Re: Drawing UI elements behind text

[Eli Zaretskii <eliz@gnu.org>]

> Date: Wed, 27 Nov 2024 19:28:58 +0100
> Cc: jdtsmith@gmail.com, emacs-devel@gnu.org
> From: Cecilio Pardo <cpardo@imayhem.com>
> 
> > If they are completely disconnected, how does this work when the
> > window is scrolled several lines?
> 
> They are anchored at locations on the buffer, specified by line/column. 
> This is transformed into pixels using the size of the default char cell 
> for the buffer.  The buffer scroll position on each window is used to 
> compute the final position on the frame/screen.
> 
> For buffers that use different font sizes or images this is probably not 
> very useful. Direct pixel positions can be used too.
> 
> They are drawn after switching the back paint buffer, so that the 
> redisplay result is left alone.

So you clear them up when redisplay starts and then redraw them in
their entirety when it ends, something like that?  Doesn't that slow
down redisplay, especially if there are many pixels and a large
window?