Why use OpenGL (was Native Mode Handling)

[This is my original post that I forgot to post to the list]

Jon Smirl <jonsmirl-/[email protected]> wrote:

> 4) xserver modified to use the GL API.

Honestly I don't see the point of building an X server to live on top of 
an OpenGL implementation. At the lowest level OpenGL is broken down into 
two components - buffer/surface management and the rendering engine. As 
long as the surface management is cleanly shared between the 2D engine 
and the 3D engine (and the Video engine for that matter), you don't need 
OpenGL itself for implementing 2D X server functionality.

One argument might be that OpenGL gives you all kinds of cool blending 
operations via the 3D engine, but OpenGL itself is completely overkill 
for this purpose. Rather what you need is to expose new 2D functionality 
(blending in hardware basically, to form a compositing window manager) 
but underneath the X server implements it using the 3D engine 
capabilities of the hadrware. You don't need a complete OpenGL pipeline 
to be able to do cool 2D stuff in the X server or window manager. Even if 

you went so far as to want 3D transformations for window buffers, you 
still don't need OpenGL for that either. Basic 3D transformations on 2D 
surfaces is really simple, so a simple geometry pipeline (possibly in 
hardware) combined with a simple triangle renderer in hardware is all you 

need. Building it simple at the 2D level means you can also build the 
software only version more easily and it will be significantly smaller 
than a complete OpenGL rendering pipeline. You don't need mip-mapping, 
multi-texturing, vertex shaders, pixel shaders, display lists, selection, 

picking, stencil buffers etc for a 2D window manager. 

Also if you take that approach, OpenGL is just another rendering engine 
that can draw stuff into offscreen memory buffers (as is the 2D engine 
and Video engine). Then you can do 2D, 3D and Video all together into a 
video memory buffers and composite them all together to form the final 
desktop. Flicker free, translucent and smooth ;-)

Oh wait! I am just describing OS X ;-)

Regards,

---
Kendall Bennett
Chief Executive Officer
SciTech Software, Inc.
Phone: (530) 894 8400
http://www.scitechsoft.com

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