bug#51821: 29.0.50; Suggest add variable or frame parameter: line-height

[Eli Zaretskii <eliz@gnu.org>]

> From: "Feng Shu" <tumashu@163.com>
> Cc: Lars Ingebrigtsen <larsi@gnus.org>,  51821@debbugs.gnu.org
> Date: Sat, 20 Nov 2021 07:03:18 +0800
> 
> yestaday, I have tested with hack version of your patch, I think
> line-height or line-height-factor is not a proper way to solve my core
> problem.
> 
>    My core problem is how to let tab/mode/header-line and minibuffer's
>    height do not change depend Chinese exist or not.

That's a different problem from that Lars wanted to solve, AFAIU.

> line-height-factor can let their height do not change, but the problem
> is that the result looks very ugly, for line-space very large, It will
> be painful in daily use.

I agree it is not very pretty, but I don't see how such a feature
could do much better.

> so I think the good approach maybe is providing a simple way, by which
> we can easy let no-ascii font use small height if a face is not used in
> table like environment.

That's no longer a display issue, I think.  And I don't really
understand how we could implement that, since faces are oblivious to
the context in which they are used.

And what do you mean by "table like environment"? do you mean
tabulated-list-mode and its descendants, or do you mean Org tables, or
do you mean just simple text display that emulates tables by aligning
text on column boundaries, like, for example, in Gnus summary buffers?

And finally, what do you mean by "no-ascii font use small height" --
how will Emacs ensure such smaller height of these fonts?

> In my opinion "1 Chinese char width = 2 * ASCII char width" is *only*
> useful in table like environment. let Chinese char's height <= ASCII
> char's height will work well in other situation, and have no
> tab/mode/header-line height change problem too.

Until now, your main concern was that the echo-area height changes
depending on whether it does or doesn't show Chinese characters.  Are
you now saying that concern is no longer important?  If so, why do we
need to do anything about the height of the Chinese font used by Emacs
in text that mixes Chinese and ASCII characters?