Re: HARDWARE: Open-Source-Friendly Graphics Cards -- Viable?

[Timothy Miller]

Kendall Bennett wrote:

> Well that is what most of the early 3D cards started out as. A lot of the 
> early SGI boxes that has '3D' were not full 3D rendering engines but span 
> based rendering engines. Not only was setup done in software, but so was 
> the walking of the triangle sides and the only thing passed to the 
> hardware was commands to render spans (flat, smooth or textured). You 
> could build any kind of complex renderer on top of this and in those days 
> it was SGI GL (pre OpenGL) that was the rendering API. The systems were 
> also reasonably fast for the day too.
>
> I think the original 3DLabs GLINT SX chipset also did span rendering and 
> support textured spans. The biggest problem is that the overhead required 
> by the CPU to process anything close to the volume of triangles per 
> second that high end cards can handle today is overwhelming. Even a 4Ghz 
> P4 probably couldn't keep up trying to match the transform, lighting and 
> span traversal to match even a basic Radeon 9000 card IMHO. And then 
> you've got no CPU cycles left for anything else such as sound and game 
> physics ;-)


The bus (PCI, AGP, whatever) is a much more severe bottleneck than even 
the CPU.

If it takes two-dozen parameters to specify a triangle that ends up 
plotting only a single pixel on the screen, it's just not worth doing. 
But that is something that happens a lot onboard 3D chips.  That's why 
triangle rate is as important a factor as pixel rate.

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