[Mesa-dev] DEFAULT_SOFTWARE_DEPTH_BITS=31

[burlen]

On 11/06/2013 12:58 PM, Brian Paul wrote:
> On 11/06/2013 12:34 PM, burlen wrote:
>> When I build osmesa with --with-osmesa-bits=32 I notice that I get 31
>> bits by way of the compile line define -DDEFAULT_SOFTWARE_DEPTH_BITS=31.
>> What's the story with the number 31? Is 31 bits really better than 32?
>
> IIRC, 32 bit Z never worked properly because of float->int conversion 
> problems and such.  I think I found that 31 bits worked though.  It's 
> been a long time...
>

I'm using OSMesa with VTK for rendering on systems that do not have 
graphics hardware. I need higher than default depth buffer with OSMesa 
to prevent z-buffer fighting artifacts in some cases when rendering in 
parallel. I found that --with-osmesa-bits=32 does the trick. however 
when building osmesa with 32 bits, most line rendering fails. Here is a 
representative image diff from our regression suite that shows an 
example of the bug 
http://open.cdash.org/testDetails.php?test=216532438&build=3087854 , 
there are 80 other failed tests, the ones I examined were all the same.

Experimenting with --with-osmesa-bits options, I've found that using 32 
causes the issue, while using 8 , 16 or not using it all doesn't. Do you 
have any idea about this?

Thanks
Burlen

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