Windows end up behind panel when maximized, with certain fractional scaling values and/or monitor refresh rates

[gkatev]

 * Cinnamon 5.0.4
 * Arch Linux
 * AMD Navi 10 (5700XT) w/ amdgpu

Issue
Hi, I'm having an issue with a new monitor, that seems to be due fractional scaling and/or >60Hz refresh rate.
The problem is, when I maximize a window (or tile it), its lowermost part ends up behind the Cinnamon Panel instead of just above it.

Expected:

Observed:

How I reproduce it

1. Monitor is at 100% scaling, 2560x1440 @ 60Hz.
2. Optionally enable Hi-DPI (2x).
3. Use xrandr --scale 1.83x1.83.
4. Switch to 165Hz (same result with 120, 144)
5. Maximize a window, via button, shorcut, or drag-to-top
6. The window ends up behind/below the panel

Unfortunately, while the problem is 100% consistent, it appears to be quite dependent on a number of factors.
Things that, if changed, may alter the observed behavior:

• 60Hz refresh rate: Usually OK, unless if going 60 -> 165 -> 60
• Different scaling value: OK (possibly ok with some, not with others)
• Side monitors attached with no scaling: OK
• Side monitors attached with specific scaling value: Not ok

Does this seem like something that could be reproduced/debugged? Let me know if I can help.
Or might this not be directly related to cinnamon or muffin? (but instead due to X?)

[mtwebster]

Hi, does this happen if you use fractional scaling via the cinnamon-settings Display page?

[gkatev]

No, it seems to be happening for specific scaling values, and I have not come across it with the predefined ones. But as I understand it, the "Display" settings page also uses xrandr behind-the-scenes? (after applying scaling with the xranrd command + hidpi switch, cinnamon shows a fractional scaling setting of 109%)

[mtwebster]

Yes it does - not with the command-line tool, though I took the tool as a reference implementation for our own.

I wonder if there could be some interference from our randr daemon. You could try killing that (csd-xrandr) - if you even have it enabled in the first place. Some people with odd monitor setups disable it and opt for an x config file instead.

If it is running, you can try modifying ~/.config/cinnamon-monitors.xml with your custom scale, then restart csd-xrandr:

There's a 'scale' property for each monitor - you should be able to set that to your 1.83 - you may need to adjust the x position of any monitor to the right - the 'width' and 'height' values should always be the monitor's actual resolution, but the x and y positions of each monitor are based on their 'logical' size.

[gkatev]

Indeed it is affected by csd-xrandr. After killing it and applying my configuration via xrandr, the problem stopped appearing.

If I apply the config via xrandr, but csd-xrandr is still running, the problem happens. And when it happens, it persists after killing csd-xrandr. After killing it, and using the xrandr command all is good.

The same is observed with the xml file. I kill csd-xrandr, edit the xml as desired, and start csd-xrandr. My desired config is applied automatically, but the problem occurs. Kill csd-xrandr, run xrandr command --> okay again.