+ nleft = pleft - tribuf;
+ nright = node->num_faces - nleft;
+
+ sa_left = aabox_surf_area(&bbleft);
+ sa_right = aabox_surf_area(&bbright);
+
+ /* intersection cost = 1, traversal cost = 0.2 * intesection cost */
+ cost_left = sa_left * nleft;
+ cost_right = sa_right * nright;
+ cost = 0.2f + (cost_left + cost_right) / area;