Implement canComputeFastBounds() for image filters.

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 160 matching lines @@
     }
 
     /**
      *  Returns true (and optionally returns a ref'd filter) if this imagefilter can be completely
      *  replaced by the returned colorfilter. i.e. the two effects will affect drawing in the
      *  same way.
      */
     bool asAColorFilter(SkColorFilter** filterPtr) const {
         return this->countInputs() > 0 &&
                NULL == this->getInput(0) &&
+               !this->affectsTransparentBlack() &&
                this->isColorFilterNode(filterPtr);
     }
 
     /**
      *  Returns the number of inputs this filter will accept (some inputs can
      *  be NULL).
      */
     int countInputs() const { return fInputCount; }
 
     /**
@@ skipping 16 matching lines @@
      *  filterImageGPU(). (The latter ensures that the resulting buffer is
      *  drawn in the correct location.)
      */
     bool cropRectIsSet() const { return fCropRect.flags() != 0x0; }
 
     CropRect getCropRect() const { return fCropRect; }
 
     // Default impl returns union of all input bounds.
     virtual void computeFastBounds(const SkRect&, SkRect*) const;
 
+    // Can this filter DAG compute the resulting bounds of an object-space rectangle?
+    bool canComputeFastBounds() const;
+
     /**
      * Create an SkMatrixImageFilter, which transforms its input by the given matrix.
      */
     static SkImageFilter* CreateMatrixFilter(const SkMatrix& matrix,
                                              SkFilterQuality,
                                              SkImageFilter* input = NULL);
 
 #if SK_SUPPORT_GPU
     /**
      * Wrap the given texture in a texture-backed SkBitmap.
@@ skipping 128 matching lines @@
      *
      *  The effect can assume its vertexCoords space maps 1-to-1 with texels
      *  in the texture.  "matrix" is a transformation to apply to filter
      *  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**, GrProcessorDataManager*, GrTexture*,
                                      const SkMatrix&, const SkIRect& bounds) const;
 
+    /**
+     * Returns true if this filter can cause transparent black pixels to become
+     * visible (ie., alpha > 0). The default implementation returns false. This
+     * function is non-recursive, i.e., only queries this filter and not its
+     * inputs.
+     */
+    virtual bool affectsTransparentBlack() const;
+
 private:
     friend class SkGraphics;
     static void PurgeCache();
 
     bool usesSrcInput() const { return fUsesSrcInput; }
 
     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