[Paraview] offscreen display trouble revisited

[Francois Bertel]

Hi,

Assuming you use cvs version of ParaView, there was some change related to offscreen rendering in VTK on October 26. Is it when the warnings started to occur?

Under X11, if vtk was compiled with OSMESA (OS=OffScreen) it creates an OSMesa window and an OSMesa context.
Otherwise, (NEW) it tries to use a hardware accelerated offscreen rendering by creating a window and an OpenGL context and asking for OpenGL extensions GL_EXT_framebuffer_object and GL_ARB_texture_non_power_of_two.
It those extensions are not available, the OpenGL context and window are destroyed and it tries to use a Pbuffer offscreen. If not available, it uses a GLX Pixmap.

Under Win32, it first tries the hardware accelerated offscreen rendering (NEW). If the extensions are not available, an Offscreen Device Context is used.

The source code is in VTK/Rendering: vtkXOpenGLRenderWindow, vtkWin32OpenGLRenderWindow and the superclass vtkOpenGLRenderWindow.

Kent Eschenberg wrote:
> No fixes here - just some related info.
> 
> --On 11/16/2006 02:55:05 PM +0100 biddisco at cscs.ch wrote:
>> I keep getting a warning that one or more of the servers cannot access
>> a display and so compositing will be disabled.
> ...
>> It used to work ok, but I must have broken something. Anyone got any idea?
> 
> 1) Another possible cause is that something changed in your OS' defaults. Upgrades to some of our systems sometimes replaces various graphics header files.
> 
> 2) You might try changing
> 
>> and set environment to (also tried blank for DISPLAY)
>> DISPLAY :0
> 
> to instead set DISPLAY to localhost:0.0.
> 
> 3) Using X Windows and using OpenGL are two different issues; linking t Mesa does not always eliminate the need to access X.
> 
> For example, the code may ask X for a font definition that it uses to prepare the equivalent font in Mesa.
> 
> There is also a bug (may not be on the formal list) where pvbatch (and maybe pvserver) still need to see an X server though they don't really use it.
> 
> 4) Finally, keep in mind that there are 2 different types of "off screen rendering".
> 
> The one that is officially known by that name has been in OpenGL from the beginning (see glXCreateGLXPixmap). It writes to an X pixmap instead of the screen (I suspect there is also a Windows version). I *think* this approach still uses the graphics card
> for acceleration.
> 
> In addition, Mesa can render off screen, into a buffer, and does not need a graphics card or an X pixmap - it tries to hide all that from the application.
> 
> Of course, all this is just a list of options; perhaps someone who knows the internals can comment on how VTK/ParaView actually does things???
> 
> Kent
> Pittsburgh Supercomputing Center


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François Bertel, PhD  | Kitware Inc. Suite 204
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