Add support for reading the dst pixel value in an effect. Use in a new effect for the kDarken xfer …

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 170 matching lines @@
     // DEPRECATED: call 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
         to call this with 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 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. If the function returns true then the src and dst coeffs
-        will be applied to the draw regardless of whether an effect was returned.
+        set *effect to NULL beforehand. If the function returns true and *effect is NULL then the
+        src and dst coeffs will be applied to the draw. When *effect is non-NULL the coeffs are
+        ignored.
      */
-    virtual bool asNewEffect(GrContext*, GrEffectRef** effect, Coeff* src, Coeff* dst) const;
+    virtual bool asNewEffectOrCoeff(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);
+    static bool AsNewEffectOrCoeff(SkXfermode*,
+                                   GrContext*,
+                                   GrEffectRef** effect,
+                                   Coeff* src,
+                                   Coeff* dst);
 
     SkDEVCODE(virtual void toString(SkString* str) const = 0;)
     SK_DECLARE_FLATTENABLE_REGISTRAR_GROUP()
 protected:
     SkXfermode(SkFlattenableReadBuffer& rb) : SkFlattenable(rb) {}
 
     /** The default implementation of xfer32/xfer16/xferA8 in turn call this
         method, 1 color at a time (upscaled to a SkPMColor). The default
         implmentation of this method just returns dst. If performance is
         important, your subclass should override xfer32/xfer16/xferA8 directly.
@@ skipping 43 matching lines @@
         fProc = proc;
     }
 
 private:
     SkXfermodeProc  fProc;
 
     typedef SkXfermode INHERITED;
 };
 
 #endif