/// <summary>
/// Test the triad against its 3 neighbours and flip it with any neighbour whose opposite point
/// is inside the circumcircle of the triad
/// </summary>
/// <param name="triads">The triads</param>
/// <param name="triadIndexToTest">The index of the triad to test</param>
/// <param name="triadIndexFlipped">Index of adjacent triangle it was flipped with (if any)</param>
/// <returns>true iff the triad was flipped with any of its neighbours</returns>
bool FlipTriangle(List <Triad> triads, int triadIndexToTest, out int triadIndexFlipped)
{
int oppositeVertex = 0, edge1, edge2, edge3 = 0, edge4 = 0;
triadIndexFlipped = 0;
Triad tri = triads[triadIndexToTest];
// test all 3 neighbours of tri
if (tri.bc >= 0)
{
triadIndexFlipped = tri.bc;
Triad t2 = triads[triadIndexFlipped];
// find relative orientation (shared limb).
t2.FindAdjacency(tri.b, triadIndexToTest, out oppositeVertex, out edge3, out edge4);
if (tri.InsideCircumcircle(points[oppositeVertex]))
{ // not valid in the Delaunay sense.
edge1 = tri.ab;
edge2 = tri.ac;
if (edge1 != edge3 && edge2 != edge4)
{
int tria = tri.a, trib = tri.b, tric = tri.c;
tri.Initialize(tria, trib, oppositeVertex, edge1, edge3, triadIndexFlipped, points);
t2.Initialize(tria, tric, oppositeVertex, edge2, edge4, triadIndexToTest, points);
// change knock on triangle labels.
if (edge3 >= 0)
{
triads[edge3].ChangeAdjacentIndex(triadIndexFlipped, triadIndexToTest);
}
if (edge2 >= 0)
{
triads[edge2].ChangeAdjacentIndex(triadIndexToTest, triadIndexFlipped);
}
return(true);
}
}
}
if (tri.ab >= 0)
{
triadIndexFlipped = tri.ab;
Triad t2 = triads[triadIndexFlipped];
// find relative orientation (shared limb).
t2.FindAdjacency(tri.a, triadIndexToTest, out oppositeVertex, out edge3, out edge4);
if (tri.InsideCircumcircle(points[oppositeVertex]))
{ // not valid in the Delaunay sense.
edge1 = tri.ac;
edge2 = tri.bc;
if (edge1 != edge3 && edge2 != edge4)
{
int tria = tri.a, trib = tri.b, tric = tri.c;
tri.Initialize(tric, tria, oppositeVertex, edge1, edge3, triadIndexFlipped, points);
t2.Initialize(tric, trib, oppositeVertex, edge2, edge4, triadIndexToTest, points);
// change knock on triangle labels.
if (edge3 >= 0)
{
triads[edge3].ChangeAdjacentIndex(triadIndexFlipped, triadIndexToTest);
}
if (edge2 >= 0)
{
triads[edge2].ChangeAdjacentIndex(triadIndexToTest, triadIndexFlipped);
}
return(true);
}
}
}
if (tri.ac >= 0)
{
triadIndexFlipped = tri.ac;
Triad t2 = triads[triadIndexFlipped];
// find relative orientation (shared limb).
t2.FindAdjacency(tri.a, triadIndexToTest, out oppositeVertex, out edge3, out edge4);
if (tri.InsideCircumcircle(points[oppositeVertex]))
{ // not valid in the Delaunay sense.
edge1 = tri.ab; // .ac shared limb
edge2 = tri.bc;
if (edge1 != edge3 && edge2 != edge4)
{
int tria = tri.a, trib = tri.b, tric = tri.c;
tri.Initialize(trib, tria, oppositeVertex, edge1, edge3, triadIndexFlipped, points);
t2.Initialize(trib, tric, oppositeVertex, edge2, edge4, triadIndexToTest, points);
// change knock on triangle labels.
if (edge3 >= 0)
{
triads[edge3].ChangeAdjacentIndex(triadIndexFlipped, triadIndexToTest);
}
if (edge2 >= 0)
{
triads[edge2].ChangeAdjacentIndex(triadIndexToTest, triadIndexFlipped);
}
return(true);
}
}
}
return(false);
}