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

BUG=skia:

Review URL: https://codereview.chromium.org/1113963002

2 files changed, 21 insertions, 0 deletions

diff --git a/src/pathops/SkDCubicLineIntersection.cpp b/src/pathops/SkDCubicLineIntersection.cpp
index f658b09f0b..ee1e3d3a34 100644
--- a/src/pathops/SkDCubicLineIntersection.cpp
+++ b/src/pathops/SkDCubicLineIntersection.cpp
@@ -425,3 +425,13 @@ int SkIntersections::intersectRay(const SkDCubic& cubic, const SkDLine& line) {
     }
     return fUsed;
 }
+
+// SkDCubic accessors to Intersection utilities
+
+int SkDCubic::horizontalIntersect(double yIntercept, double roots[3]) const {
+    return LineCubicIntersections::HorizontalIntersect(*this, yIntercept, roots);
+}
+
+int SkDCubic::verticalIntersect(double xIntercept, double roots[3]) const {
+    return LineCubicIntersections::VerticalIntersect(*this, xIntercept, roots);
+}
diff --git a/src/pathops/SkPathOpsCubic.h b/src/pathops/SkPathOpsCubic.h
index f9d291056e..3d68151852 100644
--- a/src/pathops/SkPathOpsCubic.h
+++ b/src/pathops/SkPathOpsCubic.h
@@ -97,6 +97,17 @@ struct SkDCubic {
     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];