Subject: bug#66247: 29.1; Transient frame problems with Emacs 29 on MS Windows

From: Eli Zaretskii <[email-masked]>
Date: Tue, 10 Oct 2023 15:00:21 +0300

> From: Drew Adams <[email-masked]>
> CC: "[email-masked]" <[email-masked]>,
>         "[email-masked]"
> 	<[email-masked]>
> Date: Mon, 9 Oct 2023 19:49:14 +0000
> 
> emacs -Q
> 
> M-x customize-option default-frame-alist
> 
> Add an entry for inhibit-double-buffering as t.
> 
> Set the option value for the current session.
> 
> `C-x 5 2' or in some other way get a new frame,
> so `default-frame-alist' kicks in.
> 
> Grab the right frame edge with your mouse and
> move it to the right.  I see a lag: the scroll
> bar stays where it is briefly, then finally
> catches up with the new position of the right
> frame edge.

I see the same in Emacs 28, so this isn't a regression in Emacs 29.
When Emacs needs to redraw the frame, it actually asks the MS-Windows
GUI subsystem to do that, and the update takes time (and happens in a
separate UI thread).  So these small lags are expected.