[vtk-developers] GLXPixmap vs OSMesa

[Jeff Lee]

Moreland, Kenneth wrote:

>Jeff,
>
>I like the idea of the UseOffScreenRendering flag working without Mesa.
>However, we also often use Mesa builds on clusters that do not have an X
>host running.  I think using GLXPixmap still requires a connection to an
>X host.  Thus if you stripped out the Mesa stuff, our applications may
>cease to work.  Could you implement this such that if you build with
>Mesa you use Mesa offscreen rendering and otherwise use a GLXPixmap?
>  
>
Hi Kenneth,
I was under the impression that mesa has its own glx implementation - 
fakeglx.  I could be wrong, but I think it just turns everything into 
X.  I was hoping that if an application uses mesa, the fakeglx 
implementation of glxPixmap would just work (mapping down to Pixmap).  I 
think pbuffers will work the same way.  Does this make sense?  If not, 
mabey someone could straighten me out on this.
Jeff

>-Ken
>
>   ****      Kenneth Moreland
>    ***      Sandia National Laboratories
>***********  
>*** *** ***  email: kmorel at sandia.gov
>**  ***  **  phone: (505) 844-8919
>    ***      fax:   (505) 845-0833
>
>
>  
>
>>-----Original Message-----
>>From: vtk-developers-bounces at vtk.org 
>>[mailto:vtk-developers-bounces at vtk.org] On Behalf Of Jeff Lee
>>Sent: Thursday, March 10, 2005 3:02 PM
>>To: vtk-developers
>>Subject: [vtk-developers] GLXPixmap vs OSMesa
>>
>>Hi All,
>>I have been tooling around with glpixap for offscreen 
>>rendering.  I started with vtkXOpenGLRenderWindow and managed 
>>to strip out the osmesa stuff and replace its implementation 
>>with rendering to a glxpixmap instead (a'la John Schalf and 
>>Glenn Lehmann).  All of this works great, all I have to do is 
>>call SetOffScreenRendering(1) on the renderWindow, and then I 
>>can dump the image to a file.  Eventually I can have it such 
>>that switching between onscreen/offscreen will work similar 
>>to windows.  
>>I can also see a pbuffer implementation as a straightforward 
>>extension of this.
>>
>>The question is, can anyone see any major drawbacks of 
>>dropping osmesa for this approach?  The benefits that I can see are;
>>
>>   1. No more mangled mesa, this approach (glxPixmap)  works both in
>>      mesa and in hardware drivers.
>>   2. We can stop tiling the display to get high-resolution images.
>>   3. Similar behavior to that of vtkWin32OpenGLRenderWindow.
>>   4. Can further extend to hardware-accelerated pbuffers with drivers
>>      that support it.
>>
>>Possible Drawbacks:
>>
>>   1. Perhaps not everyone has a driver which supports glx1.3.
>>   2. glxpixmap is slow (not when compared to osmesa).
>>
>>I would like to eventually replace what's in 
>>vtkXOpenGLRenderWindow with glxpixmap.  Does anyone have 
>>other arguments which I am perhaps not seeing, or reasons for 
>>not doing this?  Thanks in advance.
>>Regards,
>>Jeff
>>
>>--
>>Jeff Lee
>>Senior Software Engineer
>>Computational Dynamics North America Ltd
>>21 Lafayette Street, Suite 230
>>Lebanon NH 03766 USA
>>fax:   603 643 9994
>>phone: 603 643 9993 x109
>>http://www.cd-adapco.com
>>
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>>
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