Did nobody understand
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I wrote? I thought it was fairly clear what was different about them.
You know if you open up a Windows Bitmap, and the first 2 bytes are always the ascii characters "BM" and the third is usually ascii "0"? Or if you open an executable and the first two bytes are always "MZ"? If you changed those first two bytes you could still read all the data right? But most programs would refuse to touch it, because it just doesn't look like it's the right kind of file.
This is common practice, since most OS don't specify "file extensions" like .exe or .bmp so programs should make sure that the file a user has asked them to load is actually the kind of data this program is designed to handle. Even in DOS / Windows, it's too easy to change the extension from .exe to .bmp and try to open a program in MSPaint.exe. If it didn't check something very simple at the start of the file, the potential for disastrous crashes while reading completely unrelated data in a specific format which it may not fit is usually considered too great.
That "unique identifier" is usually only between 2 and 4 bytes long, and is typically stored (officially) as a 16 or 32 bit integer which, for convenience, is often visibly recognisable in ascii text. Other common ones are "RIFF" used in AIFF, WAV, AVI and QT (all matching International File Format standards for interleaved data chunks) "JFIF" for jpeg images, "TIFF" for Tiff images, and "PNG" in Portable Network Graphics files.
The one in PT for it's binarized ASE files is really long. 23 bytes long. It's just "SMD Model data Ver 0.62". If you tell the PT client to only read ""SMD Model data Ver 0.6
3" it won't touch any of your meshes any more. If you run a search and replace on all your SMDs and SMBs to "update" them all to ""SMD Model data Ver 0.63" as well, then your PT client will
only read your meshes, and won't load any from another PT client.
You can actually use any sequence of 23 non-zero bytes to make sure that only SMDs and SMBs with that exact sequence of starting bytes is
ever read by your client.
That's what rPT did.
You can make your client read only rPT client SMDs and SMBs by changing the string in your client, or you can make rPT models work in a regular client by replacing the first 23 bytes with ""SMD Model data Ver 0.62"".