break out of cubic stroker loop on degenerate case

src/core/SkStroke.cpp

 /*
  * Copyright 2008 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkStrokerPriv.h"
 #include "SkGeometry.h"
 #include "SkPath.h"
@@ skipping 887 matching lines @@
 #endif
 
     this->postJoinTo(pt2, normalBC, unitBC);
 }
 
 #ifdef SK_QUAD_STROKE_APPROXIMATION
 // Given a point on the curve and its derivative, scale the derivative by the radius, and
 // compute the perpendicular point and its tangent.
 void SkPathStroker::setRayPts(const SkPoint& tPt, SkVector* dxy, SkPoint* onPt,
         SkPoint* tangent) const {
+    SkPoint oldDxy = *dxy;
     if (!dxy->setLength(fRadius)) {  // consider moving double logic into SkPoint::setLength
-        double xx = dxy->fX;
-        double yy = dxy->fY;
+        double xx = oldDxy.fX;
+        double yy = oldDxy.fY;
         double dscale = fRadius / sqrt(xx * xx + yy * yy);
         dxy->fX = SkDoubleToScalar(xx * dscale);
         dxy->fY = SkDoubleToScalar(yy * dscale);
     }
     SkScalar axisFlip = SkIntToScalar(fStrokeType);  // go opposite ways for outer, inner
     onPt->fX = tPt.fX + axisFlip * dxy->fY;
     onPt->fY = tPt.fY - axisFlip * dxy->fX;
     if (tangent) {
         tangent->fX = onPt->fX + dxy->fX;
         tangent->fY = onPt->fY + dxy->fY;
@@ skipping 484 matching lines @@
     SkVector normalAB, unitAB, normalCD, unitCD;
     this->preJoinTo(*tangentPt, &normalAB, &unitAB, false);
     SkScalar tValues[2];
     int count = SkFindCubicInflections(cubic, tValues);
     SkScalar lastT = 0;
     for (int index = 0; index <= count; ++index) {
         SkScalar nextT = index < count ? tValues[index] : 1;
         SkQuadConstruct quadPts;
         this->init(kOuter_StrokeType, &quadPts, lastT, nextT);
         if (!this->cubicStroke(cubic, &quadPts)) {
-            return;
+            break;
         }
         this->init(kInner_StrokeType, &quadPts, lastT, nextT);
         if (!this->cubicStroke(cubic, &quadPts)) {
-            return;
+            break;
         }
         lastT = nextT;
     }
+    // emit the join even if one stroke succeeded but the last one failed
+    // this avoids reversing an inner stroke with a partial path followed by another moveto
     this->setCubicEndNormal(cubic, normalAB, unitAB, &normalCD, &unitCD);
 #else
     bool    degenerateAB = SkPath::IsLineDegenerate(fPrevPt, pt1);
     bool    degenerateBC = SkPath::IsLineDegenerate(pt1, pt2);
     bool    degenerateCD = SkPath::IsLineDegenerate(pt2, pt3);
 
     if (degenerateAB + degenerateBC + degenerateCD >= 2
             || (degenerateAB && SkPath::IsLineDegenerate(fPrevPt, pt2))) {
         this->lineTo(pt3);
         return;
@@ skipping 303 matching lines @@
         default:
             break;
     }
 
     if (fWidth < SkMinScalar(rw, rh) && !fDoFill) {
         r = rect;
         r.inset(radius, radius);
         dst->addRect(r, reverse_direction(dir));
     }
 }