/* An Efficient Ray/Polygon Intersection by Didier Badouel from "Graphics Gems", Academic Press, 1990 just code, not a procedure. */ /* the value of t is computed. * i1 and i2 come from the polygon description. * V is the vertex table for the polygon and N the * associated normal vectors. */ P[0] = ray.O[0] + ray.D[0]*t; P[1] = ray.O[1] + ray.D[1]*t; P[2] = ray.O[2] + ray.D[2]*t; u0 = P[i1] - V[0][i1]; v0 = P[i2] - V[0][i2]; inter = FALSE; i = 2; do { /* The polygon is viewed as (n-2) triangles. */ u1 = V[i-1][i1] - V[0][i1]; v1 = V[i-1][i2] - V[0][i2]; u2 = V[i ][i1] - V[0][i1]; v2 = V[i ][i2] - V[0][i2]; if (u1 == 0) { beta = u0/u2; if ((beta >= 0.)&&(beta <= 1.)) { alpha = (v0 - beta*v2)/v1; inter = ((alpha >= 0.)&&(alpha+beta) <= 1.)); } } else { beta = (v0*u1 - u0*v1)/(v2*u1 - u2*v1); if ((beta >= 0.)&&(beta <= 1.)) { alpha = (u0 - beta*u2)/u1; inter = ((alpha >= 0)&&((alpha+beta) <= 1.)); } } } while ((!inter)&&(++i < poly.n)); if (inter) { /* Storing the intersection point. */ ray.P[0] = P[0]; ray.P[1] = P[1]; ray.P[2] = P[2]; /* the normal vector can be interpolated now or later. */ if (poly.interpolate) { gamma = 1 - (alpha+beta); ray.normal[0] = gamma * N[0][0] + alpha * N[i-1][0] + beta * N[i][0]; ray.normal[1] = gamma * N[0][1] + alpha * N[i-1][1] + beta * N[i][1]; ray.normal[2] = gamma * N[0][2] + alpha * N[i-1][2] + beta * N[i][2]; } } return (inter);