I've been thinking about starting a new graphics project and I want to use Java. Java has wrappers for all of the relevant GL functionality but I wonder how many people, including casual users, actually have decent GL drivers installed. By decent, I mean somewhat stable and fairly new (GL 1.5 support would probably do although the GLSL support that comes with 2.0 would be great). I could DirectX, even with Java, but I pretty much hate it and this project is supposed to be 'fun'. Also, I like the at least near-cross-platformedness of GL. So, anyone know of any non-imaginary stats on what percentage of Windows users have the drivers to run a GL app?
Every modern day video card supports OpenGL ... Shouldnt you be questioning how many Windows boxes have the Java runtime?
I'd say that all Windows users have some support for OpenGL. The latest versions usually are reserved for Vista users, gamers, and developers.
As I recall, Windows XP comes with 1.1 support out of the box. Vista upgrades this to 1.5. So you can at least count on those as an absolute minimum.
Apart from that, the GPU drivers from pretty much any vendor gives you at least 2.0 support.
But if I were you, I'd reconsider DirectX. I don't know what you hate about it, but it does have some advantages. The tool support is vastly better (ie, there are tools available. And PIX is nothing short of amazing), the API is up to date, and well designed, rather than accumulated over 20 years of a committee working at cross purposes, and if this is limited to Windows anyway, cross-platform doesn't really matter. (On the other hand, of course, if you do need cross-platform capabilities, it doesn't really matter what else DirectX can offer, it won't deliver that one killer feature)
The Steam Hardware Survey is probably the best and most detailed source for info about what gamers have. Accurate statistics for the general population will be harder to come by. Instead, you should look at this in terms of how recent you want the graphics hardware. For example, any ATI chip from the R300 series (Radeon 9550+) onward supports OpenGL 2.0. On the NVidia side, any GeForce 6000+ series chip will support OpenGL 2.0, and their predecessors, the FX series, almost supported OpenGL 2.0. The R300 series and the FX series were both introduced in 2002, so if you know what portion of your target market is using a PC from 2003 or later, you'll have a fairly good idea of how widespread OpenGL 2.0 support is among users with discrete graphics.
If you want to support integrated graphics (which are the largest segment of the market, but aren't particularly common with those who are serious about graphics of any kind) your users will need at least a GMA X3000 for hardware acceleration of OpenGL 2.0 features, which means their system has to be from 2006 or later.
If you're interested in support on other operating systems, any Intel Mac will support OpenGL 2.0 with software fallbacks, and hardware acceleration whenever the chip would support it under Windows. On Linux, any system with Mesa 7 or later (June 2007 or later) will support OpenGL 2.0 software rendering. Hardware acceleration is less reliable, but there are decent open-source drivers for ATI chips from R300 and newer.
Nearly everybody has SOME form of OpenGL support. Experience has shown that the actual drivers involved can be quite poor when dealing with ATI and especially Intel hardware, but it will at least work, aforementioned bugs notwithstanding. If nothing else, Windows can fall back to its built in 1.1 (XP and earlier) or 1.4 (Vista and higher) implementation. It won't work well, but it will work.
Windows XP comes with OpenGL 1.1 (quite slow though). Windows Vista also comes with OpenGL 1.1 (but for some special applications it has OpenGL 1.4 emulator on top of D3D).
When you install a graphics driver on Windows, it installs a more OpenGL version. OpenGL 1.5 is roughly "DX9 shader model 2.0" capable hardware. How many machines have that kind of hardware depends on your target market. In traditional/hardcore games space, almost all will (see Steam Hardware Survey).
In more casual/small games space, quite a lot of machines have much older hardware (see Unity Hardware Stats - almost 30% in 2009 Q1 are older than "DX9 shader model 2.0"). Also, a lot of machines in that space do not have custom drivers; they use whatever display drivers are shipped in Windows (which do not provide anything more than GL 1.1). Again, see Unity Hardware Stats - the most popular driver versions are the ones that come with Windows.
Stability wise, I'd strongly suggest using D3D9 on Windows instead of OpenGL. Driver quality is much better for D3D9 (less crashes inside drivers, less incorrect rendering, better performance, ...).