Re: Cursor drawing

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Date: Thu, 20 Dec 2018 10:39:53 -0500
> 
> I was wondering whether it would make sense to introduce a clear notion
> of layers.  IIUC the current situation is:
> 
> - redisplay renders buffers into glyph matrix.
> - redraw of a clipping region is done by "rendering" the corresponding
>   part of a glyph matrix into pixels.

This is not entirely accurate, but I'm not yet sure a more accurate
description will matter (I will publish one if we conclude it will
help).  I think what matters for this discussion is the "rendering
into pixels" part: I suspect that you have some mental model of that
which is not entirely consistent with what the code actually does.

So maybe you should say more about how you imagine this works, and how
under that mental model you envision this part:

> - redraw of a clipping region is done by "rendering" the corresponding
>   part of a glyph matrix combined with the corresponding part of the
>   overlay layer into pixels.

The crucial part here, for me, is how this "combination" would be
different from "shoehorning crosshairs into the glyph matrix".  Can
you elaborate on what you had in mind?

> The advantage would be mostly that the overlay data structure could be
> designed completely differently from glyph-matrices

Like what, for example?