kiln/kiln-core/src/scripts/spinner.rhai

// Rotates this object's 8 neighbours one step around a ring every 0.5s, shoving
// each pushable into the next ring slot via a single simultaneous `swap`. The spin
// direction comes from the `BUILTIN_spinner_*` tag the map loader attaches (it
// defaults to clockwise when no tag is present).
//
// A neighbour may only rotate if its destination slot will actually be free: the
// slot is a hole (`passable`), or that slot's own occupant also rotates out. We
// can't decide that with `can_shift` alone — `can_shift(j) == false` is ambiguous
// between "j is empty" and "j is a blocked solid" — so we seed with `can_shift`
// and then cascade-demote using `passable` to spot the genuine holes.
fn tick(dt) {
    // Only start a new rotation when the previous one (and its delay) has drained,
    // exactly like the built-in pusher's pacing.
    if Queue.length() != 0 { return; }

    // Direction from the builtin tag; clockwise unless explicitly counter-clockwise.
    let cw = !Me.has_tag("BUILTIN_spinner_ccw");

    // The 8 neighbour offsets in clockwise order, starting at North.
    let cw_ring = [
        [Me.x, Me.y-1],   // N
        [Me.x+1, Me.y-1], // NE
        [Me.x+1, Me.y],   // E
        [Me.x+1, Me.y+1], // SE
        [Me.x, Me.y+1],   // S
        [Me.x-1, Me.y+1], // SW
        [Me.x-1, Me.y],   // W
        [Me.x-1, Me.y-1], // NW
    ];

    // For CCW, it's the same list in reverse
    let ccw_ring = [];
    for neighbor in cw_ring {
        ccw_ring.insert(0, neighbor);
    }

    // Rotate the neighbor cells:
    if cw {
        shift(cw_ring);
    } else {
        shift(ccw_ring);
    }

    // Animate the glyph one frame per rotation (changing only the character): the
    // line spins '/'-'\'-, slash-swapped for counter-clockwise. Frame state lives in
    // the board Registry, keyed per spinner, since script scope resets each tick.
    let frames = if cw { [47, 0xc4, 92, 0xb3] } else { [92, 0xc4, 47, 0xb3] };
    let fkey = `spin_${Me.id}`;
    let f = Registry.get_or(fkey, 0);
    set_tile(frames[f % 4]);
    Registry.set(fkey, (f + 1) % 4);

    delay(0.5);
}