canvas.go
func FillRect(x, y, w, h int, r rune) {
	x, y, w, h = clip(x, y, w, h)
	if w < 1 || y < -1 {
		return
	}

	for yy := y; yy < y+h; yy++ {
		for xx := x; xx < x+w; xx++ {
			putCharUnsafe(xx, yy, r)
		}
	}
}
func FillRect(x, y, w, h int, r rune) {
	x, y, w, h = clip(x, y, w, h)
	if w < 1 || y < -1 {
		return
	}

	for yy := y; yy < y+h; yy++ {
		for xx := x; xx < x+w; xx++ {
			putCharUnsafe(xx, yy, r)
		}
	}
}
// FillRect paints the area with r character using the current colors