Steam Big Picture won't launch in full-screen when using a custom desktop session

[amura11]

Your system information

• Steam client version (build number or date): 1709846872
• Distribution (e.g. Ubuntu): Ubuntu 22.04.4 (Budgie)
• Opted into Steam client beta?: No
• Have you checked for system updates?: Yes
• Steam Logs: steam-logs.tar.gz
• GPU: Nvidia

Please describe your issue in as much detail as possible:

I'm setting a desktop to launch directly into Steam big picture using a custom desktop session. When Steam launches it starts in big picture mode but it's not full-screen, it only fills a portion of the upper left hand side of the screen. Eg:

I found by pressing Alt + Enter I get dropped out of big picture mode and when I start it again it will be full screen. If I log out and log back in I start to have inconsistent results. In some cases when logging back in Steam will remain in full-screen correctly but in other cases it will revert to partially filling the screen. I was having this issue on a Mint install and decided to try fresh with Ubuntu as that other install was a bit of a mess only to still have this issue. I have no idea why this is happening and why it's so inconsistent.

Below are the custom session and the script the custom session runs:

![PXL_20240321_161558707](https://github.com/ValveSoftware/steam-for-linux/assets/1559993/14f83985-0af2-48ff-baae-5fd54dc71b45)

[Desktop Entry]
Name=Steam Big Picture Mode
Comment=Start Steam in Big Picture Mode
Exec=/usr/local/bin/start-steam-big-picture
Type=Application

#!/bin/bash

xrandr --output HDMI-0 --mode 1920x1080

openbox-session &
steam -bigpicture

Notes
The xandr is in there as the display connected is a 4k TV and Steam is unusable at 4k, probably due to a weaker CPU. Removing that line doesn't seem to make a difference. In one instance where I had that line removed the setup was all fullscreen but when I logged out and in again it was back to not filling the screen.

I've tried not using openbox-session and it seems to be worse. I haven't thoroughly tested this but without it the Alt + Enter trick doesn't seem to work at all.

Steps for reproducing this issue:

1. Install a fresh version of Ubuntu
2. Create the launch script as defined above
3. Create the .desktop file as described above
4. Install Steam sudo apt install Steam
5. Create a test user
6. From the login screen select the Steam Big Picture Mode session

[amura11]

I came back to this and finally found a workaround. When trying to turn the windowed mode option on and off I noticed the window was the same size as the instance of steam in the picture above. I eventually found that setting steam to run fullscreen in openbox did the trick. I added this to my ~/.config/openbox/rc.xml

<applications>
    <application class="steam">
        <fullscreen>yes</fullscreen>
    </application>
</applications>

I'm not sure why this is needed. Could it be when the window is created it isn't being set to fullscreen in a way that openbox understands?

[casasfernando]

Thanks for sharing the above @amura11 . I was having exactly the same issue and this solved it!

I still find some minor strange behaviors here and there, like the initial animation not using the full screen width, or the buttons not appearing until I hover over them with the mouse , or the Steam menu displaying white bars at the top and the bottom with the height of the top and bottom bars.
It seems that Steam and Openbox don’t get along well without some workarounds.