Xenos - RSX - What was left out?

[blakjedi]

A couple days ago folks were discussing the trade-off the NV and ATI made in making their GPUs.

Is there any feature that you would expect on this gen's hardware (other than more power) that was left out?

Programmable ALU's - check
Geometry tesselation units - check
"Free" AA - check
Extreme bandwidths for graphics work- check
Displacement mapping capability - check

What other goodies were left out?

 

[Titanio]

Shadowing and Interreflection logic

 

[jvd]

"Free" AA - check

ONly 1 of them support free aa so far

 

[Titanio]

"Free" AA - check

ONly 1 of them support free aa so far

I think he was talking about everything that has been offered between the systems, not on each..

And what constitutes free is up for debate, but lets not go there here - it's been combed over again and again in other threads.

 

[Arun]

Since those are closed box systems, I would have liked to see some more flexibility when it comes to AF. That is, being able to select how much AF each kind of surface gets, potential optimizations, etc. but it might be a bit renderstate-change-heavy.
Although maybe that functionality is in there for all I know? Any console programmers here care to comment?

Uttar

 

[ERP]

Since those are closed box systems, I would have liked to see some more flexibility when it comes to AF. That is, being able to select how much AF each kind of surface gets, potential optimizations, etc. but it might be a bit renderstate-change-heavy.
Although maybe that functionality is in there for all I know? Any console programmers here care to comment?

Uttar

Given Xbox and GC altready let you do this along with every recent PC graphics card I know of.

No real point doing it on the PC since people just turn it on in the control panel and crap all over any setting the dev might choose to make.

 

[blakjedi]

"Free" AA - check

ONly 1 of them support free aa so far

Thats why I used "" ;-)

 

[ralexand]

Do those gpus have geometry tessellation units?

 

[Megadrive1988]

Do those gpus have geometry tessellation units?

this has been hinted at, and mentioned, but I haven't seen anything conclusive as far as
'yes they absolutely do have geometry tessellation units'

 

[ralexand]

Do those gpus have geometry tessellation units?

this has been hinted at, and mentioned, but I haven't seen anything conclusive as far as
'yes they absolutely do have geometry tessellation units'

Thanks for the info. It would seem that if they did have them it would be talked about more.

 

[The GameMaster]

Do those gpus have geometry tessellation units?

XENOS has a geometry tessellation unit... that is for sure, as it was stated in various articles, including the one by Dave, that the tessellation unit in XENOS is capable of outputting 250 million polygons per second by itself. There is no tessellation unit in the Geforce6800/7800 series that I know of (at least based on the block diagrams of the NV4x/5x GPUs and no person has ever made mention of a tessellation unit in the NV4x/5x GPUs) and as the RSX is based on the 7800 series GPUs... there is likely no tessellation unit there also. You can still do software based tessellation... though that is much slower than having a dedicated unit handling that particular function.

Tessellation is helpful in "Level of Detail" functions. Here is a quote from HardOCP on this...

"The Xbox 360 also makes using curved surfaces possible in-game, meaning that it can calculate the polygons from the proper curved surface math in order to draw it on your screen “correctly.â€￾ Much in line with this is the ability to do high order surface deformation. Moreover, if you are familiar with high order surfaces, you are likely familiar with what gamers and hardware enthusiasts commonly refer to as “LODâ€￾ or Level of Detail. Mr. Feldstein shared with us that the Xbox 360 GPU has some “really novel LOD schemes.â€￾ Therefore, it appears as if the days of pentagonal shaped wheels on the cars in the distance in new Grand Theft Auto titles is a thing of the past."

But the answer to the thread's question is not yet known... there are things about XENOS we do not know yet and it is still covered by NDAs. XENON has yet to of been unvieled and no one knows exactly what it is and Sony seems to have purposely left out details on the RSX for other reasons... I am very interested in finding official information about both, but it seems that won't occur until later this year.

 

[Shifty Geezer]

Tessellation is helpful in "Level of Detail" functions. Here is a quote from HardOCP on this...

"The Xbox 360 also makes using curved surfaces possible in-game, meaning that it can calculate the polygons from the proper curved surface math in order to draw it on your screen “correctly.â€￾

I thought Dave's article said HOS weren't supported on Xenos, though the tesselator was? The idea being the XeCPU processes surfaces and the Xenos creates them, I think.

For thread title response, I agree with Titanio. Where's my third chip?

 

[Guden Oden]

Traditionally, parametric surfaces have generally proven to be unsuitable for videogame use, for example they tend to cause cracks or gaps in models and other issues. Sometimes, they have found use as roads etc in racing games, but overall they've proven to be rather universally hated by developers and have had little use.

For example, geforce 3 supported tesselated surfaces and that feature was dumped in the geforce 4. Radeon 8xx0 series supported tesselated surfaces, and that feature was dumped in the 9xx0 series.

 

[Laa-Yosh]

Xenos seems to have a tesselator, but it's fixed function. It also takes a few loops between the GPU and the CPU to use it properly, ie. do view-dependent tesselation, and do it after the control mesh of the model has been skinned and/or transformed.

 

[Laa-Yosh]

Traditionally, parametric surfaces have generally proven to be unsuitable for videogame use, for example they tend to cause cracks or gaps in models and other issues.

It's probably an issue of precision - 32 bit floats are not good enough to keep tesselated and displaced patches together, especially with sub-pixel precision (FSAA).

 

[blakjedi]

According to Dave's article

"An additional functional element that Xenos provides to developers is a Geometry Tessellation Unit. The tessellation unit is a fixed function engine that accepts triangles, rectangles and quads as its primitive input, along with a tessellation level per edge such that the level of tessellation is completely variable across the surface of the original primitive...

The combination of the shader array and tessellation unit can now make the, oft spoken of but rarely seen, capability of displacement mapping an attainable method to use as this truly becomes a single pass algorithm for Xenos. A simple primitive can be sent to the tessellation unit which is then subdivided into a vertex mesh and then that can be applied to a vertex shader program that does displacement map lookups via the vertex fetch texture units and then the geometry mesh altered according to the sampled values from the texture sampler. Alternatively, if the screen-space projection of the input primitive to the tessellation unit is calculated prior to tessellation then the per-edge tessellation level can be figured out dependant on that projection such that displacement mapping with correct, dynamic level of detail can be achieved."

 

[BenQ]

The only feature I can think of off the top of my head that I would like to see is the ability to do BOTH HDR and MSAA at the same time on the PS3. However if the RSX is as close to the G70 as I think it is, then I doubt it will be possible.

Yes, I know that the G70 "can" do SSAA and HDR at the same time, but in the context of next gen games, it really "can't."

And I've been reading other posts about the Xenos's geometry tesselation unit ( GTU ). Does the RSX have one?

What exactly are the benefits of a GTU? Can the RSX manage displacement mapping aswell as the Xenos without a GTU?

 

[The GameMaster]

The only feature I can think of off the top of my head that I would like to see is the ability to do BOTH HDR and MSAA at the same time on the PS3. However if the RSX is as close to the G70 as I think it is, then I doubt it will be possible.

Yes, I know that the G70 "can" do SSAA and HDR at the same time, but in the context of next gen games, it really "can't."

And I've been reading other posts about the Xenos's geometry tesselation unit ( GTU ). Does the RSX have one?

What exactly are the benefits of a GTU? Can the RSX manage displacement mapping aswell as the Xenos without a GTU?

As far as my information goes XENOS is capable of HDR and MSAA at the same time and with little or no performance penalty. I know that the Geforce 7800 is also capable of MSAA and HDR, though it will do so at a performance penalty and will be a greater problem on the RSX due to the fact it has much less video memory bandwidth than the regular Geforce 7800 series GPUs... the only reason why XENOS can get away with this is because of the eDRAM and the extremely high internal bandwidth that it has.

As for your last question the Geforce 6800 and 7800 series GPUs (NV4x/NV5x) does not have a geometry tessellation unit and as the RSX in the PS3 is based on the NV5x series GPUs it also does not have a geometry tessellation unit (GTU). It can be useful in a number of areas such as displacement mapping or level of detail functions and can be done without impacting the rest of the graphics processor as this is seperate from the vertex pipelines (or in XENOS's case the unified pipelines). As stated in Dave's article this does mean that single cycle displacement mapping can be achieved and this is a very good thing. The fact the Geforce 6800/7800 series as well as the RSX does not have a geometry tessellation unit does not mean the RSX won't be capable of displacement mapping or higher order surfacing... it can be done through other methods, but the performance will be significantly less in doing these functions. Long story short... the fact XENOS contains a geometry tessellation unit will certainly help it's performance versus the RSX which does not have one.

Like I said though... just because the RSX does not have a GTU does not mean it can't do displacement mapping, geometry tessellation, or level of detail schemes... it just a lot slower doing those functions compared to XENOS.

 

[cho]

FP10 HDR - ?
FP10 AA - ?

 

[mckmas8808]

I know that the Geforce 7800 is also capable of MSAA and HDR, though it will do so at a performance penalty and will be a greater problem on the RSX due to the fact it has much less video memory bandwidth than the regular Geforce 7800 series GPUs... the only reason why XENOS can get away with this is because of the eDRAM and the extremely high internal bandwidth that it has.

Long story short... the fact XENOS contains a geometry tessellation unit will certainly help it's performance versus the RSX which does not have one.

So can you or anybody else explain to me why the Xenos is not better than the RSX?