Graphics glitching on Gmoccapy

Noticed this glitching on three different PCs now (two realtime, one non-realtime ) running current master (does not happen when running 2.9.10 on the same PCs). Also happens in the demo configs but to a lesser extent than with my machine config in the video. Has anybody else noticed this?

20261031_172902.mp4

Another example running one of the demo configs on a different PC:

2026-10-31.17-43-55.mp4

Both PCs are running Debian13 Trixie with the preempt-rt kernel.

Not those periodic ones, only some little spurious ones.
Are those with the sample config reproducible?

Well, 'reproducible' is maybe not the right word. In the sim configs they are sporadic and I have not been able to find a pattern but it always happens at some time and in different places. I've had it happen in the gcode editor where it would start jumbling lines of text. It is really bad when testing current master on my mill. It is basically unusable.
I have suspected the recent changes in the preview but it also happens on screens where the preview is not visible so I'm not sure if that rules it out.

What hardware do your test PCs have?

user@debian:~$ lscpu
Architecture:             x86_64
  CPU op-mode(s):         32-bit, 64-bit
  Address sizes:          36 bits physical, 48 bits virtual
  Byte Order:             Little Endian
CPU(s):                   4
  On-line CPU(s) list:    0-3
Vendor ID:                GenuineIntel
  Model name:             Intel(R) Core(TM) i5-3570 CPU @ 3.40GHz
    CPU family:           6
    Model:                58
    Thread(s) per core:   1
    Core(s) per socket:   4
    Socket(s):            1
    Stepping:             9
    CPU(s) scaling MHz:   76%
    CPU max MHz:          3800.0000
    CPU min MHz:          1600.0000
    BogoMIPS:             6784.28
    Flags:                fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx rdtscp lm constant_tsc arch_perfmon pebs bts rep_good 
                          nopl xtopology nonstop_tsc cpuid aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm pcid sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx f1
                          6c rdrand lahf_lm cpuid_fault epb pti ssbd ibrs ibpb stibp tpr_shadow vnmi flexpriority ept vpid fsgsbase smep erms xsaveopt dtherm ida arat pln pts flush_l1d
Virtualization features:  
  Virtualization:         VT-x
Caches (sum of all):      
  L1d:                    128 KiB (4 instances)
  L1i:                    128 KiB (4 instances)
  L2:                     1 MiB (4 instances)
  L3:                     6 MiB (1 instance)
NUMA:                     
  NUMA node(s):           1
  NUMA node0 CPU(s):      0-3
Vulnerabilities:          
  Gather data sampling:   Not affected
  Itlb multihit:          KVM: Mitigation: VMX disabled
  L1tf:                   Mitigation; PTE Inversion; VMX conditional cache flushes, SMT disabled
  Mds:                    Vulnerable: Clear CPU buffers attempted, no microcode; SMT disabled
  Meltdown:               Mitigation; PTI
  Mmio stale data:        Unknown: No mitigations
  Reg file data sampling: Not affected
  Retbleed:               Not affected
  Spec rstack overflow:   Not affected
  Spec store bypass:      Mitigation; Speculative Store Bypass disabled via prctl
  Spectre v1:             Mitigation; usercopy/swapgs barriers and __user pointer sanitization
  Spectre v2:             Mitigation; Retpolines; IBPB conditional; IBRS_FW; STIBP disabled; RSB filling; PBRSB-eIBRS Not affected; BHI Not affected
  Srbds:                  Vulnerable: No microcode
  Tsx async abort:        Not affected

user@debian:~$ lspci | grep -i --color 'vga\|3d\|2d'
00:02.0 VGA compatible controller: Intel Corporation Xeon E3-1200 v2/3rd Gen Core processor Graphics Controller (rev 09)
user@debian:~$ echo $XDG_CURRENT_DESKTOP
X-Cinnamon

Note though that I have this problem also on a laptop running Mint 22 and on a different PC running Debian13 with the XFCE Desktop.

What about on master? Is it only my PR or master as well?

Actually it is just as bad on current master as with your branch. Edited my post above.

It is somewhat less bad when I run the Gmoccapy sims on the mill as compared to my actual machine config but it is still very noticeable.

I have switched my test PC to 'Gnome Wayland' and I have not seen a glitch yet. I'll have to see if it fixes the issue on the mill as well.

While it seems that Wayland 'fixes' the glitching it also seems to have broken something.
I can no longer run any config that actually uses my real hardware, even after switching back to 'Xorg':

hm2/hm2_7i95.0: Smart Serial port 0: DoIt not cleared from previous servo thread. Servo thread rate probably too fast. This message will not be repeated, but the hm2_7i95.0.sserial.0.fault-count pin will indicate if this is happening frequently.

I can reproduce the behavior on two of my PC and my laptop.
All running Trixie and cinnamon desktop. One other with xfce

Using master I have it
Using 2.9.10 it does not happen

Norbert

probably related to the recent move to gtkglarea.
try this branch: #4776 (but doesnt fix the cause, will only glitch less often)
also try: GDK_GL=software-draw-surface
or GDK_GL=software-draw

also, run gtk3-demo and run the glarea demo. if that is glitching, its a gtk bug, or a driver bug.

Both parameters do solve the problem of glitching on my computer.
Thanks for your help

Norbert

Thanks!

GDK_GL=software-draw seems to have fixed the glitching on my test PC (Dell Optiplex 7010). Changes the look of some buttons:

Neither GDK_GL=software-draw-surface nor GDK_GL=software-draw fixes the glitching on my mill which also runs trixie but on different hard ware.

Interesting! Did you try both, or is that a copy and paste error?
What hardware is it? Graphics driver? glxinfo?

Copy-paste error indeed, I tried both.

user@debian:~$ lscpu
Architecture:                x86_64
  CPU op-mode(s):            32-bit, 64-bit
  Address sizes:             39 bits physical, 48 bits virtual
  Byte Order:                Little Endian
CPU(s):                      2
  On-line CPU(s) list:       0,1
Vendor ID:                   GenuineIntel
  Model name:                Intel(R) Celeron(R) CPU G1820TE @ 2.20GHz
    CPU family:              6
    Model:                   60
    Thread(s) per core:      1
    Core(s) per socket:      2
    Socket(s):               1
    Stepping:                3
    CPU(s) scaling MHz:      100%
    CPU max MHz:             2200.0000
    CPU min MHz:             800.0000
    BogoMIPS:                4389.71
    Flags:                   fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pg
                             e mca cmov pat pse36 clflush dts acpi mmx fxsr sse 
                             sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm cons
                             tant_tsc arch_perfmon pebs bts rep_good nopl xtopol
                             ogy nonstop_tsc cpuid aperfmperf pni pclmulqdq dtes
                             64 monitor ds_cpl est tm2 ssse3 sdbg cx16 xtpr pdcm
                              pcid sse4_1 sse4_2 movbe popcnt tsc_deadline_timer
                              xsave rdrand lahf_lm abm cpuid_fault epb pti ssbd 
                             ibrs ibpb stibp fsgsbase tsc_adjust erms invpcid xs
                             aveopt dtherm arat pln pts md_clear flush_l1d
Caches (sum of all):         
  L1d:                       64 KiB (2 instances)
  L1i:                       64 KiB (2 instances)
  L2:                        512 KiB (2 instances)
  L3:                        2 MiB (1 instance)
NUMA:                        
  NUMA node(s):              1
  NUMA node0 CPU(s):         0,1
Vulnerabilities:             
  Gather data sampling:      Not affected
  Indirect target selection: Not affected
  Itlb multihit:             KVM: Mitigation: VMX unsupported
  L1tf:                      Mitigation; PTE Inversion
  Mds:                       Mitigation; Clear CPU buffers; SMT disabled
  Meltdown:                  Mitigation; PTI
  Mmio stale data:           Unknown: No mitigations
  Reg file data sampling:    Not affected
  Retbleed:                  Not affected
  Spec rstack overflow:      Not affected
  Spec store bypass:         Mitigation; Speculative Store Bypass disabled via p
                             rctl
  Spectre v1:                Mitigation; usercopy/swapgs barriers and __user poi
                             nter sanitization
  Spectre v2:                Mitigation; Retpolines; IBPB conditional; IBRS_FW; 
                             STIBP disabled; RSB filling; PBRSB-eIBRS Not affect
                             ed; BHI Not affected
  Srbds:                     Mitigation; Microcode
  Tsa:                       Not affected
  Tsx async abort:           Not affected
  Vmscape:                   Mitigation; IBPB before exit to userspace

user@debian:~$ lspci | grep -i --color 'vga'
00:02.0 VGA compatible controller: Intel Corporation Xeon E3-1200 v3/4th Gen Core Processor Integrated Graphics Controller (rev 06)

glxinfo.txt

@Sigma1912

@Sigma1912 does the gtk3 demo glitch on your machine?

does the gtk3 demo glitch on your machine?

Yes, it does glitch on the mill.

then its a regression of a gtk bug, or a new mesa bug, and I suggest you report it there.
I cant give you a starting point, as their bugtracker is currently down.

Ok thanks.
I also notice that on the mill the buttons don't change after running either $GDK_GL=software-draw-surface or $GDK_GL=software-draw in the terminal.

I believe it is a regression of this: https://gitlab.gnome.org/GNOME/gtk/-/merge_requests/1868

https://gitlab.gnome.org/GNOME/gtk/-/work_items/64#note_783520

Thanks for looking into it. Getting different hardware will likely be the easiest solution for me.

I still think you should report it referencing the old issue, include the kernel version, distro, glxinfo, lspci, and gtkversion.

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hansu commented on Oct 31, 2026

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