When mirroring a display with different geometry, old data appear in margin

[chaimleib]

My laptop's display is 2560x1600 which is 16:10. I want to mirror that on a 1080p TV with pillarboxing (black bars at the right and left), as it is 16:9.

My config looks like this:

# Laptop display
monitor=eDP-2, highres, auto, 1
# TV
monitor=desc:Panasonic Industry Company PanasonicTV0 0x01010101, highres, auto, 1, mirror, eDP-2
# Fallback
monitor=, preferred, auto, auto

I expect that I see black bars at the right and left and the mirrored video in the center.

Instead, the bars at the right and left flicker at various scales of old video data in very distracting ways. The center is not entirely stable either and tends to flicker.

Other thing I tried: Swap the mirroring direction

If instead of mirroring the laptop display to the TV, I mirrored the TV to the laptop, with letterboxing (black bars above and below) on the laptop, that worked almost perfectly. Here's my config for that:

# TV
monitor=desc:Panasonic Industry Company PanasonicTV0 0x01010101, highres, auto, 1 
# Laptop display
monitor=eDP-2, highres, auto, 1, mirror, desc:Panasonic Industry Company PanasonicTV0 0x01010101
# Fallback
monitor=, preferred, auto, auto

When starting unplugged, my laptop display works at native res and my preferred scaling. That's good.

When the TV is connected, my laptop display is letterboxed and scales 1080p to fill the width of my laptop display. The TV shows video at full frame and full resolution. That's also good.

When I disconnect the TV again is where things are not-quite perfect. My windows disappear, and I have to switch workspaces to get them back. Another issue: The Waybar disappeared, and only reappears when I reconnect the TV. (Seems like #10495)

[IiroUllin]

Confirm: just used a projector with 16x9 aspect ratio rather that 16x10 (my monitor) in the mirror mode. All kinds of random video buffer data appear in the margins.

[ddogfoodd]

Same here. The Waybar disappearing happened to me even when using the same aspect ratio.

However, when different aspect ratios are involved, my windows are not only gone after disconnecting, I also cannot open another Ghostty window. My app launcher appears at the top of the screen and is much larger, normally it would open in the center of the screen and be smaller.

Do you also experience something like this @chaimleib @IiroUllin ?

I ran hyprctl monitors and hyprctl clients before, during and after mirroring a monitor with a different aspect ratio.
EDIT: Note that this is the case for the mirroring direction where the laptops 16:10 mirrors the external 16:9.

I noticed that hyprctl monitor reports reserved: 0 0 0 0 after disconnecting, whereas it reports reserved: 0 36 0 0 before and during mirroring.

Probably more interesting: hyprctl clients shows a weird size and position for the terminal window that disappeared after disconnecting. However, if I am not mistaken it should still be partly visible on my 2560x1600 screen if it is of size 946x526 and starts at position 2055x7.

Outputs of hyprctl clients and hyprctl monitors:
clients_before_mirror.txt
clients_during_mirror.txt
clients_after_mirror.txt

monitors_before_mirror.txt
monitors_during_mirror.txt
monitors_after_mirror.txt

[IiroUllin]

I don't see most of the effects that you describe, @ddogfoodd The only issue that I have is: on some setups where the aspect ratio of the external device (monitor or projector) is different from my laptop's screen and that device is configured to mirror the laptop screen, random junk appears (and flickers) in the margins. The main rectangle containing the mirror image of the laptop's screen can also occasionally shift within the screen of the external device. Unfortunately I cannot thoroughly diagnose the issue, because it doesn't appear on any of my home monitors and only appears on some devices where I sporadically connect for lectures or presentations with limited available time. (I should also note that in all those cases I connected via HDMI cables, while I only have DP at home -- maybe that is somehow related...)

[ddogfoodd]

I also use HDMI. I noticed I didn't describe it clear enough. The behavior you describe, happens to me, when my external 16:9 mirrors my laptops 16:10. The behavior that I described happens when my laptops 16:10 mirrors the external 16:9.