`Presets` are really just collections of config changes across one or more emulators. RetroDECK has pre-configured configs for all emulators [RetroDECK: Emu-Configs](https://github.com/XargonWan/RetroDECK/tree/main/emu-configs) that sets up things like basic controller bindings, optimal graphics settings etc. The pre-configured settings are considered the `default` states, and by default all `preset` changes are disabled.
Make sure the emulator you want to make a `preset` for is in its `default` RetroDECK state. Open the emulator and change the settings needed for the `preset`. Either diff the emulator settings file against the `default` or generate a RA override file. If working in RA, make sure to note the full path to the override file.
To build a new `preset` for an emulator that isn't a RetroArch core, we open the emulator manually, make any changes needed to put the emulator settings in whatever state it should be when the `preset` is enabled, and then diff the `default` and current settings to collect whatever changed. Eg. If we were building a `preset` where the emulator would auto-save state when closed and auto-open state when run, open the emulator, go to settings, enable those features and then diff the emulator running config vs the RetroDECK `default`.
RetroArch uses a different process because it uses override files, so we don't need to change the core config file. Run a game in the RA core you want to build a `preset` for, open the Quick Menu (L3+R3) change the settings that are needed for the `preset` then under Quick Menu use the Save Core Override option. This generates an override file in a path we also need to know [RetroArch Overrides](https://docs.libretro.com/guides/overrides/) and we can generally use the entire contents of the override file in the `preset`.
Once we have the settings that need to change for the new `preset`, and the core override path for RA cores if needed, they are stored in emulator or core-specific files that hold all settings for all `preset`s for that emulator [RetroDECK: Presets](https://github.com/XargonWan/RetroDECK/tree/main/emu-configs%2Fdefaults%2Fretrodeck%2F`preset`s) These files contain any setting changes needed for any `preset` for each emulator to be considered `enabled`.
When a `preset` is `enabled` for one or more emulators, these settings are changed from the `enabled` reference files. When a `preset` is disabled, the setting values from the `default` files are used.
There are some other factors like validating that two `preset`s the user wants `enabled` at the same time don't conflict (like you can't have both borders and widescreen `enabled` at the same time) but that is the basics of gathering information for `presets`.
Depending on the settings being gathered, all this can probably be done on any system and not necessarily on a Deck running RetroDECK, the settings are the same either way. Generally settings relating either to the screen/visual output or controls should be done on a Deck, so make sure we capture correct values.
