Re: Bigger fringe bitmaps

[Eli Zaretskii <eliz@gnu.org>]

> From: Yuri D'Elia <wavexx@thregr.org>
> Cc: emacs-devel@gnu.org
> Date: Thu, 17 Mar 2022 09:34:08 +0100
> 
> On Thu, Mar 17 2022, Eli Zaretskii wrote:
> > I did comment on that.  To repeat: it could be a useful new feature,
> > but I don't think it should be _the_ solution for showing stuff on the
> > fringes on hidpi terminals; we should be able to produce legible
> > display of the bitmaps on those terminals.
> 
> Seen it, I was just prompting for more feedback on the idea and discuss
> if this could be a good and/or bad idea.

I think it's a good idea.  It "just" needs to be implemented...

> > Solving this in the limited fringe screen estate will need some
> > non-trivial ideas. And what about 'half-width' or 'minimal'
> > fringe-styles?
> 
> I mentally imagine this as just scaling the font smaller to fit the
> fringe width, centering each character vertically.

Emacs doesn't know how to scale a font at display time.  The font is
"scaled" (or, rather, selected) when the face using the font is
defined.  So dynamically changing the font of a face when the user
plays with fringe-style would be another complication that needs to be
taken care of.

> >> Especially the fact that this would potentially mean an usable fringe
> >> mode on character displays that can be toggled, so that you don't need
> >> to provide an alternate signaling mechanism if you rely on the fringe to
> >> show makers (like gud).
> >
> > I don't think I follow.  Emacs doesn't support fringes on TTY
> > displays, so what do you mean by "usable fringe mode on character
> > displays"?
> 
> That would be part of the advantage of allowing a character to be used
> in lieu of a bitmap (either as a feature or as a fallback).
> 
> On a TTY we could just reserve the first/last column for the "fringe"
> and display the lowest-common-denominator format available.

How is this different from what overlay-arrow already does?  It is
even more flexible, as it is not limited to a single column.

> > This is already supported, see overlay-arrow-string. Or do you mean
> > something else?
> 
> Yes, but it doesn't behave exactly in the same way as the fringe does.

In what way does it not behave the same?

> (and I also as I just discovered, if I disable the fringe on a graphical
> display I do not get the overlay arrows as a fallback -- or did I miss
> some variable to control this behavior?)

What did you try?  See the "Overlay Arrow" node in the ELisp manual
for what is available.