Xbox GPU and PC-side

yep, NV2A has 2 TMUs per pipeline, thus 8 TMUs in total.

like

NV15/NV16 (GF2 GTS, GF2 Ultra)
NV20 (GF3, GF3 ti200, GF3 ti500)
NV25 (GF4 ti4200, GF4 ti4400, GF4 ti4600)


are all 4x2 configurations

 

And NV30/35

 

Yeah, but I was less certain of what NV30/NV35's configurations are, heh.

With ATI, it's alot more straight forward

 

Apart from texture-lights and blending between two adjacent maps, what else is two TMUs per pipe really good for?

And also 8 TMUs x 233Mhz = 1864 Mtexels, then how come people keep citing the PS2 as having more fillrate than xbox (PS2 = 1200 Mtexels)?
Is it because real games rarely use the two TMUs per pipe?

 

Ps2 has 16 pixel pipelines running at 150mhz.

150 * 16 = 2400M

 

But not for texturing, Only gouraud shading.
When texturing it only uses eight pixel pipelines.
All right, lambert and gouraud shading has many applications such as light/shadow volumes, geometry for reflection-maps, highest mip-level, small details and so on. But when we are talking about textured polygons (which the majority in a scene are) PS2 doesn’t seem better equipped than xbox?

 

probably not, but I suppose the raw filrate can be used to an advantage if a good LOD model is applied (i.e. Jak & Daxter).

 

more textures, more texels, more single cycle (per clock) effects without losing performance. other than that, I really cannot answer.

XBox has a higher texel rate than PS2, but PS2 has a higher pixel fillrate when not using textures because PS2's graphics chip, the GS, has 16 pixel pipelines. 16 pipes x 150 Mhz = 2400 Mpixels (or 2.4 Gpixels) but that gets cut in half when using textured pixels. XBox has only 4 pixel pipes but 8 TMUs. so at 233 Mhz, thats 932 Mpixels/sec and 1864 Mtexels/sec. so when doing textured pixels the XBox has higher texel fillrate (1864M) than PS2's texel fillrate (1200M)

 

Thank you for clarifying that once again.

What I really meant was, exactly what kind of effects and texture methods benefit from double TMUs? I know bumpmapping doesn’t and detail texturing either, how about DOT3, and does trilinear benefit?

As I already wrote, apart from lightmaps, double texturing at the same resolution on both maps would seem to me, only to be good for breaking repetition in tiled textures, although in a bit expensive way (memorywise)?

 

I for one feel that the gpu in the xbox really limits what can be done with the system. Where as the next system with a more advanced pixel shader and vertex shader will show more of a trend that we see with the ps2. The games will continue to get better looking as the life wears on and more and more can be tweaked .

Of course for the time period the xbox is a very nice piece of kit but then again so is the ps2 , gamecube , dreamcast , virtual boy .

 

Assuming you were planning on using the virtual boy to permanently damage someone's vision it was a nice piece of hardware anyway.

 

XB only has higher texel rate in theory. PS2s eDRAM framebuffer gives it a tremendous advantage vs. XB in raw fillrate circumstances despite a few hunded texels/s lower theoretical fillrate.

*G*

 

This makes no sense. The GPU IS what Xbox can do graphically.

Besides, if anything in Xbox is lacking it's the memory. 128 would have been better.

 

Is it yeay that Ps2 texel fillrate cuts in half with every additional layer of textures, while Xbox can do 4 at a go

 

XBox's fillrate gets cut too, if more than 2 texture are used per cycle, per pipe. it's just that XBox GPU has loopback and does not have to re-setup geometry unlike PS2.

 

yup.

I though only the triangle list had to be resubmitted, or is htis just in certain circumstances?

 

I don't thing MS where lying, it's was just a case of seeing how fast they could run a 65 million transistor chip in the case, it obviously was running to hot and thus scaled back. It may of been running at 300Mhz when they said it but it just didn't cut it.

I dream of a day when MS suddenly say, "Ummm, there's actually 128MB of ram in the machine, we will unlock it for the devleoper now, good bye!"

... IT'S MY DREAM DON'T LAUGH AT IT!!!

 

No. The fillrate only get cut in half for the first two texture layers on the PS2. The Xbox can use 4 textures in one go, but the fillrate is cut in half if you use more than 2 textures.

Pixelfillrate:

Code:

textures Xbox  PS2
0        933  2400
1        933  1200
2        933   600
3        466   400
4        466   300

Remember that the untextured fillrate is also useful for z/stencil passes.

If, on the PS2, you go from 2 to 3 texture layers the fillrate goes down by 33%. On the Xbox the fillrate cuts in half going from 2 to 3 textures.

The Xbox has, in theory, a huge advantage when it comes to AA fillrate, but the PS2 has a huge advantage when it comes to framebuffer bandwidth.

The PS2 has an disadvantage in that it has to redraw polygons to add more texture layers, but unlike the Xbox the PS2 doesn't have to recalculate the vertices to redraw them, you can program the VU to resend the same data several times.

 

Yeah I've heard of a lot of developers using that techniq to get added texture passes.

 

What sort of texturing is loopback really good for? I’ve never been able to find any unbiased texts on that.
I seem to remember that again both popular multitexture techniques like detail texturing and bumpmapping require resending geometry to the XGPU.