func (b *Board) Size() (int, int) {
	x := b.size*tileSize + (b.size+1)*tileMargin
	y := x
	return x, y
}
func (b *Board) Size() (int, int) {
	x := b.size*tileSize + (b.size+1)*tileMargin
	y := x
	return x, y
}
// Size returns the board size.