A quick look at Gold Disk Animation

Since I’m still looking for a thing to reverse engineer, I decided to see if this file service at discmaster.textfiles.com could offer some exotic formats. And indeed it can.

So there’s this AWI or AWM file format (it’s called AWI in the decoder libraries but the files I could find have extension .awm).

So this is more of a presentation format which has nested structure with chunk names in capital letters containing other chunks while chunks (i.e. everything is contained inside GDAW chunk, actual assets like PALT or BKGD stored inside RSRC chunk and presentation scenario probably being stored in SEEN chunk) with lowercase names having various specific data attached to them (e.g. psnm is followed by Pascal-style string with asset name, tzim contains compressed image data and nndn marks end of object data).

I have not looked too deep into it (no idea how the scenario works or what are the various object parameters) but here’s some information about resource types:

  • RLE4—a 16-colour RLE-compressed BMP, I presume;
  • RLE8—ditto but with 256 colours;
  • PALT—some global palette (but images still have their own);
  • BKGD—DCL-compressed background BMP;
  • ACTR—DCL-compressed BMP used as sprite;
  • WIPE—transition effect definition;
  • SWND—DCL-compressed WAV.

The most curious thing for me is that it used Pkware Data Compression Library to compress data. And while WAV files are compressed in one piece, BMPs are compressed as separate chunks—14-byte BMP header, 40-byte DIB header, palette, and image data. I think this was a conscious decision from the format and tool designers (in order to improve compression ratio a bit).

I’ll probably try to dig some more details and document it but the most interesting part for me (i.e. figuring out its outstanding design features) is done already.

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