more /root/File Formats/GMP File Format (v1.0).thread
2009-04-15 02:22:13IsmAvatar
What is GMP?
GMP is the file made by Game Maker Extension Package Builder/Maker v 1.01. Obviously, then, a GMP file is an Extension Package, without the data such as the contents of the dlls or libs or whatever - such information is stored in a .dat file, which I believe uses a form of compression, and possibly encryption. Extension Packages were created for GM 7.0.

The license for this documentation is the same as the license for the GM6 File Format Documentation.
Game Maker Extension Package Builder has its own license which you should read. It is essentially exactly the same as the Game Maker license, with the words "Game Maker" replaced with "Extension Maker". As such, just like gm6 files, I have free range on gmp files, so this documentation is perfectly legal, as is modification of gmp files.

Technical Info
There is only 1 mystery integer, and that is the 4th byte. It always seems to hold the value 1. If you change it to 0, it cannot load, but if you change it to something like 2 or 4, it still loads fine. My guess is that this holds the Extension Package Builder version number, 1 = 1.01, 0 = 1.00 (a bug was noticed in 00 before I had a chance to download it).
When specifying argument and return types, a value of 0 seems to be interpretted as Real.

Work In Progress
This is a continual work in progress, so if you have any corrections, please re-download the latest version to make sure I didn't silently correct it, and then (if I haven't) please report it. I'm marking it as a finished product because it's as finished as it will ever be, with version updates from this point on.

Please download the gm6 file format to get an understanding behind my format and other background information like that.

There is only 1 version of this, as I don't bother with Inclusions or Positions, since you can easily figure these out yourself. I do, however, make marks to indicate default values and where an inclusion would appear.

Version 1:

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2009-04-15 07:20:04Clam
I think I mentioned it on the old forums, but the ged format is essentially identical to gmp. There are one or two differences, but I don't recall what they are.
2009-04-15 14:09:35PickleMan
I didn't copy over the posts, just the documentations I could find.
2009-04-16 03:00:59Clam
Yep, just repeating it so the info's here too.
2009-04-17 01:47:58PickleMan
2009-04-26 19:09:32Bob the BlueBerry
The 4th byte could be something like GM libs have to you can't open standard ones.
2010-12-02 06:30:42antidote
It's a flag stating whether you can edit it or not,basically a boolean value.