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DOCSSCRIPTING LANGUAGESLUA 5.4

Scripting Rustic games with Lua 5.4

Lua 5.4 is the most direct Rustic scripting option: the runtime is bundled, each script is an isolated module, and Script API mutations are applied immediately. Create a .lua file through the Explorer's scripting commands; do not create an Asset ID or edit a scene file manually.

Attach and choose a scope

  • Global Startup Script: one game-lifetime instance, started when Play starts.
  • Scene Startup Script: one scene-lifetime instance, started after globals when

its scene/{name}.scene loads.

  • Object Component Script: one instance per attachment, created and removed with

its object. Select the object and use + Add Component, or drag the script from Explorer onto the viewport.

Moving or renaming the .lua file in the editor is safe because the attachment holds its persistent Asset ID. Do not edit config/scripts.ron.

Module and callbacks

Return one behavior table. Every member is optional; Rustic looks up a callback before calling it. Returning no value is also accepted and creates a no-op behavior.

lua
local speed = 4.0 -- private state for this behavior instance

return {
  Start = function()
    rustic.log("info", "started " .. rustic.entity_id())
  end,

  OnEnable = function() end,

  FixedUpdate = function(dt)
    local key = rustic.key("KeyW")
    if key.held then
      local x, y, z = rustic.get_translation()
      rustic.set_translation(x, y, z + speed * dt)
    end
  end,

  Update = function(dt) end,
  OnDisable = function() end,
  OnDestroy = function() end,
}

Canonical public names are Start, FixedUpdate, Update, OnEnable, OnDisable, and OnDestroy. The legacy spellings on_start, fixed_update, update, on_enable, on_disable, and on_destroy still work. The legacy internal hooks on_create and on_stop are also recognized. If both canonical and legacy names are present, the canonical callback wins. Use FixedUpdate(dt) for physics and deterministic movement; use Update(dt) for frame-rate work. OnStart is not a Lua callback name. A script with OnStart can load successfully while its startup function never runs; rename it to Start.

The engine-wide callback model also defines OnCollisionEnter, OnCollisionStay, and OnCollisionExit. The current embedded Lua adapter does not yet bind those three names, so do not rely on them in Lua code in this release.

Script API

The read API returns engine-owned snapshots; writes validate against the host:

lua
local id = rustic.entity_id()                 -- stable entity ID string
local frame_dt = rustic.delta_time()
local fixed_dt = rustic.fixed_delta_time()
local x, y, z = rustic.get_translation()
rustic.set_translation(x, y + 1, z)

local health = rustic.get_property("health") -- nil if absent
rustic.set_property("health", 90)             -- declared property only

local name = rustic.GetAttribute("Name")
rustic.EditAttribute("Anchored", true)
print("entity", id)
warn("entity needs attention", id)
rustic.set_enabled(false)

print(...) writes an info entry and warn(...) writes a warn entry to the Rustic console. Multiple arguments are converted with Lua's tostring and separated by tabs. rustic.log(level, message) remains available when an explicit level is needed.

get_attribute/GetAttribute and edit_attribute/EditAttribute are aliases. Built-in attributes are Name, Position, Size, Color, CanTouch, CanCollide, Anchored, and Parent. Attribute and property writes must match the existing value's type. Attribute setters accept scalar values, exactly three finite numbers in a table for Position, Size, and RGB Color, and a stable entity ID string or nil for Parent. Public-property setters retain their existing scalar write rules. To edit another object, use rustic.game.Demo.Room.Player:EditAttribute("Position", {1, 2, 3}); see Edit scene objects for setup and supported types. Invalid values fail and disable the offending script.

Finding and creating objects

lua
local table_id = Game.scene.Find("Room.Table")
local all_in_room = Game.scene.List("Room")
local direct_root_child = Game.scene.Camera

local new_id = instance.add("Cube")
local model_id = instance.add("assets/models/chair.glb", table_id)
local copy_id = instance.clone("Room.Table")
Game.setCurrentCamera("Room.Camera")

Paths may be dotted or slash-separated. Find returns an ID or nil; List returns stable IDs. instance.add accepts an entity ID/path, an Explorer model path, or Part, Cube, Sphere, Cylinder, Plane, Rectangle2D, or Circle2D. clone copies an existing scene object. The optional parent must be a stable entity ID string. Both calls return the new ID immediately. Camera selection accepts a path, ID, or the compatibility form { "Game.scene.Room.Camera" }.

Input

What works in the editor's Play viewport

The editor forwards held keys to scripts while its Play viewport is hovered or focused. Click the game view once if another panel has focus. The forwarded names are KeyW, KeyA, KeyS, KeyD, ArrowUp, ArrowDown, ArrowLeft, ArrowRight, ShiftLeft, and ShiftRight. Either physical Shift key sets both Shift names because the editor currently receives a combined Shift modifier. For these names, rustic.key(name).held is true while the key is held and false after release or when the Play viewport loses keyboard focus. axis is 1 when held and 0 otherwise.

The rustic.key(name) result also has pressed and released fields, but the current Play bridge does not forward press/release edges. Those fields remain false. rustic.key_events() returns an empty list, and rustic.any_key_pressed() remains false. Named rustic.input("action") actions remain inactive. Other names, including Space, Escape, Digit1, and function keys, are not forwarded yet. Keyboard forwarding currently applies to the editor's embedded Play viewport; a separate New Window or Standalone runtime window does not send its keyboard events to scripts. Use .held with the names listed above for gameplay movement in this build.

Copyable top-down controller

  1. In the editor, create a Lua 5.4 .lua Object Component Script. .luau uses a different adapter. If the file already exists, select the player object and attach it with + Add Component in the Inspector.
  2. Replace the script contents with the example below. Keep return { ... } and use Start, not OnStart.
  3. Start Play, hover or click the game viewport, then hold WASD or an arrow key. Hold Shift to sprint. The Console should show both startup messages.
lua
local WALK_SPEED = 4.0
local SPRINT_SPEED = 7.0
local PLAYER_HEIGHT = 1.0

local function held(primary, alternate)
  return rustic.key(primary).held or rustic.key(alternate).held
end

return {
  Start = function()
    print("Character ready - use WASD or arrow keys to move")
    warn("Movement controller is running")
  end,

  FixedUpdate = function(dt)
    local horizontal = 0
    local vertical = 0
    if held("KeyA", "ArrowLeft") then horizontal = horizontal - 1 end
    if held("KeyD", "ArrowRight") then horizontal = horizontal + 1 end
    if held("KeyW", "ArrowUp") then vertical = vertical - 1 end
    if held("KeyS", "ArrowDown") then vertical = vertical + 1 end

    if horizontal == 0 and vertical == 0 then return end

    local length = math.sqrt(horizontal * horizontal + vertical * vertical)
    local speed = WALK_SPEED
    if held("ShiftLeft", "ShiftRight") then speed = SPRINT_SPEED end
    local x, _, z = rustic.get_translation()
    rustic.set_translation(
      x + horizontal / length * speed * dt,
      PLAYER_HEIGHT,
      z + vertical / length * speed * dt
    )
  end,
}

This moves the object carrying the component, not a player object found by name. Diagonal motion is normalized so it has the same speed as straight motion. PLAYER_HEIGHT is applied when movement starts; change it to match your scene. Make sure the active game camera can see the object and has enough room to show the translation.

If the startup messages are missing, check that the file is .lua, the script is attached and enabled, the callback is named Start, and Play actually started. If messages appear but movement does not, use the editor's embedded Play viewport, hover or click it, and try KeyW first. Check the Console for a script error: a failing callback is disabled until the script is fixed and reloaded or Play restarts.

Isolation and failures

Lua cannot directly call a JavaScript or external-process behavior. API 1.0 does not yet expose the scheduler's Engine Event emit/subscribe surface to scripts, so use shared engine state for cross-language coordination.

Lua cannot access io, os, package, debug, dofile, loadfile, require, or collectgarbage. It has no filesystem, network, process, registry, or editor access. An exception or exhausted instruction budget disables only that behavior. Use the Console diagnostic to open the source location, fix it, then reload scripts.

Target another scene object

See Edit scene objects for named-scene hierarchy calls, supported attributes, copyable examples, and native SDK calls to edit another object. Use your language's native call syntax and its current runtime limitations.

Lua owner and path-based EditAttribute calls accept three-number tables for Position, Size, and RGB Color; Parent accepts a stable entity ID string or nil. Vectors require exactly three finite components. These conversions apply to built-in attributes; script public-property setters retain their existing value rules.