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[SOLVED] Rainbow flash glitch with LightDM + XFCE

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Re: Rainbow flash glitch with LightDM + XFCE

#41 Post by Aki »

Hello,
CwF wrote: 2023-01-08 01:11 Is this garbled vga buffer memory present after a warm reboot?
Or is this a cold boot also?
The screen photo in my previous post was acquired during a new login in lightdm+XFCE4 after a previous logout from lightdm+KDE (without powering off the computer).

The screen is garbled in different way if you try to login after a cold start with the same card: it is attached below. It seems to me that it resembles the random contents of the memory of graphic card in this case (even if a pattern it recognizable).
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Re: Rainbow flash glitch with LightDM + XFCE

#42 Post by None1975 »

CwF wrote: 2023-01-08 01:11 Is this garbled vga buffer memory present after a warm reboot?
Or is this a cold boot also?
Hello. In my case it happens both ways (after a warm reboot and cold boot).
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Re: Rainbow flash glitch with LightDM + XFCE

#43 Post by None1975 »

Aki wrote: 2023-01-07 15:34I tested Debian Stable 11.6 (lightdm + xfwm4) in two different virtual environments
Thank you for the detailed test.

I also took the test not so long ago. I used KVM and virtmanager for the test. In kvm no glitch whatsoever. On the bare metal with with an open source video driver (i using Nvidia GTX 650. It is pretty old card), glitch always appears.

With closed source video driver (nvidia 470), glitch appears sometimes. I'm not using xfce at the moment, I'm using fvwm along with xdm. I can tell you that this glitch never happens.

Aki wrote: 2023-01-07 15:34ThanksAre you aware of bug reports or patches about the issue in the Debian bug tracking system or in XFCE bug report system ?
Unfortunately, I didn't dig in that direction because, as I said, I don't use xfce4. By the way, it's not that long since I used FreeBSD 13 with xfce. But xfce started without any login manager. It started out simple startx. I can confirm that I have not experienced such a glitch either.
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Re: Rainbow flash glitch with LightDM + XFCE

#44 Post by CwF »

I think this more gpu related than anything. I vaguely remember a security issue discussion concerning warm reboots on a locked computer displaying fragments? Maybe even a 'plymouth' issue, or it was a fix. I also think I've seen it rebooting a vm with a nvidia gpu.

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Re: Rainbow flash glitch with LightDM + XFCE

#45 Post by MiracleDinner »

Hello all and please accept my apology for not posting for a few days,

Blacklisting the nvidia driver does not seem to affect the bug.

The effect occurs with or without the proprietary drivers installed (as stated previously, it occurs even on a totally fresh install of Debian 11.6 Xfce.)

The rainbow flash does seem to be contingent on the xfwm4 package, as using the 4.18 version self-backported from bookworm does resolve the rainbow flash (it still has a black flicker but i find this far more tolerable than the rainbow flash). But it also seems as if something else, possibly hardware related, is part of the cause of this, since I don't experience the bug in VirtualBox virtual machines or on my much older laptop (which has no NVIDIA dGPU, only a intel iGPU).

I also used to run Arch Linux + Lightdm + gtk-greeter + xfce on this machine and I don't recall having any rainbow flash glitch.

I'm not aware of any bug reports for this glitch either on the Debian bug reporting system or on the Xfce bug reporting system
Last edited by MiracleDinner on 2023-01-13 08:21, edited 1 time in total.

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Re: Rainbow flash glitch with LightDM + XFCE

#46 Post by None1975 »

MiracleDinner wrote: 2023-01-11 16:26 I'm not aware of any bug reports for this glitch either on the Debian bug reporting system or on the Xfce bug reporting system
Hello.

Maybe you wouldn't mind reporting this glitch to Debian bug tracking system? I would do it myself, but I don't use xfce4.
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Re: Rainbow flash glitch with LightDM + XFCE

#47 Post by MiracleDinner »

None1975 wrote: 2023-01-12 12:56
MiracleDinner wrote: 2023-01-11 16:26 I'm not aware of any bug reports for this glitch either on the Debian bug reporting system or on the Xfce bug reporting system
Hello.

Maybe you wouldn't mind reporting this glitch to Debian bug tracking system? I would do it myself, but I don't use xfce4.
But the rainbow flash glitch appears to have been fixed in Xfwm 4.18? I'm not sure if the small black flicker after logging in is "normal" but it doesn't very much bother me.

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Re: Rainbow flash glitch with LightDM + XFCE

#48 Post by Aki »

Hello
MiracleDinner wrote: 2023-01-11 16:26 Blacklisting the nvidia driver does not seem to affect the bug. The install glitch occurs with or without the proprietary drivers installed (as stated previously, it occurs even on a totally fresh install of Debian 11.6 Xfce.)
@MiracleDinner: thanks for having tested it.

@MiracleDinner , @None1975:
I further investigated the issue in xfce4 (version: 4.16) on bare metal with Debian Stable (11.6): let me know if you are interested in more details.

I used two different computers:
a) computer with NVIDIA G96CM [GeForce 9600M GT] (driver: nouveau)
b) computer with Intel HD Graphics 620 (driver: i915).

I found that the glitches I reported in [1] disappear if the xfwm4's internal compositor is disabled.

The xfwm4's internal compositor can be disabled in many ways [2]: I tested the "--compositor=off" option (using a stub file for /usr/bin/xfwm4) and the xfwm4-tweaks-settings program.

xfce4 runs much faster disabling the internal compositor, by the way.

Let me know if it works for you.
MiracleDinner wrote: 2023-01-11 16:26 The rainbow flash does seem to be contingent on the xfwm4 package, as using the 4.18 version self-backported from bookworm does resolve the rainbow flash (it still has a black flicker but i find this far more tolerable than the rainbow flash).
This is an interesting finding that could be investigated.
MiracleDinner wrote: 2023-01-11 16:26 But it also seems as if something else, possibly hardware related, is part of the cause of this, since I don't experience the bug in VirtualBox virtual machines or on my much older laptop (which has no NVIDIA dGPU, only a intel iGPU).
I agree: probably, different graphic cards / kernel card drivers initialize themselves and their memory in different ways.


[1] https://forums.debian.net/viewtopic.php?p=765404#p765404
[2] https://wiki.archlinux.org/title/Xfwm#Composite_manager
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Re: Rainbow flash glitch with LightDM + XFCE

#49 Post by None1975 »

Aki wrote: 2023-01-13 07:38 I further investigated the issue in xfce4 (version: 4.16) on bare metal with Debian Stable (11.6): let me know if you are interested in more details.

I used two different computers:
a) computer with NVIDIA G96CM [GeForce 9600M GT] (driver: nouveau)
b) computer with Intel HD Graphics 620 (driver: i915).

I found that the glitches I reported in [1] disappear if the xfwm4's internal compositor is disabled.

The xfwm4's internal compositor can be disabled in many ways [2]: I tested the "--compositor=off" option (using a stub file for /usr/bin/xfwm4) and the xfwm4-tweaks-settings program.

xfce4 runs much faster disabling the internal compositor, by the way.

Let me know if it works for you.
Hello! It would be great if you could do more tests.

P.S.

By the way, what concerns the composer. Yes, you're right. I seem to remember that turning off the compositor makes this glitch go away. But I don't think that's an option. However, many people would like to use that compositor...
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Re: Rainbow flash glitch with LightDM + XFCE

#50 Post by Aki »

Hello,
None1975 wrote: 2023-01-13 12:32 [..] By the way, what concerns the composer. Yes, you're right. I seem to remember that turning off the compositor makes this glitch go away. But I don't think that's an option. However, many people would like to use that compositor...
I'm not a regular xfce4 user, but I haven't noted major graphical differences with xfce4's internal compositor disabled.
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Re: Rainbow flash glitch with LightDM + XFCE

#51 Post by None1975 »

Aki wrote: 2023-01-14 09:37 I'm not a regular xfce4 user, but I haven't noted major graphical differences with xfce4's internal compositor disabled.
I don't use xfce4 either.

By the way, as far as the composer is concerned, the differences are noticeable. This includes terminal transparency and subtle shadows and much more. Of course, this is all a matter of taste…
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Re: Rainbow flash glitch with LightDM + XFCE

#52 Post by Aki »

Hello,
MiracleDinner wrote: 2023-01-12 17:27 But the rainbow flash glitch appears to have been fixed in Xfwm 4.18? I'm not sure if the small black flicker after logging in is "normal" [..]
@MiracleDinner
I temporary installed xfwm4 4.18 from testing in my Debian Stable 11.6.

The glitch (lightdm+xfce4) is changed with 4.18: it's now a black square with a thin blue frame (the latter from the background of the greeter, I suppose). It appears in the transition between lightdm and xfwm4 when the compositor is activated, while it disappears when the compositor is disabled.

Therefore, the new glitch (black square with a thin blue frame) can probably can go unnoticed if the greeter uses a dark screen background. It's different in color, but it's there: therefore, it's only partially fixed in xfwm4 version 4.18, unfortunately.

I suspect that this [1] is the patch to the compositor that changed the behavior of the glitch from xfwm4 4.16 to 4.18.

Just now I have found a bug report [2] about this issue for xfwm4 that recall the aforementioned patch [1] with a proposal for an intermediate patch. There's still no followup to [2], but it looks promising.

Probably it worths opening a bug in the Debian Bug Tracking system with a reference to [2].

---
[1] https://gitlab.xfce.org/xfce/xfwm4/-/co ... 0c911bb670
[2] https://gitlab.xfce.org/xfce/xfwm4/-/issues/684
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Re: Rainbow flash glitch with LightDM + XFCE

#53 Post by MiracleDinner »

Can confirm that the black flicker on Xfwm4.18 does not occur when the compositor is disabled using the graphical "Window Manager Tweaks" application

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Re: Rainbow flash glitch with LightDM + XFCE

#54 Post by Aki »

Hello,
MiracleDinner wrote: 2023-01-16 18:19 Can confirm that the black flicker on Xfwm4.18 does not occur when the compositor is disabled using the graphical "Window Manager Tweaks" application
Thank you for taking the time to conduct the test.

To whom it may interest, I tested in Debian Stable (11.6) the patch proposed in [1] (also attached for your convenience). I applied it it to xfwm4 version 4.18 from Debian Bookworm (12). I installed the patched version 4.18 of xfwm4 into Debian Stable: it works for me. These are the commands that can be used to download the source code from Debian Bookworm (12), patch it, rebuild the package and install it in Debian Stable (11.6):

Code: Select all

script log.txt
mkdir workdir
cd workdir
su -l -c "apt-get build-dep  xfwm4"
su -l -c "apt install build-essential devscripts fakeroot patch quilt"
dget http://deb.debian.org/debian/pool/main/x/xfwm4/xfwm4_4.18.0-1.dsc
cd xfwm4-4.18.0/
# download and decompress the attached patch in the current directory 
patch -p1 < compositor.patch
dpkg-buildpackage -b -uc
cd ..
exit
All the commands and their outputs will be in the file named log.txt.
In the current directory is the new package for xfwm4_4.18.0-1 that can be installed:

Code: Select all

su -l -c "cd $PWD; dpkg -i xfwm4_4.18.0-1_amd64.deb"
HTH.

---
[1] https://gitlab.xfce.org/xfce/xfwm4/-/issues/684
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Re: Rainbow flash glitch with LightDM + XFCE

#55 Post by MiracleDinner »

Hi,

I'm so sorry it took me so long to get round to this, but it looks like your (@Aki ) instructions did prevent the black flicker, and I now have a completely smooth and okay to look at transition between LightDM and my XFCE desktop. Thank you very much. Marking this thread as solved.

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Re: Rainbow flash glitch with LightDM + XFCE

#56 Post by Aki »

MiracleDinner wrote: 2023-02-04 17:26 [..] it looks like your (@Aki ) instructions did prevent the black flicker, and I now have a completely smooth and okay to look at transition between LightDM and my XFCE desktop. Thank you very much. Marking this thread as solved.
I'm glad to helped you to sort it out. Happy Debian & happy hacking. :-)
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