add gm for path-arcs, and catch degenerate arc in conic-case

src/core/SkPath.cpp

 /*
  * Copyright 2006 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 "SkBuffer.h"
 #include "SkErrorInternals.h"
 #include "SkGeometry.h"
@@ skipping 916 matching lines @@
 static int build_arc_points(const SkRect& oval, const SkVector& start, const SkVector& stop,
                             SkRotationDirection dir, SkPoint pts[kSkBuildQuadArcStorage]) {
     SkMatrix    matrix;
 
     matrix.setScale(SkScalarHalf(oval.width()), SkScalarHalf(oval.height()));
     matrix.postTranslate(oval.centerX(), oval.centerY());
 
     return SkBuildQuadArc(start, stop, dir, &matrix, pts);
 }
 #else
+/**
+ *  If this returns 0, then the caller should just line-to the singlePt, else it should
+ *  ignore singlePt and append the specified number of conics.
+ */
 static int build_arc_conics(const SkRect& oval, const SkVector& start, const SkVector& stop,
-                            SkRotationDirection dir, SkConic conics[SkConic::kMaxConicsForArc]) {
+                            SkRotationDirection dir, SkConic conics[SkConic::kMaxConicsForArc],
+                            SkPoint* singlePt) {
     SkMatrix    matrix;
 
     matrix.setScale(SkScalarHalf(oval.width()), SkScalarHalf(oval.height()));
     matrix.postTranslate(oval.centerX(), oval.centerY());
 
-    return SkConic::BuildUnitArc(start, stop, dir, &matrix, conics);
+    int count = SkConic::BuildUnitArc(start, stop, dir, &matrix, conics);
+    if (0 == count) {
+        matrix.mapXY(start.x(), start.y(), singlePt);
+    }
+    return count;
 }
 #endif
 
 void SkPath::addRoundRect(const SkRect& rect, const SkScalar radii[],
                           Direction dir) {
     SkRRect rrect;
     rrect.setRectRadii(rect, (const SkVector*) radii);
     this->addRRect(rrect, dir);
 }
 
@@ skipping 214 matching lines @@
     SkPoint pts[kSkBuildQuadArcStorage];
     int count = build_arc_points(oval, startV, stopV, dir, pts);
     SkASSERT((count & 1) == 1);
 
     this->incReserve(count);
     forceMoveTo ? this->moveTo(pts[0]) : this->lineTo(pts[0]);
     for (int i = 1; i < count; i += 2) {
         this->quadTo(pts[i], pts[i+1]);
     }
 #else
+    SkPoint singlePt;
     SkConic conics[SkConic::kMaxConicsForArc];
-    int count = build_arc_conics(oval, startV, stopV, dir, conics);
+    int count = build_arc_conics(oval, startV, stopV, dir, conics, &singlePt);
     if (count) {
         this->incReserve(count * 2 + 1);
         const SkPoint& pt = conics[0].fPts[0];
         forceMoveTo ? this->moveTo(pt) : this->lineTo(pt);
         for (int i = 0; i < count; ++i) {
             this->conicTo(conics[i].fPts[1], conics[i].fPts[2], conics[i].fW);
         }
+    } else {
+        forceMoveTo ? this->moveTo(singlePt) : this->lineTo(singlePt);
     }
 #endif
 }
 
 void SkPath::addArc(const SkRect& oval, SkScalar startAngle, SkScalar sweepAngle) {
     if (oval.isEmpty() || 0 == sweepAngle) {
         return;
     }
 
     const SkScalar kFullCircleAngle = SkIntToScalar(360);
@@ skipping 1576 matching lines @@
     switch (this->getFillType()) {
         case SkPath::kEvenOdd_FillType:
         case SkPath::kInverseEvenOdd_FillType:
             w &= 1;
             break;
         default:
             break;
     }
     return SkToBool(w);
 }