Re: Flicker on MS Windows

[Eli Zaretskii <eliz@gnu.org>]

> From: Po Lu <luangruo@yahoo.com>
> Cc: emacs-devel@gnu.org
> Date: Mon, 07 Mar 2022 08:40:16 +0800
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Also, how did "scroll from top to bottom" -- with what command(s)?
> 
> I held down "C-v".

Then I'm afraid I cannot reproduce this.  I tried Emacs 27 on 2
different versions of Windows 10, and I don't see any abnormal
flickering when I lean on C-v.  The menu bar does flicker once in a
few seconds (and that is expected, given how eagerly we update our
menus)), but by that time Emacs scrolled many window-fulls.

Are you trying this with an optimized build or an unoptimized build?
An unoptimized build cannot keep up with the auto-repeat rate of the
keyboard, so the first scroll through the file could cause Emacs to
become stuck until you release the key.  But once you scroll the file
once (i.e. it is all fontified), even an unoptimized build behaves
reasonably, and I see no particular flickering, at least not on the
menu bar.  I certainly don't see any artifacts like left-over text --
that smells like some "optimization" of your video driver.  Try
disabling any advanced features of the display adapter you have there.

> > And how did you determine that this is related to w32_scroll_run, or
> > even that w32_scroll_run was called while you scrolled in this case?
> 
> I assumed that was the case, since commenting out that function makes
> the part that doesn't flicker stop being updated when scrolling.

Ah, you mean the call to w32_scroll_run in dispnew.c...  Does setting
w32-use-visible-system-caret non-nil help in any way?