fix cubic/line intersection; add skp tests

src/pathops/SkDCubicLineIntersection.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 "SkPathOpsCubic.h"
 #include "SkPathOpsLine.h"
 
@@ skipping 284 matching lines @@
 
     bool pinTs(double* cubicT, double* lineT, SkDPoint* pt, PinTPoint ptSet) {
         if (!approximately_one_or_less(*lineT)) {
             return false;
         }
         if (!approximately_zero_or_more(*lineT)) {
             return false;
         }
         double cT = *cubicT = SkPinT(*cubicT);
         double lT = *lineT = SkPinT(*lineT);
+        SkDPoint lPt = fLine.ptAtT(lT);
+        SkDPoint cPt = fCubic.ptAtT(cT);
+        if (!lPt.moreRoughlyEqual(cPt)) {
+            return false;
+        }
+        // FIXME: if points are roughly equal but not approximately equal, need to do 
+        // a binary search like quad/quad intersection to find more precise t values
         if (lT == 0 || lT == 1 || (ptSet == kPointUninitialized && cT != 0 && cT != 1)) {
-            *pt = fLine.ptAtT(lT);
+            *pt = lPt;
         } else if (ptSet == kPointUninitialized) {
-            *pt = fCubic.ptAtT(cT);
+            *pt = cPt;
         }
         SkPoint gridPt = pt->asSkPoint();
         if (gridPt == fLine[0].asSkPoint()) {
             *lineT = 0;
         } else if (gridPt == fLine[1].asSkPoint()) {
             *lineT = 1;
         }
         if (gridPt == fCubic[0].asSkPoint() && approximately_equal(*cubicT, 0)) {
             *cubicT = 0;
         } else if (gridPt == fCubic[3].asSkPoint() && approximately_equal(*cubicT, 1)) {
@@ skipping 30 matching lines @@
 }
 
 int SkIntersections::intersectRay(const SkDCubic& cubic, const SkDLine& line) {
     LineCubicIntersections c(cubic, line, this);
     fUsed = c.intersectRay(fT[0]);
     for (int index = 0; index < fUsed; ++index) {
         fPt[index] = cubic.ptAtT(fT[0][index]);
     }
     return fUsed;
 }