Carmack on NV30 vs R300

Nexxpert writes "John Carmack has posted his thoughts on the NV30 vs R300 (featured via www.bluesnews.com. Highlights some of the shortcomings of Nvidia's next step as well as pointing out what they've done right. Interesting read." In particular the arb2 vs nv30 path differences mean that it's not as simple as saying "ATI roX0rs nVidia" or vice versa.(update: sorry bout the misspelling, don't know how I missed that)

Comments

I worry about NVIDIA

[szquirrel]

NVIDIA got where they are today by beating 3dfx on their own turf: high-end gaming performance. Remember when 3dfx released the Voodoo 4 & 5? More expensive than the GeForce256 but not decisively better performance. Now I'm hearing similar things about the GeForceFX vs. ATI's three month old Radeons. NVIDIA is getting bigger but they still aren't a huge company. Can they really afford to lose the lucrative high-end sales right now?

One thing NVIDIA does seem to have going well is their motherboard chipsets. The new nForce2 really kicks ass by all accounts. I remember a while back hearing about an ATI mobo chipset based on tech they acquired from ArtX, but apparently end-user mobo chipsets aren't ATI's plan.

Good luck, NVIDIA. Hope y'all can keep up the pace.

Re:I like my cards quiet

[Elledan]

"The fan only runs at full RPM when the card is doing a lot of 3d work. 2D stuff causes the fan to run a lot slower (not sure if it ever turns off completely tho)..."

From the [H]ard|OCP review:

"Using a decibel meter we tested the sound level of the GFFX at three feet away, directly in front of the exhaust vent. In 2D mode, the reading was 56dB."

I don't know about you, but I find 56 dB to be very noisy.

Re:R300 path

[jpaana]

ATI doesn't have any proprietary extensions for exposing the R300 shader functionality, only "ARB2" (ARB_vertex_program and ARB_fragment_program) so there's no way to do "specific" R300 path.

The leaked alpha does support ATI's two-sided stencil extension (ATI_separate_stencil) which is only implemented on R300.

Re:Um - can anyone explain this?

[cthulhubob]

OK, I did some 3D imaging math about 10 years ago (when you had to code your own drivers to get SuperVGA mode under DOS), so I think I get what he's talking about: the problem of how to show the reflection of one object (or light source) off another object. I've never heard of "interpolated half-angle" or "specular highlights", or the "triangulation line". Anyone know what he is talking about?

You didn't get much beyond Gouraud shading, did you? :)

Of course, depending on your hardware ten years ago, specularity might not have been feaasible if you were doing something big and real-time. Certainly not with the standard PC of that era.

• Specular highlights: the white (or colored, if a non-white light) spot you see reflected on a non-matte surface from an incoming light. If you've got a standard office-black telephone at your desk like I do right now, looking at the corner edge of the handset you should see a bit of yellowish or bluish white which is a reflection from the overhead lights. If you move your head (change the viewing angle) you can see it shift over the surface of the phone. This is a specular highlight. The strength of the highlight depends on the "Shininess" of the surface - the less shiny, the more diffuse, until you reach sheet-of-paper-matte, which has little to no visible highlight - only shading.
• Triangulation line: Unfortunately, the state of 3d graphics not being ideal when compared to the telephone handset on your desk, the surface of that phone will be composed of triangles rather than molded plastic. Under the traditional Gouraud shading plus specular highlight model, to conserve computing resources the angle of the incoming light is only calculated at each vertex of each triangle on the surface of each object, and then the angle between it and the reflection toward the viewer is interpolated linearly along the edges of the polygon. Thus, when triangles get too large, instead of a nice highlight resembling the shape of the light source (usually spherical in computer graphics, regardless of the actual object the light is supposedly emanating from), you see a highlight along the lines making up the triangle, that quickly fades toward the outside edges. Very big ugly obvious rendering mistake.
• Interpolated half-angle: you can probably figure out what this is based on my explanation of "triangulation line", but just in case -- this is the interpolated angle (actually interpolated cosine of two angles, which is why it's referred to here as a half-angle) used to figure out the strength of the highlight at any given fragment (new word for pixel) of the triangle being rendered.

Hope that helps!

Re:Once again...

[John Carmack]

>But he mentioned something about next gen cards having less bandwidth. Does that make sense to anyone?

The RATIO of bandwidth to calculation speed is going to decrease. It is nothing short of miraculous that ram bandwidth has made the progress is has, but adding gates is cheaper than adding more pins or increasing the clock on external lines.

Bandwidth will continue to increase, but calculation will likely get faster at an even better pace. If all calculations were still done in 8 bit, we would clearly be there with this generation, but bumping to 24/32 bit calculations while keeping the textures and framebuffer at 8 bit put the pressure on the calculations.

John Carmack