Defold Core

Structure, wire and verify a Defold game: editor resource files, the Lua script lifecycle, addressing and messages, runtime spawning and world loading, and a Bob build-and-run check. Examples target Defold 1.14.0; they were built with Bob 1.14.0 and run on the 1.14.0 headless engine. An existing project keeps its Defold version (see Version).

When to use

Use when adding or fixing game objects, collections, scripts, input, messages, spawning or level loading in a Defold project (
```
game.project
```
in the root,
```
.collection
```
,
```
.go
```
,
```
.script
```
,
```
.gui_script
```
files), or when Bob reports a missing resource.

When not to use: plain Lua or LÖVE projects (

love2d-core

); GUI layout, sprites, tilemaps and physics depth beyond the pointers in the references; engine-agnostic design handled by the related skills below.

Workflow

Inspect first. Read
```
game.project
```
(
```
[bootstrap] main_collection
```
,
```
[input] game_binding
```
,
```
[project] dependencies
```
), the main collection, and the scripts near the request. Follow the project's folder layout, id naming and message names; do not reorganize. Note which Defold/Bob version CI or the team uses.
Edit the right file type. Game objects (
```
.go
```
) hold components; collections (
```
.collection
```
) place game objects and other collections; logic goes in
```
.script
```
(game objects),
```
.gui_script
```
(GUI) or shared
```
.lua
```
modules. Editor files are protobuf text: keep their structure, and copy shapes from
```
references/file-formats.md
```
instead of guessing fields.
Check references. Run
```
python scripts/check_defold_project.py <project-dir>
```
(path relative to this skill folder; Python 3.10+, no Defold install needed). Fix every
```
ERROR
```
(missing or wrong-case
```
/paths
```
, a
```
game.project
```
path without the compiled
```
c
```
suffix, a
```
require
```
whose file does not exist). Warnings cover files nothing uses yet, unfetched library dependencies and runtime-loaded files. Re-run until it exits 0.
Build with Bob.
```
java -jar bob.jar --root . --variant headless --archive resolve build
```
needs JDK 25 and a
```
bob.jar
```
matching the project's Defold version. Exit 1 plus an
```
ERROR:
```
line means a broken reference or a Lua syntax error (with file and line);
```
references/file-formats.md
```
shows how to trace an error that names a generated file.
Run it. A build does not prove the game works. Run a headless bundle under a timeout (
```
references/build-and-run.md
```
) and read the log:
```
ERROR:SCRIPT:
```
lines are Lua runtime errors,
```
ERROR:GAMEOBJECT:
```
lines bad addresses or socket clashes. Require a line your test prints when it finishes; the exit code alone proves nothing. The headless engine has no keyboard or mouse, so check input changes in the editor or a desktop build, and say what you could not verify.

Patterns

Project and resource references

game.project

is an INI file in the project root. Resource paths everywhere are root-absolute (

/main/player.go

). In

game.project

they name the compiled file, so the source path gets a trailing

ini

[bootstrap]
main_collection = /main/main.collectionc

[input]
game_binding = /input/game.input_bindingc

Bob builds only what is reachable from

game.project

;

/builtins/...

ships with the engine.

Collections, game objects, components

A collection places instances and can override script properties per instance; a game object lists file components and embedded components (escaped

data:

strings). Full verified files are in

references/file-formats.md

text

# main.collection (excerpt): place player.go and override its script's speed
instances {
  id: "player"
  prototype: "/main/player.go"
  component_properties {
    id: "player"
    properties { id: "speed" value: "250.0" type: PROPERTY_TYPE_NUMBER }
  }
}

Script lifecycle,

self

and properties

lua

go.property("speed", 200)                   -- top level only, literal default; editable per instance

local LEFT = hash("left")                   -- hash ids once, not every frame
local RIGHT = hash("right")
local FIRE = hash("fire")

function init(self)
	msg.post(".", "acquire_input_focus")    -- no focus, no on_input calls
	self.held = {}                          -- per-instance state lives on self
end

function update(self, dt)
	local dir = (self.held[RIGHT] and 1 or 0) - (self.held[LEFT] and 1 or 0)
	if dir ~= 0 then
		local pos = go.get_position()
		pos.x = pos.x + dir * self.speed * dt    -- dt-scaled: same speed at any frame rate
		go.set_position(pos)
	end
end

function on_input(self, action_id, action)
	if action_id == LEFT or action_id == RIGHT then
		if action.pressed then self.held[action_id] = true
		elseif action.released then self.held[action_id] = nil end
		return true                         -- consumed: listeners lower on the stack skip it
	elseif action_id == FIRE and action.pressed then
		factory.create("#bulletfactory", go.get_position(), nil,
			{ velocity = vmath.vector3(0, 600, 0) })
		return true
	end
end

function final(self)
	msg.post(".", "release_input_focus")
end

Callbacks:

init

final

fixed_update

update

late_update

(after every

update

, before render),

on_message

on_input

on_reload

. Update order between game objects is unspecified.

fixed_update

runs 0..N times per frame at

[engine] fixed_update_frequency

; set

[physics] use_fixed_timestep = 1

too so physics steps at the same rate, and put physics-driven code there.

self

is userdata: store fields on it, but

pairs(self)

and

pprint(self)

do not work. Property types: number, boolean, hash,

msg.url

vmath.vector3

vector4

vmath.quat

, resources such as

resource.atlas("/main/main.atlas")

, and (since 1.13.2) strings.

Input bindings and the input stack

.input_binding

maps devices to action names (

key_trigger

mouse_trigger

, plus gamepad, touch and text triggers). Every component that acquired focus sits on an input stack; the last to acquire is on top and gets input first, and returning

true

from

on_input

stops it there, which is how pause menus block gameplay input. Key actions report

pressed

and

released

; track held keys yourself as above.

Addressing and messages

A URL is

[socket:][path][#fragment]

"."

is this game object,

"#"

this component,

"#sprite"

a sibling component,

"enemy#ai"

a relative object,

"/manager#controller"

an absolute one,

"main:/loader#loader"

an object in another world. Collections create naming scopes, so a string id is resolved relative to the sender's collection; a pre-hashed id is always absolute.

lua

msg.post("/manager#controller", "enemy_spotted", { id = go.get_id() })

function on_message(self, message_id, message, sender)
	if message_id == hash("enemy_spotted") then
		print("from", sender, "id", message.id)
	end
end

Messages are queued and dispatched later in the frame; the table is capped at 2 KB. A bad address logs

ERROR:GAMEOBJECT: Instance '/x' could not be found when dispatching message

Factories and collection factories

lua

-- factory component "#bulletfactory" -> one game object; properties override go.property values
local id = factory.create("#bulletfactory", pos, nil, { velocity = vmath.vector3(0, 600, 0) })

-- collectionfactory component "#wavefactory" -> table of collection ids -> new instance ids
local ids = collectionfactory.create("#wavefactory", vmath.vector3(480, 500, 0))
local leader = ids[hash("/leader")]         -- e.g. hash: [/collection0/leader]
go.delete(ids, true)                        -- later: delete them and their children

Position and rotation default to the spawning object's.

go.delete()

takes effect at the end of the frame. Per-instance properties for a collection factory are keyed by id:

{ [hash("/leader")] = { hp = 5 } }

Collection proxies (load another world)

lua

-- excerpt from the loader script; the collection's "#levelproxy" component is a collectionproxy
function init(self)
	msg.post(".", "acquire_input_focus")        -- else the loaded world gets no input
	msg.post("#levelproxy", "async_load")       -- or "load"
end

function on_message(self, message_id, message, sender)
	if message_id == hash("proxy_loaded") then
		msg.post(sender, "init")
		msg.post(sender, "enable")
	elseif message_id == hash("level_done") then
		msg.post("#levelproxy", "unload")       -- disables and finalizes first
	elseif message_id == hash("proxy_unloaded") then
		-- safe to load the next level here
	end
end

The loaded world's socket is the name:
of the loaded collection file, so scripts in it reply with

msg.post("main:/loader#loader", ...)

and its own URLs read

level1:/level#level

set_time_step { factor = 0, mode = 0 }

pauses a proxy world.

Version

game.project

has no engine version key. Use the Defold editor or

bob.jar

version the project is built with (CI often pins a release sha1), and

library.defold_min_version

when the project is a library.

java -jar bob.jar --version

prints the version and sha1. Keep that version; do not migrate unless asked.

Pitfalls

Bob:
the bootstrap.main_collection '/main/main.collectio' can't be found
→ the setting lacks the compiled suffix and Bob stripped the last letter. Write

/main/main.collectionc

(same for

input.game_binding

→

.input_bindingc

Bob:
ERROR: build/default/_generated_….factory:0: the prototype '/main/x.go' can't be found
→ an embedded component in some
```
.go
```
points at a missing file. Search the sources for the quoted path (
```
/main/x.go
```
), not the generated name, or run the checker.
on_input
never fires → the object never sent
```
acquire_input_focus
```
, the action name differs from the binding,
```
input.game_binding
```
points elsewhere, or a listener higher on the stack returns
```
true
```
.
Input dead inside a proxy-loaded level → the game object holding the collection proxy did not acquire input focus.
already a socket with the same name
and the proxy never sends
proxy_loaded
→ the loaded collection's
```
name:
```
equals an already loaded world (often both are
```
"main"
```
or
```
"default"
```
). Give every proxied collection a unique name.
fixed_update
never runs →
```
[engine] fixed_update_frequency
```
is 0 (default 60). For physics also set
```
[physics] use_fixed_timestep = 1
```
, as the manual requires both.
module 'modules.util' not found
at run time although Bob succeeded → a
```
require
```
used slashes (
```
require "modules/util"
```
). Use the dotted path from the project root,
```
require "modules.util"
```
for
```
/modules/util.lua
```
.
tostring(id)
prints
hash: [<unknown:…>]
→ hashes keep their source text only in debug builds. Compare hashes, never their strings.
A second engine logs
Failed to initialize Remotery
, or a test run never ends → the debug engine opens an engine service (port 8001), a log server and a profiler port, and waits forever without
```
sys.exit
```
. Run one engine at a time and always use a timeout.

References

```
references/file-formats.md
```
— verified minimal
```
game.project
```
,
```
.collection
```
,
```
.go
```
,
```
.atlas
```
,
```
.input_binding
```
and script files, and how to trace build errors back to a source file; read before writing editor files by hand.
```
references/build-and-run.md
```
— JDK 25 and
```
bob.jar
```
, Bob commands, platforms and variants, a headless smoke test with timeout and log checks, and pointers for GUI, sprites, tilemaps and collision objects.
```
scripts/check_defold_project.py
```
— read-only reference checker;
```
--help
```
lists every check.

Related skills

```
input-systems
```
— rebinding, gamepad support and buffering on top of Defold bindings.
```
game-ui-ux
```
— HUD and menu design to build with GUI scenes and
```
.gui_script
```
.
```
physics-tuning
```
— fixed-timestep and collision tuning for collision objects.
```
camera-systems
```
— follow/deadzone logic, typically applied in
```
late_update
```
.
```
save-systems
```
— save formats and slots; pair with Defold's
```
sys.save
```
/
```
sys.load
```
.
```
game-feel
```
— juice built from
```
go.animate
```
and timers.
```
platformer
```
,
```
level-design
```
— genre and layout guidance that binds to this skill.
```
love2d-core
```
— the other Lua engine in this catalog, for LÖVE projects.

defold-core

NPX Install

Tags

SKILL.md Content