Fast path for blurred round rects -- blur a small 9patch rect on the CPU

src/effects/SkBlurMask.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 SkBlurMask_DEFINED
 #define SkBlurMask_DEFINED
 
 #include "SkBlurTypes.h"
 #include "SkShader.h"
 #include "SkMask.h"
 #include "SkRRect.h"
 
 class SkBlurMask {
 public:
     static bool BlurRect(SkScalar sigma, SkMask *dst, const SkRect &src, SkBlurStyle,
                          SkIPoint *margin = NULL,
                          SkMask::CreateMode createMode =
                                                 SkMask::kComputeBoundsAndRenderImage_CreateMode);
     static bool BlurRRect(SkScalar sigma, SkMask *dst, const SkRRect &src, SkBlurStyle,
                          SkIPoint *margin = NULL,
                          SkMask::CreateMode createMode =
                                                 SkMask::kComputeBoundsAndRenderImage_CreateMode);
+
+    // forceQuality will prevent BoxBlur from falling back to the low quality approach when sigma
+    // is very small -- this can be used predict the margin bump ahead of time without completely
+    // replicating the internal logic.  This permits not only simpler caching of blurred results,
+    // but also being able to predict precisely at what pixels the blurred profile of e.g. a
+    // rectangle will lie.
+
     static bool BoxBlur(SkMask* dst, const SkMask& src,
                         SkScalar sigma, SkBlurStyle style, SkBlurQuality quality,
-                        SkIPoint* margin = NULL);
+                        SkIPoint* margin = NULL, bool force_quality=false);
 
     // the "ground truth" blur does a gaussian convolution; it's slow
     // but useful for comparison purposes.
     static bool BlurGroundTruth(SkScalar sigma, SkMask* dst, const SkMask& src, SkBlurStyle,
                                 SkIPoint* margin = NULL);
 
     static SkScalar ConvertRadiusToSigma(SkScalar radius);
 
     /* Helper functions for analytic rectangle blurs */
 
@@ skipping 25 matching lines @@
     */
 
     static void ComputeBlurredScanline(uint8_t* pixels, const uint8_t* profile,
                                        unsigned int width, SkScalar sigma);
 
 
 
 };
 
 #endif