[osg-users] [Fwd: Mesa and gldirect]

Guy guy at dvp.co.il
Tue Mar 24 00:05:07 PDT 2009


 The only suggestion I can give in this matter is to compare performance
with tools that already support both OGL and DX.

 I hope I'm not a sinner mentioning OGRE. I'm not familiar with OGRE but
if someone knows that library as well as OSG, it is possible to build a
set of programs comparing different features between these libraries
when OGRE using OGL. Then it is possible to run all these OGRE programs,
now using DX on windows platform and this could give an assumption of
the performance improvement for OSG on windows platforms if using
OGL->DX mapping.

---- -----

Hi Jan,

> Honestly, I think this will be counterproductive. It will only give
> companies an excuse to neglect OpenGL support further or to drop it
> completely ("You can use the emulation!"). The latter would be
> disastrous for all non-Microsoft platforms.

Since the OpenGL over Direct3D layer will only work on Microsoft 
platforms for obvious reasons, I don't see how this will affect other 
platforms at all. If some developer wants to do 3D on Linux, they have 
to use OpenGL.

Basically, this is a follow-up to an earlier discussion (a rather long 
and heated one as I recall) saying that there were two ways to improve 
the OSG experience on Windows platforms or for ATI/AMD hardware, where 
OpenGL drivers are pretty bad compared to nVidia:

1. Demand better OpenGL support in drivers (which may be hard and does 
not depend on us, i.e. we can ask but we have no control over the

2. Create a technological solution, of which an OpenGL over Direct3D 
layer is one example.

Of course, it would be much preferable if vendors would, out of their 
own volition, improve OpenGL driver quality on Windows. However, since 
most games run on Direct3D, there is little incentive for them to do 
this. In most markets where OpenGL support is important, the software is

already cross-platform, and thus moving to Linux is less of an issue. 
This means that the situation with OpenGL driver quality on Windows is 
likely to get worse as developers who depend on OpenGL move to other 
platforms and stop demanding good OpenGL driver quality.

> I fail to see the benefits of such move - why to run OpenGL on top of
> Direct3D? Is there *any* usable hardware that has only D3D drivers and
> does not support OpenGL?

Perhaps not, but for most hardware which has Direct3D support, the 
Direct3D driver quality is higher than the OpenGL driver quality on 
Windows (either in speed, number of serious/show-stopper bugs, etc.). 
There's a big difference between supporting OpenGL and supporting it 
*well*, and since there are no enforced conformance tests, vendors can 
support it only partly if they want...

Basically, I'm trying to find a way so that OpenGL apps can run well on 
Windows, independent of what vendor made the graphics card. Since there 
is a large pool of Direct3D applications on Windows, making OpenGL calls

go through Direct3D before getting to the video card driver might be one

way of doing that.

Of course, this is all theoretical, we can't know what the trade-offs 
are until we get a prototype running. And in any case, I'm just relaying

info I got, seeing as this discussion was raised before. If the majority

of people don't see the benefit, nothing will come of it and it'll just 
die, and we'll just go on as we have in the past.

Jean-Sebastien Guay    jean-sebastien.guay at cm-labs.com
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