Re: What is the proper way to scale fringe-bitmaps for high-DPI displays?

[Eli Zaretskii]

> Cc: address@hidden
> From: Clément Pit-Claudel <address@hidden>
> Date: Wed, 20 Mar 2019 15:34:26 -0400
> 
> > Instead, I think when a frame is created, we should record its
> > high-DPI state in the frame structure, or maybe in the frame's
> > parameters, and then use that when we prepare the fringe bitmaps for
> > display.
> 
> That would be nice.  In fact, we already have code to detect high-DPI 
> displays in C, in x_get_scale_factor in xterm.c (used to scale wavy 
> underlines).  Would the way to go be to record the value returned by this 
> function in the frame's parameters?

The frame's parameters is a better way if we think such a parameter
will be useful to Lisp programs, and calling a function for that is
too much overhead.  Otherwise, a simple field of 'struct frame' will
be somewhat less hassle, because you don't need to mess with the likes
of frame-parameter to teach them about this new parameter.  But either
way, the job is not hard.

> I guess that another approach would be to support scalable images in the 
> fringe, rather than bitmaps.  If the fringe image was SVG instead of a 
> bitmap, for example, we could make it fill the whole width of the fringe.
> 
> Do you have a sense of how hard that would be?

No, I don't, sorry.

And in any case, I don't think we should rely on SVG support for a
feature as basic as fringe bitmaps, since we use that in the most
basic display on GUI frames, whereas some people intentionally build
Emacs without SVG support.