Re: [Mesa3d-users] XFree86 4.0 and Mesa3d.

[Stephen J B. <sj...@li...>]

On Wed, 21 Jun 2000, Martin Olveyra wrote:

> question 2:
> What is exactly GLX? Why doesnt appears neither in XFree86 4.0 nor Mesa3D
> distributions? Does GLX works through DRI?
 
GLX is two (confusingly similarly named) things:

1) The glX API which has the necessary hooks to allow applications
   to connect X windows and OpenGL rendering contexts.

   eg
        glXChooseVisual
        glXCreateContext
        glXSwapBuffers

   glX isn't portable outside of X-windows - so under M$-windoze you
   have 'wgl' calls like 'wglSwapBuffers'.  Under MacOS you get 'agl'
   ...and so on.  This usage of the term "glX" is present in all OpenGL
   implementations under X-windows, including Mesa/XFree4.0.

2) A protocol layer that theoretically exists between the application
   and the underlying renderer to pass rendering commands to the renderer
   and results back to the application.

   I say "theoretically exists" because DRI's objective is eliminate
   the GLX layer and let you do "Direct Rendering" (the 'DR' in 'DRI').

   However, GLX is still important when (for example) you are running
   your program on a remote host machine and your local machine is
   simply acting like an X-terminal.  The OpenGL commands made by the
   program on the host are sent via the GLX protocol (like other X
   commands) to the machine on your desk that does the rendering.

   Theoretically, GLX allows this to work even when one machine is
   (say) an SGI box running IRIX and SGI's own OpenGL and the other
   a PC running Linux and Mesa.  In practice that doesn't work all
   that well (yet).

   Some OpenGL implementations (eg Utah-GLX) use GLX even on a
   single machine - which is why they are (currently) slower than
   DRI.  The idea is to merge the two and have OpenGL use DRI when
   it can - and fall back on GLX when it can't.

   I don't think other (non-X-windows-based) OS's have an equivelent
   to the GLX protocol.

> question 3:
> Does glut works through DRI?
 
GLUT uses the glX API (under X-windows) or wgl (under M$-windoze) and
OpenGL - so if those use DRI, so will GLUT.   If they use the GLX
protocol then GLUT will too.

GLUT is nothing really magical - it's just a chunk of application
code provided for convenience.

Try to say 'glX' when you mean the API and 'GLX' when you mean
the protocol and that'll minimise confusion.

Steve Baker                      (817)619-2657 (Vox/Vox-Mail)
L3Com/Link Simulation & Training (817)619-2466 (Fax)
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