[vtkusers] Offscreen rendering and text mapper.

[Berk Geveci]

Hiho,

This is a known problem (or feature, if you wish :-). Currently,
accessing font information on X requires a connection to a server.
I don't know if there is anybody with a solution out there but
if there is, I will be more than happy to help incorporate it
into VTK.

-Berk

On Wed, 2002-04-24 at 00:57, JL wrote:
> Hi,
> 
> I'm running into a minor problem while using off-screen rendering.
> 
> Here's the scenario:
> vtk version: 3.2
> OS: Linux 2.4 (Red-Hat 7.1).
> Mesa version: 4.0.1
> 
> I have a very simple program that uses off-screen rendering (i.e.,
> it calls renWin->OffScreenRenderingOn()).  It works fine (no window
> pops-up, no X server connection is required, etc).
> 
> I have a second program that is slightly more elaborated.  For
> instance, it creates and uses vtkScalarBarActor and
> vtkCubeAxesActor2D objects.
> 
> When I execute the second program it prints the following message:
> 
> ERROR: In ../../src/graphics/vtkXRenderWindow.cxx, line 176
> vtkMesaRenderWindow (0x8057dd8): bad X server connection.
> 
> after that the program 'seg faults'.
> 
> After exploring a little bit here and there, it seems to me that
> the problem is caused by the vtkXTextMapper which is used by
> both vtkScalarBarActor and vtkCubeAxesActor2D.
> 
> My questions are:
> 1. Does this problem occur only with vtkXTextMapper, or does it
>    occur with other 2D actors/mappers?
> 2. More important, is there a way I can use off-screen rendering
>    with these actors / mappers? or
> 3. is this a well known 'feature'?  (I skimmed the mailing list
>    and didn't find anything relevant).
> 4. If so, do I have to use a different off-screen rendering
>    approach, like use vtkOpenGLOffscreenRenderWindow?
> 5. Or is this a 'bug' that has been fixed in the CVS version or
>    in a later release (i.e. 4.x)?
> 
> Thanks in advance for any information you can provide,
> 
> -- Julio
> 
> P.S.:  If it is of any help, I've included additional details about how and
> where the problem occurs.
> 
> 
> 
> ----------------------------------------------------------------------
> 
> I tracked the problem down to:
> 
> vtkXTextMapper::DetermineSize(vtkViewport* viewport, int* size)
> 
> near the beginning, this method tries to get the display id ->
> 
> Display* displayId = (Display*) window->GetGenericDisplayId();
> this in turns calls vtkXRenderWindow::GetDisplayId(), which in turn
> calls XOpenDisplay((char *)NULL);
> 
> XOpenDisplay returns NULL since there's no X server running (i.e.,
> the DISPLAY variable is not set), but that's intended since the goal
> is to do off-screen rendering.  And here is where the error message
> gets printed, and a NULL display is returned.
> 
> later vtkXTextMapper::DetermineSize(...) calls
> XLoadFont(displayId,  fontname );  with a NULL display and this is
> where the program crashes.
> 
> Here's a trace of the stack when the program crashes.
> 
> #0  0x414c5cbe in XListFonts () from /usr/X11R6/lib/libX11.so.6
> #1  0x40f9789c in vtkXTextMapper::DetermineSize(vtkViewport*, int*) ()
>     at eval.c:41
> #2  0x40f97426 in vtkXTextMapper::GetSize(vtkViewport*, int*) () at
> eval.c:41
> #3  0x40f79e13 in vtkScalarBarActor::SizeTitle(int*, int*, vtkViewport*) ()
>     at eval.c:41
> #4  0x40f786ef in vtkScalarBarActor::RenderOpaqueGeometry(vtkViewport*) ()
>     at eval.c:41
> #5  0x4044e4be in vtkRenderer::UpdateGeometry() () at eval.c:41
> #6  0x404f2cdd in vtkMesaRenderer::DeviceRender() () at eval.c:41
> #7  0x4044d882 in vtkRenderer::Render() () at eval.c:41
> #8  0x40451e10 in vtkRendererCollection::Render() () at eval.c:41
> #9  0x40449657 in vtkRenderWindow::DoStereoRender() () at eval.c:41
> #10 0x404495f4 in vtkRenderWindow::DoFDRender() () at eval.c:41
> #11 0x40449174 in vtkRenderWindow::DoAARender() () at eval.c:41
> #12 0x4044891c in vtkRenderWindow::Render() () at eval.c:41
> #13 0x4050b1e9 in vtkXRenderWindow::Render() () at eval.c:41
> #14 0x0804ac33 in ?? () at eval.c:41
> #15 0x0804b1bc in ?? () at eval.c:41
> #16 0x411b6306 in __libc_start_main (main=0x804b170, argc=10,
> 
> 
> 
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