"Our" game.exe client (I mean an episo 4/5 client) hard-codes the filenames of mini-maps.
The directory (in data.saf structure) is stored at offset 0x2B0298 and is "data/interface/MiniMap", the names of the mini-maps come immediatly after and each is stored on 8 bytes (that grants than even 3 digits (eg '102') map-name (so "102.tga") is no more than 7 chars and so names are zero-terminated).
the hard-coded names are: "
70.tga..69.tga..68.tga..108.tga.105.tga.104.tga.10 3.tga.102.tga
47.tga..46.tga..45.tga..44.tga..43.tga..36.tga..35 .tga..30.tga
29.tga..28.tga..20.tga..19.tga..18.tga..2.tga...1. tga...0.tga..."
so 24 names, used by a method that gains access to this array, reads the names, loads the designated file, and uses a DirectX service (or an internal decoder) to decode the TGA file into bitmaps, then it stores these bitmaps into a predefined bitmap-array with 24 slots.
(note that names have no intrisic meaning, the minimap of map 0 is called "0.tga" by simplicity, it would be called "foo.tga" it does not change what maps support minimap display, the map 0 will simply display that foo.tga image).
when the map is to be displayed, the client verifies that its ID matches one of these ones (it uses the *same* predefined / pre-supported maps), if so it displays the map.
to allow the display of all maps, one has to:
- re-allocate the bitmap array (to 128 entries or more)
- recode the loading method to no longer use the array of names present at @002002B0 but to iterate all filenames, and to store generated bitmaps into the new array.
- recode the tests done before the map is displayed to no longer filter on the pre-allowed map IDs.
as far as I know, nobody has done such changes for a p-svr.
what you may have seen is the use of a limited number of maps and re-assignment of their IDs to match those present in the list above. if you are not using the maps 100+ you can renum the Fantasia (or other) map to be (for instance) the 102 one. of course you will also modify the gatekeeper and portal information for all access to the former map to use the new ID 102.
this option requires less work - I mean it's some possible customization while the previous is an huge development task.