GNU bug report logs - #6763
24.0.50.1; Doc string of `window-line-height'

Previous Next

Full log

View this message in rfc822 format

From: Eli Zaretskii <eliz <at> gnu.org>
To: IRIE Shinsuke <irieshinsuke <at> yahoo.co.jp>
Cc: 6763 <at> debbugs.gnu.org
Subject: bug#6763: 24.0.50.1; Doc string of `window-line-height'
Date: Fri, 30 Jul 2010 21:34:57 +0300

> Date: Sat, 31 Jul 2010 03:12:09 +0900
> From: IRIE Shinsuke <irieshinsuke <at> yahoo.co.jp>
> Cc: 6763 <at> debbugs.gnu.org
> 
> > I think you misunderstood the doc string.  It means that instead of
> > 
> >   (window-line-height)
> > 
> > you should use
> > 
> >   (pos-visible-in-window-p)
> 
> `pos-visible-in-window-p' doesn't return a line height, so we can never
> use it as a substitute of `window-line-height'.

window-line-height doesn't return the line height, either.  It returns
a list of 4 values.  pos-visible-in-window-p can also return a similar
list, see its doc string.

> >   (or (window-line-height)
> >       (pos-visible-in-window-p))
> 
> Why? If `window-line-height' returns nil, the result of this expression
> becomes t or nil.

No, `or' returns the value of the first expression whose value is
non-nil.  It doesn't necessarily return a boolean.  See its doc
string.

> I guess the doc string means "`pos-visible-in-window-p' updates the
> matrices' information, so call it before `window-line-height'."

It doesn't update the matrices, it just works in a way that doesn't
need the glyph matrices to be up-to-date.  And no, calling
pos-visible-in-window-p before window-line-height will not help,
because the glyph matrices used by window-line-height are still not up
to date after a call to pos-visible-in-window-p.

> In that case, however, it seems redisplaying is necessary for getting
> the useful result. As I wrote in the previous mail, the following
> expression properly returns the line height.
> 
>   (progn (redisplay t)
>          (window-line-height))

Yes, but the call to `redisplay' is quite expensive, so this is
inappropriate in many use-cases.

> I think `pos-visible-in-window-p' in the doc string should be changed
> to `redisplay'.

Sorry, I disagree.  I think the doc string is generally correct, it
just might need an example to make clear what it means.

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.