pbuffers (was: xserver on OpenGL)

Jon Smirl wrote:
> It's going to take Brian, Keithw and myself another month or two to get a full
> standalone OpenGL running. We are missing two major pieces of code, pbuffers and
> mode support.

I started looking at what it would take to get pbuffers going with 
mesa-solo, in the r200 driver.  It looks like it'll be some work.

For rendering to off-screen color/depth/stencil buffers we need to 
pass the buffer's start and stride to the kernel module.  Luckily, it 
looks like that's transferred in the drm_radeon_context_regs_t 
structure, and not fixed at initialization time.

However, this info seems to be ignored in the 
radeon_cp_dispatch_clear() function; it seems to assume you're always 
clearing the front/back color and depth/stencil buffers.

A work-around would be to draw a filled polygon to implement the 
clear, but I'm wondering where else there might be similar assumptions 
to trip us up.

The other thing we need is a mechanism to allocate the memory for 
pbuffers.  My first guess is that this would have to be allocated out 
of the space used for textures.  I think the DRI texture memory 
allocator could be adapted to do this.

I'll keep poking around.

-Brian