use pathops utils to improve precision of cubic chopping in scan converter

src/core/SkGeometry.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 SkGeometry_DEFINED
 #define SkGeometry_DEFINED
 
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 /** Return 1 for no chop, 2 for having chopped the cubic at a single
     inflection point, 3 for having chopped at 2 inflection points.
     dst will hold the resulting 1, 2, or 3 cubics.
 */
 int SkChopCubicAtInflections(const SkPoint src[4], SkPoint dst[10]);
 
 int SkFindCubicMaxCurvature(const SkPoint src[4], SkScalar tValues[3]);
 int SkChopCubicAtMaxCurvature(const SkPoint src[4], SkPoint dst[13],
                               SkScalar tValues[3] = NULL);
 
+bool SkChopMonoCubicAtX(SkPoint src[4], SkScalar y, SkPoint dst[7]);
+bool SkChopMonoCubicAtY(SkPoint src[4], SkScalar x, SkPoint dst[7]);
+
 enum SkCubicType {
     kSerpentine_SkCubicType,
     kCusp_SkCubicType,
     kLoop_SkCubicType,
     kQuadratic_SkCubicType,
     kLine_SkCubicType,
     kPoint_SkCubicType
 };
 
 /** Returns the cubic classification. Pass scratch storage for computing inflection data,
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 private:
     enum {
         kQuadCount = 8, // should handle most conics
         kPointCount = 1 + 2 * kQuadCount,
     };
     SkAutoSTMalloc<kPointCount, SkPoint> fStorage;
     int fQuadCount; // #quads for current usage
 };
 
 #endif