I just spent about 45 minutes playing with Beryl, a 3d window manager/environment for X11. As 3d on my laptop is generally pretty dicey, I used my PC TV, which has a reasonably nice 3d card (GeForce 7600GS). Impressions: Even with plenty of additional effects turned on and playing videos with mplayer while playing around, my video card didn't sweat in the least. Beryl has a lot of (poorly documented) options that are really cool to see, from letting me use my mousewheel to set opacity for various windows to plenty of things that look like they were lifted from OSX. Unfortunately, the configuration utility is far too complex and poorly designed, and while experimenting with all the options, it's easy to forget where some things were set if one were to want to revert them because things are so big and disorganised. Some of the keyboard shortcuts were highly nonintuitive, and some didn't work (I don't think it understood any shortcuts that involved the super key). I was hoping to be able to rotate individual windows and take notes on them (as some option names suggested I'd be able to do), but haven't figured out how yet (this might just involve changing the activation keys). That said, it is very cool - I think Beryl is aiming to be the Emacs of 3d X11 environments - if/when I put in the time to figure it out and remap everything to my liking, I'm sure it'll be pretty cool, although the defaults are pretty poor.
I'm not entirely certain what the different parts of Beryl are doing - there are plenty of different named components that have separate control panels, some of them probably representing new concepts that traditional X doesn't have. Classical thinking on doing 3d with X, IIRC, involved putting each window into its own Xnest (or moral equivalent) and then use the data from that to let windows be individually rotated, opaquified, and similar. Some time back, I toyed with a system someone put together that did this - it was fairly slow, ate a lot of memory, and was one of those gross hacks that show that that old phrase about premature optimisation being the root of all evil has limits - if an idea is a gross enough hack, it may be nearly impossible to optimise. But... then I don't really know what's going on here - maybe the X server, with help from some extensions, is doing something like that behind the scenes. I'll probably read up on it sometime in the next few weeks.
I imagine the next generation of 3d window managers will be pretty interesting.
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