Improve the curve tessellation subdivision of the path renderers.

src/gpu/GrPathUtils.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 GrPathUtils_DEFINED
 #define GrPathUtils_DEFINED
 
@@ skipping 150 matching lines @@
     // represent the implicit form of the cubic as f(x,y,w) = K^3 - LM. The w term
     // will always be 1. The output is stored in the array klm, where the values are:
     // K = (klm[0], klm[1], klm[2])
     // L = (klm[3], klm[4], klm[5])
     // M = (klm[6], klm[7], klm[8])
     //
     // Notice that the klm lines are calculated in the same space as the input control points.
     // If you transform the points the lines will also need to be transformed. This can be done
     // by mapping the lines with the inverse-transpose of the matrix used to map the points.
     void getCubicKLM(const SkPoint p[4], SkScalar klm[9]);
+
+    // When tessellating curved paths into linear segments, this defines the maximum distance
+    // in screen space which a segment may deviate from the mathmatically correct value.
+    // Above this value, the segment will be subdivided.
+    // This value was chosen to approximate the supersampling accuracy of the raster path (16
+    // samples, or one quarter pixel).
+    static const SkScalar kDefaultTolerance = SkDoubleToScalar(0.25);
 };
 #endif