Re: How to Display a Zero Height Line

[Eli Zaretskii <eliz@gnu.org>]

> From: Psionic K <psionik@positron.solutions>
> Date: Sun, 1 Dec 2024 10:04:32 +0900
> 
> 1. There is vertical space between a target line and the line above or
> top of the buffer
> 2. This vertical space does not have a side effect of extending the
> background or `:inverse-video' background of the target line or the
> line above it
> 3. The vertical space can be drawn at zero height and at fractional
> heights up to the distance content is slid in from

What do you mean by "extending the background of :inverse-video
background" of a line?  Can you show some simple Lisp which produces
this effect on display?

Since this seems to be the main obstacle you found, it is very
important to understand what it is and how it is created.

> Within a fontified buffer, I have been unable to make actual newlines
> into fractional or zero height using overlays.  I have neither been
> able to use `:before-string` or `:after-string` as properties or
> overlays.

Did you try to use an overlay with just the line-height overlay
property, and put that overlay on the newline at end of line?

IOW, I don't understand why you are talking about before-string and
after-string: those are used to show text that doesn't come from the
buffer (but from strings instead), which AFAIU is not your case, at
least not for the purpose of affecting the height of a text line.