skids/docs/FORMATS.md

Super Skidmarks data formats

Notes from reverse engineering the AGA/CD32 release of Super Skidmarks (Acid Software, 1995). Everything here was worked out from the data on disks 2–6. Disk 1, which holds the executable, is missing from this archive, so anything that lives only in the executable (palettes, sound, handling) is unknown. See Gaps.

All multi-byte values are big-endian unless noted.

Disks

Each disk is a standard 880 KB double-density ADF (1760 blocks of 512 bytes) formatted as OFS (DOS\0). The [HD] in the file names refers to the hard-drive-installable release, not high-density disks. Each disk holds a single file:

Disk	File	Contents
1	smcd32a.lha	missing
2	smcd32b.lha	vehicles/cow.aga, track/TRACK1
3	smcd32c.lha	track/TRACK2, vehicles/TRUCK.aga
4	smcd32d.lha	track/TRACK3, vehicles/PORSCHE.aga
5	smcd32e.lha	track/track4, vehicles/vw.aga
6	smcd32f.lha	vehicles/F1.aga, Midget.aga, mini.aga, Police.aga

Each disk's archive stands on its own (the set isn't one archive split across disks). They use level-0 headers and the -lh0- method (stored), under a top-level super_skidmarks_cd³²\ directory. Most members are individually packed with CrunchMania.

CrunchMania

0   4   id: "CrM!" (LZ + fixed codes) or "CrM2" (LZ + Huffman)
        lower-case "Crm" = delta-encoded samples (running byte sum)
4   2   unused
6   4   unpacked size
10  4   packed size (excludes this 14-byte header)
14  …   packed stream

The stream is read backwards from 14 + packed - 6, a byte at a time, LSB first. The last six bytes seed the bit buffer: a 32-bit word shifted right by 16 - shift with 16 + shift valid bits, where shift is the final 16-bit word. Output is also written from the end towards the start. src/formats/crm.rs implements both variants. Every packed file on the disks decodes exactly: the output buffer fills completely and the input is consumed to its first byte.

Tracks (track/TRACKn)

0x00  7 × u32   end offset of sections 0..6
0x1C  …         section 0: track-selector thumbnails (20622 bytes, raw)
…               sections 1..6: one track each, CrunchMania-packed

So the four files hold 24 tracks. Each track section unpacks to 281240 (0x44A98) bytes:

Offset	Size	Contents
0x0000	8192	Height map: 64 × 64 u16, 8.8 fixed point, row-major. Each cell covers 16 × 8 screen pixels.
0x2000	8192	Unused, zero on every track.
0x4000	8	u16 gate count, u16 start x, u16 start y, u16 flags.
0x4008	8 × n	Gates: x1 y1 x2 y2, world coordinates × 32. The list repeats after the last gate.
…		Unknown data, mostly a bit pattern, up to 0x4A98.
0x4A98	4 × 65536	Four non-interleaved 1024 × 512 bitplanes, giving 16 colours.

Track geometry

Gates are line segments across the road and run in race order; gate 0 is the start/finish line. They're defined on an isometric ground plane rotated 45° to the picture. The projection that best fits the data is:

screen x = wx - wy + 512
screen y = (wx + wy) × 31/64 - 252

With these constants, 96% of points sampled along the gates land on road pixels across all 24 tracks (92% minimum). A plain screen-aligned 2:1 squash gives 40–70%. Adding a height term doesn't improve the fit, so the height map is used only for slope physics and body tilt.

The stored start point is on the road for 14 of the 24 tracks read as screen coordinates, and 10 read as world coordinates. It isn't used; the grid forms up behind gate 0.

Palette use

The track pixel indices are ordered from dark to light. Indices 0–7 are scenery and 8–15 the driving surface, so the fourth bitplane is effectively a road mask. The game uses it as such here: off-road means less grip and lower speed.

Vehicles (vehicles/*.aga)

CrunchMania-packed, 409600 bytes unpacked: 25 tilt blocks × 32 headings × 512-byte frames.

A frame is a 64 × 32 AGA hardware sprite. Each line holds 8 bytes of plane 0, then 8 bytes of plane 1, giving 3 colours plus transparent:

Index	Use
0	transparent
1	tyres, shadow, dark
2	trim / accent
3	bodywork

• Heading: frame 12 faces screen-right, and frames advance clockwise in 11.25° steps. In world terms, frame = 12 + (angle + 45°) / 11.25°.
• Tilt: block = roll × 5 + pitch, each in 0..4, with 2 = level. Block 12 is the car on flat ground.

Police.aga reads as all zeros with one third-party ADF tool, but it's intact when read directly from the disk image.

Gaps

These almost certainly live on the missing disk 1:

• The main executable, and with it the real handling model, AI, rules, menus and fonts. This port's versions are reconstructions.
• Colour palettes. Neither the track nor the vehicle files carry any. The engine uses a reconstructed palette, and real ones can be dropped in as .pal files (see the README).
• Sound effects and music.
• Any tracks or vehicles beyond the 24 and 8 above.

The engine's own editable formats, which skids extract converts all of the above into, are described in assets/README.md.

If disk 1 turns up, put it next to the others and run skids info. Anything in a track/ or vehicles/ directory inside its archive is picked up automatically.