ToMeshPart.lua

--!strict

local ChangeHistoryService = game:GetService("ChangeHistoryService")
local InsertService = game:GetService("InsertService")
local Selection = game:GetService("Selection")

local props = {
	"Name",
	"Color",
	"CFrame",
	"Anchored",
	"Material",
	"CanCollide",
	"Transparency",
}

local function toMeshPart(part: Instance?): MeshPart?
	if not (part and part:IsA("BasePart")) then
		return nil
	end

	local mesh = part:FindFirstChildWhichIsA("FileMesh", true)

	if not mesh then
		return nil
	end

	local id = mesh.MeshId
	local scale = mesh.Scale

	local isHead = false
	local doubleSide = false
	local originalSize = part:FindFirstChild("OriginalSize")

	if id == "" then
		if mesh:IsA("SpecialMesh") and mesh.MeshType.Name == "Head" then
			local size = part.Size
			local y = (size.Y * scale.Y) / 1.25
			local xz = math.min(size.X * scale.X, size.Z * scale.Z) / 1.25

			id = "rbxasset://avatar/heads/head.mesh"
			scale = Vector3.new(xz, y, xz)

			mesh.MeshType = Enum.MeshType.FileMesh
			mesh.Scale = scale
			mesh.MeshId = id

			isHead = true
		else
			return nil
		end
	end

	local xMod = scale.X < 0 and -1 or 1
	local yMod = scale.Y < 0 and -1 or 1
	local zMod = scale.Z < 0 and -1 or 1

	if xMod < 0 or yMod < 0 or zMod < 0 then
		scale *= Vector3.new(xMod, yMod, zMod)
		doubleSide = true
	end

	local meshPart = InsertService:CreateMeshPartAsync(mesh.MeshId, "Box", "Performance")
	meshPart.Size = meshPart.MeshSize * scale
	meshPart.TextureID = mesh.TextureId
	meshPart.DoubleSided = doubleSide

	if originalSize and originalSize:IsA("Vector3Value") then
		local ratio = originalSize.Value / part.Size
		originalSize.Value = meshPart.Size * ratio
	end

	for i, child in part:GetChildren() do
		if child ~= mesh then
			if child:IsA("Decal") and not isHead then
				local success = pcall(function()
					local surface = Instance.new("SurfaceAppearance")
					surface.ColorMap = child.Texture
					surface.Parent = meshPart

					if part.Transparency >= 1 then
						part.Transparency = 0
						surface.AlphaMode = Enum.AlphaMode.Transparency
					end
				end)

				if success then
					continue
				end
			end

			child.Parent = meshPart
		end
	end

	for i, prop in props do
		meshPart[prop] = (part :: any)[prop]
	end

	return meshPart
end

ChangeHistoryService:SetWaypoint("PreMeshPartConvert")

for i, desc in Selection:Get() do
	if desc:IsA("Part") then
		local meshPart = toMeshPart(desc)

		if meshPart then
			meshPart.Parent = desc.Parent
			desc.Parent = nil
		end
	end
end

ChangeHistoryService:SetWaypoint("PostMeshPartConvert")