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Start here

Your first script, the hooks the engine calls, and the globals every script has.

Part of the scripting guide · every call, as a reference

#Contents

• 1. A first script
• 2. Lifecycle: start, update, fixedUpdate
• 6. Globals: params, time, dt, log
• 12. Recipe: a walkable first-person character
• 13. Bundled example scripts

#1. A first script

-- spin.lua — slowly rotate the node it's attached to.
defaults = { speed = 45 }            -- tunables (also editable in the Inspector)

function update(node, dt)
  node.yaw = node.yaw + math.rad(params.speed) * dt
end

Attach it by dragging the .lua from Assets onto a node, dropping it on the Inspector's Scripting section, or Inspector → Scripting → + Add Script. Press F1 to Play.

Compound assignment operators work: += -= *= /= %= ^= ..=.

node.yaw += math.rad(params.speed) * dt

#2. Lifecycle: start, update, fixedUpdate

function start(node)             -- optional; runs once when Play begins
end

function update(node, dt)        -- runs every frame while playing
end

function fixedUpdate(node, dt)   -- runs every GAMEPLAY TICK (60 Hz, constant dt)
end

function lateUpdate(node, dt)    -- runs after physics each frame (the camera pass)
end

Each attached script keeps its own state across frames — assign a variable in start (or at the top level) and read it back in update.

Which one do I use? The split is simple:

Why lateUpdate for cameras: the engine's frame order is scripts → animation → physics → interpolated transform writeback → lateUpdate. A camera positioned in update reads its target's pose from before this frame's physics — one frame stale, a follow error of velocity × dt that turns frame-time noise into visible movement jitter. In lateUpdate the target's pose is final for the frame, so the follow is exact. The stock third_person_camera.lua does this.

fixedUpdate runs on the same fixed clock physics steps on, right before each physics tick — so gameplay code behaves identically at 30 fps and 240 fps, and input.pressed(...) edges are delivered per tick there (a press between two ticks is never lost). It's also the cadence multiplayer prediction will replay, so code you put in fixedUpdate today is already netcode-shaped.

Inside fixedUpdate, the input API reads the tick's input snapshot; inside update, the frame's. Both work everywhere — only the timing window differs.

#6. Globals: params, time, dt, log

The full Lua standard library (math, string, table, …) is available.

defaults → params: every key you put in defaults is readable as params.<key>. Declaring defaults is what makes a value tweakable per-node in the Inspector; if you don't override it there, params.<key> is just the default.

#String params

A plain string default becomes an Inspector text field on each instance — so two portals share one script but carry different destinations:

-- portal.lua
defaults = { destination = "hub" }   -- each portal's Inspector shows a text box

function onTriggerEnter(node, other, hit)
  if other:hasTag("player") then scene.load(params.destination) end
end

Numbers and strings follow the same rules (seeding, live Inspector sync, the two-way behavior below). A string that looks like noderef() output is a reference param, not a string — those keep their picker.

#Describing your tunables to the Inspector

defaults says what your tunables are. --@ comments say how they should be presented — and the Inspector then draws a designed panel instead of a stack of anonymous drag values, in declaration order:

defaults = {
  --@header Movement
  -- How fast you walk on flat ground.        <- a plain comment is the tooltip
  --@range 0 20 --@units m/s
  walk = 4.5,

  --@desc Blend between the walk and run animations.
  --@slider 0 1 --@step 0.05
  blend = 0.35,

  --@header Assist
  --@options Off|On|Auto
  assist = 1,               -- a NUMBER + options → dropdown, value = the index
  --@options walk|run|sprint
  gait = "walk",            -- a STRING + options → dropdown of those strings
  invert = false,           -- a boolean default → a checkbox, no annotation needed
  --@color
  tint = "#ff8800",         -- a swatch; the script still reads the hex string
  --@hidden
  debugScale = 1.0,         -- kept out of the Inspector entirely
}

They're comments: nothing changes at runtime, deleting them breaks nothing, a misspelled one is ignored rather than fatal, and several can share a line.

Booleans are real booleans. A flag = false default round-trips as a boolean, so if params.flag then means what it says — it's carried as 0/1 between the Inspector and the script, and converted back on the way in (every number is truthy in Lua, so a leaked 0 would have been permanently true).

#params is two-way

Writing a declared tunable persists — the next frame reads your value back, the Inspector shows it update live during Play, and other scripts see it through a handle. Stop reverts it with the rest of the play session. So state you'd otherwise keep in a local can live in params when you want it visible and tweakable:

defaults = { distance = 6.0 }

function lateUpdate(node, dt)
  params.distance = params.distance - input.scroll()   -- sticks, shows live
end

• Only declared keys persist (present in defaults, or already stored on the node). Assigning an undeclared key works for the current frame but is not saved — declare it if you want it kept.
• Reference params (noderef() & friends) never round-trip — they stay wired by the Inspector.
• Inspector edits during Play flow the other way instantly, so you can tune a value the script is also reading. If the script writes the same key every frame, its write wins — write only when changing (like the scroll above).

#12. Recipe: a walkable first-person character

No glue code required:

1. Add a Camera node and mark it Active.
2. Give it a Rigidbody, shape = Capsule.
3. Attach first_person.lua.

Press Play — you are the capsule. It moves under physics and the camera rides along, so you walk the world in first person:

• hold Right Mouse — free-look (yaw + pitch)
• W A S D — move along the ground, relative to where you face
• Space — jump (when grounded)
• Shift — run · hold C — crouch

It works on normal Down gravity and Radial (planet) gravity — drop a Gravity Volume → Radial node at a planet's center and you can run all the way around it.

A minimal controller that shows the velocity loop:

defaults = { speed = 6, jump = 7 }

function update(node, dt)
  local f = (input.key("w") and 1 or 0) - (input.key("s") and 1 or 0)
  local vy = node.vy                                  -- keep gravity/jump
  if node.grounded and input.pressed("space") then vy = params.jump end
  node.vx = -math.sin(node.yaw) * f * params.speed
  node.vz = -math.cos(node.yaw) * f * params.speed
  node.vy = vy
end

#13. Bundled example scripts

Every project ships these under scripts/ — open one for a working start: