code: func (p *player) MoveForward() {
  	w, h := gophersImage.Size()
  	mx := w * 16
  	my := h * 16
  	s, c := math.Sincos(float64(p.angle) * 2 * math.Pi / maxAngle)
  	p.x16 += int(round(16*c) * 2)
  	p.y16 += int(round(16*s) * 2)
  	for mx <= p.x16 {
  		p.x16 -= mx
  	}
  	for my <= p.y16 {
  		p.y16 -= my
  	}
  	for p.x16 < 0 {
  		p.x16 += mx
  	}
  	for p.y16 < 0 {
  		p.y16 += my
  	}
  }
docs: // MoveForward moves the player p forward.