void Travail ()
{ // create random acceleration vector
acceleration = Vect (Random (-1.0, 1.0), Random (-1.0, 1.0), 0);
acceleration.Scale (0.5);
// add acceleration
velocity += acceleration;
// limit the speed, see Limit method below
velocity = Limit (velocity, top_speed);
// update position, translating velocity onto Feld size and orientation
IncTranslation (MapToFeld (velocity));
// detect bounds
Vect v = Translation ();
if (v . Dot (over) > (loc + over * wid / 2.0) . Dot (over))
IncTranslation (MapToFeld (Vect (-wid, 0, 0)));
if (v . Dot (over) < (loc - over * wid / 2.0) . Dot (over))
IncTranslation (MapToFeld (Vect (wid, 0, 0)));
if (v . Dot (up) > (loc + up * hei / 2.0) . Dot (up))
IncTranslation (MapToFeld (Vect (0, -hei, 0)));
if (v . Dot (up) < (loc - up * hei / 2.0) . Dot (up))
IncTranslation (MapToFeld (Vect (0, hei, 0)));
}
