On Wed, Apr 29, 2020 at 07:54:02PM +0300, Eli Zaretskii wrote:

[...]

> Drawing over normal text, if we don't want to redesign the entire
> display engine, needs some new kind of "display element" ( a sibling
> to "character", "image", "stretch", etc.), one that doesn't
> necessarily have any effect on the metrics of the screen lines it is
> drawn upon.  I'm not sure I have a clear idea about what features such
> a drawing will need to support, but it could be possible to add such
> an element with not too much effort.  Would someone want to come up
> with a reasonable list of requirements for such a feature?

That sounds... exciting. Basically, Emacs would have to have a "display
list" of graphical elements to draw, each one perhaps having a bounding
box (to discard those from redisplay which aren't currently visible)
and perhaps a "layer" (more to the background or foreground).

Hmmm.

Cheers
-- t