vism_at
int vism_at(int, int);
if(!vism_at(u.udisx, u.udisy))
if(!vism_at(x,y)) {
if(!vism_at(obj->ox,obj->oy))
if(!vism_at(x,y)) atl(x,y,'^');
if(!vism_at(zx, zy))