def line_width( segs ):
	"""
	Return the screen column width of one line of a text layout structure.

	This function ignores any existing shift applied to the line,
	represended by an (amount, None) tuple at the start of the line.
	"""
	sc = 0
	seglist = segs
	if segs and len(segs[0])==2 and segs[0][1]==None:
		seglist = segs[1:]
	for s in seglist:
		sc += s[0]
	return sc