Re: Emacs canvas support

[Eli Zaretskii <eliz@gnu.org>]

> Date: Wed, 29 Apr 2020 20:51:28 +0200
> From: tomas@tuxteam.de
> Cc: emacs-devel@gnu.org
> 
> > That's not how Emacs controls what's on display.  It basically
> > represents each window as a 2D array of glyphs, each one of which has
> > a certain graphical representation.
> 
> ...a display list of sorts.

It's a far cry from any "list" in my book...

> >                                     The representation itself is of
> > no concern to the display engine (well, almost); the only thing it
> > cares about is the metrics of each glyph, because that's what it needs
> > to do layout calculations.
> 
> A graphical overlay wouldn't have "glyph metrics", the graphical
> objects would (I think) have "absolute" [1] positions (possibly
> precalculated by something else).

The position is basically determined by the place in a buffer or a
string where they were found.

> 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.