[Lazarus] TOpenGLControl: multisampling not working (Linux/GLX)

[Michalis Kamburelis]

> I was testing TOpenGLControl.MultiSampling on Linux (with Radeon
> GPU), it worked fine for me.

I just did some more testing, and things look a little weird.
TOpenGLControl.MultiSampling works fine for Radeon GPU, but silently 
fails with NVidia GPU (GeForce GTS 450 with propriatary NVidia OpenGL). 
On NVidia GLX behaves like we have multi-sampling config, but the actual 
context doesn't have multi-sampling. Both systems (Radeon and NVidia) 
run Linux (recent Debian testing version).

What is weirder is that I can get multi-sampling on both these systems 
(both Radeon and NVidia) with a very similar multi-sampling code inside 
my Castle Game Engine TCastleWindow class (that directly uses GTK and 
GTKGlExt, without Lazarus TOpenGLControl, to create window with OpenGL 
context). Seems like there is something specific in 
Lazarus/TOpenGLControl that causes (some?) drivers to just ignore 
multi-sampling (even though glx seems to behave like we found 
multi-sampling context correctly, just like Reimar describes).

Not really sure what is wrong at this point.

Michalis