// find an ear (always a triangle) of the polygon and return the index of the middle (second) vertex in the ear
public static int FindEar(Polygon poly)
{
for (int i = 0; i < poly.PtList.Count - 2; i++)
{
if (poly.VertexType(i + 1) == PolygonType.Convex)
{
// get the three points of the triangle we are about to test
PointF a = poly.PtList[i];
PointF b = poly.PtList[i + 1];
PointF c = poly.PtList[i + 2];
bool foundAPointInTheTriangle = false; // see if any of the other points in the polygon are in this triangle
for (int j = 0; j < poly.PtListOpen.Count; j++) // don't check the last point, which is a duplicate of the first
{
if (j != i && j != i+1 && j != i+2 && PointInTriangle(poly.PtList[j], a, b, c)) foundAPointInTheTriangle = true;
}
if (!foundAPointInTheTriangle) // the middle point of this triangle is convex and none of the other points in the polygon are in this triangle, so it is an ear
return i + 1; // EXITING HERE!
}
}
throw new ApplicationException("Improperly formed polygon");
}
