turn off debugging printfs

src/pathops/SkDLineIntersection.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #include "SkIntersections.h"
 #include "SkPathOpsLine.h"
 
 /* Determine the intersection point of two lines. This assumes the lines are not parallel,
    and that that the lines are infinite.
    From http://en.wikipedia.org/wiki/Line-line_intersection
  */
 SkDPoint SkIntersections::Line(const SkDLine& a, const SkDLine& b) {
     double axLen = a[1].fX - a[0].fX;
     double ayLen = a[1].fY - a[0].fY;
     double bxLen = b[1].fX - b[0].fX;
     double byLen = b[1].fY - b[0].fY;
     double denom = byLen * axLen - ayLen * bxLen;
     SkASSERT(denom);
     double term1 = a[1].fX * a[0].fY - a[1].fY * a[0].fX;
     double term2 = b[1].fX * b[0].fY - b[1].fY * b[0].fX;
     SkDPoint p;
     p.fX = (term1 * bxLen - axLen * term2) / denom;
     p.fY = (term1 * byLen - ayLen * term2) / denom;
     return p;
 }
 
 int SkIntersections::computePoints(const SkDLine& line, int used) {
-    fPt[0] = line.xyAtT(fT[0][0]);
+    fPt[0] = line.ptAtT(fT[0][0]);
     if ((fUsed = used) == 2) {
-        fPt[1] = line.xyAtT(fT[0][1]);
+        fPt[1] = line.ptAtT(fT[0][1]);
     }
     return fUsed;
 }
 
 int SkIntersections::intersectRay(const SkDLine& a, const SkDLine& b) {
     double axLen = a[1].fX - a[0].fX;
     double ayLen = a[1].fY - a[0].fY;
     double bxLen = b[1].fX - b[0].fX;
     double byLen = b[1].fY - b[0].fY;
     /* Slopes match when denom goes to zero:
@@ skipping 52 matching lines @@
     double axLen = a[1].fX - a[0].fX;
     double ayLen = a[1].fY - a[0].fY;
     double bxLen = b[1].fX - b[0].fX;
     double byLen = b[1].fY - b[0].fY;
     /* Slopes match when denom goes to zero:
                       axLen / ayLen ==                   bxLen / byLen
     (ayLen * byLen) * axLen / ayLen == (ayLen * byLen) * bxLen / byLen
              byLen  * axLen         ==  ayLen          * bxLen
              byLen  * axLen         -   ayLen          * bxLen == 0 ( == denom )
      */
-    double denom = byLen * axLen - ayLen * bxLen;
-    if (0 != denom) {
+    double axByLen = axLen * byLen;
+    double ayBxLen = ayLen * bxLen;
+    // detect parallel lines the same way here and in SkOpAngle operator <
+    // so that non-parallel means they are also sortable
+    bool parallel = AlmostEqualUlps(axByLen, ayBxLen);
+    if (!parallel) {
         double ab0y = a[0].fY - b[0].fY;
         double ab0x = a[0].fX - b[0].fX;
         double numerA = ab0y * bxLen - byLen * ab0x;
         double numerB = ab0y * axLen - ayLen * ab0x;
+        double denom = axByLen - ayBxLen;
         if (between(0, numerA, denom) && between(0, numerB, denom)) {
             fT[0][0] = numerA / denom;
             fT[1][0] = numerB / denom;
-            return computePoints(a, 1);
+            computePoints(a, 1);
         }
     }
-    if (fAllowNear || 0 == denom) {
+    if (fAllowNear || parallel) {
         for (int iA = 0; iA < 2; ++iA) {
             if ((t = b.nearPoint(a[iA])) >= 0) {
                 insert(iA, t, a[iA]);
             }
         }
         for (int iB = 0; iB < 2; ++iB) {
             if ((t = a.nearPoint(b[iB])) >= 0) {
                 insert(t, iB, b[iB]);
             }
         }
@@ skipping 173 matching lines @@
 // 4 subs, 2 muls, 1 cmp
 static bool ccw(const SkDPoint& A, const SkDPoint& B, const SkDPoint& C) {
     return (C.fY - A.fY) * (B.fX - A.fX) > (B.fY - A.fY) * (C.fX - A.fX);
 }
 
 // 16 subs, 8 muls, 6 cmps
 bool SkIntersections::Test(const SkDLine& a, const SkDLine& b) {
     return ccw(a[0], b[0], b[1]) != ccw(a[1], b[0], b[1])
             && ccw(a[0], a[1], b[0]) != ccw(a[0], a[1], b[1]);
 }