#37 Fix bug in "is flip needed" test (isFlipNeeded)

Previously flip was rejected only if both vertices of flip-candidate belong to the super-tri.
The change rejects the flip if at least one vertex belongs to super-tri and original edge does not touch super-tri.
If both original edge and flipped edge touch super-tri: use normal circumcircle test as a tie-breaker.

Add two test files for regression testing.

CDT/include/CDT.hpp

@@ -451,16 +451,23 @@ bool Triangulation<T>::isFlipNeeded(
  const Triangle& tOpo = triangles[iTopo];
  const Index i = opposedVertexInd(tOpo, iT);
  const VertInd iVopo = tOpo.vertices[i];
- if(m_superGeomType == SuperGeometryType::SuperTriangle)
- if(iVert < 3 && iVopo < 3) // opposed vertices belong to super-triangle
- return false; // no flip is needed
  const VertInd iVcw = tOpo.vertices[cw(i)];
  const VertInd iVccw = tOpo.vertices[ccw(i)];
  const V2d<T>& v1 = vertices[iVcw].pos;
  const V2d<T>& v2 = vertices[iVopo].pos;
  const V2d<T>& v3 = vertices[iVccw].pos;
  if(m_superGeomType == SuperGeometryType::SuperTriangle)
  {
+ if(iVert < 3 || iVopo < 3) // flip-candidate edge touches super-triangle
+ {
+ if(iVcw < 3 || iVccw < 3) // but so does original edge
+ {
+ // let the normal circumcircle test decide
+ return isInCircumcircle(pos, v1, v2, v3);
+ }
+ return false; // no flip is needed
+ }
+
  if(iVcw < 3)
  return locatePointLine(v1, v2, v3) == locatePointLine(pos, v2, v3);
  if(iVccw < 3)

visualizer/data/regression_issue_38_wrong_hull.txt

@@ -0,0 +1,37 @@
+36 0
+0.15147567518991 -5.144230291488
+0.10442 -5.06098
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+0.2499264107145 -5.032151486545
+0.284064991072 -4.980986604815

visualizer/data/regression_issue_38_wrong_hull_small.txt

@@ -0,0 +1,7 @@
+6 0
+0.15147567518991 -5.144230291488
+0.10442 -5.06098
+0.1228735248885 -5.12897066233
+0.1322969035965 -5.141286788425
+0.115882234089 -5.115648852375
+0.13262891777369 -5.119598039304