[Open-graphics] The 3D feature set

[Hugh Fisher]

Just sat down and wrote up what I want from the open
source graphics card.

Who am I? Sysadmin and researcher/lecturer in 3D graphics
as part of a Comp Sci university department. I've been
involved in various forms of scientific visualisation,
VR research, and teaching computer graphics for a number
of years.

Coincidentally, this afternoon I had a discussion with
the guy in charge of buying the couple of hundred Linux
PCs we use around the place. The spec for next years PC
purchases didn't include a 3D card, or even one of the
Intel 3D chipsets. He said that this wasn't because of
pricing, but that there were too many stability issues
with the current closed source drivers.

Over the past four or five years a huge gap has grown
between what the hard core 3D gaming market wants, and
what everybody else who does 3D wants. I don't believe
that the lack of an open source graphics card, in itself,
is why there are so few games for Linux. I suggest that
it is therefore not worthwhile, at least in the first
iteration, trying to build a DirectX 9 equivalent card.

A card aimed at the education/scientific 3D market can
leave out a lot of stuff:

Hardware transform and lighting. The CPU is fine.

Multitexturing or texture combiners. The majority of 3D
software does Gouraud shading with one texture layer.

Vertex or pixel shaders. Nobody outside the hard core
game industry has the time to become an expert on Phong
fragment shaders with multipass bump maps and cubic
environment maps.


So what do we want?

Alpha blending.

Bilinear texture filtering. Trilinear is nice, but we
can live without it.

32 bit frame buffers and depth buffers.


This is roughly what an SGI O2 does, or a 3DFX Voodoo
Banshee. Triangle rasterisation with one texture unit.

Please note that doing transform and lighting on the CPU
does not significantly increase the bandwidth. Triangle
geometry data (coords, normals, tex coords) is usually
the same size before and after the T & L stage, plus
texture bandwidth swamps the geometry anyway.

A card that did everything would be nice, but KISS.


	Hugh Fisher
	DCS, ANU