Rendering and physics

Render backends#

The renderer targets a backend per platform. It is chosen automatically and can be overridden.

[render]
backend = "auto"
vsync = true
msaa = 4
shadow-quality = "high"       # off | low | medium | high

MyGame.exe --render-backend vulkan --no-vsync

Users can override at runtime with those flags, which is worth remembering when a player reports a driver-specific crash — asking them to try another backend is often a one-message fix.

Lighting#

Lighting behaves as it does on Roblox, including Technology:

local Lighting = game:GetService("Lighting")

Lighting.Technology = Enum.Technology.Future
Lighting.Ambient = Color3.fromRGB(60, 65, 80)
Lighting.OutdoorAmbient = Color3.fromRGB(140, 150, 170)
Lighting.ClockTime = 14.5
Lighting.GeographicLatitude = 41.7
Lighting.ExposureCompensation = 0.25

Post-processing effects — BloomEffect, ColorCorrectionEffect, DepthOfFieldEffect, SunRaysEffect, BlurEffect — all parent to Lighting and work the same way.

Resolution and presentation#

if Engine.Platform ~= Enum.Platform.Roblox then
	Engine.Window:SetSize(1920, 1080)
	Engine.Window:SetFullscreen(true)
	Engine.Window:SetVSync(true)

	-- Render at 70% and upscale — a cheap quality slider
	Engine.Render:SetResolutionScale(0.7)
	Engine.Render:SetFrameRateCap(144)
end

Engine.Render:GetStats() returns draw calls, triangle count, GPU frame time and VRAM usage, which is enough to build an in-game performance overlay without the MicroProfiler.

Physics#

The physics solver is the same one Roblox uses, so behaviour carries across unchanged: constraints, assemblies, network ownership, collision groups and PhysicsService all behave as documented for Roblox.

local PhysicsService = game:GetService("PhysicsService")

PhysicsService:RegisterCollisionGroup("Players")
PhysicsService:RegisterCollisionGroup("Projectiles")
PhysicsService:CollisionGroupSetCollidable("Players", "Projectiles", false)

part.CollisionGroup = "Projectiles"

Determinism#

Standalone targets can opt into a fixed-step deterministic solver, which Roblox does not expose. This is what you need for lockstep multiplayer or replay files:

[physics]
mode = "deterministic"     # realtime | deterministic
step-rate = 60

In deterministic mode the solver runs at a fixed rate independent of frame rate, and floating-point behaviour is pinned across platforms. It costs some performance and is not available on the Roblox target.

Tuning#

workspace.Gravity = 196.2
workspace:SetAttribute("SolverIterations", 8)

local part = Instance.new("Part")
part.CustomPhysicalProperties = PhysicalProperties.new(0.7, 0.3, 0.5, 1, 1)

Performance#

Both profilers from Studio come across:

• MicroProfiler (Ctrl+F6) — per-frame CPU breakdown
• Developer Console (F9) — memory, network and script performance

Plus a CLI profiler for headless runs, which is how you profile a dedicated server:

luauengine profile --target windows --duration 30 --out profile.json
luauengine profile view profile.json

The trace file is Chrome Trace format, so chrome://tracing and Perfetto open it directly if you prefer those.