Well, GP4's menus are the second most important thing i personnaly searched for after rim colors.
So i studied all files carefully, but it was about 6 month ago and i wasn't as skilled as today in file reading. Nevermind, here is what i found :
All files describing menus are in GP4folder/MenuData/PC/GP2001 folder.
As you know, .gps files store menus strings but they also store some strange numbers (just open the file in notepad and browse 2-3 pages down), but maybe Madman could gain some infos about those numbers.
gpi files are stored in the images folder and are 32bit pictures (containing an alpha channel).
All menus drawings and pictures are stored in gpi files.
But not all gpis are used by the game, in fact gpis from 388 to 401 are not used cause they are already there in previous gpis.
The tool i talked about on my forum is not a gpm browser but a gpi browser, allowing preview only of all gpi files.
gph file is storing descriptions about gpi files stored in the images folder.
As madman said, you can got there Number of gpis used, gpis ID, width and height and other datas that Madman might be right about even if i never test them personnaly.
gpt file is a copy of the gph file and is not used by the game.
gst file is not used by the game either but gives interesting datas on gp4s internal labels.
main_menu.men is not used by the game either and might be a workflow file.
menu.gpm is core file for gp4 menu's.
We took the challenge with Sven (Mitlehner) to understand it but we wasn't able to read more than the first part containing menus links to strings and waiting about 23Kb on the 1.4Mb of the whole file.
Rest of the file seems to be menu description but under an harcoded form, not an organized and structured file format. it might contain pages links, objects positions in each pages etc...
Videos folder store all gp4 videos and even a useless one : intro4.bik cause the one used (and which is exactly the same) is gp4_intro.bik.
they are in bink format, a free format giving a great compression ratio and that is more and more used in gaming industry (all Blizzard videos are in bink !).
To learn more about bink, just go on radgametools'site.
objects folder is completely useless as the files used are in maps/track2001 folders and are now known to store track road layout.
fonts folder contain all gp4 fonts wich are in facts 256 grey levels gpi files. You can switch file names to see the differences :) And yes, i built a gpf reader too, but as for gpf, it can't save anything.
So here it is, i think i reviewed all Menudata folder's files.
As you can see, most of the interesting things are still hidden in the gpm file, so we will have to go deeper with it if we ever want to tweak gp4 menus furthermore...
Best regards,
Lo2k