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991060
07-04-04, 12:46 PM
http://graphics.csail.mit.edu/~ericchan/papers/smapSV/

the algorithm is kinda straightforward, maybe there will be a new demo from nvidia's developer site about this method, I hope so.

euan
07-04-04, 01:13 PM
http://graphics.csail.mit.edu/~ericchan/papers/smapSV/

the algorithm is kinda straightforward, maybe there will be a new demo from nvidia's developer site about this method, I hope so.


NV40 exclusive? The article is very much generic, and talks about how the techinique is possible on a wide range of hardware from NV4x to R3x0, R4x0

Just to spoil the party:

We have found that ATI's early culling mechanisms on the Radeon 9800 Pro are somewhat more effective than NVIDIA's, meaning that the relative performance gains for rejected pixels is higher in the ATI scenario. We have not performed detailed measurements, however. The purpose of this discussion is not to identify which vendors offer superior early culling performance. Instead, we simply want to point out that culling mechanisms can vary across different architectures; as these mechanisms improve in the future, so will the performance of our hybrid algorithm.

Also note that they say that currently ATI doesn't support the Opengl extension (EXT_DEPTH_BOUND_TEST), that they used for testing. But that it isn't a fixed requirement, and isn't a hardware restriction on the ATI cards. Never-the-less, Maybe some time this centurary ATI will fix there OpenGL drivers . :rolleyes:

Looks like a scene demo I watched a while back...:)

fivefeet8
07-04-04, 01:22 PM
from the article:
unfortunately ATI hardware does not support the EXT_depth_bounds_test extension.

So does ATi support it in hardware, or it just needs to support in Drivers?

991060
07-04-04, 01:22 PM
The algorithm needs EXT_DEPTH_BOUND_TEST to avoid rasterizing shadow volume geometry, this is where the saving comes. Of course, if other cards begine to support that extension or DirectX next can supply a "computation mask", the "NV40 exclusive" description can be deteled.
AFAIK, ATi's culling only happens after rasterization which means even if it's more effective, the saving could be relatively small, since rendering shadow volume itself is quite fast.

Humus
07-04-04, 01:22 PM
That's a pretty clever trick. :)
Still hard shadows though.

991060
07-04-04, 01:24 PM
That's a pretty clever trick. :)
Still hard shadows though.
Can you make a demo with it? It should be very interesting. Well, buy youself a NV40 first. :rolleyes:

Lezmaka
07-04-04, 01:45 PM
...

I guess you didn't read the 2nd half of the quote.

The purpose of this discussion is not to identify which vendors offer superior early culling performance. Instead, we simply want to point out that culling mechanisms can vary across different architectures; as these mechanisms improve in the future, so will the performance of our hybrid algorithm.

Humus
07-04-04, 07:12 PM
Can you make a demo with it? It should be very interesting. Well, buy youself a NV40 first. :rolleyes:

I could probably do it. I don't see where the NV40 part comes into the picture. This seems to work on all hardware that does early stencil rejection (interesting that another such technique popped up, entirely unrelated though).

But anyway, it takes a bit of work, and I'm not sure I'm that interested in this technique to do it. It's still hard shadows, but just faster. I'm more interested in soft shadows.