Problems with FPS in D3 with AA

[darkswordsman17]

Ok, well I've been playing around in Doom 3, trying to find an optimal visual quality vs performance setting.

I had been playing it at max everything (1600x1200, Ultra, x16 AA). It had been smooth, but then I started noticing some minor slowdown (which didn't use to happen at all). I used the control panel to enable showfps, and if I go near smoke my framerate drops to as low as 8. It usually is hovering at 20+. I never noticed it being that low before.

I switched it to 8x AA and noticed no difference at all.

Next I went to 4x AA, and my framerate goes to 60 and stays there. When I go near smoke it can go down into the 30s, but not lower.

Now, I know AA impacts performance quite a bit, but should going to 8x from 4x triple my framerates? Also, going to x16 from x8 has no impact on performance?

Anybody have any ideas? Its on a GT @ Ultra speeds. Also, these are actual in game playing framerates, not from the timedemo.

 

[SynthDude2001]

I'm not entirely sure that the 6800GT can do 16x AA, so it may just be falling back to 8x (which of course would explain the similar framerates at 8x and 16x).

I have the same card myself, running at the same speeds, but I have no way of testing 8xAA vs. 4xAA at 1600x1200...my monitor won't go anywhere near that high.

 

[Matthias99]

Do you mean AF? Because AA on the 6800-series cards only goes up to 8x (and takes a HUGE performance hit at 8x). Also, there was some weirdness with trying to force AF from both the CP and the in-game settings, I think...

 

[darkswordsman17]

In the advanced options, the Anti-Aliasing option you can select Off, 2x, 4x, 8x, or 16x.

Well, it looks like my framerates aren't out of order for my system A64 3000+ @ stock speeds. I had been thinking that D3 had been tested on the settings I had and that the 6800 Ultra had gotten good framerates. I went and checked some benchmarks and mine is in line with the bench scores.

 

[vshah]

8xAA uses supersampling, which requires tons of memory bandwidth at High resolutions. 4x uses multisampling, which would explain the huge jump in performance.

-Vivan

 

[MercenaryForHire]

Originally posted by: darkswordsman17
Ok, well I've been playing around in Doom 3, trying to find an optimal visual quality vs performance setting.

I had been playing it at max everything (1600x1200, Ultra, x16 AA). It had been smooth, but then I started noticing some minor slowdown (which didn't use to happen at all). I used the control panel to enable showfps, and if I go near smoke my framerate drops to as low as 8. It usually is hovering at 20+. I never noticed it being that low before.

I switched it to 8x AA and noticed no difference at all.

Next I went to 4x AA, and my framerate goes to 60 and stays there. When I go near smoke it can go down into the 30s, but not lower.

Now, I know AA impacts performance quite a bit, but should going to 8x from 4x triple my framerates? Also, going to x16 from x8 has no impact on performance?

Anybody have any ideas? Its on a GT @ Ultra speeds. Also, these are actual in game playing framerates, not from the timedemo.

1. That's Doom3 talking. Just because it gives you the option doesn't mean your card can do it. It's falling back to what it can do - 8xAA.
2. If you had any clue how AA worked, you wouldn't even be asking this question. And yes, it will easily triple by dropping down.

1600 x 1200 = 1.92 million pixels

To get 4xAA, you're taking four times that in both dimensions.

(1600x4) x (1200x4)
6400 x 4800 = 30.72 million pixels

To get 8xAA, eight times.

12800 x 9600 = 122.88 million pixels

See where I'm going here? Exponential increases needed. 122.88 million pixels, in 32-bit colour, is worth 468MB of video RAM. You don't have 468MB on your card. However, you do have 117MB for 4xAA.

- M4H

*Yes, I know that isn't exactly how it works, since the gF6 series uses hybrid supersampling and multisampling at 8xAA, but the idea is still there.

 

[darkswordsman17]

Forgive me for not knowing exactly how AA works.

I didn't know, so thanks for explaining it.

So AA x16 and the Ultra setting are really for future cards then.

That explains it then.

Just one more question, and I know its really up to me to decide which I think looks better, but what do you people find to be better looking, lower res with higher AA or higher res with lower AA?

 

[kylebisme]

running with vsync on i take it?

 

[MercenaryForHire]

Originally posted by: darkswordsman17
Forgive me for not knowing exactly how AA works.

I didn't know, so thanks for explaining it.

So AA x16 and the Ultra setting are really for future cards then.

That explains it then.

Just one more question, and I know its really up to me to decide which I think looks better, but what do you people find to be better looking, lower res with higher AA or higher res with lower AA?

High res, lower AA. 16x12 4xAA 8xAF is what you're running now, I assume.

Personally, I'd run 1280x960 4xAA 8xAF on that rig, and have no framerate dips.

- M4H