Roblox for Unity developers

This page includes information to help experienced Unity developers get started with Roblox: basic orientation, a conceptual comparison, and key differences between the two platforms.

Get oriented

Unity's Hierarchy window and Roblox Studio's Explorer are the primary windows for organizing elements in 3D scenes:

• Both allow you to manage and organize objects (for example, characters and environmental assets).
• Both use a tree structure for the parent-child relationships between objects.

However, the Hierarchy window has no predefined structure, whereas the Explorer window has a strict structure. It might help to think of the Explorer window as a combination of Unity's Hierarchy and Project windows, with the Workspace folder as the most recognizable element.

Similarly, the Roblox Studio Asset Manager and Toolbox overlap with the Unity Project window. The Asset Manager lets you manage all assets within your experience, whereas the Toolbox lets you access any assets you've published. The Toolbox also lets you search the Creator Store for assets from Roblox or the community, similar to the Unity Asset Store.

Philosophical differences

Roblox is a "simulation engine" rather than a traditional game engine. Unity GameObjects and Roblox Parts both serve as the fundamental building blocks for creating objects in a 3D environment, but in practice, the two are quite different:

• Representation: GameObjects in Unity are a higher-level concept for any object in a scene, whereas Parts in Roblox are designed to represent physical objects like wooden blocks and plastic spheres, rather than abstract geometry like primitive objects in Unity.
• Physics: To perform physics simulations in Unity, you attach components like Rigidbody and Collider to a GameObject. In Roblox, physics are built into the Parts data type; the engine handles interactions automatically.

You can see the difference immediately if you create a GameObject and a Part. The GameObject has nothing more than a position, rotation, and scale. The Part has that same information—plus a material and color, values for reflectance and transparency, mass and shape, and much more. Turning a Part into something more akin to an empty GameObject means removing a lot of built-in properties. Conversely, you can make a GameObject that looks a lot like a Part by adding MeshFilter, MeshRenderer, Collider, and Rigidbody components to it.

From a scripting perspective, GameObject is most similar to the Roblox Instance, the base class for all other Roblox classes, but because you don't (and can't) create objects of type Instance, the comparison isn't especially practical.

Another comparison is the Unity GameObject to the Roblox Model. Models act as a container for a collection of interconnected parts in the same way that you might establish a parent-child relationship between many GameObjects in Unity. You specify one of the model's parts as its primary part to define the pivot point. Models also hold scripts, animations, sound effects, prompts, constraints, particle emitters, and more.

For example, a Unity GameObject might have components for ParticleSystem, Physics3D, SpringConstraint, and a script. In the Hierarchy window, you see a single GameObject named SpringyFireball. The Inspector window shows the collection of components and properties.

In Roblox, a comparable SpringyFireball model in the Explorer window might look something like this:

Model
|- ParticleEmitter
|- MeshPart
|- SpringConstraint
|- ClickDetector
|  |- Script

Roblox's physics-by-default philosophy extends to the process of building 3D models. In Roblox, welding multiple parts together into an assembly is an excellent way to quickly build things, because Roblox treats the welded parts as a single rigid body. This approach isn't available in Unity.

Rather than using standard metric units for length and mass, Roblox uses notional units called studs and Roblox Mass Units (RMUs). For approximate metric conversions and recommendations around use, see Units.

Location matters

Roblox experiences are multiplayer by default, so Roblox Studio includes many different storage locations with specific behaviors. For example, a script might run when you put it in ReplicatedStorage, but not when you put it into StarterPlayerScripts. For more information, see Client-server runtime and Object organization.

Scripting

Roblox experiences support three different types of Luau scripts:

• Client scripts

  These scripts run on the client, and the server has no visibility into their behavior. For legacy reasons, these scripts can take the form of LocalScripts or Scripts with a RunContext value of Client. Client scripts typically live in ReplicatedStorage, StarterPlayerScripts, or StarterCharacterScripts.

• Server scripts

  These scripts run on the server, and the client has no visibility into their behavior. Server scripts have a RunContext value of Server and typically live in ServerScriptService, the contents of which are not replicated to the game client.

• Module scripts

  These scripts are reusable pieces of code that return exactly one value, typically a function or table (or a table of functions). Rather than duplicating code in client and server scripts, use module scripts to share code and data between the two. Module scripts often live in ReplicatedStorage, but can live elsewhere if you want to share code between scripts on the same side of the client-server boundary.

Unity doesn't have the concept of different script types. If you choose to make a multiplayer game, Unity uses its networking libraries to indicate when a GameObject (and its scripts) should be exclusive to the server.

In Unity, much of the engine's functionality is available through the methods of MonoBehaviour. For example, to run code before the render loop, you add code to the Update() method. To handle physics collision events, you add code to the OnCollideEnter() method.

Roblox scripts are more event-driven. You access similar functionality by subscribing to services and listening for updates.

C# and Luau

For scripting, Unity uses C#. Roblox uses Luau, a scripting language derived from Lua 5.1.

Compared to C#, Luau is gradually typed and generally has a less verbose syntax. In larger projects, however, gradual typing can introduce categories of bugs that strongly typed languages like C# avoid, so consider enabling strict type checking in Roblox scripts.

For basic syntax differences between the scripting languages, see Luau and C# comparison.

Luau code sample

The following Luau code sample demonstrates how to, after a player equips a fishing pole, listen for user input (in this case, the E key) and call additional functions:

-- Get the necessary game services
local ContextActionService = game:GetService("ContextActionService")
local ReplicatedStorage = game:GetService("ReplicatedStorage")

-- Get a module script from ReplicatedStorage that returns a single function
local performSomeAction = require(ReplicatedStorage.performSomeAction)

-- Assumes that this script is a child of the fishing pole
local fishingPole = script.Parent
local ACTION_CAST = "Cast"

-- Check that the key is down, then call another function
local function castLine(_actionName, inputState, _inputObject)
	if inputState == Enum.UserInputState.Begin then
		performSomeAction()
	end
end

-- Only enable the action when the player equips the fishing pole
fishingPole.Equipped:Connect(function()
	ContextActionService:BindAction(ACTION_CAST, castLine, true, Enum.KeyCode.E)
end)

-- Disable the action when the player unequips the fishing pole
fishingPole.Unequipped:Connect(function()
	ContextActionService:UnbindAction(ACTION_CAST)
end)

The Roblox script can be relatively concise because Roblox has many built-in assumptions: a Player with a Humanoid character connected to the server and can equip Tools. These assumptions don't exist in Unity, so the implementation would be very different.

Assets

Unity and Roblox both support importing custom meshes and models in .fbx format. Certain types of assets may require specific configurations and export settings from your third-party modeling software. For more information, see the following pages:

• 3D Importer
• General specifications
• Blender and Maya export requirements

In Unity, objects import into your Assets directory, visible in the Project window. In Roblox, assets import into your Workspace and into the Toolbox or Inventory section of the Asset Manager.

Roblox also offers an open-source Blender plugin to streamline the import process.

Transforms

Unity's transforms and Roblox's CFrames serve similar purposes in representing 3D transformations of objects:

• Both transforms and CFrames represent the position and rotation of an object in 3D space. Transforms include scale, whereas Roblox uses a BasePart.Size property that isn't part of the CFrame.
• Both support multiplication (i.e. composition) for complex transformations and have built-in methods for other manipulations.

Collaboration

In Unity, you collaborate with standard version control systems or paid services like Unity Version Control.

Roblox files live in the cloud (although you can export copies), so Roblox Studio provides built-in collaboration workflows for simultaneous editing, group management, permissions, script drafting, and more. See Collaboration.

Plugins

Similar to Unity tools, Roblox Studio supports plugins, which can simplify or give you additional control over various aspects of the development process. Plugins are available in the Creator Store, just like assets, many for free.

Glossary