// https://twitter.com/brunolevy01/status/1229664999179726848
// "(Moller-Tumblore). A, B, C is the triangle, O, D is the ray."
// gives barycentric coordinates and normal for free.
bool ray_triangle_intersection(vec3 A, vec3 B, vec3 C, vec3 O, vec3 D)
{
vec3 E1 = B - A;
vec3 E2 = C - A;
vec3 N = cross(E1, E2);
float det = -dot(D, N);
vec3 AO = O - A;
vec3 DAO = cross(AO, D);
float u = dot(E2, DAO) / det;
float v = -dot(E1, DAO) / det;
float t = dot(AO, N) / det;
return (t > 0. && u > 0. && v > 0. && (u + v) < 1.);
}