does this use up some memory?
a big map with 12 players and many trees (destructible) , many items on floor and many units... would using this system increase lag?
It's not a system. It's just a model, so it doesn't affect anything else than visuals. You can even change the model for selected players only by using
if GetLocalPlayer() == Player(0) then
i understand a little from what you say but i am not sure:
so basically setting the DNC will alter the map lightning...
felwood light environment is a type of DNC...
Both correct.
is it possible to fully customize the DNC lightning and is it easy to do it?
It requires certain tools like MDLVIS or WC3ModelEditor, as you'd need to edit a model file and import it to your map.
and changing the DNC would alter both day and night? or is it possible to alter them separately?
The DNC model is basicly just a giant light source attached to the camera which has a 60 second animation. Those 60 seconds are adapted to the game speed and translated into a specific time of day. Over those 60 seconds, the light environment (this means the intensity of the light emitted, the color, etc.) changes multiple times.
With WC3ModelEditor or MDLVIS, you can freely edit the color and intensity for any frame that is defined in the model according to your tastes. By looking at the color values, you will easily find what is the frame for "morning (having more blue colors)", "evening (having more red colors)", night (all colors pretty dark), etc..
does model has to be special model to use the DNC, or any doodad, unit, destructible allready is set to interact with DNC?
Nope, all units and the entire terrain is affected. But you can set a different DNC for terrain and units.
also not about DNC, but is the global fog able to be set to be transparent and not affect vision but still give so color modification to environment?
Nope. Because it's fog. Fog always reduces vision. If it wouldn't, it wouldn't be fog, right?