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Will the Lack of DX10 on XP Spur OpenGL Dev?
Sparr0 asks: "Microsoft has announcement that DirectX 10 will not be released for Windows XP (which means no Shader Model 4.0 and no Geometry Shaders). I have since been waiting for news of game developers switching to OpenGL, in order to get the best graphics on the best hardware on the most popular gaming OS, however there is nary a whisper of such. Will such a shift occur, even if only in small amounts? When? Why not? It is probably safe to say that Unreal Tournament 3 (AKA UT2007) will have OpenGL as an option in Windows, but that is both unsurprising and also a long way off. Ditto for Quake Wars, and most other games that are planning a native Linux clients. Where are all of the other big names with Windows-only offerings? Why haven't we heard from Valve, Blizzard, Sony, or EA, to name a few?"
The answer is sort of. Ultimately they each have similar capabilities, but for the more advanced features it's just easier to do in DX10. OpenGL takes longer than Direct3d to get any set of features pushed into the base spec, so it tends to lag Direct3D revisions.
One "good" part of OpenGL is that graphics companies don't need to wait for approval to include new features. They can release access to cutting edge features using vendor specific extensions. This was really important in the early days of consumer 3d graphics, and helped spur game development.
Of course this makes programming hard as the extensions are different between vendors and may even vary between different cards in a family (usually they try to just add on). This requires developers to create completely unique rendering paths for each card they want to support to get the best speed/features. Over time though Microsoft's Direct3D caught up with OpenGL and sort of sucked up all the good extensions into their API.
Direct3D 10's advantage is that it puts out a spec and requires all cards fully implement it. Unlike previous versions of DX you can't be DX 10 compatible and leave out features. This really helps eliminate the need for separate rendering paths to make any specific feature work, and so makes development much easier.
So the short of it is they can both do the same stuff, it's just more difficult at the moment with OpenGL.
(Another interesting thing to note is that I have heard rumors that once Direct3d came out Microsoft, who also happens to sit on the OpenGL ARB, slowed down the adoption of some features into the main OpenGL spec. This left them ramping Direct3D at a faster rate.)