custom obj hax

[karlis]

i found such hax in race resource:

-- This is a hax file to make custom model loading work reliably
-- Usage: loadCustomModel(objID, dffFile, txdFile) in the main script body,
-- then createObject() in an event handler. Or: loadCustomModel in an event,
-- and createObject() in an event that gets triggered later.
 
local preloads = {}
local pendingEvents = {}
 
local _addEventHandler = addEventHandler
function addEventHandler(event, elem, handler, getPropagated)
if event == 'onClientRender' then
return _addEventHandler(event, elem, handler, getPropagated)
end
return _addEventHandler(
	event,
	elem,
function(...)
if not next(preloads) then
			handler(...)
else
table.insert(pendingEvents, { fn = handler, source = source, args = { ... } })
end
end,
	getPropagated
)
end
 
local function customModelPreloaded()
local id = table.find(preloads, 'elem', source)
if not id then
return
end
local preload = preloads[id]
local txd = engineLoadTXD(preload.txd)
engineImportTXD(txd, id)
local dff = engineLoadDFF(preload.dff, id)
engineReplaceModel(dff, id)
removeEventHandler('onClientElementStreamIn', source, customModelPreloaded)
destroyElement(source)
preloads[id] = nil
while not next(preloads) and #pendingEvents > 0 do
local event = table.remove(pendingEvents, 1)
	source = event.source
	event.fn(unpack(event.args))
end
end
 
function loadCustomModel(id, dff, txd)
if preloads[id] then
return
end
local x, y, z = getElementPosition(getLocalPlayer())
local elem
if id <= 609 then
	elem = createVehicle(id, x, y, z - 10)
else
	elem = createObject(id, x, y, z - 10)
end
setCameraTarget(getLocalPlayer())
preloads[id] = { dff = dff, txd = txd, elem = elem }
_addEventHandler('onClientElementStreamIn', elem, customModelPreloaded, false)
end
 
 
-- Make sure the preloads are near the player so the onClientElementStreamIn event gets triggered
local function checkPreloads()
for id,preload in pairs(preloads) do
local px, py, pz = getElementPosition(getLocalPlayer())
local ex, ey, ez = getElementPosition(preload.elem)
local dist = getDistanceBetweenPoints3D ( px, py, pz, ex, ey, ez )
if( dist > 50 ) then
setElementPosition( preload.elem, px, py, pz - 10 )
end
end
end
 
setTimer(checkPreloads, 500, 10 )

what does it exactly do, how to use it propertly(i failed), why its not specified in meta, whats is his idea to do, could i make it much simpler and smaller if ill attach lines to general script, not making it as new scriptfile?