Beatnik

http://techreport.com/articles.x/15261/1

Crazy stuff. Now I'll be able to play GRAW again! haha

Still, this is a very very cool bonus for us Nvidia owners.

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jepzilla

Interestingly, NVidia has been quietly helping AMD port PhysX to ATI cards too. Personally I'm surprised it has taken as long as it has. One downside is that the PhysX kernels will be timesliced with normal rendering tasks, so physx could potentially cost you framerate (depending on where your system's bottleneck is).

I think NVidia may have made a mistake in their architecture... they're using a HAL to run PhysX on whatever hardware is available (either the original Ageia accelerator, or spare CPU cores, or a GPU). A major cost in this is it requires shuttling data back and forth across the PCI Express bus which in practical terms runs between 1-1.5GB/s, as opposed to the 60-120GB/s internal bandwidth of the GPU.

PhysX is primarily used to drive advanced geometry for the graphics engine - I don't know of any game that substantially incorporates PhysX into the actual gameplay physics - so dumping that data off the card is really pointless. A lot of that data could be piped directly into vertex buffers. And with DirectX 10 it becomes even more bizarre, since DX10 is offloads geometry onto the GPU too. So you dump the PhysX geometry off the card over the slow bus, then back ONTO the card for geometry processing and rendering... Hopefully they'll release an update to the PhysX API which removes this bottleneck. But if that's the case, why bother with the expense of implementing a HAL?

Bizarre. But hey, what do I know...

Snail

my head just exploded reading that post

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jaymind

But you can't affect any of the primitives directly on the GPU any way so you would ultimately have to dump of the physics results back to the CPU regardless for primitive setup, etc...

Maybe there is some sort of obscure way to use it in certain circumstances via a geometry shader, but I can't imagine that would be nice performance.

With CUDA (which is what the GPU physics is encoded in) you can store what you would like in the vertex buffers (i.e. cache) but I don't I'm pretty sure you can not be running in CUDA and graphics mode at the same time, not to mention that if you tried to store physics and graphics in the vertex buffer I think you would have some serious issues.

Or, I could be talking out of my ass. However, if you get into it Beyond3D with a few of the developers there and a few of the driver writers there, they can probably get into it much better.

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jepzilla

But my point is game engines don't really need to touch the geometry generated by the physics engine directly, since AFAIK PhysX isn't being used for accelerating game physics. The geometry generated by PhysX is just used to provide more eyecandy (prettier explosions and environmental effects and stuff).

As for running CUDA and DirectX/OpenGL at the same time, it depends what you mean. Current hardware is non-concurrent, even kernels you dispatch in independent streams are serialized. However you can use CUDA while you have a graphics context constructed- you alternate between drawing frames and doing physics updates. Vertex buffers and textures can be mapped onto GPU memory allocated with CUDA.

Certainly there may be some data from the physics engine that needs to be copied back to the CPU. If you're going to let PhysX manage the 'light' stuff too (stuff that impacts gameplay, like object collisions) then all that will need to be copied back to the CPU every frame. But the 'heavy' stuff, like the big particle systems, cloth models, etc... are basically just eyecandy. That's data that could be dumped directly into the renderer's geometry shaders, bypassing the CPU. But with their current architecture you have to funnel all that back and forth across the bus, unnecessarily.

I could be misunderstanding PhysX though

Personal opinion, not opinion of employer, etc...

BHack

This is good news. Color me excited for the future of more physicalized game worlds! I imagine everyone who bought one of those Aegia cards is sitting around going... "Welp".

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icky

All we need now is a dedicated AI processor or two (or 20), and my dreams will have come true.

We're scratching the surface of physics right now in a similar way to how Wolf3D was scratching the surface of 3D first-person gaming. There's really good stuff still to come in gaming.

jepzilla

NVIDIA have released GPU PhysX demo apps/games. Download page.

Darksteel525

Thanks for the link. That's a pretty big download.

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-F- Darksteel

Conscript

Tell me if its worth dling all those demos and stuff.

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