private static bool CanIntersect(InfPlane plane, Vector3D lineStart, Vector3D lineEnd)
{
var startAbove = IsPointAbovePlane(lineStart, plane);
var endAbove = IsPointAbovePlane(lineEnd, plane);
return((startAbove && !endAbove) || (!startAbove && endAbove));
}
private static bool TryIntersect(Mesh mesh, Face face, InfPlane plane, out LineSegment intersection)
{
intersection = null;
if (face.IndexCount != 3)
{
throw new Exception("Face not triangular!");
}
var ia = face.Indices[0];
var ib = face.Indices[1];
var ic = face.Indices[2];
var a = mesh.Vertices[ia];
var b = mesh.Vertices[ib];
var c = mesh.Vertices[ic];
var ab = CanIntersect(plane, a, b);
var bc = CanIntersect(plane, b, c);
var ca = CanIntersect(plane, c, a);
var planeNormal = plane.Normal;
var planePoint = plane.Point;
if (ab && bc)
{
var start = IntersectPoint(a, b, planeNormal, planePoint);
var end = IntersectPoint(b, c, planeNormal, planePoint);
intersection = new LineSegment(start, end, face);
}
else if (bc && ca)
{
var start = IntersectPoint(b, c, planeNormal, planePoint);
var end = IntersectPoint(c, a, planeNormal, planePoint);
intersection = new LineSegment(start, end, face);
}
else if (ca && ab)
{
var start = IntersectPoint(c, a, planeNormal, planePoint);
var end = IntersectPoint(a, b, planeNormal, planePoint);
intersection = new LineSegment(start, end, face);
}
else
{
return(false);
}
return(true);
}
public static List <LineSegment> Slice(Mesh mesh, InfPlane plane)
{
var segments = new List <LineSegment>();
foreach (var face in mesh.Faces)
{
if (!TryIntersect(mesh, face, plane, out var intersection))
{
continue;
}
segments.Add(intersection);
}
return(segments);
}
private static bool IsPointAbovePlane(Vector3D point, InfPlane plane)
{
return(plane.Normal.Dot(point - plane.Point) > 0);
}