Daryll Strauss wrote:
>
> > This is one area where a binary-only driver lets us down. If 3dfx is
> > anything like the g200 hardware, then the function of grDrawTriangle is
> > to compute the area of the triangle and hence the slopes of everything
> > that must be interpolated across the triangle. It feeds this down to
> > the hardware, either all three vertices at once, or perhaps like the
> > g200, breaking the triangle up into 2 degenerate quadrilaterals.
> >
> > In any case, grDrawTriangle almost certainly computes the area, and we
> > must also compute the area to do glPolygonOffset. This plus living with
> > the inconvenience and unknown mechanism of grDepthBias are the
> > compromises ncessary for slope-dependent triangle offset using glide.
>
> That was true for the Voodoo1 where triangle setup was done on the
> CPU. That's not true for V2 or later. It can be all calculated on the
> hardware, although you can turn on modes where it isn't done that
> way.
I was a little suprised to see that the g200 worked that way - it seems
incredibly low level, and somewhat at odds with the splash-blurb in the
adds, which talks about support for strips & fans. But in any case, we
are still left doing the area calculation per triangle ourselves.
> > I would rate these as regrettable annoyances for the implementor (hi!)
> > but otherwise nothing to get in a tizz about.
>
> If you think there are functions missing that would make your life
> easier bring them up. There's nothing preventing modifications to Glide
> for appropriate reasons. In fact, Glide3 makes extensions easier. So
> we could probably get 3dfx to create a "Mesa" extension. We can send
> specifications to their developer program and let 3dfx evaluate them.
Sounds like a pretty slow process... I imagine whatever issues we will
have with glide3 they are also having trying to build their own OpenGL
on top of it, but a quick glance at the docs doesn't show anything that
improves on grDepthBias. I don't pin too much hope for a near term
solution to this from 3dfx, given that we are still working with glide2.
Keith
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