For all you PC gamers out there enjoying the beta for Battlefield: Bad Company 2 you probably searched the graphics options and seen HBAO. If you were like me you probably thought "Wtf is HBAO?". Well, I did a bit of research and found this: http://developer.nvidia.com/object/siggraph-2008-HBAO.html . What I gathered from that presentation is that it's shadowing based off the angle of a light source on an object. Kind of like dynamic lighting but not exactly.
 
Well, that all sounds good in theory but in practice it sharply cuts FPS, sometimes even in half. Something that's so heavy must be good, right? Well, that's what I'm here to show you guys.
 
Note: This is on all maxed settings with 4x AA on a DirectX 10.1 XFX 4890.
Note 2: The screenshots are in window mode because you are unable to take screenshots while in-game. 
Final note: These screenshots taken are from the BETA. These do NOT represent the final retail product.
  
Of course GB doesn't allow high res pics so here's the album: 
http://yfrog.com/7ghbao14px     
And here's the individual pics:
http://img268.yfrog.com/img268/9527/hbao14.png
http://img96.yfrog.com/img96/425/hbao13.png
http://img229.yfrog.com/img229/7734/hbao12.png
http://img707.yfrog.com/img707/2410/hbao11.png
http://img222.yfrog.com/img222/8094/hbao10.png
http://img21.yfrog.com/img21/4914/hbao9.png
http://img11.yfrog.com/img11/7149/hbao8.png
http://img8.yfrog.com/img8/2262/hbao7.png
http://img218.yfrog.com/img218/3935/hbao6.png
http://img43.yfrog.com/img43/5706/hbao5.png
http://img229.yfrog.com/img229/2044/hbao4.png
http://img268.yfrog.com/img268/6594/hbao3.png
http://img690.yfrog.com/img690/6997/hbao2.png
http://img684.yfrog.com/img684/9611/hbao1.png 
 
As you can see the preformance hit is pretty huge and the differences are very little. They certainly do not justify the FPS drop. Unless you're running 2 GPUs you're going to have a hard time running HBAO.

I knew that HBAO had something to do with shadowing, but that was it.  It doesn't really matter to me, as I'm keeping all my settings down to low anyways for maximum FPS, except for my AA at 8X and my AF at 8X.

Those differences aren't that little. I find ambient occlusion adds a good sense of depth to the environment on screen, so I leave it on!

I like ambient occlusion as an effect, it's been in quite a few games.  Sometimes it's overused, Star Trek Online has kind of a poorly made implementation.  Really it's something that could have been adjusted to look better by the developers with no extra performance cost (in STO).  Crysis lets you tweak all sorts of variables if you edit the ini, and there are ways to make the effect look very excellent.
 
To help you guys understand, just randomly put an object in front of a white wall in a well lit room.  There will be a shadow even in indirect lighting due to less photons bouncing around between the object and the wall (or another object).  Obviously in real time 3D graphics in games they aren't simulating photons (There is computer graphics that can and does do that), it simply creates a faked simulation of the effect in post processing.
 
To the best of my knowledge BFBC2 on PC is the first game to use the specific horizon based ambient occlusion effect, but many other games have used other simpler ambient occlusion effects (often times called SSAO (or screen space ambient occlusion), although I don't personally know which games might use SSAO or another similar effect with a different name.  If you really want to know the technical depths, read the nvidia article above.

I can't tell the difference :(

I have a Radeon 5770 and I STILL can't run Red Faction Guerrilla with ambient occlusion. It's ridiculous how big of a performance hit the GPU takes with ambient occlusion turned on. With that performance hit, I could have bumped up antialiasing 4x.

SSAO takes a huge hit in performance in RF:G  because the engine has to calculate all the alpha differences on top of those which are processed naturally do the game having glass walls and ceilings on many buildings. SSAO is a while away from being properly integrated into GPU ALU's and so is largely processed on the CPU, yes even with Nvidia cards.

They said they've now gotten the HBAO filter to perform much better than how it is in the beta. And I think the HBAO looks great. Abient Occlusion is as important as MSAA to me. But neither are as important as SSAA, which this game sadly can't do.  Even BF2 and 2142 could use SSAA if your forced it with nhancer.
 
The MSAA in this game has a weird light edge to it sometimes. At first I tohught I needed to check the 'gamma corrected AA' box in nhancer... but that didn't fix it. I might post a screen.

" @MrKlorox: No idea, but I too have problems applying SSAA or even MSAA in games sometimes.  Seems to change based on drivers I use.  Surprised BFBC2 wouldn't take SSAA if other games do though.  There's an in-game AA setting in BFBC2?  I must have not noticed that, or I heard that it didn't work...  I'm confused now. "

Jesus, you must have a nice PC to get over 60 FPS on max (without HBAO).  I don't even get 60 FPS on low.

Thanks for the thread! I've been wondering about this myself but haven't been able to take the time to look into it. My FPS is pretty solid with all things on max and 4xFSAA, but I do notice drops here and there so I'll prob end up dropping this for the time being.