// 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)
{
double splitTolerance = 0.00001;
// Classify each point as well as the entire polygon into one of the above
// four classes.
PolyType polygonType = PolyType.COPLANAR;
List <PolyType> types = new List <PolyType>();
for (int i = 0; i < polygon.vertices.Count; i++)
{
double t = Vector3.Dot(this.normal, polygon.vertices[i].Position) - this.w;
PolyType type = (t < -splitTolerance) ? PolyType.BACK : ((t > splitTolerance) ? PolyType.FRONT : PolyType.COPLANAR);
polygonType |= type;
types.Add(type);
}
// Put the polygon in the correct list, splitting it when necessary.
switch (polygonType)
{
case PolyType.COPLANAR:
{
if (Vector3.Dot(this.normal, polygon.plane.normal) > 0)
{
coplanarFront.Add(polygon);
}
else
{
coplanarBack.Add(polygon);
}
break;
}
case PolyType.FRONT:
{
front.Add(polygon);
break;
}
case PolyType.BACK:
{
back.Add(polygon);
break;
}
case PolyType.SPANNING:
{
List <IVertex> frontVertices = new List <IVertex>();
List <IVertex> backVertices = new List <IVertex>();
for (int firstVertexIndex = 0; firstVertexIndex < polygon.vertices.Count; firstVertexIndex++)
{
int nextVertexIndex = (firstVertexIndex + 1) % polygon.vertices.Count;
PolyType firstPolyType = types[firstVertexIndex];
PolyType nextPolyType = types[nextVertexIndex];
IVertex firstVertex = polygon.vertices[firstVertexIndex];
IVertex nextVertex = polygon.vertices[nextVertexIndex];
if (firstPolyType != PolyType.BACK)
{
frontVertices.Add(firstVertex);
}
if (firstPolyType != PolyType.FRONT)
{
backVertices.Add(firstVertex);
}
if ((firstPolyType | nextPolyType) == PolyType.SPANNING)
{
double planDotFirstVertex = Vector3.Dot(this.normal, firstVertex.Position);
double firstDistToPlane = this.w - planDotFirstVertex;
Vector3 deltaFromFirstToNext = nextVertex.Position - firstVertex.Position;
double t = firstDistToPlane / Vector3.Dot(this.normal, deltaFromFirstToNext);
IVertex newVertex = firstVertex.CreateInterpolated(nextVertex, t);
frontVertices.Add(newVertex);
backVertices.Add(newVertex);
}
}
if (frontVertices.Count >= 3)
{
front.Add(new CsgPolygon(frontVertices));
}
if (backVertices.Count >= 3)
{
back.Add(new CsgPolygon(backVertices));
}
}
break;
default:
throw new NotImplementedException();
}
}
