Verticies: Z-cull vs game engine.

[MrWizard6600]

I've got a question for someone who knows there stuff about graphics cards.

When Im in a level, such as De_nuke in counter strike source, and theres a wall behind a wall, like say, the concrete wall behind the aluminum wall of hut as you look at it from the upper (aka inner) bomb site, whos in charge of that concrete wall? Z-cull? The game engine? Or some other power I dont know about?

Right now, Id asume that the game engine says to the graphics card "ok, from his current location the most he could possibly see (from upper bomb site) is maybe connector, red crate outside, and maybe lobby (inner), and maybe even radio room." So, the graphics card loads all the verticies for these rooms, straps on the textures, and then Z-cull tells various polygons "your in the frame, your also in the frame, he cant see you yet but he will shortly, stay in the buffer, your not in the frame and he wont see you for a long time..." etc, where something far away like CT spawn isnt even drawn.

Is that how it works? does it differ from engine to engine? Surly the graphics card doesnt have the whole map rendered every frame? Is it backlogged from Z-cull saying "your too far away to possibly be in any scene in the near future", then disgarded until its needed, or does the game engine give the graphics card all the information that could possibly be seen, as the player moves room to room?

anyways, thanks for any response, I think my theory is correct I'd just like to be sure.