Subject: bug#28652: 26.0.60; Display often "flashes" due to double buffering when switching to Emacs frames

From: "N. Jackson" <[email-masked]>
Date: Fri, 03 Sep 2021 07:52:32 -0400

Hello Lars,

At 09:57 +0200 on Friday 2021-09-03, Lars Ingebrigtsen wrote:
>
> [email-masked] (N. Jackson) writes:
>
>> When switching between windows in Gnome using Alt-Tab there is
>> often a bright flash just after switching to an Emacs frame.
>>
>> It seems as if the Emacs frame is displayed and then a window of
>> some other application appears for a fraction of a second before
>> the display settles down to the showing the Emacs frame.
>>
>> Because the flash is so quick, I Initially thought the Emacs frame
>> was being displayed in white before being painted to it's correct
>> display, but this is not the case. By choosing distinctive colours
>> or distinctive images in my other applications, I can tell that it
>> is the window of another application that is flashing up.
>>
>> [This flashing might be particularly noticeable on this system as
>> I use a dark theme in Emacs (Wheatgrass) and most other
>> application windows are predominantly white. Also I keep all my
>> Emacs frames and all my other application windows maximised or
>> full screen (because I have a small display).]
>
> (I'm going through old bug reports that unfortunately weren't resolved
> at the time.)
>
> I'm also using Gnome (I'm on Debian bullseye), but I can't see these
> flashes (I've tried in Emacs 26.1 and Emacs 28) when Alt-Tab-ing between
> something that has a bright background and Emacs (which has a black
> background).
>
> Are you still seeing this in recent Emacs/Gnome versions?

No, I haven't seen this problem -- at all -- in quite a few Emacs
versions.

(Sorry I didn't update the bug report with that information -- I had
completely forgotten about the bug.)

[The only time I see any "flashing" of any sort in Emacs now is
while it starts up and restores my desktop frames and windows. My
understanding is that this is expected. (It is also much less
frenetic that it was in the past.)]

Thank you and best regards,
Neil.