Unity to Defold: Understanding the Shift in Component Architecture

Unity to Defold: Understanding the Shift in Component Architecture

For developers coming from Unity, one of the biggest mental model changes when moving to Defold is how behavior is organized on a GameObject.

At first glance, Unity and Defold may seem very different. Unity uses multiple MonoBehaviour scripts attached directly to a single GameObject, while Defold usually uses only one .script component attached to a game object.

But functionally, both engines can support the same modular architecture.

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The Unity Way: Multiple MonoBehaviours on One GameObject

In Unity, it is common to structure a player like this:

Player GameObject

• Player.cs
• PlayerMovement.cs
• PlayerAttack.cs
• EnemyFinder.cs
• Health.cs

Each script is usually a MonoBehaviour, attached to the same GameObject.

Example:

public class PlayerMovement : MonoBehaviour { }
public class PlayerAttack : MonoBehaviour { }
public class EnemyFinder : MonoBehaviour { }

Then a main Player.cs script often acts as the coordinator:

public class Player : MonoBehaviour
{
    PlayerMovement movement;
    PlayerAttack attack;

    void Awake()
    {
        movement = GetComponent<PlayerMovement>();
        attack = GetComponent<PlayerAttack>();
    }
}

This gives Unity developers:

• Separation of responsibility
• Reusable components
• Inspector-friendly workflow
• Familiar component composition model

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The Defold Way: One Script + Multiple Lua Modules

In Defold, a game object typically has:

• Sprite component
• Collision component
• One main script (player.script)

Instead of attaching many behavior scripts, you place logic into Lua modules.

Player Game Object

• player.script (attached to object)
• player_movement.lua
• player_attack.lua
• enemy_finder.lua

So the attached script becomes the host/controller, while modules behave similarly to Unity components.

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Example Comparison

Unity

PlayerMovement.SpeedUp();
PlayerAttack.Attack();
EnemyFinder.Scan();

Defold

local Movement = require "modules.player_movement"
local Attack   = require "modules.player_attack"
local Finder   = require "modules.enemy_finder"

function init(self)
    self.movement = Movement.new(self)
    self.attack = Attack.new(self)
    self.finder = Finder.new(self)
end

function update(self, dt)
    self.movement:update(dt)
    self.attack:update(dt)
    self.finder:update(dt)
end

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What This Means Conceptually

The difference is mostly how behaviors are mounted, not whether modular architecture exists.

Unity:

Behavior modules are attached through the editor.

Defold:

Behavior modules are composed in code.

That means:

Unity	Defold
Multiple MonoBehaviours on GameObject	One script + multiple Lua modules
GetComponent<T>()	self.attack, self.movement
Inspector composition	Code composition
Lifecycle per component	Lifecycle routed through main script

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Why Defold Uses This Model

Defold is intentionally lightweight.

Rather than many script instances on one object, Defold encourages:

• Explicit ownership
• Low overhead
• Clear update flow
• Lua-based composition
• Easier debugging of execution order

You always know where updates start: the attached .script.

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Similarity Unity Developers Should Notice

Even though the syntax changes, the architecture can stay familiar.

Your old Unity structure:

• Movement system
• Attack system
• Target finder
• Health module

Can remain exactly the same in Defold.

Only the hosting model changes.

Instead of:

Attach five MonoBehaviours

You now:

Attach one script, instantiate five Lua modules

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The Pattern that I Use for this situation

When porting habits from Unity, I sometime use this structure:

player.go
 ├── sprite
 ├── collisionobject
 └── player.script

scripts/
  player.script

modules/
  player_movement.lua
  player_attack.lua
  enemy_finder.lua
  health.lua

Then player.script becomes the glue layer, just like your old Player.cs.

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Important Mindset Shift

Do not think:

Defold only allows one script, so I lose modularity.

Think instead:

Defold separates runtime host scripts from reusable logic modules.

That is a different workflow—but not a weaker one.

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Final Thought

For Unity developers, Defold may initially feel restrictive because you cannot stack many MonoBehaviour scripts on one object.

But once understood, Defold offers the same modular design with less hidden magic and more explicit control.

You still build components.

You just build them in Lua, and assemble them through code instead of the Inspector.

Just like component-based architecture is not mandatory in Unity, it is also not mandatory in Defold. This is only one approach among many. We will explore other ways to solve the same problems in upcoming blogs.