// This clips a polygon and returns the triangles
// The polygon may not have any holes or islands
// See: http://www.geometrictools.com/Documentation/TriangulationByEarClipping.pdf
private int DoEarClip(EarClipPolygon poly, List <Vector2D> verticeslist, List <Sidedef> sidedefslist)
{
LinkedList <EarClipVertex> verts = new LinkedList <EarClipVertex>();
List <EarClipVertex> convexes = new List <EarClipVertex>(poly.Count);
LinkedList <EarClipVertex> reflexes = new LinkedList <EarClipVertex>();
LinkedList <EarClipVertex> eartips = new LinkedList <EarClipVertex>();
LinkedListNode <EarClipVertex> n1, n2;
EarClipVertex v, v1, v2;
EarClipVertex[] t, t1, t2;
int countvertices = 0;
// Go for all vertices to fill list
foreach (EarClipVertex vec in poly)
{
vec.SetVertsLink(verts.AddLast(vec));
}
// Remove any zero-length lines, these will give problems
n1 = verts.First;
do
{
// Continue until adjacent zero-length lines are removed
n2 = n1.Next ?? verts.First;
Vector2D d = n1.Value.Position - n2.Value.Position;
while ((Math.Abs(d.x) < 0.00001f) && (Math.Abs(d.y) < 0.00001f))
{
n2.Value.Remove();
n2 = n1.Next ?? verts.First;
if (n2 != null)
{
d = n1.Value.Position - n2.Value.Position;
}
else
{
break;
}
}
// Next!
n1 = n2;
}while(n1 != verts.First);
// Optimization: Vertices which have lines with the
// same angle are useless. Remove them!
n1 = verts.First;
while (n1 != null)
{
// Get the next vertex
n2 = n1.Next;
// Get triangle for v
t = GetTriangle(n1.Value);
// Check if both lines have the same angle
Line2D a = new Line2D(t[0].Position, t[1].Position);
Line2D b = new Line2D(t[1].Position, t[2].Position);
if (Math.Abs(Angle2D.Difference(a.GetAngle(), b.GetAngle())) < 0.00001f)
{
// Same angles, remove vertex
n1.Value.Remove();
}
// Next!
n1 = n2;
}
// Go for all vertices to determine reflex or convex
foreach (EarClipVertex vv in verts)
{
// Add to reflex or convex list
if (IsReflex(GetTriangle(vv)))
{
vv.AddReflex(reflexes);
}
else
{
convexes.Add(vv);
}
}
// Go for all convex vertices to see if they are ear tips
foreach (EarClipVertex cv in convexes)
{
// Add when this is a valid ear
t = GetTriangle(cv);
if (CheckValidEar(t, reflexes))
{
cv.AddEarTip(eartips);
}
}
#if DEBUG
if (OnShowPolygon != null)
{
OnShowPolygon(verts);
}
#endif
// Process ears until done
while ((eartips.Count > 0) && (verts.Count > 2))
{
// Get next ear
v = eartips.First.Value;
t = GetTriangle(v);
// Only save this triangle when it has an area
if (TriangleHasArea(t))
{
// Add ear as triangle
AddTriangleToList(t, verticeslist, sidedefslist, (verts.Count == 3));
countvertices += 3;
}
// Remove this ear from all lists
v.Remove();
v1 = t[0];
v2 = t[2];
#if DEBUG
if (TriangleHasArea(t))
{
if (OnShowEarClip != null)
{
OnShowEarClip(t, verts);
}
}
#endif
// Test first neighbour
t1 = GetTriangle(v1);
if (IsReflex(t1))
{
// List as reflex if not listed yet
if (!v1.IsReflex)
{
v1.AddReflex(reflexes);
}
v1.RemoveEarTip();
}
else
{
// Remove from reflexes
v1.RemoveReflex();
}
// Test second neighbour
t2 = GetTriangle(v2);
if (IsReflex(t2))
{
// List as reflex if not listed yet
if (!v2.IsReflex)
{
v2.AddReflex(reflexes);
}
v2.RemoveEarTip();
}
else
{
// Remove from reflexes
v2.RemoveReflex();
}
// Check if any neightbour have become a valid or invalid ear
if (!v1.IsReflex && (CheckValidEar(t1, reflexes)))
{
v1.AddEarTip(eartips);
}
else
{
v1.RemoveEarTip();
}
if (!v2.IsReflex && (CheckValidEar(t2, reflexes)))
{
v2.AddEarTip(eartips);
}
else
{
v2.RemoveEarTip();
}
}
#if DEBUG
if (OnShowRemaining != null)
{
OnShowRemaining(verts);
}
#endif
// Dispose remaining vertices
foreach (EarClipVertex ecv in verts)
{
ecv.Dispose();
}
// Return the number of vertices in the result
return(countvertices);
}