public static CSGPlane CalcPolygonPlane(ControlMesh controlMesh, short polygonIndex)
{
if (controlMesh == null ||
controlMesh.Polygons == null ||
polygonIndex >= controlMesh.Polygons.Length)
{
return(new CSGPlane(Vector3.up, 0));
}
var edgeIndices = controlMesh.Polygons[polygonIndex].EdgeIndices;
if (edgeIndices.Length == 3)
{
var v0 = controlMesh.GetVertex(edgeIndices[0]);
var v1 = controlMesh.GetVertex(edgeIndices[1]);
var v2 = controlMesh.GetVertex(edgeIndices[2]);
return(new CSGPlane(v0, v1, v2));
}
// newell's method to calculate a normal for a concave polygon
var normal = MathConstants.zeroVector3;
var prevIndex = edgeIndices.Length - 1;
if (prevIndex < 0)
{
return(new CSGPlane(MathConstants.upVector3, MathConstants.zeroVector3));
}
var prevVertex = controlMesh.GetVertex(edgeIndices[prevIndex]);
for (var e = 0; e < edgeIndices.Length; e++)
{
var currVertex = controlMesh.GetVertex(edgeIndices[e]);
normal.x = normal.x + ((prevVertex.y - currVertex.y) * (prevVertex.z + currVertex.z));
normal.y = normal.y + ((prevVertex.z - currVertex.z) * (prevVertex.x + currVertex.x));
normal.z = normal.z + ((prevVertex.x - currVertex.x) * (prevVertex.y + currVertex.y));
prevVertex = currVertex;
}
normal = normal.normalized;
var d = 0.0f;
var count = 0;
for (var e = 0; e < edgeIndices.Length; e++)
{
var currVertex = controlMesh.GetVertex(edgeIndices[e]);
d += Vector3.Dot(normal, currVertex);
count++;
}
d /= count;
return(new CSGPlane(normal, d));
}
