ZDoom

Hello. I'm writing my own launcher of GZDoom mods and i would like to have an option to select a monitor to start GZDoom in by appending apropriate '+vid_adapter x' to the launch command. This works fine in Windows, but is problematic in Linux.
I wrote some code that enumerates monitors using libXrandr, but the order of the monitors in the list is different from the order that GZDoom uses for its vid_adapter command,
which means when i select the first monitor from my list and start GZDoom with +vid_adapter 1, it starts on the second monitor and vice versa.
In order for this to work, i must use the exact same way of enumerating monitors as GZDoom so that the order in my launcher matches the order in GZDoom.
Can you please explain how it works?

You need take a look at SDL2 source code. GZDoom passes the value of vid_adapter CVAR to its functions as is. Also, the primary monitor should have zero index I think.

So i open GZDoom sources and first thing i see is
looks i'm not the only one fighting these issues

Taking into account that the mentioned code is Windows-specific, it has nothing to do with display enumeration on Linux.