make explicit the requirement that all colorfilters are reentrant-safe

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
 #define SkXfermode_DEFINED
 
 #include "SkFlattenable.h"
 #include "SkColor.h"
 
 class GrContext;
 class GrEffectRef;
 class GrTexture;
 class SkString;
 
 /** \class SkXfermode
 
     SkXfermode is the base class for objects that are called to implement custom

[mtklein, 2013/10/10 17:33:14]

add some stars up here?

     "transfer-modes" in the drawing pipeline. The static function Create(Modes)
     can be called to return an instance of any of the predefined subclasses as
     specified in the Modes enum. When an SkXfermode is assigned to an SkPaint,
     then objects drawn with that paint have the xfermode applied.
-*/
+
+ *  All subclasses are required to be reentrant-safe : it must be legal to share
+ *  the same instance between several threads.
+ */
 class SK_API SkXfermode : public SkFlattenable {
 public:
     SK_DECLARE_INST_COUNT(SkXfermode)
 
     SkXfermode() {}
 
     virtual void xfer32(SkPMColor dst[], const SkPMColor src[], int count,
                         const SkAlpha aa[]) const;
     virtual void xfer16(uint16_t dst[], const SkPMColor src[], int count,
                         const SkAlpha aa[]) const;
@@ skipping 240 matching lines @@
         return fProc;
     }
 
 private:
     SkXfermodeProc  fProc;
 
     typedef SkXfermode INHERITED;
 };
 
 #endif