When we develop web pages we can broadly work out which browsers to support based on market share.
When we develop in .NET we can broadly work out which .NET version to develop for based on which Windows versions have it installed.
But when developing OpenGL or Direct3D applications, how do we know which video cards people (I mean "people" as opposed to "hard core gamers" or "companies using CAD" :P) are using? Are there statistics on such things? Is there some common logic that people use to work out what version to support? Just as most companies have supported (perhaps until just recently) a minimum of IE6 in web pages, is there a general consensus to support a minimum of, say, OpenGL 1.5, or DirectX 8 or something?
I note that we can find out which specific video cards support which versions of these APIs, but how do we know which video cards people are actually using, is there any kind of research on this?
N.B. I'm more interested in OpenGL because that's what I'm using, but I mention Direct3D because I assume the same problem applies.
OpenGL 2.1 is a good bet. The newer OpenGL 3 doesn't offer that much more functionality. You have to check for the availability of all of the OpenGL extension anyway,so you don't loose much by sticking with 2.1.
For DirectX: Use DirectX 9c. That is the latest version that still runs on WindowsXP. Drivers are stable and very mature. DirectX 10 offers more functionality but you will lock out the user-base that still runs WindowsXP.
About compatibility for non-gamers: Graphic cards that don't support these APIs (at least to a usable degree) have died out more than five years ago. Given the typical life-cycle of a PC you can be almost sure noone will have problems.
If any user complains that the software doesn't run on his 10 year old matrox-parhelia card he should just buy the cheapest graphic card he can get. It will run much faster and will cost a fraction of the software.