compute initial winding from projected rays

src/pathops/SkPathOpsLine.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 SkPathOpsLine_DEFINED
 #define SkPathOpsLine_DEFINED
 
 #include "SkPathOpsPoint.h"
 
 struct SkDLine {
     SkDPoint fPts[2];
 
     const SkDPoint& operator[](int n) const { SkASSERT(n >= 0 && n < 2); return fPts[n]; }
     SkDPoint& operator[](int n) { SkASSERT(n >= 0 && n < 2); return fPts[n]; }
 
-    void set(const SkPoint pts[2]) {
+    const SkDLine& set(const SkPoint pts[2]) {
         fPts[0] = pts[0];
         fPts[1] = pts[1];
+        return *this;
     }
 
     double exactPoint(const SkDPoint& xy) const;
     static double ExactPointH(const SkDPoint& xy, double left, double right, double y);
     static double ExactPointV(const SkDPoint& xy, double top, double bottom, double x);
 
     // only used by testing
     double isLeft(const SkDPoint& pt) const;
 
     double nearPoint(const SkDPoint& xy, bool* unequal) const;
     bool nearRay(const SkDPoint& xy) const;
     static double NearPointH(const SkDPoint& xy, double left, double right, double y);
     static double NearPointV(const SkDPoint& xy, double top, double bottom, double x);
     SkDPoint ptAtT(double t) const;
 
     void dump() const;
     void dumpID(int ) const;
     void dumpInner() const;
 };
 
 #endif