canvas.go
func DrawVerticalLine(x, y, h int, r rune) {
	x, y, _, h = clip(x, y, 1, h)
	if h == 0 {
		return
	}

	for i := y; i < y+h; i++ {
		putCharUnsafe(x, i, r)
	}
}
func DrawVerticalLine(x, y, h int, r rune) {
	x, y, _, h = clip(x, y, 1, h)
	if h == 0 {
		return
	}

	for i := y; i < y+h; i++ {
		putCharUnsafe(x, i, r)
	}
}
// DrawVerticalLine draws the part of the vertical line that is inside current
// clipping rectangle