Re: Emacs canvas support

[Eli Zaretskii]

> Date: Wed, 29 Apr 2020 21:08:54 +0200
> From: address@hidden
> Cc: address@hidden
> 
> > > I think the "interesting" problem is to know (quickly) which
> > > graphical objects intersect the (visible) window -- something
> > > graphics programs do as their main job.
> > 
> > That's easy, we have infrastructure for that already -- it is used in
> > expose_frame and its subroutines.
> 
> This sounds... encouraging :-)
> 
> (TBH I was coming from the other side: index the graphics objects
> in a way that one doesn't need to look at most of those which
> are currently hidden).

The current display engine works by screen lines, so if we want to
keep it, we must use the existing framework.  When a portion of a
window is exposed, we redraw all the glyphs in the exposed area(s),
and we find the glyphs that need to be redrawn by comparing their
coordinates with those of the exposed rectangle(s).