pathops: Split loop type cubics only when there is a self-intersection.

src/pathops/SkPathOpsCubic.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 "SkGeometry.h"
 #include "SkLineParameters.h"
 #include "SkPathOpsConic.h"
 #include "SkPathOpsCubic.h"
@@ skipping 222 matching lines @@
     SkScalar d[3];
     SkCubicType cubicType = SkClassifyCubic(pointsPtr, d);
     if (cubicType == kLoop_SkCubicType) {
         // crib code from gpu path utils that finds t values where loop self-intersects
         // use it to find mid of t values which should be a friendly place to chop
         SkScalar tempSqrt = SkScalarSqrt(4.f * d[0] * d[2] - 3.f * d[1] * d[1]);
         SkScalar ls = d[1] - tempSqrt;
         SkScalar lt = 2.f * d[0];
         SkScalar ms = d[1] + tempSqrt;
         SkScalar mt = 2.f * d[0];
-        if (between(0, ls, lt) || between(0, ms, mt)) {
+        if (between(0, ls, lt) && between(0, ms, mt)) {  // Both in [0, 1] interval.
             ls = ls / lt;
             ms = ms / mt;
-            SkScalar smaller = SkTMax(0.f, SkTMin(ls, ms));
-            SkScalar larger = SkTMin(1.f, SkTMax(ls, ms));
-            *t = (smaller + larger) / 2;
-            return *t > 0 && *t < 1;
+            SkASSERT(ls >= 0 && ls <= 1 && ms >= 0 && ms <= 1);  // Both in [0, 1].

[caryclark, 2016/04/25 14:46:30]

use between, e.g.:
 SkASSERT(between(0, ls, 1) && between(0, ms, 1));

+            *t = (ls + ms) / 2;
+            SkASSERT(*t >= 0 && *t <= 1);  // Average should also be in [0, 1].

[caryclark, 2016/04/25 14:46:30]

use between

+            return *t > 0 && *t < 1;  // Check that the cut isn't on an endpoint.

[caryclark, 2016/04/25 14:46:30]

use zero_or_one(t)

         }
     } else if (kSerpentine_SkCubicType == cubicType || kCusp_SkCubicType == cubicType) {
         SkDCubic cubic;
         cubic.set(pointsPtr);
         double inflectionTs[2];
         int infTCount = cubic.findInflections(inflectionTs);
         if (infTCount == 2) {
             double maxCurvature[3];
             int roots = cubic.findMaxCurvature(maxCurvature);
 #if DEBUG_CUBIC_SPLIT
@@ skipping 429 matching lines @@
     for (int index = 0; index < roots; ++index) {
         double t = startT + (endT - startT) * extremeTs[index];
         SkDPoint mid = dCurve.ptAtT(t);
         if (topPt->fY > mid.fY || (topPt->fY == mid.fY && topPt->fX > mid.fX)) {
             topT = t;
             *topPt = mid;
         }
     }
     return topT;
 }