[vtk-developers] OSMesa depth buffer issues

[burlen]

> Anyway the typical values for on-screen are 24 bits for depth buffer,
> 8 bits for stencil buffer, 16 bits per channel for accumulation
> buffer.
the patch used 32 bits depth buffer, 8 bits stencil buffer and 16 
bits/channel accumulation buffer sorry for the mix up.

burlen wrote:
> Hi Guys,
>
> Yes I did try the environment variable. Just to be clear, we are 
> talking about OSMesa. OSMesa doesn't honor that environment variable. 
> To check me on this you can take a look at the mesa source code where 
> OSMesaCreateContext is defined. 
> Mesa-7.7/src/mesa/drivers/osmesa/osmesa.c:1068:
>
> To get a default value for the depth buffer it uses the compile time 
> constant DEFAULT_SOFTWARE_DEPTH_BITS, which is conditionally #defined 
> as 16 at Mesa-7.7/src/mesa/main/config.h:280
>
> I guess this does present another solution, that I didn't see before, 
> namely to add a -D DEFAULT_SOFTWARE_DEPTH_BITS=32 in my CFLAGS when I 
> build mesa. at the same time it doesn't seem right for VTK to default 
> to a 16 bit depth buffer...
>
> 24 bits of depth also solves the problem. but I would guess that 32 
> might be advantageous form a performance standpoint given this is a 
> natural size of the intel registers... just a guess. How come you want 
> 24?
>
> Francois Bertel wrote:
>> Excellent point!
>>
>> On Thu, Jan 28, 2010 at 4:33 PM, Jeff Lee <jeff at cdnorthamerica.com> 
>> wrote:
>>  
>>> I am surprised it doesn't honor
>>>
>>>  MESA_GLX_DEPTH_BITS=24
>>>  export MESA_GLX_DEPTH_BITS
>>>
>>> - this seems to work fine for me.
>>> -Jeff
>>>
>>> On Thu, Jan 28, 2010 at 4:30 PM, Francois Bertel
>>> <francois.bertel at kitware.com> wrote:
>>>    
>>>> Hi Burlen,
>>>>
>>>> I just looked at vtkWindow/vtkRenderWindow and too bad, there is no
>>>> API to let the user specify the render window settings regarding the
>>>> depth in bit of each type of buffer (color buffer, depth buffer,
>>>> stencil buffer, accumulation buffers) in the framebuffer.
>>>> That would have be better than hardcoding the values in
>>>> vtkXOpenGLRenderWindow.
>>>>
>>>> Anyway the typical values for on-screen are 24 bits for depth buffer,
>>>> 8 bits for stencil buffer, 16 bits per channel for accumulation
>>>> buffer.
>>>> What happen in your case if you use these values instead the one you
>>>> provided in your patch?
>>>>
>>>> On Thu, Jan 28, 2010 at 4:14 PM, burlen <burlen.loring at gmail.com> 
>>>> wrote:
>>>>      
>>>>> Hi Guys,
>>>>>
>>>>> I'm having some issues in ParaView that relate back to VTK's OSMesa
>>>>> rendering context. Specifically VTK asks OSMesa for the default RGBA
>>>>> context, which only has a 16 bit depth buffer. That's causing some
>>>>> artifacts
>>>>> and compositing issues in certain situations. for example:
>>>>>
>>>>>
>>>>>
>>>>> http://nashi-submaster.ucsd.edu/movies/PV/tube-filter-artifact/mesa-artifacts.png 
>>>>>
>>>>>
>>>>>
>>>>> http://nashi-submaster.ucsd.edu/movies/PV/tube-filter-artifact/mesa-artifacts-decomp.png 
>>>>>
>>>>>
>>>>> Explicitly requesting a 32 bit depth buffer solves the problems.
>>>>>
>>>>> I attached a small patch that makes this change in VTK. It 
>>>>> replaces the
>>>>> call
>>>>> to OSMesaCreateContext with one to OSMesaCreateContextExt 
>>>>> specifying a
>>>>> 32
>>>>> bit depth buffer and carries forward the current default values for
>>>>> accumulation and stencil buffers. I guess this function was The
>>>>> OSMesaCreateContextExt was added to in mesa release 3.5, the current
>>>>> release
>>>>> is 7.7.
>>>>>
>>>>> Is this the right fix? Or is something more sophisticated necessary?
>>>>> e.g.
>>>>> run time configurable. And while we're on the subject, are OSMesa's
>>>>> other
>>>>> buffer defaults reasonable? accum (8 bits per channel) and stencil
>>>>> buffers
>>>>> (16 bits).
>>>>>
>>>>> Thanks
>>>>> Burlen
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> Powered by www.kitware.com
>>>>>
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>>>>>
>>>>>
>>>>>         
>>>>
>>>> -- 
>>>> François Bertel, PhD  | Kitware Inc. Suite 204
>>>> 1 (518) 371 3971 x113 | 28 Corporate Drive
>>>>                      | Clifton Park NY 12065, USA
>>>> _______________________________________________
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>>>>       
>>>     
>>
>>
>>
>>   
>