Doom3 AA

[Reverend]

I'm not sure if this has been brought up before but I've asked a couple of ATI guys about this (instead of bugging JC) and am actually awaiting sireric's answer to the key question :

Why does the app report more than we can do? Well, that's more of an app question.

It's not just "reporting more than you can do" -- your (and NV's) hardware is actually doing more than it can do! Which is basically my question -- how can this be so?! If a hardware can't do 16 samples AA but it _is_ actually being done in Doom3, *what* is doing the AA? The app or the hardware?

Most games will offer AA modes as exposed by the CAPS. That means 2 and 4 (max) samples for NV and 2, 4 & 6 (max) samples for ATI.

However, and as you know, you can ask Doom3 to use up to 16 samples (and it actually does). That's basically the question -- how? And not only "how" this is posiible, but what sort of AA are we seeing with, say, 16x... jittering or... ?

 

[LeGreg]

We already answered that.
It's just supersampling, by doing jittered screenshots and taking the mean of all samples per pixel. To take n screenshots in a row does not require any special capability.

Why do you keep asking the same question ?
What is the part that you do not understand in this?

 

[Reverend]

You're saying this only applies to screenshots. I'm saying this applies while playing the game. That is the part I do not understand.

Have you ever tried 16x in the game and play it before assuming I'm too dumb to understand the difference between "screenshots" and "in-game"?

 

[LeGreg]

Have you ever tried 16x in the game and play it before assuming I'm too dumb to understand the difference between "screenshots" and "in-game"?

I'm playing without AA (9700pro power)

but anyway I just made the test:
4xAA -> aa in game
16xAA-> no aa in game

Note that the 6800 supports 16x modes at least as a hidden control panel options, but I'm not sure that changes something to the problem ??

 

[LeGreg]

actually it's more something like that:

-no aa is set.
-Set it to 16x
-vid_restart
-no AA is set
-set aa to 6x
-vid_restart
-aa 6x is set
-set aa to 16x
-vid restart
-aa 6x is set (regular multisampling)

In fact when you set aa to 16x, since it is an incorrect value either the game or the driver assumes the last correct value apparently. Of course if it's the driver then your mileage may vary.

 

[Reverend]

Note that the 6800 supports 16x modes at least as a hidden control panel options

Hmm... didn't know that...

 

[kyleb]

The Geforce's do x8 and x16; they are both slow as hell so we don't have control panel options for them, but you can turn them on in doom3. x8 and x16 from the doom3 options does nothing on ati hardware as radeons don't support either. Is this what you were confused about in your "software antialising" thread?

*edit* n/m

 

[dan2097]

Nvidias 16xfsaa wouldnt be able to be exposed by a generic fsaa command though would it as its not like its 16xmsaa?

I mean Nvidias definition of what 8xfsaa is on its hardware changes between drivers so how exactly an in game option for it would work makes very little sense. It would have to be particular to Nvidia cards as you'd want it to pick 8xmsaa when cards become available that support it rather than an nvidia specific mode which would obviously fail on other cards.

 

[GameCat]

If Doom 3 uses the standard OpenGL way to control AA, there is no option for anything other than straight multi sampling, that's the way it's speced. Nvidia have an extension that relaxes these restrictions and allows yuo to request stuff like Quincunx, but I don't know if Doom 3 uses it. I doubt it though.

 

[Ailuros]

You're saying this only applies to screenshots. I'm saying this applies while playing the game. That is the part I do not understand.

Have you ever tried 16x in the game and play it before assuming I'm too dumb to understand the difference between "screenshots" and "in-game"?

I gave it a shot the other day in 1024*768*32. 16x definitely slows down performance by a lot, yet in the few spots where a few edges actually get some shreds of light occassionally it doesn't look to me at least, like anything higher than a 4*4 grid.

It most likely looks like it's the 16x sample hybrid mode that was already present on NV3x and hidden from the public. It was operational only in OpenGL and it's a combination of 4xOGMS and 4xOGSS, which does seem to result into a 4*4 grid:

http://www.3dcenter.de/artikel/ati_nvidia_aa_performance/index2_e.php

IMHO it's a waste of fill-rate, especially since even 1280*1024 with just 2xRGMS and 8xAF seems to give me overall a better result, performance included. Would this be theoretically a 16*16 grid then it would be a totally different story.