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

Previous Next

To add a comment to this bug, you must first unarchive it, by sending
a message to control AT debbugs.gnu.org, with unarchive 6763 in the body.
You can then email your comments to 6763 AT debbugs.gnu.org in the normal way.

Toggle the display of automated, internal messages from the tracker.

Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: IRIE Shinsuke <irieshinsuke <at> yahoo.co.jp>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.0.50.1; Doc string of `window-line-height'
Date: Fri, 30 Jul 2010 22:55:17 +0900

Hi,

Doc string of `window-line-height' says:

  Return nil if window display is not up-to-date.  In that case, use
  `pos-visible-in-window-p' to obtain the information.

However, using `pos-visible-in-window-p' seems ineffectual.
In fact, the following expression often returns nil:

  (progn (pos-visible-in-window-p)
         (window-line-height))

So I use `redisplay' instead of `pos-visible-in-window-p' as:

  (or (window-line-height)
      (and (redisplay t)
           (window-line-height)))

and it correctly works.

Please correct the doc string.

IRIE Shinsuke

Message #8 received at 6763 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: IRIE Shinsuke <irieshinsuke <at> yahoo.co.jp>
Cc: 6763 <at> debbugs.gnu.org
Subject: Re: bug#6763: 24.0.50.1; Doc string of `window-line-height'
Date: Fri, 30 Jul 2010 17:53:07 +0300

> Date: Fri, 30 Jul 2010 22:55:17 +0900
> From: IRIE Shinsuke <irieshinsuke <at> yahoo.co.jp>
> Cc: 
> 
> Doc string of `window-line-height' says:
> 
>   Return nil if window display is not up-to-date.  In that case, use
>   `pos-visible-in-window-p' to obtain the information.
> 
> However, using `pos-visible-in-window-p' seems ineffectual.
> In fact, the following expression often returns nil:
> 
>   (progn (pos-visible-in-window-p)
>          (window-line-height))

I think you misunderstood the doc string.  It means that instead of

  (window-line-height)

you should use

  (pos-visible-in-window-p)

Using progn doesn't cut it, since it always returns the value of the
last form.  What you mean is probably this:

  (or (window-line-height)
      (pos-visible-in-window-p))

If this doesn't work for you, please show a precise recipe, starting
from "emacs -Q", to reproduce the situation where
pos-visible-in-window-p returns nil when it shouldn't.

Message #11 received at 6763 <at> debbugs.gnu.org (full text, mbox):

From: IRIE Shinsuke <irieshinsuke <at> yahoo.co.jp>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 6763 <at> debbugs.gnu.org
Subject: Re: bug#6763: 24.0.50.1; Doc string of `window-line-height'
Date: Sat, 31 Jul 2010 03:12:09 +0900

> 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'.

> Using progn doesn't cut it, since it always returns the value of the
> last form.  What you mean is probably this:
> 
>   (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. What I want to obtain is a line height, not a boolean.

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

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

IRIE Shinsuke

Message #14 received at 6763 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: IRIE Shinsuke <irieshinsuke <at> yahoo.co.jp>
Cc: 6763 <at> debbugs.gnu.org
Subject: Re: 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.

Message #17 received at 6763 <at> debbugs.gnu.org (full text, mbox):

From: IRIE Shinsuke <irieshinsuke <at> yahoo.co.jp>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 6763 <at> debbugs.gnu.org
Subject: Re: bug#6763: 24.0.50.1; Doc string of `window-line-height'
Date: Sat, 31 Jul 2010 06:18:54 +0900

> > > 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.

Of course I've well known that both of them can return a list, but I
also know these lists contain the considerably different information.

  (window-line-height)                => (HEIGHT VPOS YPOS OFFBOT)

  (pos-visible-in-window-p nil nil t) => (X Y [RTOP RBOT ROWH VPOS])

If (window-line-height) is non-nil, we can obtain the number of pixels
of line height as:

  (car (window-line-height))

However, the latter has normally only two elements X and Y unless
point is in the bottom row, and never includes the line height. ROWH
is the height of displayed part of the bottom row, not a line height.
How can we obtain the line height from such a list???

> > >   (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.

`pos-visible-in-window-p' with no args returns t or nil, so this
expression returns a boolean if (window-line-height) is nil.
Since `pos-visible-in-window-p' can't be the substitute, such an
expression merely causes a meaningless result.

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

Yeah, even if the doc string is correct, it's quite unclear and
useless, unfortunately. As Drew reported a similar issue in #3602,
no one can resolve the problem by reading it.

IRIE Shinsuke

Message #20 received at 6763 <at> debbugs.gnu.org (full text, mbox):

From: Lars Magne Ingebrigtsen <larsi <at> gnus.org>
To: IRIE Shinsuke <irieshinsuke <at> yahoo.co.jp>
Cc: Eli Zaretskii <eliz <at> gnu.org>, 6763 <at> debbugs.gnu.org
Subject: Re: bug#6763: 24.0.50.1; Doc string of `window-line-height'
Date: Thu, 14 Jul 2011 15:33:11 +0200

IRIE Shinsuke <irieshinsuke <at> yahoo.co.jp> writes:

> `pos-visible-in-window-p' with no args returns t or nil, so this
> expression returns a boolean if (window-line-height) is nil.
> Since `pos-visible-in-window-p' can't be the substitute, such an
> expression merely causes a meaningless result.

Do you have a test case that shows this bug?

The doc of `pos-visible-in-window-p' says:

---
If POS is visible, return t if PARTIALLY is nil; if PARTIALLY is non-nil,
return value is a list of 2 or 6 elements (X Y [RTOP RBOT ROWH VPOS]),
where X and Y are the pixel coordinates relative to the top left corner
of the window.  The remaining elements are omitted if the character after
POS is fully visible; otherwise, RTOP and RBOT are the number of pixels
off-window at the top and bottom of the row, ROWH is the height of the
display row, and VPOS is the row number (0-based) containing POS.
---

ROWH should be what you're looking for, otherwise?

-- 
(domestic pets only, the antidote for overdose, milk.)
  bloggy blog http://lars.ingebrigtsen.no/

Message #23 received at 6763 <at> debbugs.gnu.org (full text, mbox):

From: Lars Magne Ingebrigtsen <larsi <at> gnus.org>
To: IRIE Shinsuke <irieshinsuke <at> yahoo.co.jp>
Cc: Eli Zaretskii <eliz <at> gnu.org>, 6763 <at> debbugs.gnu.org
Subject: Re: bug#6763: 24.0.50.1; Doc string of `window-line-height'
Date: Tue, 02 Aug 2011 21:07:02 +0200

Lars Magne Ingebrigtsen <larsi <at> gnus.org> writes:

> ROWH should be what you're looking for, otherwise?

No further response was made to this in three weeks, so I'm closing the
report.

-- 
(domestic pets only, the antidote for overdose, milk.)
  bloggy blog http://lars.ingebrigtsen.no/

Previous Next

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