Vixen
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Gameplay · guide

Mounts and vehicles

One type with seats — a mount is a single-seat vehicle whose model is a creature. The seat model only; the transform half waits on parent-relative replication.

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What it is

Vixen.Gameplay.Movement models mounts and vehicles as one type with seats. A vehicle is a compiled Vehicle — kind, seats, roles, requirements, tags — and one of them in the world is a VehicleInstance that tracks who is sitting where.

⚠ Nothing here touches a transform, and that is deliberate rather than unfinished. Doc 28 puts mounts and vehicles at the point where parent-relative replication stops being optional, *"because a passenger replicating world coordinates fights the vehicle's own"* — and that is still owed. Building the networked half now would mean building a workaround for something that is meant to land, so this library is the seat model and nothing else. Where a vehicle is remains the scene's answer.

What it is for

A mount is a single-seat vehicle whose model is a creature

Doc 28's point exactly, and it collapses two systems people usually write twice. VehicleKind changes which physics configuration a game reaches for and changes nothing at all in this library.

Exactly one seat steers, and the compiler says so

A vehicle with no driving seat is one nobody can drive. A vehicle with two is one where two clients both believe they are authoritative over the same rigid body — a networking bug that presents as jitter and gets diagnosed for a week. Both are reported in MovementLibrary.Problems.

The driver leaving does not eject anybody

The vehicle becomes driverless and the passengers stay. Whether one of them may take the wheel is PassengersMaySteer, which is a policy rather than a rule, because both answers ship: a taxi nobody may steer and a raft anybody may steer are equally real, and a library that picked one would pick it for every vehicle in every game.

Moving seats is checked before anybody moves

⚠ Getting off and then failing to get back on is how somebody ends up standing in the road at sixty miles an hour. MoveTo is one operation for that reason — it is not Dismount followed by Mount.

Using it

Mount, and let the vehicle grant the tags the seat carries:

csharp
using Vixen.Gameplay;using Vixen.Gameplay.Movement;static class Riding {    public static bool Ride(VehicleInstance vehicle, PlayerId player, IRequirementContext context, GameplayTagSet tags) {        // The requirement context is what a seat's requirements are evaluated against — "may only be        // gunned by somebody with the artillery training" is authored, not coded.        var refusal = vehicle.Mount(player, vehicle.Vehicle.DriverSeat, context, tags);        return refusal == SeatRefusal.None;    }}

⚠ Pass the same tag set to Dismount that you passed to Mount. The seat's tags are granted into the set the caller owns, and the library has no reference to it afterwards — a dismount that forgets leaves the rider tagged as mounted for the rest of the session.

MountAny is the "get in" button: it takes the first seat the player qualifies for and returns its index, or −1.

Examples

The whole seat lifecycle, with the refusals a client greys buttons out on:

csharp
using Vixen.Gameplay;using Vixen.Gameplay.Movement;static class Taxi {    public static int Board(VehicleInstance vehicle, PlayerId player) {        // −1 when nothing is free or nothing they qualify for is free. The two are not distinguished        // here on purpose: a client that could tell them apart could probe a requirement.        return vehicle.MountAny(player);    }    public static SeatRefusal Shuffle(VehicleInstance vehicle, PlayerId player, int seat) {        // One operation, checked before anybody moves — see "moving seats is checked before anybody        // moves". Dismount-then-Mount is the version that strands people.        return vehicle.MoveTo(player, seat);    }    public static bool StillDriven(VehicleInstance vehicle, PlayerId driver) {        vehicle.Dismount(driver);        // The passengers stay. Whether one of them may now steer is the vehicle's own policy.        return vehicle.IsDriven || (!vehicle.IsEmpty && vehicle.Vehicle.PassengersMaySteer);    }}

Watching who moved, for the replication layer that will eventually care:

csharp
using System;using Vixen.Gameplay.Movement;static class Watching {    public static void Attach(VehicleInstance vehicle, Action<SeatChange> onChange) {        // SeatChange carries the player, the seat index and whether that seat drives — which is the        // one bit anything downstream branches on.        vehicle.Changed += onChange;    }}

See also

  • Gameplay tags — what a seat grants.
  • Requirements — what gates a seat.
  • Travel — getting somewhere, as opposed to riding something.
  • Shooting — where a SeatRole.Gunner's weapon would come from.

Next

  • Gameplay tags — One hierarchical, interned tag type, numbered so that "is this under Damage.Fire" is two integer comparisons.
  • Requirements — "Can I do this" answered once, by code the client runs for the tooltip and the realm runs for the truth.
  • Weapons and hit claims — The weapon model and the claim's validation rules — the two things that are new, because the lag compensation underneath is already built.
  • Maps, discovery and travel — A revealed-area bitmap per character per map, completion that only counts what a designer opted in, and five ways of getting somewhere that all resolve to one transfer.