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

src/core/SkCoreBlitters.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 SkCoreBlitters_DEFINED
 #define SkCoreBlitters_DEFINED
 
 #include "SkBitmapProcShader.h"
 #include "SkBlitter.h"
 #include "SkBlitRow.h"
 #include "SkShader.h"
 #include "SkSmallAllocator.h"
 
 class SkRasterBlitter : public SkBlitter {
 public:
     SkRasterBlitter(const SkBitmap& device) : fDevice(device) {}
 
 protected:
     const SkBitmap& fDevice;
 
 private:
     typedef SkBlitter INHERITED;
 };
 
 class SkShaderBlitter : public SkRasterBlitter {
 public:
-    SkShaderBlitter(const SkBitmap& device, const SkPaint& paint);
+    // TODO(dominikg): Should this class have its own SkSmallAllocator for storing the

[scroggo, 2014/04/03 15:35:54]

Didn't you determine that this wouldn't work without some more refactoring since
we create the context first?

[Dominik Grewe, 2014/04/04 10:59:41]

Yes, you're right. I'll remove this.

+    //                 shader context? Would avoid weird ownership issues (see below).
+    /**
+      *  The storage for shaderContext is owned by the caller, but the object itself is not.
+      *  The blitter only ensures that the storage always holds a live object.
+      */
+    SkShaderBlitter(const SkBitmap& device, const SkPaint& paint,
+                    SkShader::Context* shaderContext);
     virtual ~SkShaderBlitter();
 
+    /**
+      *  Create a new shader context and uses it instead of the old one if successful.
+      *  Will create the context at the same location as the old one (this is safe
+      *  because the shader itself is unchanged).
+      */
+    virtual bool resetShaderContext(const SkBitmap& device, const SkPaint& paint,
+                                    const SkMatrix& matrix) SK_OVERRIDE;
+
+    virtual SkShader::Context* getShaderContext() const SK_OVERRIDE { return fShaderContext; }
+
 protected:
-    uint32_t    fShaderFlags;
-    SkShader*   fShader;
+    uint32_t            fShaderFlags;
+    const SkShader*     fShader;
+    SkShader::Context*  fShaderContext;
 
 private:
     // illegal
     SkShaderBlitter& operator=(const SkShaderBlitter&);
 
     typedef SkRasterBlitter INHERITED;
 };
 
 ///////////////////////////////////////////////////////////////////////////////
 
@@ skipping 22 matching lines @@
     unsigned fSrcA;
 
     // illegal
     SkA8_Blitter& operator=(const SkA8_Blitter&);
 
     typedef SkRasterBlitter INHERITED;
 };
 
 class SkA8_Shader_Blitter : public SkShaderBlitter {
 public:
-    SkA8_Shader_Blitter(const SkBitmap& device, const SkPaint& paint);
+    SkA8_Shader_Blitter(const SkBitmap& device, const SkPaint& paint,
+                        SkShader::Context* shaderContext);
     virtual ~SkA8_Shader_Blitter();
     virtual void blitH(int x, int y, int width);
     virtual void blitAntiH(int x, int y, const SkAlpha antialias[], const int16_t runs[]);
     virtual void blitMask(const SkMask&, const SkIRect&);
 
 private:
     SkXfermode* fXfermode;
     SkPMColor*  fBuffer;
     uint8_t*    fAAExpand;
 
@@ skipping 45 matching lines @@
     SkARGB32_Black_Blitter(const SkBitmap& device, const SkPaint& paint)
         : INHERITED(device, paint) {}
     virtual void blitAntiH(int x, int y, const SkAlpha antialias[], const int16_t runs[]);
 
 private:
     typedef SkARGB32_Opaque_Blitter INHERITED;
 };
 
 class SkARGB32_Shader_Blitter : public SkShaderBlitter {
 public:
-    SkARGB32_Shader_Blitter(const SkBitmap& device, const SkPaint& paint);
+    SkARGB32_Shader_Blitter(const SkBitmap& device, const SkPaint& paint,
+                            SkShader::Context* shaderContext);
     virtual ~SkARGB32_Shader_Blitter();
     virtual void blitH(int x, int y, int width) SK_OVERRIDE;
     virtual void blitV(int x, int y, int height, SkAlpha alpha) SK_OVERRIDE;
     virtual void blitRect(int x, int y, int width, int height) SK_OVERRIDE;
     virtual void blitAntiH(int x, int y, const SkAlpha[], const int16_t[]) SK_OVERRIDE;
     virtual void blitMask(const SkMask&, const SkIRect&) SK_OVERRIDE;
 
 private:
     SkXfermode*         fXfermode;
     SkPMColor*          fBuffer;
@@ skipping 17 matching lines @@
 
     1. If there is an xfermode, there will also be a shader
     2. If there is a colorfilter, there will be a shader that itself handles
        calling the filter, so the blitter can always ignore the colorfilter obj
 
     These pre-conditions must be handled by the caller, in our case
     SkBlitter::Choose(...)
  */
 
 SkBlitter* SkBlitter_ChooseD565(const SkBitmap& device, const SkPaint& paint,
+                                SkShader::Context* shaderContext,
                                 SkTBlitterAllocator* allocator);
 
 #endif