float plane_dist(const struct plane *p, const cgm_vec3 *pt);
float plane_sdist(const struct plane *p, const cgm_vec3 *pt);
-void midplane(struct plane *p, const cgm_vec3 *a, const cgm_vec3 *b);
+void midplane(struct plane *p, const cgm_vec3 *a, const cgm_vec3 *b, float offs);
void poly_plane(const struct poly *poly, struct plane *plane);
int plane_poly(const struct plane *plane, struct poly *poly, float size);