> My point exactly. Like I said about the Voodoo, it's all in the
> fillrate. It does not have good polygon performance becaus […]
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> My point exactly. Like I said about the Voodoo, it's all in the
> fillrate. It does not have good polygon performance because it
> doesn't do the transforms to be considered to have any inherent
> polygon throughput.
Mike, you're completely wrong here. NO consumer 3D graphics chip does
transformations today. NONE. You have three basic classes of consumer
3D chips when it comes to throughput -- those that require the CPU to do
edge scanning, those that require the CPU to do setup, and those that
only require the CPU to send parameters.
In first category is exceedingly rare these days, and on its way out.
The second category encompasses most current 3D chips. The last
category covers only a handful of existing 3D chips, but most new 3D
chips will have full triangle setup on board.
Now, the Verite DOES support triangle setup on-chip, but its setup
engine is SLOWER than a Pentium doing the same work. This is a fact.
The setup engine attempts to gain back this performance in parallelism,
something it typically does a pretty good job with, but for pure peak
throughput it doesn't match even a Pentium/90 for setup performance.
The Voodoo supports some triangle setup, but not full parameter
computation. This was done for a reason -- the designers of the Voodoo
wanted system performance to scale as processor speeds got faster, not
stall at some artifically low number. They did a very good job of this,
I might add.
> And in games with high polygon counts, even decent CPUs (P166) can't
> keep up with a simple, inexpensive bus mastering, programmable 3d
> card.
This pure techno-babble nonsense.
? The voodoo chokes while the $150 verite flies along. And the
> verite is doing more work (I don't know what the nature of its poly
> transforms are, how much the CPU assists, but whatever it's doing
> works very well).
You are woefully misinformed. The Verite performs NO true geometry
calculations on board. It does triangle setup on board, but that's it
-- lighting, transformations, and clipping are done on the host CPU, not
on the Verite. Ask the folks at Rendition, they'll confirm this.
I'd also like to see comprehensive data (not outliers) that shows me a
case where the Verite flies and the Voodoo chokes. The only example I'm
aware of this are in very busy scenes in Descent 2 where a poor software
implementation on Voodoo significantly slows overall performance down --
this is not the hardware's fault, it was a particular implementation
performance bug that could be fixed in less than a few days. Note that
when this particular bug isn't manifested that Voodoo shows performance
radically higher than Verite.
And also note that this has NOTHING to do with polygon throughput. The
Voodoo suffers performance degradation as a result of texture download
speed, NOT because of higher polygon counts. 3Dfx has demonstrated 500K
triangles/second on a P90 and 1M+ triangles/second on a P5/166 -- I
don't believe Rendition has ever gotten NEAR these numbers.
The Verite has SUBSTANTIALLY slower triangle throughput than the
Voodoo. I own and use both on a daily basis and have Direct3D programs
(that I've written) that use both, and the Verite isn't even CLOSE to
the Voodoo in throughput -- we're talking about half the speed, on a
good day, and it gets worse as CPUs get faster.
> thread, which started when a certain person objected to my saying that
> the Voodoo's performance was all in its fillrate, and proves nothing
> about the benefits of DMA. He had seemed to claimed that the Voodoo
> being such a fast rasterizer was proof that DMA was useless, or
> something.
Reread my original post Mike, I said nothing of the sort. I said that
the Voodoo was evidence that PIO was NOT a performnace killer -- I did
NOT say that DMA itself was "useless". It's a lot easier to win
arguments when you can put words in other people's mouths....
The Voodoo has good performance for several reasons. For starters, yes,
it has mondo fill rate. Second, it can sink data at a huge rate and
will NOT stall the PCI bus except in extreme circumstances. Third, it
has well written drivers and a fast proprietary API (Glide). Finally,
it's a simple chip to program -- you don't need to know about DMA
buffers, TLBs, locking down memory, polling for DMA buffer contention,
etc. This is stuff that application developers don't really want to see
or know about. Because the Voodoo is such a straightforward
accelerator, it's difficult to make it go slow. Developers appreciate
this.
There were lots of folks claiming that DMA was the no-brainer for higher
polygon throughput, and I have offered both theoretical (sample code)
and real (benchmark) data that contradicts this.
Contrary to your beliefs, the Voodoo, with its PIO and lack of DMA,
still possesses the fastest polygon throughput rates* AND fill rates of
any commercially available consumer 3D graphics accelerator. This
doesn't mean that DMA doesn't have its place (it does -- texture
downloads), but it DOES mean that PIO is not necessarily inferior to DMA
for command traffic and, more to the point, a PIO based graphics adapter
has demonstrated that it can achieve POLYGON THROUGHPUT performance well
beyond that of ANY of the DMA based solutions available today.
Brian