Z-buffers and floating points

[Nigel Nunn]

Hi John,

> The latest changes to the clipping planes in nightly releases 
> have totally destroyed my stuff. I may have a lovely Z-buffer, 
> but its bugger all use when the graphics card randomly clips 
> away anything it likes irrespective of distance. Clearly there 
> are floating point instabilites in the calculations done on 
> the card to decide what to clip, chunks of screen flicker in 
> and out of visibility, odd patches of repeating black spots 
> flip in and out of view and generally it's just painful to view.
>  
> I suspect that when the clipping planes get close to the camera, 
> everything just dies and I have no idea why. 


I am not at my machine right now, but the first thing that comes 
to mind is that the 8MB Diamond FireGL-1000 can only do a 16-bit 
z-buffer, and if the lateset Vtk is using doubles instead of 
floats, this may be part of the problem.

I also have an 8MB Diamond FireGL-1000, and built a v3.0 Vtk on 
Thursday (been using v2.3 since September).  Will let you know 
if I notice the same problems, or get any bright ideas!

Cheers,
Nigel


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