GNU bug report logs - #43506
26.1; line-height sometimes has no effect on the line height

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Package: emacs; Reported by: Markus Triska <triska@HIDDEN>; Keywords: notabug; dated Sat, 19 Sep 2020 07:22:01 UTC; Maintainer for emacs is bug-gnu-emacs@HIDDEN.
Added tag(s) notabug. Request was from Eli Zaretskii <eliz@HIDDEN> to control <at> debbugs.gnu.org. Full text available.

Message received at 43506 <at> debbugs.gnu.org:


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From: Eli Zaretskii <eliz@HIDDEN>
To: Markus Triska <triska@HIDDEN>
In-Reply-To: <m21riyjkot.fsf@HIDDEN> (message from Markus Triska on Sat, 
 19 Sep 2020 09:21:38 +0200)
Subject: Re: bug#43506: 26.1;
 line-height sometimes has no effect on the line height
References: <m21riyjkot.fsf@HIDDEN>
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tags 43506 notabug
thanks

> From: Markus Triska <triska@HIDDEN>
> Date: Sat, 19 Sep 2020 09:21:38 +0200
> 
>     (progn
>       (goto-char (point-max))
>       (insert "\n")
>       (insert (propertize "\n" 'line-height 3))
>       (forward-line -1)
>       (line-pixel-height))
> 
> In my case, the minibuffer then states "17". The expected result is 3,
> because documentation states:
> 
>        A newline can have a ‘line-height’ text or overlay property that
>     controls the total height of the display line ending in that newline.

That's not all the documentation says about 'line-height'.  It also
says this (in the "Line Height" node referenced from the place you
cite):

     There are several ways to explicitly specify a larger line height,
  either by specifying an absolute height for the display line, or by
  specifying vertical space.  However, no matter what you specify, the
  actual line height can never be less than the default.
  [...]
     Finally, a newline can have a ‘line-spacing’ text or overlay property
  that can enlarge the default frame line spacing and the buffer local
  ‘line-spacing’ variable: if its value is larger than the buffer or frame
  defaults, that larger value is used instead, for the display line ending
  in that newline.

IOW, this property can only enlarge the line's height, which is
confirmed by the fact that using 300 in your example does work as
expected.

This is not a bug.  This property exists so a Lisp program could
produce higher lines than the default.

To produce lower lines, you can use a face with a low :height
attribute, and arrange for the newline to have that face.  You can
find an example of doing that in log-edit.el.

> If possible, could you please make line-height control the total height
> of the display line also in the original example, or alternatively
> consider changing the documentation to mention all relevant exceptions?

The documentation already mentions the limitations, see above.




Information forwarded to bug-gnu-emacs@HIDDEN:
bug#43506; Package emacs. Full text available.

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From: Markus Triska <triska@HIDDEN>
To: bug-gnu-emacs@HIDDEN
Subject: 26.1; line-height sometimes has no effect on the line height
Date: Sat, 19 Sep 2020 09:21:38 +0200
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To reproduce this issue, please start Emacs with "emacs -Q" and then
evaluate the following form:

    (progn
      (goto-char (point-max))
      (insert "\n")
      (insert (propertize "\n" 'line-height 3))
      (forward-line -1)
      (line-pixel-height))

In my case, the minibuffer then states "17". The expected result is 3,
because documentation states:

       A newline can have a =E2=80=98line-height=E2=80=99 text or overlay p=
roperty that
    controls the total height of the display line ending in that newline.

For comparison, it works exactly as expected if I change "3" to "300" in
the snippet above, yielding "300" in the minibuffer.

If possible, could you please make line-height control the total height
of the display line also in the original example, or alternatively
consider changing the documentation to mention all relevant exceptions?

Thank you and all the best!
Markus

In GNU Emacs 26.1 (build 1, x86_64-apple-darwin15.3.0, X toolkit, Xaw scrol=
l bars)
 of 2018-09-22 built on mt-laptop
Windowing system distributor 'The X.Org Foundation', version 11.0.11502000




Acknowledgement sent to Markus Triska <triska@HIDDEN>:
New bug report received and forwarded. Copy sent to bug-gnu-emacs@HIDDEN. Full text available.
Report forwarded to bug-gnu-emacs@HIDDEN:
bug#43506; Package emacs. Full text available.
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Last modified: Sat, 19 Sep 2020 09:00:02 UTC

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