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

SkShader currently stores some state during draw calls via setContext(...).
Move that mutable state into a separate SkShader::Context class that is
constructed on demand for the duration of the draw.

Calls to setContext() are replaced with createContext() which returns a context
corresponding to the shader object or NULL if the parameters to createContext
are invalid.

TEST=out/Debug/dm
BUG=skia:1976
R=scroggo@google.com, skyostil@chromium.org, tomhudson@chromium.org, senorblanco@chromium.org, reed@google.com, bungeman@google.com

Author: dominikg@chromium.org

Review URL: https://codereview.chromium.org/207683004

git-svn-id: http://skia.googlecode.com/svn/trunk@14216 2bbb7eff-a529-9590-31e7-b0007b416f81

6 files changed, 214 insertions, 127 deletions

diff --git a/include/core/SkColorShader.h b/include/core/SkColorShader.h
index 975156c0eb..56e5add4a3 100644
--- a/include/core/SkColorShader.h
+++ b/include/core/SkColorShader.h
@@ -30,16 +30,35 @@ public:
     */
     SkColorShader(SkColor c);
 
-    virtual ~SkColorShader();
-
-    virtual uint32_t getFlags() SK_OVERRIDE;
-    virtual uint8_t getSpan16Alpha() const SK_OVERRIDE;
     virtual bool isOpaque() const SK_OVERRIDE;
-    virtual bool setContext(const SkBitmap& device, const SkPaint& paint,
-                            const SkMatrix& matrix) SK_OVERRIDE;
-    virtual void shadeSpan(int x, int y, SkPMColor span[], int count) SK_OVERRIDE;
-    virtual void shadeSpan16(int x, int y, uint16_t span[], int count) SK_OVERRIDE;
-    virtual void shadeSpanAlpha(int x, int y, uint8_t alpha[], int count) SK_OVERRIDE;
+
+    virtual SkShader::Context* createContext(const SkBitmap& device,
+                                             const SkPaint& paint,
+                                             const SkMatrix& matrix,
+                                             void* storage) const SK_OVERRIDE;
+
+    virtual size_t contextSize() const SK_OVERRIDE {
+        return sizeof(ColorShaderContext);
+    }
+
+    class ColorShaderContext : public SkShader::Context {
+    public:
+        ColorShaderContext(const SkColorShader& shader, const SkBitmap& device,
+                           const SkPaint& paint, const SkMatrix& matrix);
+
+        virtual uint32_t getFlags() const SK_OVERRIDE;
+        virtual uint8_t getSpan16Alpha() const SK_OVERRIDE;
+        virtual void shadeSpan(int x, int y, SkPMColor span[], int count) SK_OVERRIDE;
+        virtual void shadeSpan16(int x, int y, uint16_t span[], int count) SK_OVERRIDE;
+        virtual void shadeSpanAlpha(int x, int y, uint8_t alpha[], int count) SK_OVERRIDE;
+
+    private:
+        SkPMColor   fPMColor;
+        uint32_t    fFlags;
+        uint16_t    fColor16;
+
+        typedef SkShader::Context INHERITED;
+    };
 
     // we return false for this, use asAGradient
     virtual BitmapType asABitmap(SkBitmap* outTexture,
@@ -56,11 +75,7 @@ protected:
     virtual void flatten(SkWriteBuffer&) const SK_OVERRIDE;
 
 private:
-
     SkColor     fColor;         // ignored if fInheritColor is true
-    SkPMColor   fPMColor;       // cached after setContext()
-    uint32_t    fFlags;         // cached after setContext()
-    uint16_t    fColor16;       // cached after setContext()
     SkBool8     fInheritColor;
 
     typedef SkShader INHERITED;
diff --git a/include/core/SkComposeShader.h b/include/core/SkComposeShader.h
index b54e5efa97..9833a9f4ad 100644
--- a/include/core/SkComposeShader.h
+++ b/include/core/SkComposeShader.h
@@ -34,10 +34,38 @@ public:
     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&, SkMatrix* totalInverse = NULL) 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:
+        // When this object gets destroyed, it will call contextA and contextB's destructor
+        // but it will NOT free the memory.
+        ComposeShaderContext(const SkComposeShader&, const SkBitmap&,
+                             const SkPaint&, const SkMatrix&,
+                             SkShader::Context* contextA, SkShader::Context* contextB);
+
+        SkShader::Context* getShaderContextA() const { return fShaderContextA; }
+        SkShader::Context* getShaderContextB() const { return fShaderContextB; }
+
+        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;
+    };
+
+#if SK_DEBUG
+    SkShader* getShaderA() { return fShaderA; }
+    SkShader* getShaderB() { return fShaderB; }
+#endif
 
     SK_TO_STRING_OVERRIDE()
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkComposeShader)
@@ -47,7 +75,6 @@ protected:
     virtual void flatten(SkWriteBuffer&) const SK_OVERRIDE;
 
 private:
-
     SkShader*   fShaderA;
     SkShader*   fShaderB;
     SkXfermode* fMode;
diff --git a/include/core/SkEmptyShader.h b/include/core/SkEmptyShader.h
index d2ebb61221..7494eff3d0 100644
--- a/include/core/SkEmptyShader.h
+++ b/include/core/SkEmptyShader.h
@@ -15,20 +15,28 @@
 
 /**
  *  \class SkEmptyShader
- *  A Shader that always draws nothing. Its setContext always returns false,
- *  so it never expects that its shadeSpan() methods will get called.
+ *  A Shader that always draws nothing. Its createContext always returns NULL.
  */
 class SK_API SkEmptyShader : public SkShader {
 public:
     SkEmptyShader() {}
 
-    virtual uint32_t getFlags() SK_OVERRIDE;
-    virtual uint8_t getSpan16Alpha() const SK_OVERRIDE;
-    virtual bool setContext(const SkBitmap&, const SkPaint&,
-                            const SkMatrix&) SK_OVERRIDE;
-    virtual void shadeSpan(int x, int y, SkPMColor span[], int count) SK_OVERRIDE;
-    virtual void shadeSpan16(int x, int y, uint16_t span[], int count) SK_OVERRIDE;
-    virtual void shadeSpanAlpha(int x, int y, uint8_t alpha[], int count) SK_OVERRIDE;
+    virtual size_t contextSize() const SK_OVERRIDE {
+        // Even though createContext returns NULL we have to return a value of at least
+        // sizeof(SkShader::Context) to satisfy SkSmallAllocator.
+        return sizeof(SkShader::Context);
+    }
+
+    virtual bool validContext(const SkBitmap&, const SkPaint&,
+                              const SkMatrix&, SkMatrix* totalInverse = NULL) const SK_OVERRIDE {
+        return false;
+    }
+
+    virtual SkShader::Context* createContext(const SkBitmap&, const SkPaint&,
+                                             const SkMatrix&, void*) const SK_OVERRIDE {
+        // validContext returns false.
+        return NULL;
+    }
 
     SK_TO_STRING_OVERRIDE()
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkEmptyShader)
diff --git a/include/core/SkShader.h b/include/core/SkShader.h
index 076ecf5460..58e5a6ad2e 100644
--- a/include/core/SkShader.h
+++ b/include/core/SkShader.h
@@ -38,7 +38,7 @@ public:
     virtual ~SkShader();
 
     /**
-     * Returns true if the local matrix is not an identity matrix.
+     *  Returns true if the local matrix is not an identity matrix.
      */
     bool hasLocalMatrix() const { return !fLocalMatrix.isIdentity(); }
 
@@ -96,7 +96,7 @@ public:
         */
         kIntrinsicly16_Flag = 0x04,
 
-        /** set (after setContext) if the spans only vary in X (const in Y).
+        /** set if the spans only vary in X (const in Y).
             e.g. an Nx1 bitmap that is being tiled in Y, or a linear-gradient
             that varies from left-to-right. This flag specifies this for
             shadeSpan().
@@ -112,84 +112,111 @@ public:
     };
 
     /**
-     *  Called sometimes before drawing with this shader. Return the type of
-     *  alpha your shader will return. The default implementation returns 0.
-     *  Your subclass should override if it can (even sometimes) report a
-     *  non-zero value, since that will enable various blitters to perform
-     *  faster.
-     */
-    virtual uint32_t getFlags() { return 0; }
-
-    /**
      *  Returns true if the shader is guaranteed to produce only opaque
      *  colors, subject to the SkPaint using the shader to apply an opaque
      *  alpha value. Subclasses should override this to allow some
-     *  optimizations.  isOpaque() can be called at any time, unlike getFlags,
-     *  which only works properly when the context is set.
+     *  optimizations.
      */
     virtual bool isOpaque() const { return false; }
 
-    /**
-     *  Return the alpha associated with the data returned by shadeSpan16(). If
-     *  kHasSpan16_Flag is not set, this value is meaningless.
-     */
-    virtual uint8_t getSpan16Alpha() const { return fPaintAlpha; }
+    class Context : public ::SkNoncopyable {
+    public:
+        Context(const SkShader& shader, const SkBitmap& device,
+                const SkPaint& paint, const SkMatrix& matrix);
 
-    /**
-     *  Called once before drawing, with the current paint and device matrix.
-     *  Return true if your shader supports these parameters, or false if not.
-     *  If false is returned, nothing will be drawn. If true is returned, then
-     *  a balancing call to endContext() will be made before the next call to
-     *  setContext.
-     *
-     *  Subclasses should be sure to call their INHERITED::setContext() if they
-     *  override this method.
-     */
-    virtual bool setContext(const SkBitmap& device, const SkPaint& paint,
-                            const SkMatrix& matrix);
+        virtual ~Context();
 
-    /**
-     *  Assuming setContext returned true, endContext() will be called when
-     *  the draw using the shader has completed. It is an error for setContext
-     *  to be called twice w/o an intervening call to endContext().
-     *
-     *  Subclasses should be sure to call their INHERITED::endContext() if they
-     *  override this method.
-     */
-    virtual void endContext();
+        /**
+         *  Called sometimes before drawing with this shader. Return the type of
+         *  alpha your shader will return. The default implementation returns 0.
+         *  Your subclass should override if it can (even sometimes) report a
+         *  non-zero value, since that will enable various blitters to perform
+         *  faster.
+         */
+        virtual uint32_t getFlags() const { return 0; }
 
-    SkDEBUGCODE(bool setContextHasBeenCalled() const { return SkToBool(fInSetContext); })
+        /**
+         *  Return the alpha associated with the data returned by shadeSpan16(). If
+         *  kHasSpan16_Flag is not set, this value is meaningless.
+         */
+        virtual uint8_t getSpan16Alpha() const { return fPaintAlpha; }
 
-    /**
-     *  Called for each span of the object being drawn. Your subclass should
-     *  set the appropriate colors (with premultiplied alpha) that correspond
-     *  to the specified device coordinates.
-     */
-    virtual void shadeSpan(int x, int y, SkPMColor[], int count) = 0;
+        /**
+         *  Called for each span of the object being drawn. Your subclass should
+         *  set the appropriate colors (with premultiplied alpha) that correspond
+         *  to the specified device coordinates.
+         */
+        virtual void shadeSpan(int x, int y, SkPMColor[], int count) = 0;
+
+        typedef void (*ShadeProc)(void* ctx, int x, int y, SkPMColor[], int count);
+        virtual ShadeProc asAShadeProc(void** ctx);
+
+        /**
+         *  Called only for 16bit devices when getFlags() returns
+         *  kOpaqueAlphaFlag | kHasSpan16_Flag
+         */
+        virtual void shadeSpan16(int x, int y, uint16_t[], int count);
+
+        /**
+         *  Similar to shadeSpan, but only returns the alpha-channel for a span.
+         *  The default implementation calls shadeSpan() and then extracts the alpha
+         *  values from the returned colors.
+         */
+        virtual void shadeSpanAlpha(int x, int y, uint8_t alpha[], int count);
 
-    typedef void (*ShadeProc)(void* ctx, int x, int y, SkPMColor[], int count);
-    virtual ShadeProc asAShadeProc(void** ctx);
+        /**
+         *  Helper function that returns true if this shader's shadeSpan16() method
+         *  can be called.
+         */
+        bool canCallShadeSpan16() {
+            return SkShader::CanCallShadeSpan16(this->getFlags());
+        }
+
+    protected:
+        // Reference to shader, so we don't have to dupe information.
+        const SkShader& fShader;
+
+        enum MatrixClass {
+            kLinear_MatrixClass,            // no perspective
+            kFixedStepInX_MatrixClass,      // fast perspective, need to call fixedStepInX() each
+                                            // scanline
+            kPerspective_MatrixClass        // slow perspective, need to mappoints each pixel
+        };
+        static MatrixClass ComputeMatrixClass(const SkMatrix&);
+
+        uint8_t             getPaintAlpha() const { return fPaintAlpha; }
+        const SkMatrix&     getTotalInverse() const { return fTotalInverse; }
+        MatrixClass         getInverseClass() const { return (MatrixClass)fTotalInverseClass; }
+
+    private:
+        SkMatrix            fTotalInverse;
+        uint8_t             fPaintAlpha;
+        uint8_t             fTotalInverseClass;
+
+        typedef SkNoncopyable INHERITED;
+    };
 
     /**
-     *  Called only for 16bit devices when getFlags() returns
-     *  kOpaqueAlphaFlag | kHasSpan16_Flag
+     *  Subclasses should be sure to call their INHERITED::validContext() if
+     *  they override this method.
      */
-    virtual void shadeSpan16(int x, int y, uint16_t[], int count);
+    virtual bool validContext(const SkBitmap& device, const SkPaint& paint,
+                              const SkMatrix& matrix, SkMatrix* totalInverse = NULL) const;
 
     /**
-     *  Similar to shadeSpan, but only returns the alpha-channel for a span.
-     *  The default implementation calls shadeSpan() and then extracts the alpha
-     *  values from the returned colors.
+     *  Create the actual object that does the shading.
+     *  Returns NULL if validContext() returns false.
+     *  Size of storage must be >= contextSize.
      */
-    virtual void shadeSpanAlpha(int x, int y, uint8_t alpha[], int count);
+    virtual Context* createContext(const SkBitmap& device,
+                                   const SkPaint& paint,
+                                   const SkMatrix& matrix,
+                                   void* storage) const = 0;
 
     /**
-     *  Helper function that returns true if this shader's shadeSpan16() method
-     *  can be called.
+     *  Return the size of a Context returned by createContext.
      */
-    bool canCallShadeSpan16() {
-        return SkShader::CanCallShadeSpan16(this->getFlags());
-    }
+    virtual size_t contextSize() const = 0;
 
     /**
      *  Helper to check the flags to know if it is legal to call shadeSpan16()
@@ -322,7 +349,7 @@ public:
      *  The incoming color to the effect has r=g=b=a all extracted from the SkPaint's alpha.
      *  The output color should be the computed SkShader premul color modulated by the incoming
      *  color. The GrContext may be used by the effect to create textures. The GPU device does not
-     *  call setContext. Instead we pass the SkPaint here in case the shader needs paint info.
+     *  call createContext. Instead we pass the SkPaint here in case the shader needs paint info.
      */
     virtual GrEffectRef* asNewEffect(GrContext* context, const SkPaint& paint) const;
 
@@ -360,26 +387,14 @@ public:
     SK_DEFINE_FLATTENABLE_TYPE(SkShader)
 
 protected:
-    enum MatrixClass {
-        kLinear_MatrixClass,            // no perspective
-        kFixedStepInX_MatrixClass,      // fast perspective, need to call fixedStepInX() each scanline
-        kPerspective_MatrixClass        // slow perspective, need to mappoints each pixel
-    };
-    static MatrixClass ComputeMatrixClass(const SkMatrix&);
-
-    // These can be called by your subclass after setContext() has been called
-    uint8_t             getPaintAlpha() const { return fPaintAlpha; }
-    const SkMatrix&     getTotalInverse() const { return fTotalInverse; }
-    MatrixClass         getInverseClass() const { return (MatrixClass)fTotalInverseClass; }
 
     SkShader(SkReadBuffer& );
     virtual void flatten(SkWriteBuffer&) const SK_OVERRIDE;
+
 private:
     SkMatrix            fLocalMatrix;
-    SkMatrix            fTotalInverse;
-    uint8_t             fPaintAlpha;
-    uint8_t             fTotalInverseClass;
-    SkDEBUGCODE(SkBool8 fInSetContext;)
+
+    bool computeTotalInverse(const SkMatrix& matrix, SkMatrix* totalInverse) const;
 
     typedef SkFlattenable INHERITED;
 };
diff --git a/include/effects/SkPerlinNoiseShader.h b/include/effects/SkPerlinNoiseShader.h
index dfd5a8c1e7..5b270293b1 100644
--- a/include/effects/SkPerlinNoiseShader.h
+++ b/include/effects/SkPerlinNoiseShader.h
@@ -72,10 +72,32 @@ public:
     }
 
 
-    virtual bool setContext(const SkBitmap& device, const SkPaint& paint,
-                            const SkMatrix& matrix);
-    virtual void shadeSpan(int x, int y, SkPMColor[], int count) SK_OVERRIDE;
-    virtual void shadeSpan16(int x, int y, uint16_t[], int count) SK_OVERRIDE;
+    virtual SkShader::Context* createContext(
+        const SkBitmap& device, const SkPaint& paint,
+        const SkMatrix& matrix, void* storage) const SK_OVERRIDE;
+    virtual size_t contextSize() const SK_OVERRIDE;
+
+    class PerlinNoiseShaderContext : public SkShader::Context {
+    public:
+        PerlinNoiseShaderContext(const SkPerlinNoiseShader& shader, const SkBitmap& device,
+                                 const SkPaint& paint, const SkMatrix& matrix);
+        virtual ~PerlinNoiseShaderContext() {}
+
+        virtual void shadeSpan(int x, int y, SkPMColor[], int count) SK_OVERRIDE;
+        virtual void shadeSpan16(int x, int y, uint16_t[], int count) SK_OVERRIDE;
+
+    private:
+        SkPMColor shade(const SkPoint& point, StitchData& stitchData) const;
+        SkScalar calculateTurbulenceValueForPoint(
+            int channel, const PaintingData& paintingData,
+            StitchData& stitchData, const SkPoint& point) const;
+        SkScalar noise2D(int channel, const PaintingData& paintingData,
+                         const StitchData& stitchData, const SkPoint& noiseVector) const;
+
+        SkMatrix fMatrix;
+
+        typedef SkShader::Context INHERITED;
+    };
 
     virtual GrEffectRef* asNewEffect(GrContext* context, const SkPaint&) const SK_OVERRIDE;
 
@@ -92,14 +114,6 @@ private:
                         const SkISize* tileSize);
     virtual ~SkPerlinNoiseShader();
 
-    SkScalar noise2D(int channel, const PaintingData& paintingData,
-                     const StitchData& stitchData, const SkPoint& noiseVector) const;
-
-    SkScalar calculateTurbulenceValueForPoint(int channel, const PaintingData& paintingData,
-                                              StitchData& stitchData, const SkPoint& point) const;
-
-    SkPMColor shade(const SkPoint& point, StitchData& stitchData) const;
-
     // TODO (scroggo): Once all SkShaders are created from a factory, and we have removed the
     // constructor that creates SkPerlinNoiseShader from an SkReadBuffer, several fields can
     // be made constant.
@@ -110,8 +124,6 @@ private:
     /*const*/ SkScalar                  fSeed;
     /*const*/ SkISize                   fTileSize;
     /*const*/ bool                      fStitchTiles;
-    // TODO (scroggo): Once setContext creates a new object, place this on that object.
-    SkMatrix fMatrix;
 
     PaintingData* fPaintingData;
 
diff --git a/include/effects/SkTransparentShader.h b/include/effects/SkTransparentShader.h
index 7428d442e3..790e5ae9fd 100644
--- a/include/effects/SkTransparentShader.h
+++ b/include/effects/SkTransparentShader.h
@@ -14,21 +14,31 @@ class SK_API SkTransparentShader : public SkShader {
 public:
     SkTransparentShader() {}
 
-    virtual uint32_t getFlags() SK_OVERRIDE;
-    virtual bool    setContext(const SkBitmap& device,
-                               const SkPaint& paint,
-                               const SkMatrix& matrix) SK_OVERRIDE;
-    virtual void    shadeSpan(int x, int y, SkPMColor[], int count) SK_OVERRIDE;
-    virtual void    shadeSpan16(int x, int y, uint16_t span[], int count) SK_OVERRIDE;
+    virtual SkShader::Context* createContext(const SkBitmap& device, const SkPaint& paint,
+                                             const SkMatrix& matrix, void* storage) const
+            SK_OVERRIDE;
+    virtual size_t contextSize() const SK_OVERRIDE;
+
+    class TransparentShaderContext : public SkShader::Context {
+    public:
+        TransparentShaderContext(const SkTransparentShader& shader, const SkBitmap& device,
+                                 const SkPaint& paint, const SkMatrix& matrix);
+        virtual ~TransparentShaderContext();
+
+        virtual uint32_t getFlags() const SK_OVERRIDE;
+        virtual void shadeSpan(int x, int y, SkPMColor[], int count) SK_OVERRIDE;
+        virtual void shadeSpan16(int x, int y, uint16_t span[], int count) SK_OVERRIDE;
+
+    private:
+        const SkBitmap* fDevice;
+
+        typedef SkShader::Context INHERITED;
+    };
 
     SK_TO_STRING_OVERRIDE()
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkTransparentShader)
 
 private:
-    // these are a cache from the call to setContext()
-    const SkBitmap* fDevice;
-    uint8_t         fAlpha;
-
     SkTransparentShader(SkReadBuffer& buffer) : INHERITED(buffer) {}
 
     typedef SkShader INHERITED;