Now do I have 3D-Acceleration or not?
Until this weekend I happened to think that when glxinfo tells you "Direct Rendering: Yes" you can actually enjoy accelerated 3D.
Well, it seems that I was wrong, and that this indicator alone does not give you fast 3D.
A bit of history:
I was playing around as in KDE I was still using 1024x768, as posted here I had a little problem with 1240x1024. I was working to fix this problem by disabling my DVI-output, which for some reason gets detected as connected, which it clearly isn't.
So I ended up checking different things and somehow I got the idea to have a look at glxinfo, being fully aware that this of course isn't in any way related to the problem (which, btw, I finally fixed by disabled RandR and the DVI-output and editing the configuration of Plasma, have to check though if it's not possible to re-enable RandR and the DVI-output without breaking the Plasma-config again).
So, to my surprise it now showed me that direct rendering in fact was enabled. It was surprising because I knew that the RadeonHD-driver offers 3D for R500-cards, but since my X1250 is a R650 (or so) I didn't pay much attention yet to this.
As a quick test I fired up Celestia, which, btw, is a really cool program. To my disappointment it was still a bit slow.
Now I see it as a fact that my parents didn't raise a stupid guy, so I used all my wit and had another look at glxinfo, which showed me that as renderer in fact not my GPU is used, but Mesa, which of course explains the speed-issue, as it's still software-rendering.
Some googling revealed that the RadeonHD-driver does in fact support fast 3D for some cards (I didn't check though if mine is in that list of cards, I'll just try it out tonight), but not at the same time as fast 2D.
Now it seems all I have to do to make the switch from accelerated 2D to accelerated 3D is adding Option "DRI" to my driver-section in the X-configuration and then, in theory, I should be able to enjoy Celestia (and other 3D-stuff) with much sweeter speed.
Well, I'm going to try that out tonight and will keep you posted on this.
What I have learned from this is: "Direct Rendering: Yes" alone is no fool-proof indication that you actually have 3D-acceleration. Also look at the line showing the actual renderer to make sure.
This may only apply to users using RadeonHD, as it's the first time I've run into this "phenomena", but might be a good idea in general.