Re: [dev] [dwm] dwm breaks on synchronized screens

From: Thomas Oltmann <>
Date: Fri, 12 Nov 2021 17:22:17 +0100

Hi again,

In terms of reproducing this behaviour, all that it seems to take for me is
to 'mirror' the screens, optionally with some windows already open,
and then try to
open/move some more windows. It was relatively consistent so far in
that strange things happened pretty quickly.

I use lxrandr to configure the mirrored screen setup, since that
interface literally has a button to do just that.
I should note that my two displays have differing resolutions
(differing aspect ratios, in fact).
The main (Laptop) monitor has a resolution of 1366 x 768.
The beamer I don't actually know, but it's some sort of 4:3 so I
reckon 1024 x 768, in case that helps.

The issue that v4hn has described sounds like a plausible cause for
the problems I'm having.
I very specifically get the feeling that dwm thinks it is managing two
independent monitors, when there is in
fact only one, leading to such things like active windows getting
stacked directly on top of each other in tiled mode.

          Thomas Oltmann

Am Fr., 12. Nov. 2021 um 12:33 Uhr schrieb v4hn <>:
> Hey everyone,
> I can verify issues with multi-monitor setups when screens are overlapping/mirrored.
> I usually avoid this by working with independent screens as well.
> With XINERAMA support in dwm you can dynamically configure monitors via xrandr.
> If you configure them to coincide, e.g.,
> `xrandr --output <display2> --auto --same-as <display1>`,
> it seems that at least for some configurations dwm creates separate `Monitor` structs
> unconditionally and you can cycle through the monitors via shortcuts.
> But because they overlap you will not even see the bar for one of the monitors
> and window management is screwed up as well.
> Notice that there is actually logic in the code that should prevent this
> for the case where virtual screen positions coincide. (`isuniquegeom`)
> Along the same lines of code I recently noticed that dynamically adding an
> independent/unique screen via xrandr can change the Monitor->physical screen association
> and thus move all existing windows to a different physical screen.
> Maybe it's a different bug altogether though, I did not have time to investigate.
> v4hn
> On Fri, Nov 12, 2021 at 09:18:22AM +0100, Laslo Hunhold wrote:
> > On Thu, 11 Nov 2021 19:34:08 +0100
> > Thomas Oltmann <> wrote:
> >
> > Dear Thomas,
> >
> > > What do I do about this?
> > > Is it even a bug or just me using dwm for stuff it's not intended to
> > > do? One way or another, how can I do my presentations without
> > > fighting the WM all the time?
> >
> > do you have a way so we can reproduce this?
> >
> > With best regards
> >
> > Laslo
> >
> --
> Michael 'v4hn' Görner, M.Sc. Cognitive Science, PhD Student
> Universität Hamburg
> Faculty of Mathematics, Informatics and Natural Sciences
> Department of Informatics
> Group Technical Aspects of Multimodal Systems
> Vogt-Kölln-Straße 30
> D-22527 Hamburg
> Room: F-315
> Phone: +49 40 42883-2432
> Website:
Received on Fri Nov 12 2021 - 17:22:17 CET

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