local distance = 1000
local eye_origin = vector_origin

distance = distance * distance

hook.Add("RenderScene", "hide_entities", function(pos)
    eye_origin = pos
end)

local function IsAllowed(ent)
    return ent:IsValid() and not ent:IsPlayer()
end

local function ShouldHide(ent)
    return (ent:GetPos() - eye_origin):LengthSqr() > distance
end

local init_hidden = {}

local function CheckEntity(ent)
    if not init_hidden[ent:EntIndex()] then
        ent:SetNoDraw(true)
        init_hidden[ent:EntIndex()] = ent
    end
    if ShouldHide(ent) then
        if not ent.he_hiding then
            ent:SetNoDraw(true)
            ent.he_hiding = true
            print("hiding ", ent)
        end
    else
        if ent.he_hiding then
            ent:SetNoDraw(false)
            ent.he_hiding = nil
            print("showing ", ent)
        end
    end
end

timer.Create("hide_entities", 0.2, 0, function()
    for key, ent in pairs(ents.GetAll()) do
        if IsAllowed(ent) then
            CheckEntity(ent)
        end
    end
end)