How many triangles can draw 1 VMX unit in Xenon ?

[Rockster]

> "It can set up 1 triangle per clock cycle and it cycles 500 million times per second."

Edge, he is talking about the setup engine here, and not the shader core ALU's or the XeCPU.

 

[Shifty Geezer]

So that would either be roughly 6 billion transformed verts/second which could be as many as 12 billion tri's if you want to stretch the numbers.

But these are copmpletly meaningless numbers......

Shhhh! With info like this, soon....Oh no! Too late!

XB360 capable of 12 billion triangles per second!

 

[ShootMyMonkey]

XB360 capable of 12 billion triangles per second!

That's nothing. Xbox does 100 billion. All you have to do is make sure that you have no textures/colors/blending of any kind, and you drew the same single triangle over and over again -- what happened was the verts would remain in the post-transform cache and not be transformed again, and all the pixels would fail z-tests and what not after it was drawn once, so subsequent draws occupy no fillrate. End result -- 100 billion tris!

 

[pc999]

Ok, now i am confused.

So from here are coming those 500Mp/s , if they can do a lot more even if they split 50/50 in vertex/pixel shader power

BTW, for set up you mean create/ put a new vertex in the GPU

Edit

I got a reply here

http://www.beyond3d.com/forum/viewtopic.php?p=549983#549983

Thanks anyway

 

[ralexand]

Has sony quoted how many triangles a second the ps3 will produce.

 

[ERP]

Ok, now i am cunfused.

So from here are coming those 500Mp/s , if they can do a lot more even if they split 50/50 in vertex/pixel shader power

BTW, for set up you mean create/ put a new vertex in the GPU

You need to understand how a graphics pipeline works.

Gross Simplification
Transform verts ->Triangle Setup->Pixel Shading->Destination Blending

Generally Transform verts just converts inpout coordinates to homogenous camera space coordinates.

The Triangle setup projects these into 2D and computes the values for the interpolators (for things like rasterisation and texture lookup).

Pixel shading does work on the interpolated data

And the blender blednds thjose colors into the framebuffer


It doesn't matter how many verts you can transform IF you can only setup 500 million tris which is the case on Xenos.

In a real application I very much doubt you'll get 500 Million tris, but you'll probably get a lot closer to this number than you would see in a traditional PC architecture, where the transform rate is the limiting factor.

 

[Edge]

OK, so then how does ATI come up with 500 million per second? Entertain us with the math.

Nice to know the X360 is a torus generating monster.

 

[ralexand]

Ok, now i am cunfused.

So from here are coming those 500Mp/s , if they can do a lot more even if they split 50/50 in vertex/pixel shader power

BTW, for set up you mean create/ put a new vertex in the GPU

You need to understand how a graphics pipeline works.

Gross Simplification
Transform verts ->Triangle Setup->Pixel Shading->Destination Blending

Generally Transform verts just converts inpout coordinates to homogenous camera space coordinates.

The Triangle setup projects these into 2D and computes the values for the interpolators (for things like rasterisation and texture lookup).

Pixel shading does work on the interpolated data

And the blender blednds thjose colors into the framebuffer


It doesn't matter how many verts you can transform IF you can only setup 500 million tris which is the case on Xenos.

In a real application I very much doubt you'll get 500 Million tris, but you'll probably get a lot closer to this number than you would see in a traditional PC architecture, where the transform rate is the limiting factor.

Interesting, so what part of the Xenos is doing the transforming?

 

[pc999]

Thank you very, very much
.I has missing the set up part.
I think that now I already understand that .

 

[Rockster]

That was 100 million for XBox 1 not billion.

The math has already been done. The setup engine is can process 1 triangle per clock which equates to 500 million per second. The setup engine receives triangles from the ALU's doing the vertex shading. Unlike traditional architectures that have a set number of vertex shading units (ALU's), the Xenos can dedicate all ALU's to vertex shading. With a simple, and hence pretty meaningless vertex shader program, you could overrun the setup unit if you really wanted to. Where are you getting confused? The ALU's and setup engine are two different things (ie. seperate hardware). *** Deleted link. Potentially wrong and not a good example ***

 

[nAo]

OK, so then how does ATI come up with 500 million per second? Entertain us with the math.

No math there..it's very simple: Xenon's GPU CAN't setup more than one triangle per clock so you can't draw more than one triangle per clock, end of the story.

 

[Rockster]

The confusion is stemming from the fact that it can transform more than it can setup.

 

[Edge]

OK, let's keep it simple.

How many vertices can a SINGLE vertex SHADER transform every second @ 500 MHz?

My assumption it takes four cycles to calculate a vertice, but I assume the ALU's are pipelined, and can do 1 vertice per cycle, so would that not give us 500 million vertices per second per ALU?

If that's the case, would not the setup engine of 500 million polygons per second be the limiting factor? Sounds to me, you would need no more than 2 to 3 ALU's to reach your polygon limit.

edit: I see you say the setup engine is the limiting factor.

 

[pc999]

Ok I think I understud, while Xenus can calculate x triangles/cicle, it can only (in a very, very no programing language) "put 1 in the final image"(the setup) per cicle (500Mhz/s ---> 500Mp/s).

So that mean that the rest will be used in pixel shader, I wonder what they mean by no trivial shaders, or what they coud do with all those (about 11/12 of the full power (500.000/6.000.000), if I am correct).

Thanks, again.

 

[Megadrive1988]

It is said that Xenos will be manage up to 500 million polys with effects, but these polys must be created in the CPU. Could be enough only one of the VMX units to feed Xenos 500 million polys capacity ? If so, Xenon CPU will have allways at least two VMX units free for other tasks such as phisics ?
I am also thinking about the ability of a Xenon VMX to process near 3,2 billion dot products per second.If Xenos has a limit of 500 mill. polys wouldn´t it be also enough ,for example, 1 VMX for phisics or lightning ( i am supposing a dot product help in these tasks ) ?

I was thinking that 500 million triangles/sec is what Xenos/C1 (formerly R500) can process, render, display, on its own, with non-trivial shaders, and *without* any help from the CPU.

but then again, I don't know. maybe the 500M figure is what the entire Xenon / Xbox 360 can do.

 

[Megadrive1988]

But is not said that Xenos can´t create vertices ?

Xenos is a graphics processor (a GPU or VPU) which can calculate or process its own geometry/polygons (and lighting) as most consumer 3D chips have been able to do since NV10 (GeForce 256) in 1999.

polygon processors aka geometry processors (that can create their own polygons/vertices) was a very desired feature of 3D graphics chips during the mid to late 1990s. but it was reserved for high-end chips. only professional / industrial and arcade 3D chips had it, while consumer PC 3D chips from Rendition, 3Dfx, Nvidia, ATI, PowerVR and others did not have it until Nvidia NV10 in 1999. until the launch of NV10 GeForce 256, consumer-gaming 3D graphics *accelerators* depended on the host CPU to feed it polygons / triangles / vertices and lighting calculations.

thus, the CPU had to create vertices / polygons / geometry and lighting.

around 1999, this feature (polygon or geometry processing) was sort of renamed 'T&L' (transform & lighting) and it first came to consumer/gaming PC graphics chips in the 2nd half of 1999 with the GeForce 256 (and to a lesser extent, the Savage 2000 iirc)

Now, finally ( late 1999, NV10 forward --->) consumer-gaming 3D chips where called GPUs, because they had a geometry processor / polygon processor on-chip, and could therefore create (process or calculate) their own vertices / polygons and lighting.


what I think you are think of is this: it was said (unless I am mistaken) that Xenos cannot *destroy* vertices, as that is a feature of WGF2.0 that Xenos does not have. this is a feature that I don't have any understanding on whatsoever.

 

[Rockster]

You guys are forgetting that vertex programs are much more complex than simply transforming vertices from world space to camera space. A number of lights are typically applied, positions altered for skinning, extrusion, and effects that vary the geometry and lighting in different ways. Non-trivial means "not simple".

 

[Megadrive1988]

ok if the setup engine is the limiting factor here, then Xbox 360 should have no problems pushing 500 million polygons per second, all of the time, no matter what (pretty much) even with complex pixel shaders and effects running. and, Xbox 360 should be able to push 500 million polygons/sec second EASIER than Xbox1 is able to push 100 million polygons /sec.

am I right?

 

[Rockster]

I don't know if I would say "no matter what", because triangle size, shader lengths, bandwidth, etc. ,etc. matter, but easier than XBox 1 at 100 million is fair to say.

 

[Megadrive1988]

I don't know if I would say "no matter what", because triangle size, shader lengths, bandwidth, etc. ,etc. matter, but easier than XBox 1 at 100 million is fair to say.

okay then, agreed 8)