Re: Emacs design and architecture. How about copy-on-write?

[Eli Zaretskii <eliz@gnu.org>]

> Date: Thu, 21 Sep 2023 16:30:00 +0300
> Cc: luangruo@yahoo.com, acm@muc.de, incal@dataswamp.org, emacs-devel@gnu.org
> From: Dmitry Gutov <dmitry@gutov.dev>
> 
> On 21/09/2023 16:00, Eli Zaretskii wrote:
> > You are basically proposing us to provide broken, incorrect, and
> > outdated display in some cases.  That won't fly, so it's a
> > non-starter.
> 
> If might prove an okay experience, if the "outdated" part is within 
> certain bounds. Like if the current buffer refreshes at 30/60fps, and 
> the mode-line at 10/20fps, for example.

That's not what was proposed.  The proposal was to do a
"quick-and-dirty" layout first, and use the results if the "accurate"
layout takes too long.  The quick-and-dirty layout can only be based
on ignoring changes in fonts and disregarding images and stuff like
that, so the screen lines will be wrong, and you will see them jump
and/or rearrange after some delay, which could be some seconds.  Some
browsers do that when they need to download images, and it always jars
me when that happens.  Usually, I also lose the place where I was
reading.

I hope Emacs will never behave like that.