// 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(CSGPolygon polygon, List <CSGPolygon> coplanarFront, List <CSGPolygon> coplanarBack, List <CSGPolygon> front, List <CSGPolygon> back)
{
// Classify each point as well as the entire polygon into one of the above
// four classes.
int polygonType = 0;
int[] types = new int[polygon.vertices.Count];
for (int i = 0; i < polygon.vertices.Count; i++)
{
float t = this.normal.dot(polygon.vertices[i].pos) - this.w;
int type = (t < -EPSILON) ? BACK : (t > EPSILON) ? FRONT : COPLANAR;
polygonType |= type;
types[i] = type;
}
// Put the polygon in the correct list, splitting it when necessary.
switch (polygonType)
{
case COPLANAR:
(this.normal.dot(polygon.plane.normal) > 0 ? coplanarFront : coplanarBack).Add(polygon);
break;
case FRONT:
front.Add(polygon);
break;
case BACK:
back.Add(polygon);
break;
case SPANNING:
{
List <CSGVertex> f = new List <CSGVertex>();
List <CSGVertex> b = new List <CSGVertex>();
for (int i = 0; i < polygon.vertices.Count; i++)
{
int j = (i + 1) % polygon.vertices.Count;
int ti = types[i];
int tj = types[j];
CSGVertex vi = polygon.vertices[i];
CSGVertex vj = polygon.vertices[j];
if (ti != BACK)
{
f.Add(vi);
}
if (ti != FRONT)
{
b.Add(ti != BACK ? vi.clone() : vi);
}
if ((ti | tj) == SPANNING)
{
float t = (this.w - this.normal.dot(vi.pos)) / this.normal.dot(vj.pos.minus(vi.pos));
CSGVertex v = vi.interpolate(vj, t);
f.Add(v);
b.Add(v.clone());
}
}
if (f.Count >= 3)
{
front.Add(new CSGPolygon(f, polygon.shared));
}
if (b.Count >= 3)
{
back.Add(new CSGPolygon(b, polygon.shared));
}
break;
}
}
}