Extract most of the mutable state of SkShader into a separate Context object.

include/core/SkComposeShader.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 SkComposeShader_DEFINED
@@ skipping 16 matching lines @@
         "dst", and the result of from shader B as its "src".
         mode->xfer32(sA_result, sB_result, ...)
         @param shaderA  The colors from this shader are seen as the "dst" by the xfermode
         @param shaderB  The colors from this shader are seen as the "src" by the xfermode
         @param mode     The xfermode that combines the colors from the two shaders. If mode
                         is null, then SRC_OVER is assumed.
     */
     SkComposeShader(SkShader* sA, SkShader* sB, SkXfermode* mode = NULL);
     virtual ~SkComposeShader();
 
-    virtual bool setContext(const SkBitmap&, const SkPaint&,
-                            const SkMatrix&) SK_OVERRIDE;
-    virtual void endContext() SK_OVERRIDE;
-    virtual void shadeSpan(int x, int y, SkPMColor[], int count) SK_OVERRIDE;
+    virtual bool validContext(const SkBitmap&, const SkPaint&,
+                              const SkMatrix&) const SK_OVERRIDE;
+    virtual SkShader::Context* createContext(const SkBitmap&, const SkPaint&,
+                                             const SkMatrix&, void*) const SK_OVERRIDE;
+    virtual size_t contextSize() const SK_OVERRIDE;
+
+    class ComposeShaderContext : public SkShader::Context {
+    public:
+        // Takes ownership of contextA and contextB, and calls their destructors.
+        ComposeShaderContext(const SkComposeShader&, const SkBitmap&,
+                             const SkPaint&, const SkMatrix&,
+                             SkShader::Context* contextA, SkShader::Context* contextB);
+
+        virtual ~ComposeShaderContext();
+
+        virtual void shadeSpan(int x, int y, SkPMColor[], int count) SK_OVERRIDE;
+    private:
+        SkShader::Context* fShaderContextA;
+        SkShader::Context* fShaderContextB;
+
+        typedef SkShader::Context INHERITED;
+    };
+
 
     SK_DEVELOPER_TO_STRING()
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkComposeShader)
 
 protected:
     SkComposeShader(SkReadBuffer& );
     virtual void flatten(SkWriteBuffer&) const SK_OVERRIDE;
 
 private:
 
     SkShader*   fShaderA;
     SkShader*   fShaderB;
     SkXfermode* fMode;
 
+    friend class ComposeImpl;
+
     typedef SkShader INHERITED;
 };
 
 #endif