View Full Version : A few questions about OpenGL, please...
12-07-2008, 01:41 PM
I have a few questions about OpenGL.
I remember games using OpenGL and the game would go faster than using Direct3D.
1... What advantages does OpenGL have over Direct3D, besides speed :).
2... Is it possible to use Bloom effects with OpenGL.
3... Does Bloom effects use computer resources.
4... Is the OpenGL API more powerful than Direct3D.
Sorry for asking these questions but I need to know.
Thanks for any answers.
12-07-2008, 02:45 PM
Both OpenGL and DX can do the same effects.
With OpenGL, users without Vista can get DirectX10 effects (if they have a GeForce8x00+ card or ATi HD2x00+).
ATi doesn't let developers do most DX10-class effects easily (or at all) in OpenGL.
Bloom is a fairly simple and old effect, so it's possible with OpenGL on all non-ancient cards.
Bloom uses one or two more screen-sized textures, so it can easily take 20MB VRAM and some bandwidth.
12-07-2008, 04:21 PM
1. its simpler to use and cross platform
3. yes, as anything else would.
4. well yes and no, it does have basically the same feature set as DX10 as it's the hardware that decides that, however there are a few features that differ as the way you do things differ a bit, nothing major though.
OpenGL does tend to get all the new stuff as soon as the hardware is released through extensions and as i said iy's platform independent, so you don't need vista just for a few extra features.
12-08-2008, 01:58 AM
Ive read that most gaming companies prefer OpenGL over DX.
Heres a quote from one of them :
"We are trying hard to make the DirectX renderer as feature-complete as the OpenGL renderer. In the original version of ETS, the DirectX renderer was only supposed to be a fallback solution, but many people use it without knowing of its limitations - even though it has less features and works worse then OpenGL in majority of cases!"
OK, thanks for the replies. Been most helpful.
12-08-2008, 02:51 AM
The game, mentioned in that quote, "Euro Truck Simulator" , doesn't seem to be using modern shaders (if any) - it's where GL troubles begin.
12-08-2008, 03:25 AM
Yes, thats the game...Thought I wrote that, missed that.
I do like playing games, but also using map editors.
I tried 3DMax but just laughed because there was so much stuff in it, I dont have a clue what they are for.
Questions again, you people have to be on your toes here :)...
Would there be any speed difference if OpenGL/DX was programmer totally in assembler ?
How exactly is OpenGL used in Vista ? On the desktop or ?
12-08-2008, 06:52 AM
I'm a hardcore x86 asm supporter, but even I find it silly to use asm to call OpenGL and DX API. Especially when I measure simplistic calls take 10k+ cycles. If you'll be doing heavy traversing of objects, collision detection, etc - you can expect speedups with asm.
There's also the thing that if you make your cpu code very fast, but torture the gpu - you won't get extra fps (thus headroom for effects/detail).
OpenGL runs on Vista the same way DX10 does: as an ICD.
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