Excuse my ignorance...

What the hell is Occlusion Culling?!!?

A neat-o feature.

Right now if you look our over the landscape, but there's a prim in the way, SL draws all that landscape, then that last prim in the way.

With occlusion culling, only that last prim gets drawn, saving a lot of time

So, basically it's drawing that prim, then not rendering the landscape behind it?

Yes, nor any of the prims behind it.

I've heard people talking about this possibly helping privacy issues. I'm not sure how they figure that.

The theory behind it is sound, however if it takes more time to calculate whether or not to render a prim than to just render the prim, it doesn't help.

I wish it worked that way, but apparently it's much more limited than that, it doesn't seem to affect anything but terrain detail for obscured terrain and prims that are behind terrain.

True occlusion culling would make only the closest prim visible if it completely obscured the others.

The reason this could potentially mean more privacy is if they made it required, so you couldn't turn it off, it was true and complete occlusion culling, and if it were always calculated from your avatar's position and not your camera position.

This would mean you could make a room with no windows, and no one could see anything inside the room unless they were inside the room. If they panned their camera through the wall they'd only see a completely empty room.

It would also mean being inside a room with no windows would give you insane FPS since only the prims inside the room would be rendered. It would be like turning your draw distance down to just enough to encompass the room you are in.

Again, this is not the case with the way it is currently implemented.

Also, the culling happens with respect to the camera position (as it should!), not avatar position, so whatever you zoom on, you'll see it. This is not a privacy feature.

That would kill SL as a building platform. Imagine having to drop out of edit to walk (or fly) round the build to see behind the prims...

Oh, that is a really good point.

Active Worlds doesn't have a detachable camera, yet it's building platform is fine, though not as good as SL's. Av-based occlusion wouldn't KILL SL as a building platform but it would make it more annoying. It should remain camera-based, unless a specific sim option could be added for it to change to av-based for privacy reasons.

As has been stated elsewhere, occlusion culling has nothing to do with privacy. It only has to do with not drawing things that are just going to be drawn over by things which obscure them, from the camera's perspective. You can't "see" it, because anything that is visible should always be drawn. The only way you can tell is by turning it on and off and watching the change in framerate.

To answer Alondria, the algorithm is a smart one, designed to not impact framerate when nothing is being culled and everything is visible.

Hope that answers the question.