I’m just wondering, with the imminent release of DirectX 10/SM 4.0-capable hardware in mind and the fact that Microsoft has locked the use of that API to Vista exclusively, if it is possible to use that hardware under OpenGL and XP?
By “use” I mean that I read somewhere (possibly here at opengl.org) that a lot of the functionality in SM 4.0 is already there in OpenGL. So, in short, would it be possible to develop, in theory at least, a “DX10/SM4.0/Vista only”-game as a game for “OpenGL/XP” with the same graphical features intact?
Yes. but some new features DX10 need new GL extensions : these will appear in upcoming video drivers, along with hardware that is really able to run it.
When you say “imminent release of DirectX 10/SM 4.0-capable hardware”, do you have more specific info ? links ?
It looks however that Vista is “still-not-quite-yet-ready ™” , let alone specific hardware for full DX10 compliance (and not just basic stuff + software emulation for everything else).
Most SM4 features are already implemented in the openGL api since they are mostly invisible to the user (save for minor tweaks here and there in regards to the fragment and vertex shaders).
The only major exception is the geometry buffer, though i would suspect the first extensions for that will come out shortly after the release of the hardware.