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

J.P. Delport jpdelport at csir.co.za
Tue Mar 24 00:27:45 PDT 2009


Jean-Sébastien Guay wrote:
> 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 result)
> 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.

What always bothers me is the whole multiple window, multiple context 
thing. Correct me if I'm wrong, but I've always thought DirectX caters 
more for the single fullscreen 3D window case (games?). Is this not why 
CAD apps favour OpenGL? If DX can't do multiple windows/contexts nicely 
the wrapper won't be able to fix this. For specific cases the wrapper 
might be OK.


> J-S

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