// dot product (3D) which allows vector operations in arguments
static float dot(Vector u, Vector v)
{
return(u.x * v.x + u.y * v.y + u.z * v.z);
}
const float SMALL_NUM = 0.00000001F; // anything that avoids division overflow
#endregion Fields
#region Methods
public static int intersect_RayTriangle(Ray R, Triangle T, ref Vector I)
{
Vector u, v, n; // triangle vectors
Vector dir, w0, w; // ray vectors
float r, a, b; // params to calc ray-plane intersect
// get triangle edge vectors and plane normal
u = T.V1 - T.V0;
v = T.V2 - T.V0;
n = u * v; // cross product
Vector nullvec; nullvec.x = 0; nullvec.y = 0; nullvec.z = 0;
if (n == nullvec) // triangle is degenerate
return -1; // do not deal with this case
dir = R.P1 - R.P0; // ray direction vector
w0 = R.P0 - T.V0;
a = -dot(n, w0);
b = dot(n, dir);
if (Math.Abs(b) < SMALL_NUM)
{ // ray is parallel to triangle plane
if (a == 0) // ray lies in triangle plane
return 2;
else return 0; // ray disjoint from plane
}
// get intersect point of ray with triangle plane
r = a / b;
if (r < 0.0) // ray goes away from triangle
return 0; // => no intersect
// for a segment, also test if (r > 1.0) => no intersect
I = R.P0 + r * dir; // intersect point of ray and plane
// is I inside T?
float uu, uv, vv, wu, wv, D;
uu = dot(u, u);
uv = dot(u, v);
vv = dot(v, v);
w = I - T.V0;
wu = dot(w, u);
wv = dot(w, v);
D = uv * uv - uu * vv;
// get and test parametric coords
float s, t;
s = (uv * wv - vv * wu) / D;
if (s < 0.0 || s > 1.0) // I is outside T
return 0;
t = (uv * wu - uu * wv) / D;
if (t < 0.0 || (s + t) > 1.0) // I is outside T
return 0;
return 1; // I is in T
}