MassDriver

A launcher that fires pooled bodies on a timer. In Space Golf it is the rock chute.

What it does

Every interval seconds the driver takes a body from its pool, puts it muzzleOffset ahead of itself and sends it along direction at speed. It never creates a body: world.acquire(pool, { x, y, z }) hands back a parked slot already placed at the muzzle, and the driver only sets that body's GravityBody velocity. A full pool recycles its oldest body. A pool name with nothing registered under it fires nothing and emits massdriver.jammed.

Each shot is tilted inside a cone of half-angle spread, so the stream fans out a little and a perfect line through a gap is not a perfect answer. The tilt comes from a small seeded generator whose state lives with the driver and restarts from seed each time the driver enters play. A level fires the same stream every time it loads, and two drivers with one seed fire the same shots.

The clock expects a player to change it. Change interval mid-wait and the wait already running is scaled by the same ratio, so "slower" lands on the next rock, not one whole old interval later. A long frame fires once rather than a backlog of missed shots. Switching active back on restarts the clock at firstDelay.

Nothing in it is golf. A mortar or a waterfall of crates is the same component with other numbers.

Use it in a scene

A scene is just data — a list of entities, each with its components. At startup the SceneLoader turns this JSON into a live world; edit the file and reload to rebuild it.

Build it from scratch with the bjs CLI:

1Scaffold a project
```
npm create @babylonjsmarket/arcade@latest my-game
```
World, renderer, and dev server — ready to run.
2Install dependencies
```
cd my-game && npm install
```
3Add MassDriver
```
bjs download MassDriver
```
Copies its source into src/ so the scene resolves.
First time? Run bjs login once.
4Paste the scene into src/scenes/arcade-room.ts and run
```
npm run dev
```
SceneLoader builds the world from the JSON; reload to rebuild.

JSON

{
  "Rocks": {
    "tags": ["rock"],
    "components": {
      "Pool": { "name": "rock", "size": 24 },
      "MeshPrimitive": { "primitive": "sphere", "diameter": 1, "segments": 8 },
      "GravityBody": { "radius": 0.42, "maxSpeed": 45 }
    }
  },
  "Chute": {
    "components": {
      "MeshPrimitive": {
        "primitive": "cylinder",
        "height": 3,
        "diameterTop": 1.3,
        "diameterBottom": 2,
        "position": [-30, 0, -8]
      },
      "MassDriver": {
        "pool": "rock",
        "direction": [1, 0, 0],
        "speed": 11,
        "interval": 2.2,
        "muzzleOffset": 2,
        "spread": 0.012
      }
    }
  }
}

The rock blueprint needs a GravityBody for the shot to move. In Space Golf the chute is a pool blueprint too, with active: false and firstDelay: 0. The director places it for each level and switches it on at GO, so the first rock leaves on that frame.

Props

pool (string, default "rock") — the pool bodies are taken from.
interval (number, default 2.4) — seconds between automatic shots.
speed (number, default 10) — launch speed in units per second.
direction ([x, y, z], default [1, 0, 0]) — launch direction, any length. Zero or NaN falls back to +X.
muzzleOffset (number, default 1.6) — how far ahead of the driver, along direction, a body appears.
spread (number, default 0.015) — half-angle of the launch cone in radians. 0 fires dead straight.
active (boolean, default true) — fire on the timer.
firstDelay (number, default 0.6) — seconds before the first shot after the driver enters play or is switched on.
seed (number, default 0x5eed) — seeds the spread.

Events

Emits:

massdriver.launched — a body left the muzzle: { driverId, entityId, x, y, z, vx, vy, vz }.
massdriver.jammed — there was no pool to take from: { driverId, pool }.

Listens:

massdriver.fire — fire once now, timer or not: { driverId? }. Leave out the id to fire every driver.
massdriver.active.set — start or stop the timer: { driverId?, active }. A bare payload means on.

Dependencies

MeshPrimitive — the driver's position, and the barrel it turns.
GravityBody — on the pooled bodies. The driver sets its velocity.

Notes

The driver owns its mesh's rotation. It turns local +Y, the long axis of a cylinder or capsule, onto direction, and replaces any rotation you author.
It runs before GravityBody, so a rock fired this frame also moves this frame.
An inactive driver still answers massdriver.fire. A parked driver, or a pool blueprint, answers nothing.
A body with no GravityBody still appears at the muzzle, and massdriver.launched still carries the velocity, so another mover can pick it up.