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NVIDIA's Pixel & Vertex Shading Language
Barkhausen Criterion writes "NVIDIA have announced a high-level Pixel and Vertex Shading language developed in conjunction with Microsoft. According to this initial look, the "Cg Compiler" compiles high level Pixel and Vertex Shader language into low-level DirectX and OpenGL code. While the press releases are going amok, CG Channel (Computer Graphics Channel) has the most comprehensive look at the technology. The article writes, "Putting on my speculative hat, the motivation is to drive hardware sales by increasing the prevalence of Pixel and Vertex Shader-enabled applications and gaming titles. This would be accomplished by creating a forward-compatible tool for developers to fully utilize the advanced features of current GPUs, and future GPUs/VPUs." "
What are you talking about?? Nvidia makes great linux drivers - and from looking through the pages it looks to me like Cg just outputs regular OpenGL (Well - Nvidia-OpenGL anyway) so I would venture a guess that any of these will run just fine on the nvidia linux drivers.
:-(
My only problem is that the toolkit itself is only for windows
Anyone try it with Wine/Winex yet?? I might when I get home.
Derek
According to the web site, they are working to implement this on top of both OpenGL and DirectX. On linux and Mac as well.
Basically this is a wrapper for the assembly that you would have to write if you were going to write a shader program. It compiles a C-like (as in look a like ) language into either the DirectX shader program or the OpenGL shader program. So you'll need a compiler for each and every API that you want to support. Which means that you'll need a different compiler for OpenGL/Nvidia and OpenGL/ATI until they standardize it.
On a more technical note, the lack of branching in vertex/pixel shaders really needs to be fixed, it's really the only feature that they need to add to them. Which is why the Cg code looks so strange, it's C, but there's no loops.
It seems to me that this is probably an attempt to kill OpenGL 2.0, and secure Direct X as the dominant 3D API. OpenGL 2.0 has as far as I can tell been well thought out, and most of the feedback to it has been very positive. The frontend to its shader language is Free Software, and the work done seems to have been done with the best of intentions. I am very cynical about an offering from NVIDIA, especially when you consider their behavoir towards the rest of the 3D card market, and the fact that Microsoft are involved.
From Nvidia's Homepage you can check out the press releases and find this:
"NVIDIA's Cg Compiler is also cross platform, supporting programs written for Windows®, OS X, Linux, Mac and Xbox®."
So maybe even though the tools aren't cross platform - the compiler is. I think this is a Great step forward towards OpenGL 2.0 - this is showing that Windows doesn't have to be the only platform to write graphically intensive applications for.
Derek
Well, they're quoted in this article on ZDNet (the quote is near the bottom) as saying that they're going to release the language base so other chip makers can write their own compilers for their products.
That was the first thing that popped into my head when I read this article, but it sounds like they're going to give open access to the standards, just not to the interface with their chips.
Dark Nexus
"Sanity is calming, but madness is more interesting."
Seems like a decent number of people have absolutely no clue what Cg is all about, so I'll see if I can clear up some of the confusion:
Modern NVidia(and ATI) GPU's can execute decently complex instruction sets on the polygons they're set to render, as well as the actual pixels rendered either direct to screen or on the texture placed on a particular poly. The idea is to run your code as close to the actual rendering as possible -- you've got massive logic being deployed to quickly convert your datasets into some lit scene from a given perspective; might as well run a few custom instructions while we're in there.
There's a shit-ton of flexibility lost -- you can't throw a P4 into the middle of a rendering pipeline -- but in return, you get to stream the massive amounts of data that the GPU has computed in hardware through your own custom-designed "software" filter, all within the video card.
For practical applications, some of the best work I've seen with realtime hair uses vertex shaders to smoothly deform straight lines into flowing, flexible segments. From pixel shaders, we're starting to see volume rendering of actual MRI data that used to take quite some time to calculate instead happening *in realtime*.
It's a bit creepy to see a person's head, hit C, and immediately a clip plane slices the top of guy's scalp off and you're lookin' at a brain.
Now, these shaders are powerful, but by nature of where they're deployed, they're quite limited. You've got maybe a couple dozen assembly instructions that implement "useful" features -- dot products, reciprocal square roots, adds, multiplies, all in the register domain. It's not a general purpose instruction set, and you can't use it all you like: There's a fixed limit as to how many instructions you may use within a given shader, and though it varies between the two types, you've only got space for a couple dozen.
If you know anything about compilers, you know that they're not particularly well known for packing the most power per instruction. Though there's been some support for a while for dynamically adjusting shaders according to required features, they've been more assembly-packing toolkits than true compilers.
Cg appears different. If you didn't notice, Cg bears more than a passing resemblance to Renderman, the industry standard language for expressing how a material should react to being hit with a light source. (I'm oversimplifying horrifically, but heh.) Renderman surfaces are historically done in software *very, very* slowly -- this is a language optimized for the transformation of useful mathematical algorithms into something you can texture your polys with...speed isn't the concern, quality above all else is.
Last year, NVidia demonstrated rendering the Final Fantasy movie, in realtime, on their highest end card at the time. They hadn't just taken the scene data, reduced the density by an order of magnitude, and spit the polys on screen. They actually managed to compile a number of the Renderman shaders into the assembly language their cards could understand, and ran them for the realtime render.
To be honest, it was a bit underwhelming -- they really overhyped it; it did not look like the movie by any stretch of the imagination. But clearly they learned alot, and Cg is the fruits of that project. Whereas a hell of alot more has been written in Renderman than in strange shader assembly languages (yes, I've been trying to learn these lately, for *really* strange reasons), Cg could have a pretty interesting impact in what we see out of games.
A couple people have talked about Cg on non-nVidia cards. Don't worry. DirectX shaders are a standard; game authors don't need to worry about what card they're using, they simply declare the shader version they're operating against and the card can implement the rest using the open spec. So something compiled to shader language from Cg will work on all compliant cards.
Hopefully this helps?
Yours Truly,
Dan Kaminsky
DoxPara Research
http://www.doxpara.com