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Mercenarey

OpenGL Shader API - which should I choose? HLSL, Cg or GLSL?

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As I understand it from reading some, HLSL is DX-specific, GLSL is OpenGL, while NVidia's Cg is above both HLSL and GLSL, making use of them both, making Cg kindof technology independent - and platformindependent too since it can use GLSL. Cg looks very tempting, since it bridges the gap between DX and OpenGL - on the other hand, is it here to stay? I kindof fear that it could go down the road of 3DFX, that suddenly goes out of business, and all programs using 3DFX's API are suddenly no longer possible to use in the future. And then again, Cg is said to be as good as identical with HLSL, so maybe there is no need for the concern? What are your thoughts on this matter? [Edited by - Mercenarey on July 19, 2005 8:44:19 PM]

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Original post by Mercenarey
...and platformindependent too since it can use GLSL.


But does it? I know it can target NV's assembler interface and the ARB assembler interface, have they added support for GLSL targets as well?
heh, if they have then a game on an NV driver could end up going Cg=>GLSL=>Cg [grin]

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IIRC, Sony announced at GDC 05 they're using Cg for PS3... (duh, they're using an nvidia chip...) So PS3 success portends Cg's (i.e. I wouldn't worry :)

But as Mr Teh_Phantom suggests, whenever you go 1-layer-up, you rely more on someone supporting the ground under your feet...

(My opinion: Cg, one good language among several, here to stay).

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Personally, I'd say go with GLSL - as when ATi bring out a SM3 based card, they're not going to update the asm interfaces. Therefore, with Cg, you won't be able to get anything more than SM2 on non-vidia cards.

EDIT: or HLSL for that matter, I thought I was in the OpenGL forum for a minute there.

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Thanx for the answers. I think I will go with Ajas95.

If Cg is here to stay (and it certainly sounds like it will, if Sony is gonna use it), it is alot better than using GLSL or HLSL. I want to make it easy to port my program to other platforms, so I don't want to tie myself to HLSL. And I can't tie myself to GLSL atm, since my graphics layer uses DX at the moment :)

If Cg is an umbrella over all the shader technologies, I think that is the right way to go. Especially if it is here to stay.

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Original post by LarsMiddendorf
NVidia could create a GLSL backend for ATI SM3.0 cards.


Why exactly would they do that? GLSL isn't tied to one vendor or the other, it's a part of OpenGL. It's up to ATI to build a working GLSL implementation for a SM 3.0 card. At that point, if you "compile" a CG program to GLSL it should work on any card.

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I recommend you use:
GLSL -> if you are programming in OpenGL
HLSL -> if you are programming in DirectX
CG -> if you are poor and cant buy a book because the docomentation is great.

I would not worry too much about this, from personal experience, learning the concepts is more important than the language itself. Once you learnt the concepts, changing from one language to another is extreamly easy and intuitive.

Good luck.

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i agree with blackbox, do not worry about the language so much, all of them same in lots of ways. some syntax differences at all.
after learnt the shaders' concept, it is not a big deal to change the language.
but personally, i do not recommend CG because of portability. (but yes, its documentetion is quite well)

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I alwyas thought CG = HLSL? they just change the name for directx? I can't remember where I heard that so im probably mistaken

-THACO

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Quote:
Original post by Mercenarey
why isn't it portable?
the easiest answer is: because belonts to nvidia.

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Quote:
Original post by stroma
Quote:
Original post by Mercenarey
why isn't it portable?
the easiest answer is: because belonts to nvidia.


It is perfectly portable across API's, OS's, and graphics cards. As I said earlier though, portability across the SM3 range of cards will probably suffer in the future as the asm interfaces won't be updated. Just because it's created and managed by nVidia is totally irrelevant.

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Cg is more like HLSL for OpenGL...nVidia actually recommend HLSL over Cg for DX apps. For OpenGL apps its upto you, GLSL is just a new face to Cg on NV drivers.

But, i use Cg :D ... its more consistant atm, but i will change to GLSL/HLSL later, GLSL is just too inconsistant between graphics cards atm, probably in its major release (like 1.2 or something) i will convert back.

-Twixn-

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There are a few differences between Cg and HLSL...but its only a few of the library functions.

-Twixn-

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