Graphical glitches in GUI client

Graphical glitches in GUI client

[Nathan Yinger]

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Please answer the following questions to help us understand your issue.

What did you do before the bug happened? (Steps to reproduce your issue)

ran `git gui` in repo root.

What did you expect to happen? (Expected behavior)

The git gui client to open.

What happened instead? (Actual behavior)

About 80% of the time the git gui client opens correctly. About 20% of the
time I get a window covered in graphical glitches: parts of the window
covered in flashing black rectangles, text missing or distorted. In rare
cases the OS crashes as well (it's been a while since I saw the OS crash
from this, I don't remember further details about the crash).

What's different between what you expected and what actually happened?

The gui client was rendered unusable by graphical glitches.

Anything else you want to add:

Screenshot attached.

Fedora has Wayland enabled by default, though I'm not sure if the git gui
client uses it directly or if there's some sort of X emulation involved.

Please review the rest of the bug report below.
You can delete any lines you don't wish to share.

[System Info]
git version:
git version 2.44.0
cpu: x86_64
no commit associated with this build
sizeof-long: 8
sizeof-size_t: 8
shell-path: /bin/sh
uname: Linux 6.7.6-200.fc39.x86_64 #1 SMP PREEMPT_DYNAMIC Fri Feb 23
18:27:29 UTC 2024 x86_64
compiler info: gnuc: 13.2
libc info: glibc: 2.38
$SHELL (typically, interactive shell): /bin/bash


[Enabled Hooks]

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Re: Graphical glitches in GUI client

[Konstantin Khomoutov]

On Wed, Mar 13, 2024 at 12:06:03PM -0400, Nathan Yinger wrote:

[...]
> About 80% of the time the git gui client opens correctly. About 20% of the
> time I get a window covered in graphical glitches: parts of the window
> covered in flashing black rectangles, text missing or distorted. In rare
> cases the OS crashes as well (it's been a while since I saw the OS crash
> from this, I don't remember further details about the crash).
[...]
> The gui client was rendered unusable by graphical glitches.
[...]
> Fedora has Wayland enabled by default, though I'm not sure if the git gui
> client uses it directly or if there's some sort of X emulation involved.

git gui (and gitk) are written in Tcl and use the Tk GUI toolkit.
AFAIK, Tk does not yet have a Wayland backend, so git gui should rely on
XWayland [1].

I'm afraid, there's nothing Git devs could sensibly do to help with this
problem: it's not a bug in git gui; the problem most probably exists in
XWayland, or somewhere between XWayland and Wayland; it may be triggered
by certain patterns of how Tk uses the X11 protocol [2], and even there may
be an issue with the combination of all the stuff above and the graphic
card drivers.

So, I would suggest to explore two routes:

 - Try to solicit insights from the Tclers [3].

 - Try to search for similar problems in the Fedora issue tracker
   and also maybe ask questions using discussion venues dedicated to
   this distro.

Footnotes:

 1. There's an easy way to verify: start xkill and hover its cursor over
    a window of the app of interest: if it changes its shape to a
    characteristic cross, the window is not rendered by Wayland directly
    and uses the X11 protocol.

 2. Note that Tk is old, and it's unreasonable to expect it to use the X11
    protocol flat-out improperly.

  3. https://groups.google.com/g/comp.lang.tcl/
     This list is known to be frequented by the Tcl/Tk core devs.