andy
a4445d521f
Decoded from SKIDMARKS_CD32: - Computer drivers: the path of nodes laid 2 game units apart along the middle of the road, with side points 1 unit in from each wall. Drivers aim four nodes past where they'll be in four frames, or cut to the other side two nodes on at 70% throttle when running wide. Replaces the pure-pursuit AI; laps are quicker on every track. - Collisions: six points on the player's car (corners and sides, from .set words 6 and 7, now known to be half-length and half-width) are tested against the other car's box. Hits push the cars apart with a strength that grows with their speed difference, and spin the car. As in the original, only human players' cars collide; cars at different heights don't. - Towing: the hitch is at the car's back, the caravan sits 0.656 units behind it, and past 90 degrees both car and caravan bend back. The reconstructed collision weight (`mass`) is gone; old asset files with it still load.
177 lines
6.8 KiB
Markdown
177 lines
6.8 KiB
Markdown
# Game assets
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Everything the game uses is stored here as editable files. The build embeds
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this folder into the executable. To pick up changes:
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- **Rebuild:** `cargo run --release`.
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- **Or skip the rebuild:** run with `--data assets`. Files given with
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`--data` override the built-in copy.
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These files were converted from the original Amiga disks with
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`skids extract --data <folder with the ADFs>`. That conversion is lossless,
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and running it again overwrites your edits.
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## Tracks: `tracks/<name>/`
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### `track.png`
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The track picture: 1024 × 512, a 16-colour indexed (palette) image.
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- **Palette:** the PNG's palette is the track's palette. Change a palette
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entry to recolour every pixel that uses it.
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- **Road vs scenery:** colours 8–15 are road; colours 0–7 are scenery,
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where cars throw up dust. The picture doesn't affect handling. The
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walls come from the gates (below).
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- **Painting a new route:** paint it with the upper eight colours and
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update the gates to match.
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- **Saving:** keep the image indexed if your editor allows it. If it saves
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as full-colour RGB instead, each pixel is matched to the nearest default
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colour, which loses your palette.
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### `track.txt`
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Plain text; lines starting with `#` are comments.
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- **`gate x1 y1 x2 y2`:** lap gates in race order.
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- Gate 0 is the start/finish line, and the grid forms up behind it.
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- Cars must cross every gate, in order, to complete a lap.
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- **Walls:** the gates' ends also shape the road. One edge is a smooth
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curve through every gate's first end (`x1 y1`), the other through
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every second end (`x2 y2`). Those curves are the walls, and computer
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drivers follow the road between them. The curves pass halfway
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between neighbouring gates' ends and round off the corners, as in
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the original.
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- Coordinates are on the isometric ground plane. To find where a point
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on the ground sits in the picture, with `z` its height in pixels
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(from `height`):
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`picture x = wx - wy + 512`, `picture y = (wx + wy) / 2 − 156 − z`.
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- `skids trace --data assets --track N --out t.png` draws the walls
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(grey), the gates (gate 0 in yellow) and the computer cars' paths over
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the picture.
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- **`height`:** 64 rows of 64 numbers giving ground height in pixels × 64.
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- **Layout:** the rows run along world y and the numbers within a row
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along world x. Each covers 16 × 16 world units.
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- **Effect:** climbing slows cars and descending speeds them up. Cars
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leave the ground over crests that drop away faster than gravity, and
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the car sprites tilt with the slope.
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- **`set`:** the name of the set of tracks this one belongs to, shown under
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the menu thumbnail.
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- **`start`, `flags`:** values from the original data that the game
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doesn't use.
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### `thumb.png` (optional)
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The track's 123 × 32 thumbnail from the original track-select screen, in
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the track's palette. It's drawn at double height in the menu, because the
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original's pixels are half-width. Without one, the menu shows a shrunken
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`track.png`.
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To add a track, make a new folder with `track.png` and `track.txt`. Tracks are listed in
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name order.
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## Vehicles: `vehicles/<id>.png` and `<id>.txt`
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### `<id>.png`
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A 2048 × 800 sprite sheet: 32 headings across by 25 tilts down, each cell
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64 × 32.
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- **Colours:** use only palette indices 0–3:
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- 0 transparent
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- 1 tyres / shadow
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- 2 trim
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- 3 bodywork
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The colours in the file are only a preview; each player's car is
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recoloured at run time.
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- **Headings:** column 12 faces right, and columns advance clockwise in
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11.25° steps.
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- **Tilts:** row = roll × 5 + pitch (each 0–4), so row 12 is the car on
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flat ground.
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### `<id>-menu.png` (optional)
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The car's 64 × 32 picture from the original select screen, in the same
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four colours as the sprite sheet.
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### `<id>.txt`
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The display name, driver and handling:
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| Setting | Meaning |
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|-----------|---------|
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| `name` | name shown in the menu |
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| `driver` | driver's name, shown next to it |
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| `trailer` | `yes` for something towed behind cars (the caravan) rather than driven |
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| `handling`| the 16 values from the original `.set` file, used as the original game uses them (below) |
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The `handling` values, counting from 1:
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| Value | Meaning |
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|-------|---------|
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| 1, 2, 6 | computer drivers: drag, grip, power |
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| 9, 10, 11 | human drivers: drag, grip, power |
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| 3 | steering: 16 = 1/64 of a turn per frame at full lock |
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| 5 | gravity: 8 = 1 pixel per frame² |
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| 7, 8 | half the car's length and width, for collisions: 2 = 1 world unit. The tow hitch is at the back. |
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| 4, 12–16 | unused |
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What the driving values do:
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- **Drag** (below 64): how much of the engine's speed survives each frame.
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Low drag gives fast pick-up and fast slowing.
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- **Power:** what the throttle adds.
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- **Top speed:** `power × drag / (64 − drag) / 32` world units per frame,
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at 50 frames a second.
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- **Grip:** how quickly the car's movement turns to follow where it's
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pointing. Low grip means long slides.
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The menu's **Handling** option can replace every car's values with one of
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the original's presets.
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Older files with `original`, `top`, `accel`, `brake`, `grip`, `turn`,
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`offroad` and `mass` lines still load: `original` is read as `handling`,
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and the others are ignored. To add a car, add a new `<id>.png` / `<id>.txt` pair.
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## Sounds: `sounds/*.wav`
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8-bit mono WAV files at the original Amiga sample rates. A loop point,
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stored in the WAV's `smpl` chunk, makes a sound repeat from there; most
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sample editors keep it. The game uses these names:
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| Sound | Use |
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|-------|-----|
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| `motor3` | engine, pitched up and down with revs (falls back to `motor`, then `engine`) |
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| `screech2` | tyres sliding (falls back to `screech3`, then `screech`) |
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| `crash1`, `crash2`, `crash3` | collisions, picked at random |
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| `backfire` | lifting off at high revs |
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| `horn` | Right Shift (player 1) or Left Shift (player 2) |
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| `beep`, `beep2` | countdown, then lights out |
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Missing sounds fall back to synthesised ones. Any other WAV files are kept
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but not used.
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## Music: `music/*.med`
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The tune, an OctaMED module. Edit it in a tracker that reads MED files,
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such as OpenMPT. The game's player supports plain sample instruments (no
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synth sounds) and the commands listed in `docs/FORMATS.md`. Preview it
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with `skids music --data assets --out tune.wav`. If there are several
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files, the first in name order plays.
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## Pictures: `gfx/*.png`
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Indexed PNGs. `skidtoon.png` is the title picture at the top of the menu,
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shown at half size. The others aren't used:
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- `ball.png`: 64 frames of a spinning ball with the Acid logo, 16 frames
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across, each 32 × 33. Its real colours aren't known, so it has a grey
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palette.
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- `chat2.png`, `mouse.png`, `sign.png`: small odds and ends.
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## Palettes: `palettes/*.pal` (optional)
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16 lines of `RRGGBB`. Each file overrides the PNG palettes:
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- `track1-3.pal`: one track
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- `track1.pal`: every TRACK1 track
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- `default.pal`: all tracks
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