public SimplePolygon(Vector2[] points)
{
if (points.Length < 3)
throw new ArgumentException("Insufficent vertices.");
var face = new Face();
Vertex firstVertex = new Vertex(points[0]);
this.firstEdge = new HalfEdge();
firstEdge.Origin = firstVertex;
firstEdge.Face = face;
face.ConnectedEdge = firstEdge;
var previousEdge = firstEdge;
foreach (var point in points.Skip(1))
{
var edge = new HalfEdge();
edge.Origin = new Vertex(point);
edge.Face = face;
edge.Previous = previousEdge;
previousEdge.Next = edge;
previousEdge = edge;
}
firstEdge.Previous = previousEdge;
previousEdge.Next = firstEdge;
if (!PolygonIsSimpleAndHasSortedVertices())
throw new ArgumentException("Polygon is not simple.");
}
public bool Intersects(HalfEdge other)
{
Vector2 u0 = this.Origin.Position,
u = this.Vector,
v0 = other.Origin.Position,
v = other.Vector;
double crossProductZ = Vector2.Cross(u, v);
if (crossProductZ == 0)
return false;
double k = Vector2.Cross(v0 - u0, u) / crossProductZ,
l = Vector2.Cross(v0 - u0, v) / crossProductZ;
if (k <= 0 || k >= 1 || l <= 0 || l >= 1)
return false;
return true;
}
public Vector2 GetIntersection(HalfEdge other)
{
Vector2 u0 = this.Origin.Position,
u = this.Vector,
v0 = other.Origin.Position,
v = other.Vector;
double crossProductZ = Vector2.Cross(u, v);
if (crossProductZ == 0)
throw new ArgumentException("Edges are parallel.");
double k = Vector2.Cross(v0 - u0, u) / crossProductZ,
l = Vector2.Cross(v0 - u0, v) / crossProductZ;
if (k <= 0 || k >= 1 || l <= 0 || l >= 1)
throw new ArgumentException("Edges do not intersect each other.");
Debug.Assert(u0 + k * u == v0 + l * v);
return u0 + k * u;
}
protected HalfEdge GetNextEdge(HalfEdge current)
{
try
{
return current.Next;
}
catch (NullReferenceException)
{
throw new ArgumentNullException("Edges are not closing.");
}
}
public HalfEdgeNode(HalfEdge edge)
{
this.edge = edge;
}