func Blit(x, y, width int, cells []termbox.Cell) {
    tw, th := termbox.Size()
    height := len(cells) / width
    rw, rh := width, height
    offset := 0
    if x > tw || y > th {
        return
    }
    if x+width > tw {
        rw = tw - x
    }
    if x < 0 {
        rw += x
        offset = -x
        if offset > width {
            return
        }
    }
    if y+height > th {
        rh = th - y
    }
    if y < 0 {
        rh += y
        if rh <= 0 {
            return
        }
        y = 0
    }
    bb := termbox.CellBuffer()
    for i := 0; i < rh; i++ {
        copy(bb[(y+i)*tw+x+offset:], cells[i*width+offset:i*width+offset+rw])
    }
}