antialias matrix-image-filter to get smooth diagonals

include/core/SkImageFilter.h

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkImageFilter_DEFINED
 #define SkImageFilter_DEFINED
 
@@ skipping 63 matching lines @@
     private:
         SkMatrix fCTM;
         SkIRect  fClipBounds;
         Cache* fCache;
     };
 
     class Proxy {
     public:
         virtual ~Proxy() {};
 
+        /**
+         *  The returned device will be zero-initialized (transparent black)
+         */
         virtual SkBaseDevice* createDevice(int width, int height) = 0;
         // returns true if the proxy can handle this filter natively
         virtual bool canHandleImageFilter(const SkImageFilter*) = 0;
         // returns true if the proxy handled the filter itself. if this returns
         // false then the filter's code will be called.
         virtual bool filterImage(const SkImageFilter*, const SkBitmap& src,
                                  const Context&,
                                  SkBitmap* result, SkIPoint* offset) = 0;
         virtual const SkSurfaceProps* surfaceProps() const = 0;
     };
@@ skipping 243 matching lines @@
      *  parameters before they are used in the effect. Note that this function
      *  will be called with (NULL, NULL, SkMatrix::I()) to query for support,
      *  so returning "true" indicates support for all possible matrices.
      */
     virtual bool asFragmentProcessor(GrFragmentProcessor**, GrTexture*, const SkMatrix&,
                                      const SkIRect& bounds) const;
 
 private:
     bool usesSrcInput() const { return fUsesSrcInput; }
 
+    // Hack to optimize how we saveLayer, remove when no longer needed by SkCanvas
+    bool mayDrawWithMatrix() const { return this->onMayDrawWithMatrix(); }
+    // Return true if the subclass may draw the src transformed (e.g. w/ matrix)
+    virtual bool onMayDrawWithMatrix() const { return false; }
+    friend class SkCanvas;
+
     typedef SkFlattenable INHERITED;
     int fInputCount;
     SkImageFilter** fInputs;
     bool fUsesSrcInput;
     CropRect fCropRect;
     uint32_t fUniqueID; // Globally unique
 };
 
 /**
  *  Helper to unflatten the common data, and return NULL if we fail.
  */
 #define SK_IMAGEFILTER_UNFLATTEN_COMMON(localVar, expectedCount)    \
     Common localVar;                                                \
     do {                                                            \
         if (!localVar.unflatten(buffer, expectedCount)) {           \
             return NULL;                                            \
         }                                                           \
     } while (0)
 
 #endif