Parhelia performance under DoomIII per John Carmack.

[K6-III]

I just talked to John Carmack about Parhelia performance under DoomIII.

His exact words for how it performs: "like shit"

He cited some bad design choices, optimising only for multiple simultaneous textures, hardware bugs in regards to ScissorCut, and poor OpenGL performance.

Looks like banding isn't the only hardware bug of the parhelia.

BTW, if this belongs in Matrox Gaming, feel free to move it, or mirror it, so it gets greater exposure.

[bsdgeek]

Well they do seem to be working on their OpenGL in comparison from 1.03 to 1.04. Did he comment on that? also...What is ScissorCut?

[K6-III]

He did say they have improved performance, but it is still "like shit".

As for what it is, I don't know. Some of the people on this forum might...

[bsdgeek]

One more quick question, did you ask if he was going to write an optimised path for Parhelia, even though performance is like shit?

[K6-III]

I'll see if I can ask him later today...

[Novdid]

You seem to have a nice contact with the mighty game programmer, eh?

[Greebe]

Matrox's lawyers are going to love this thread come Monday morning...

[Tempest]

Originally posted by Greebe
Matrox's lawyers are going to love this thread come Monday morning...

Hm... Greebe, do you mean that the additional bugs in the Parhelia were supposed to be a secret?

ps. I don't know what ScissorCut is, but what I've learned in computer graphics class is that scissoring is the process of using a (rectangular) stencil for selecting/masking the updatable area(s) in a window... Or something like that.

[Greebe]

Naw

But as a BB I can't say more.

[Chrono_Wanderer]

Originally posted by Greebe
Matrox's lawyers are going to love this thread come Monday morning...

Matrox Graphics can actually afford lawyers right now? LOL

Maybe they should spend some money on RnD instead

I am thinking that there are A LOT of bugs in Parhelia. And it leads me to think the P-series also has some bugs in it...

Sad, but this is very likely the case.

[DirtFarmer]

Originally posted by Greebe
But as a BB I can't say more.

wouldn't that be exBB?
or is it
once a BB always a BB
ahh, whatever, BUT we could sure do with less Matrox lawyers about lurking the MURC.

[Greebe]

Nope, we are all BBz still except one, whom said the h*ll with this BS and he was the greatest contributor of all.

Besides even after the NDA's end, all of the original bunch are good friends and will be staying in touch the same as when Haig first started the beta testing group.

[rylan]

Cat (or should I say bugs) getting out of the bag?

[DedicatedFan3D]

Man, as a programmer you can find alot more than scissorcut bugs.

FYI folks, it is not scissorcut

Rather, Carmack did let some neat info out about Doom3....in OGL you have a scissor, which can be VERY handy when rendering shadow volumes against fragments, it just about cuts your fillrate penalty in half for very basic shadowing functions....it sounds like Carmack is making heavy use of the stencil buffer. As reference to scissorcut, I think he means scissorcut as it fillrate penalty cut for the extensive shadowing he does on the polygons.

Apparently, the lack of any sort of occlusion capability in the Parhelia (rather than a bug) causes the cut function in OpenGL to screw up. So what would be a fast efficient function in OpenGL for most other cards where you can simply cut unwanted poly's in a scene and use the scissor to manipulate geometry you now have to work around it....it is really sad to see this.

In depth a little bit more, I forgot that high level scissor rectangle support (exactly the same function we are talking here as above) is not available in DX 8.1....but it is in 9.0! I wonder if Matrox in their quest to be in between 8.1 and 9.0 compliance forgot about scissor rectangle support? That would explain what carmack is talking about, and explain why performance is like shit. The rectangle cuts would be impossible, causing a massive fillrate penalty. No wonder in 3DMark you have faster performance on a GF3. You can work around the scissor problem with occlusion tech on a visible volume that the stencil is trying to call.

This is the kind of stuff you saw in the Riva128 (the inability to render t-junctions and lack of support for palletized textures). Matrox must have lost some really bright people......

[Zao]

DedicatedFan3D:
I don't think the Parhelia supports Palletized Textures either...

I tried to play Final Fantasy VII the other day and it complained about the hardware not supporting it.