-- directx is pc only and this will make blender not be able for cross platform.
Nope...

Directx is Windows only (surely you meant windows, Xbox is not...well, yeah some people say is a Pc too

) , yes. But actually not directx *.x files. Is not actually using direct x , but that format.
Irrlitch engine has lots of linux coders behind it, the author did choose *.x format because it can be used in several platforms. It doe snot means using directx libraries, the game maker can choose to use Opengl or directx 8 and 9 with Irrlitch.
That's only to say an example to show that *.x files are just ascii files that can be used also in linux.
One of the main reasons he had to use it was that x files can be exported by many 3d packages by free plugins (Max, XSI, Lightwave, Maya,Character Fx, 3d Canvas etc.. and not free also Truespace, Hash Animation Master)
The thing is for free or cheap there's no other tool as powerful as blender to make character animations.
-----also in blender the radiosity calculation is stored in vertx information and i dont know if this is compatible with games when you talk about a second uv channel!
Well, the important part is if that can be exported as a tga or other bitmap format. You see, one could just uv map outside Blender (in Lithunwrap, Ultimate Unwrap) , do that radiosity bake in Blender, export the tga, and with Ultimate Unwrap copy the uvs of the object to a second uv channel, as Ultimate support this.
The complete solution would be to have Blender support a second uv channel. Is like another uv space, where you uv map the model, usually differently (I never thought of using same uvs anyway) and has its texture, which is the tga with the lighting/shadows baked in it, so when you load the scenery model in a game, it has its standard texture (wood, whatever) , which uv info is stored in uv channel 1, and baked lighting info in the texture assigned to uv channel 2. The game engine then like "overlays" the light/shadows baked tga, over the standard texture in the model. This can be done calculating the lights with an standard render of any renderer, or much better, with radiosity. results is like a radiosity rendered scnery, while it is not calculating anything at realtime, which is what counts
Even though, there are ways to do this with other tools, I'd priorize way more character animation tools and x full export. (for games)( imho)
-----so i understood you correct that a character animation with bones is possible to get exported out of blender into a game mod through a file converter?
sweet!
Well, not yet. Though yes to certain mods.
x files are quite universal, and indeed, the 35$ Ultimate unwrap can import full animation, bones and weights info in *.x format. As it can export to a huge load (
http://unwrap3d.com/downloads.html ) of game and other 3d formats, you already would have then a potential montain of exports available.
besides, already you can export in md5. So, any doom3 mod, if already possible. And for sure Doom3 is going be quite important in mod comunity.
Also, I found there's a NeverWinter Nights exporter, or that I think I read.
There are several quake2 "revival" mods (Tenebrae, etc) using md2 and md3 formats...If you ask me, I'd rather prefer md3. MD2 produces accurate problems, as was only using intengers, not floats, and that precission errors drives to an ugly trembling and bad deformation, specially 2000 triangle models (my preferred count these days for most games, though depends drastically on the game) But anyway, some engines use md2 and not md3, so is very good to have it too.
There's an ASE export plugin,(haven't used, but ase use to support lights and camera export--->great for porting full scene from Blender.Also, programmers use to love its simplicty and clarity) I use the objio modified plugin for all my imports; there are enough formats for static meshes.
Unreal Ed from Unreal1, 2003, etc, use ASE for scenery and objects.
And a complex bone and weights format for characters.