Add Rust revival engine for Super Skidmarks

Cross-platform (Windows/macOS/Linux) engine that plays the original
Amiga data straight from the ADF images:

- ADF (OFS/FFS), LHA and CrunchMania (CrM!/CrM2) readers
- Track decoding: 24 tracks of 1024x512 16-colour planar art, height
  maps and lap gates on an isometric ground plane
- Vehicle decoding: 8 cars, 32 headings x 25 tilt frames of 64x32
  AGA sprites
- Reconstructed handling, AI, race rules, menus and synthesised sound
  (disk 1 with the executable, palettes and audio is not in the set)
- info/extract/bench/trace/render tools, format notes, CI builds

src/data/palette.rs

@@ -0,0 +1,132 @@
+//! Colour palettes.
+//!
+//! The track and vehicle files carry no colour tables; the retail game sets
+//! them from its main executable, which lives on disk 1. Until that disk is
+//! available we use a reconstructed palette. Indices on the retail tracks are
+//! ordered dark-to-light, with 0-7 used for scenery and 8-15 for the driving
+//! surface, so two ramps give a faithful-looking result.
+//!
+//! Real palettes can be dropped in as text files (16 lines of `RRGGBB`,
+//! `#` comments allowed) next to the game data:
+//!   palettes/track1-3.pal   one track
+//!   palettes/track1.pal     all six tracks in TRACK1
+//!   palettes/default.pal    every track
+
+use super::FileSet;
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct Rgb(pub u8, pub u8, pub u8);
+
+impl Rgb {
+    pub const fn to_u32(self) -> u32 {
+        ((self.0 as u32) << 16) | ((self.1 as u32) << 8) | self.2 as u32
+    }
+
+    pub fn scale(self, f: f32) -> Rgb {
+        let s = |c: u8| ((c as f32 * f).round().clamp(0.0, 255.0)) as u8;
+        Rgb(s(self.0), s(self.1), s(self.2))
+    }
+
+    pub fn mix(self, o: Rgb, t: f32) -> Rgb {
+        let m = |a: u8, b: u8| (a as f32 + (b as f32 - a as f32) * t).round() as u8;
+        Rgb(m(self.0, o.0), m(self.1, o.1), m(self.2, o.2))
+    }
+}
+
+pub const TRACK_DEFAULT: [Rgb; 16] = [
+    // scenery: deep shadow through sunlit grass
+    Rgb(0x0c, 0x1a, 0x0e),
+    Rgb(0x18, 0x2c, 0x14),
+    Rgb(0x24, 0x40, 0x1a),
+    Rgb(0x34, 0x56, 0x20),
+    Rgb(0x48, 0x6c, 0x28),
+    Rgb(0x60, 0x84, 0x34),
+    Rgb(0x84, 0x9c, 0x4c),
+    Rgb(0xb0, 0xb8, 0x7c),
+    // driving surface: tarmac, kerbs and markings
+    Rgb(0x3a, 0x36, 0x34),
+    Rgb(0x50, 0x4c, 0x48),
+    Rgb(0x66, 0x62, 0x5c),
+    Rgb(0x7c, 0x78, 0x70),
+    Rgb(0x94, 0x90, 0x86),
+    Rgb(0xae, 0xaa, 0x9e),
+    Rgb(0xcc, 0xc8, 0xbc),
+    Rgb(0xf0, 0xee, 0xe4),
+];
+
+/// Per-player body colours for the three-colour vehicle sprites
+/// (index 1 = tyres and shadow, 2 = trim, 3 = bodywork).
+pub const TEAM_COLOURS: [Rgb; 8] = [
+    Rgb(0xe0, 0x30, 0x28),
+    Rgb(0x30, 0x60, 0xe8),
+    Rgb(0xf0, 0xc8, 0x20),
+    Rgb(0x30, 0xb0, 0x48),
+    Rgb(0xe0, 0x60, 0xd0),
+    Rgb(0x20, 0xc0, 0xc8),
+    Rgb(0xf0, 0x80, 0x20),
+    Rgb(0xe8, 0xe8, 0xe8),
+];
+
+pub fn car_palette(team: usize) -> [u32; 4] {
+    let c = TEAM_COLOURS[team % TEAM_COLOURS.len()];
+    [
+        0,
+        Rgb(0x10, 0x10, 0x14).to_u32(),
+        c.scale(0.7).to_u32(),
+        c.mix(Rgb(0xff, 0xff, 0xff), 0.35).to_u32(),
+    ]
+}
+
+pub fn parse(text: &str) -> Option<[Rgb; 16]> {
+    let mut out = [Rgb(0, 0, 0); 16];
+    let mut n = 0;
+    for line in text.lines() {
+        let line = line
+            .split('#')
+            .next()
+            .unwrap_or("")
+            .trim()
+            .trim_start_matches("0x");
+        if line.is_empty() {
+            continue;
+        }
+        if n == 16 || line.len() != 6 {
+            return None;
+        }
+        let v = u32::from_str_radix(line, 16).ok()?;
+        out[n] = Rgb((v >> 16) as u8, (v >> 8) as u8, v as u8);
+        n += 1;
+    }
+    (n == 16).then_some(out)
+}
+
+pub fn override_for(files: &FileSet, track_file: &str, section: usize) -> Option<[Rgb; 16]> {
+    let base = track_file.to_lowercase();
+    [
+        format!("palettes/{base}-{}.pal", section + 1),
+        format!("palettes/{base}.pal"),
+        "palettes/default.pal".into(),
+    ]
+    .iter()
+    .find_map(|k| {
+        files
+            .get(k)
+            .and_then(|d| parse(&String::from_utf8_lossy(d)))
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn parses_palette_file() {
+        let mut text = String::from("# test\n");
+        for i in 0..16 {
+            text.push_str(&format!("{:02x}{:02x}{:02x}\n", i, i * 2, i * 3));
+        }
+        let p = parse(&text).unwrap();
+        assert_eq!(p[15], Rgb(15, 30, 45));
+        assert!(parse("ffffff\n").is_none());
+    }
+}