// Split `polygon` by this plane if needed, then put the polygon or polygon
// fragments in the appropriate lists. Coplanar polygons go into either
// `coplanarFront` or `coplanarBack` depending on their orientation with
// respect to this plane. Polygons in front or in back of this plane go into
// either `front` or `back`.
public void SplitPolygon(CSG_Polygon polygon, List<CSG_Polygon> coplanarFront, List<CSG_Polygon> coplanarBack, List<CSG_Polygon> front, List<CSG_Polygon> back)
{
// Classify each point as well as the entire polygon into one of the above
// four classes.
EPolygonType polygonType = 0;
List<EPolygonType> types = new List<EPolygonType>();
for (int i = 0; i < polygon.vertices.Count; i++)
{
float t = Vector3.Dot(this.normal, polygon.vertices[i].position) - this.w;
EPolygonType type = (t < -CSG.EPSILON) ? EPolygonType.Back : ((t > CSG.EPSILON) ? EPolygonType.Front : EPolygonType.Coplanar);
polygonType |= type;
types.Add(type);
}
// Put the polygon in the correct list, splitting it when necessary.
switch (polygonType)
{
case EPolygonType.Coplanar:
{
if ( Vector3.Dot(this.normal, polygon.plane.normal) > 0)
coplanarFront.Add(polygon);
else
coplanarBack.Add(polygon);
}
break;
case EPolygonType.Front:
{
front.Add(polygon);
}
break;
case EPolygonType.Back:
{
back.Add(polygon);
}
break;
case EPolygonType.Spanning:
{
List<CSG_Vertex> f = new List<CSG_Vertex>();
List<CSG_Vertex> b = new List<CSG_Vertex>();
for (int i = 0; i < polygon.vertices.Count; i++)
{
int j = (i + 1) % polygon.vertices.Count;
EPolygonType ti = types[i], tj = types[j];
CSG_Vertex vi = polygon.vertices[i], vj = polygon.vertices[j];
if (ti != EPolygonType.Back)
{
f.Add(vi);
}
if (ti != EPolygonType.Front)
{
b.Add(vi);
}
if ((ti | tj) == EPolygonType.Spanning)
{
float t = (this.w - Vector3.Dot(this.normal, vi.position)) / Vector3.Dot(this.normal, vj.position - vi.position);
CSG_Vertex v = CSG_Vertex.Interpolate(vi, vj, t);
f.Add(v);
b.Add(v);
}
}
if (f.Count >= 3)
{
front.Add( new CSG_Polygon(f) );
}
if (b.Count >= 3)
{
back.Add( new CSG_Polygon(b) );
}
}
break;
} // End switch(polygonType)
}