitalized.

[egdaniel, 2014/12/01 18:18:24]

Better for now?

+                                                      GrXPFactory**, Coeff* src, Coeff* dst,
+                                                      GrTexture* background = NULL);
 
     SK_TO_STRING_PUREVIRT()
     SK_DECLARE_FLATTENABLE_REGISTRAR_GROUP()