Re: line-start?

[Eli Zaretskii <eliz@gnu.org>]

> From: Bastien <bzg@gnu.org>
> Cc: emacs-devel@gnu.org
> Date: Fri, 07 Feb 2020 11:48:02 +0100
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Then (nth 1) of what posn-at-x-y returns is not what you want.  You
> > should use the (car (nth 6)) instead.
> 
> FWIW I just tried this:
> 
> (car (nth 6 (posn-at-x-y
> 	0 (+ (cdr (posn-x-y (posn-at-point pos window)))
> 	     (- (nth 1 (window-edges nil t nil t))
> 		(nth 1 (window-edges nil nil nil t)))))))
> 
> but it always returns 0.

Ah, yes: you will have to add (window-hscroll) to that.

> The version with (nth 1 ...) works fine, though.

But that gives a buffer position, not column number.

> >> The use case was this one: given a line, display the content of this
> >> line in the header line.  When horizontally scrolled, the header has
> >> to display a substring of the line under the cursor, something like
> >> (substring (current-line-string) offset-in-columns).
> >
> > But using the buffer position, you could use buffer-substring instead,
> > right?
> 
> Yes, sure, but I still need to know the window line start to get the
> offset.

No, buffer position is absolute.