code: func (g *Game) Draw(screen *ebiten.Image) {
  	if g.boardImage == nil {
  		w, h := g.board.Size()
  		g.boardImage, _ = ebiten.NewImage(w, h, ebiten.FilterDefault)
  	}
  	screen.Fill(backgroundColor)
  	g.board.Draw(g.boardImage)
  	op := &ebiten.DrawImageOptions{}
  	sw, sh := screen.Size()
  	bw, bh := g.boardImage.Size()
  	x := (sw - bw) / 2
  	y := (sh - bh) / 2
  	op.GeoM.Translate(float64(x), float64(y))
  	screen.DrawImage(g.boardImage, op)
  }
docs: // Draw draws the current game to the given screen.