Add test to exercise extreme blur sigmas

src/effects/SkBlurMask.cpp

 
 /*
  * 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.
  */
 
 
 #include "SkBlurMask.h"
@@ skipping 854 matching lines @@
 // useful for correctness comparisons.
 
 bool SkBlurMask::BlurGroundTruth(SkScalar sigma, SkMask* dst, const SkMask& src,
                                  Style style, SkIPoint* margin) {
 
     if (src.fFormat != SkMask::kA8_Format) {
         return false;
     }
 
     float variance = sigma * sigma;
 

[robertphillips, 2013/09/05 13:30:38]

The 4x window still had some edge effects (when compared to the brute force 1D
convolution).

-    int windowSize = SkScalarCeil(sigma*4);
+    int windowSize = SkScalarCeil(sigma*6);
     // round window size up to nearest odd number
     windowSize |= 1;
 
     SkAutoTMalloc<float> gaussWindow(windowSize);
 
     int halfWindow = windowSize >> 1;
 
     gaussWindow[halfWindow] = 1;
 
     float windowSum = 1;
     for (int x = 1 ; x <= halfWindow ; ++x) {
-        float gaussian = expf(-x*x / variance);
+        float gaussian = expf(-x*x / (2*variance));

[humper, 2013/09/05 14:19:23]

WHOOPS, nice catch.

         gaussWindow[halfWindow + x] = gaussWindow[halfWindow-x] = gaussian;
         windowSum += 2*gaussian;
     }
 
     // leave the filter un-normalized for now; we will divide by the normalization
     // sum later;
 
     int pad = halfWindow;
     if (margin) {
         margin->set( pad, pad );
@@ skipping 101 matching lines @@
         (void)autoCall.detach();
     }
 
     if (style == kInner_Style) {
         dst->fBounds = src.fBounds; // restore trimmed bounds
         dst->fRowBytes = src.fRowBytes;
     }
 
     return true;
 }