Calculating the bounding box of a given model and/or ParticleEmitter

PysephDEV · March 9, 2025, 5:40am

For a project of mine I had to calculate the bounding box of a given model, but not just for the parts inside of it, but also any ParticleEmitters. After a quick perusal I realized there was no released code to achieve this, and so after two days, I got this working instead. I’m open-sourcing this in case someone else needs this as well!

gist.github.com

https://gist.github.com/Pyseph/8fee39acdb5c33d64c4df72d92cdc60a

GetBoundingBox.luau

--!strict
local function GetBoundingBox(Object: Instance | {Instance}, ModelOrientation: CFrame?, Gizmo: any?)
	local Orientation = ModelOrientation or CFrame.identity
	local Descendants: {Instance} = if typeof(Object) == "Instance" then Object:GetDescendants() else Object
	local MinX, MinY, MinZ = math.huge, math.huge, math.huge
	local MaxX, MaxY, MaxZ = -math.huge, -math.huge, -math.huge
	
	local function Update(ObjSize: Vector3, RelativeCFrame: CFrame)
		local sx, sy, sz = ObjSize.X, ObjSize.Y, ObjSize.Z
		local x, y, z, R00, R01, R02, R10, R11, R12, R20, R21, R22 = RelativeCFrame:GetComponents()

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The third parameter, Gizmo, is for my own debugging library that I used to debug this, and can be ignored.

Limitations

It does not take into account for the different EmitterShape properties such as .Shape, .ShapeInOut, and .ShapeStyle. I don’t want to spend more time on this than needed, and so if anyone else wants to implement it, feel free.

I didn’t test this out extensively, however it works fine on the following properties I tested it with:

SpreadAngle
Acceleration
Speed
EmissionDirection
Animated/different Size values
Drag (not fully correct, it seems to be off by some small values)