Level of detail script

do
  local insert, remove = table.insert, table.remove
  local LODSpecs = {}
  local function bfind(t, v)
    local a, b = 1, #t
    while a <= b do
      local u = floor((a + b) * 0.5)
      local w = t[u].Sort
      if v > w then
        a = u + 1
      elseif v < w then
        b = u - 1
      else
        return u
      end
    end
    return a
  end
  local function CalculateCenter(m)
    local Center = v3b
    local Children = m:GetChildren()
    for _, Model in next, Children, nil do
      if Model.ClassName == "Model" then
        Center = Center + Model.PrimaryPart.Position
      else
        Center = Center + Model.Position
      end
    end
    Center = Center / #Children
    return Center
  end
  function LODSplitEach(m)
    local Groups = {}
    for _, Model in next, m:GetChildren() do
      local Group = Instance.new("Model")
      Model.Parent = Group
      table.insert(Groups, Group)
    end
    for _, Model in next, Groups, nil do
      Model.Parent = m
    end
  end
  function LODSplitModel(m, n)
    local w = floor(n ^ 0.5)
    local Size = m:GetExtentsSize()
    local Center = CalculateCenter(m)
    local wx = floor(Size.X / w + 0.5)
    local wz = floor(Size.Z / w + 0.5)
    local Groups = {}
    for _, Model in next, m:GetChildren() do
      local p = Model.ClassName == "Model" and Model.PrimaryPart.Position or Model.Position
      local rx = floor((p.X - Center.X) / wx) * wx
      local rz = floor((p.Z - Center.Z) / wz) * wz
      local v = ("%d/%d"):format(rx, rz)
      local Group = Groups[v]
      if not Group then
        Group = Instance.new("Model")
        Group.Parent = workspace
        Group.Name = v
        Groups[v] = Group
      end
      Model.Parent = Group
    end
    for _, Group in next, Groups, nil do
      Group.Parent = m
    end
    return 0.25 * (wx + wz) * 1.4142135623730951
  end
  function LODAddModel(m, d)
    local Parent = m.Parent
    assert(Parent)
    local Spec = {
      Model = m,
      Parent = Parent,
      Center = CalculateCenter(m),
      MinDist = d,
      Loaded = true,
      Locked = false
    }
    table.insert(LODSpecs, Spec)
    return Spec
  end
  function LODAddModels(m, d)
    local Specs = {}
    for _, v in next, m:GetChildren() do
      local Spec = LODAddModel(v, d)
      table.insert(Specs, Spec)
    end
    return Specs
  end
  function LODRemoveModel(m)
    for i = 1, #LODSpecs do
      local Spec = LODSpecs[i]
      if Spec.Model == m then
        LODForceLoad(Spec)
        Spec.Locked = true
      end
    end
    return false
  end
  function LODForceLoad(Spec)
    Spec.Model.Parent = Spec.Parent
    Spec.Loaded = true
    Spec.Locked = true
  end
  local LoadQueue = {}
  local UnloadQueue = {}
  function LODUpdateInterest(p)
    local GFX = UserSettings():GetService("UserGameSettings").SavedQualityLevel
    local Multiplier = GFX.Value > 0 and GFX.Value/2 or 2.5
    LoadQueue = {}
    UnloadQueue = {}
    for _, Spec in next, LODSpecs, nil do
      local d = (Spec.Center - p).magnitude
      Spec.Sort = d
      local ShouldBeLoaded = d < (Spec.MinDist*Multiplier)
      if Spec.Locked then
        ShouldBeLoaded = true
      end
      local Loaded = Spec.Loaded
      if ShouldBeLoaded and not Loaded then
        local i = bfind(LoadQueue, d)
        insert(LoadQueue, i, Spec)
      elseif not ShouldBeLoaded and Loaded then
        local i = bfind(UnloadQueue, d)
        insert(UnloadQueue, i, Spec)
      end
    end
  end
  local function ProcessQueue()
    if #LoadQueue > 0 then
      local Spec = remove(LoadQueue, 1)
      Spec.Model.Parent = Spec.Parent
      Spec.Loaded = true
    end
    if #UnloadQueue > 0 then
      local Spec = remove(UnloadQueue)
      Spec.Model.Parent = nil
      Spec.Loaded = false
    end
  end
  function LODStart(i)
    ThreadLoopAdd(i, ProcessQueue,"LOD Queue Processing")
  end
end