Ok, I understand. But please tell me what is the core, I'm preparing an update and I've already added some new cores, so i could have already added it.
I'll try to explain how background works, but first I have to put a warning for everyone about this:
Platform.ini is an integral part of Wiiflow and -as I said multiple times- you should NEVER change it, unless you first ask @fledge68
There are some things that could be screwed, if you don't know exactly what you're doing, like the database for snapshots and game info, but you'd also risk of breaking other plugins that worked before. Even worse, if everyone would start sharing their "custom" platform.ini's, we would have a great number of users with a TON of issues!
Sorry if that may sound limiting, but it's really important. I only want to avoid unnecessary troubles to people.
Ok, after this important warning, let's start with the explaination:
You can't set a background just like you do for other options. It's hardcoded in Wiiflow.
Platform.ini contains all the supported
magic numbers you may need (except when someone releases a brand new emulator), associated to the
platform names, and the respective
coverflows to use.
As you may have noticed, in wiiflow/backgrounds/Rhapsodii Shiima, all the backgrounds are named
exacty like the platform names (AMIGA, AMSTRAD, APPLEII...). You'll also notice that there are a number of duplicates, with different names.
When you add a new magic number to one of your source menu .ini's (e.g. arcade.ini) you have to make sure that number it's found in platform.ini and you must duplicate the arcade background, renaming it with the exact platform name.
Then, always in platform.ini, you have to make sure that it's using the very same coverflow (e.g. _coverflow, cart_box, pc_box ...)