Re: How to Display a Zero Height Line

[Eli Zaretskii <eliz@gnu.org>]

> From: Psionic K <psionik@positron.solutions>
> Date: Sat, 30 Nov 2024 12:02:05 +0900
> Cc: Psionic K <psionik@positron.solutions>
> 
> Related dslide user issue:
> https://github.com/positron-solutions/dslide/issues/15
> 
> If I use line height or line spacing to accomplish the slide-in
> effect, text with any background color set have that background
> stretched out.
> 
> To work around this, I was going to use a zero height line but could
> not achieve the effect after a couple tries.
> 
> While I achieved vanishing line height in a fundamental mode buffer
> using an actual newline with text properties, I could not reproduce
> the effect in a fontified buffer, where I needed to use an overlay.  I
> messed around a bit with 'before-string etc.
> 
> I'm aware this might be a display limitation and want to confirm
> before labeling my user's issue accordingly.

I'm sorry, I could understand neither the problem you were trying to
solve ("slide-in effect"), nor how you tried to do that ("use line
height or line spacing"), nor the problems you've encountered while
trying to solve this ("background stretched out", zero-height line
that didn't work in a fontified buffer).

So please tell more about this, and perhaps show some simple Lisp to
illustrate.

In general, if something works in Fundamental mode but not in a
fontified buffer, it means you use 'face' properties, which
font-lock-mode wipes out.  The usual solution for this is to use
'font-lock-face' properties instead.  But this is a stub in the dark,
so apologies if it makes no sense or is completely off the target.