move compose-shader into base-class as factory

include/core/SkShader.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 SkShader_DEFINED
 #define SkShader_DEFINED
 
@@ skipping 305 matching lines @@
      *  Return a shader that will apply the specified localMatrix to this shader.
      *  The specified matrix will be applied before any matrix associated with this shader.
      */
     SkShader* newWithLocalMatrix(const SkMatrix&) const;
 
     /**
      *  Create a new shader that produces the same colors as invoking this shader and then applying
      *  the colorfilter.
      */
     SkShader* newWithColorFilter(SkColorFilter*) const;
-    
+
     //////////////////////////////////////////////////////////////////////////
     //  Factory methods for stock shaders
     
     /**
      *  Call this to create a new "empty" shader, that will not draw anything.
      */
     static SkShader* CreateEmptyShader();
 
     /**
      *  Call this to create a new shader that just draws the specified color. This should always
      *  draw the same as a paint with this color (and no shader).
      */
     static SkShader* CreateColorShader(SkColor);
 
+    static SkShader* CreateComposeShader(SkShader* dst, SkShader* src, SkXfermode::Mode);
+
+    /**
+     *  Create a new compose shader, given shaders dst, src, and a combining xfermode mode.
+     *  The xfermode is called with the output of the two shaders, and its output is returned.
+     *  If xfer is null, SkXfermode::kSrcOver_Mode is assumed.
+     *
+     *  Ownership of the shaders, and the xfermode if not null, is not transfered, so the caller
+     *  is still responsible for managing its reference-count for those objects.
+     */
+    static SkShader* CreateComposeShader(SkShader* dst, SkShader* src, SkXfermode* xfer);
+
     /** Call this to create a new shader that will draw with the specified bitmap.
      *
      *  If the bitmap cannot be used (e.g. has no pixels, or its dimensions
      *  exceed implementation limits (currently at 64K - 1)) then SkEmptyShader
      *  may be returned.
      *
      *  If the src is kA8_Config then that mask will be colorized using the color on
      *  the paint.
      *
      *  @param src  The bitmap to use inside the shader
@@ skipping 63 matching lines @@
     SkMatrix fLocalMatrix;
 
     // So the SkLocalMatrixShader can whack fLocalMatrix in its SkReadBuffer constructor.
     friend class SkLocalMatrixShader;
     friend class SkBitmapProcShader;    // for computeTotalInverse()
 
     typedef SkFlattenable INHERITED;
 };
 
 #endif