Explain initial flatpak MAME setup

[Abdull]

From the current description, it is impossible to set up a working instance.

E.g.

• how to set up directory structure for (existing) ROMs so that flatpak-based MAME can see them?
• how to set up controllers?

[jflatt]

There isn't a place in flathub for documentation. Refer to the official mame site

[Abdull]

There isn't a place in flathub for documentation.
Yes, there is; other flathub-hosted projects use their README.md. This repository already has a README.md, so all it requires is adding a short section to explain the flatpak-specific aspects in setting up flatpak-MAME.

Refer to the official mame site
The official MAME site says nothing about flatpak-specific aspects.

While my Bluetooth-attached game controller works (by now?) under Flatpak-MAME, I'm still stuck with figuring out how to set up the ROM directory. As you are a collaborator for this repository, I assume you should have at least once been able to successfully set up flatpak-MAME to load ROMs from your system's file system, and you should be aware that generally, directory setups are nontrivial between a flatpak instance and its "outside" world (due to overlays, permissions etc.). This includes aspects such as "does flatpak-MAME consider the host system's $HOME/.mame config directory, etc.?

In the flatpak-MAME GUI, General Settings > Configure Folders > ROMs > ROMs Folders lists a single entry, /app/share/mame/roms. Now this is of course the flatpak-MAME instance's own view of its own file system (explorable with flatpak enter $(flatpak ps | grep mame | awk '{print $1}') bash).

How to symlink an external ROM directory into this location? I guess you have done this at least once, maybe you can share your setup?