is_followable &= !tracer_ptr->phase_out;
is_followable &= los(tracer_ptr, tracer_ptr->y, tracer_ptr->x, oldfy, oldfx);
if (!is_followable) return;
is_followable &= !tracer_ptr->phase_out;
is_followable &= los(tracer_ptr, tracer_ptr->y, tracer_ptr->x, oldfy, oldfx);
if (!is_followable) return;