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

src/pathops/SkPathOpsCubic.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkPathOpsCubic_DEFINED
 #define SkPathOpsCubic_DEFINED
 
@@ skipping 79 matching lines @@
     bool monotonicInX() const;
     bool monotonicInY() const;
     void otherPts(int index, const SkDPoint* o1Pts[kPointCount - 1]) const;
     SkDPoint ptAtT(double t) const;
     static int RootsReal(double A, double B, double C, double D, double t[3]);
     static int RootsValidT(const double A, const double B, const double C, double D, double s[3]);
 
     int searchRoots(double extremes[6], int extrema, double axisIntercept,
                     SearchAxis xAxis, double* validRoots) const;
 
+    /**
+     *  Return the number of valid roots (0 < root < 1) for this cubic intersecting the
+     *  specified horizontal line.
+     */
+    int horizontalIntersect(double yIntercept, double roots[3]) const;
+    /**
+     *  Return the number of valid roots (0 < root < 1) for this cubic intersecting the
+     *  specified vertical line.
+     */
+    int verticalIntersect(double xIntercept, double roots[3]) const;
+
     const SkDCubic& set(const SkPoint pts[kPointCount]) {
         fPts[0] = pts[0];
         fPts[1] = pts[1];
         fPts[2] = pts[2];
         fPts[3] = pts[3];
         return *this;
     }
 
     SkDCubic subDivide(double t1, double t2) const;
 
@@ skipping 31 matching lines @@
    returned == 3 for (0, 1), (0, 2), (1, 3), (2, 3)
 given that:
    (0, 3) ^ 2 -> (2, 1)  (1, 2) ^ 2 -> (3, 0)
    (0, 1) ^ 3 -> (3, 2)  (0, 2) ^ 3 -> (3, 1)  (1, 3) ^ 3 -> (2, 0)  (2, 3) ^ 3 -> (1, 0)
 */
 inline int other_two(int one, int two) {
     return 1 >> (3 - (one ^ two)) ^ 3;
 }
 
 #endif