intersection.cpp

#include "model.h"

#define EPSILON 0.0001

// ray-triangle intersection predicate (Möller–Trumbore algorithm)
 
int ray_triangle(const vertex v0,   // triangle vertices
		 const vertex v1,
		 const vertex v2,
		 const vertex  o,   // ray origin
		 const vector  d,   // ray direction
		 float*        out)
{
    vector e0, e1, p, q, t;
    float det, inv_det, u, v, tf;
 
    // vectors of edges sharing V0
    e0 = vector(v0, v1);
    e1 = vector(v0, v2);

    // determinant calculation - also used for u parameter
    p = d % e1;

    // if det ~= zero, ray lies in plane of triangle
    det = e0 * p;

    // not culling
    if(det > -EPSILON && det < EPSILON) return 0;
    inv_det = 1.f / det;
 
    // distance from V0 to ray origin
    t = vector(v0, o);
 
    // u parameter calculation and bound test
    u = (t * p) * inv_det;
    // intersection lies outside of the triangle
    if(u < 0.f || u > 1.f) return 0;
 
    // v parameter test preparation
    q = t % e0;
 
    // v parameter calculation and bound test
    v = (d * q) * inv_det;

    // intersection outside of the triangle
    if(v < 0.f || u + v  > 1.f) return 0;
 
    tf = (e1 * q) * inv_det;
 
    if(tf > EPSILON) {
	*out = tf;
	return 1;
    }

    return 0;
}