[vtkusers] Re: Mesa/VTK problem on RedHat 7.2 (also with Mesa 4.0) [MORE INFO]

[Dave Reed]

> From: Brian Paul <brian_e_paul at yahoo.com>
> 
> Dave Reed wrote:
> > 
> > > From: Brian Paul <brian_e_paul at yahoo.com>
> > > >
> > > > I also tried a small GLUT program and Mesa4.0 appears to have bugs
> > > > that Mesa 3.4 does not. See the images:
> > > >
> > > > http://capital2.capital.edu/faculty/dreed/mesa3.4.jpg
> > > > http://capital2.capital.edu/faculty/dreed/mesa4.0.jpg
> > > >
> > > > Note that the cone is missing polygons near the top in the 4.0
> > > > example.
> > > >
> > > > I can provide code for any of these if anyone wants it.
> > >
> > > If you send me the code for small GLUT program I'll take a look.
> > > Do you have the MESA_DEBUG env var set?
> > 
> > Forgot to set MESA_DEBUG before. Here's the error message:
> > 
> > Mesa warning: glEnable(GL_DEPTH_TEST) but no depth buffer
> > 
> > That's obviously the problem and I fixed it by doing:
> > 
> > glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
> > 
> > (forgot the GLUT_DEPTH before).
> > 
> > However, the error message doesn't show up with the VTK problem.
> 
> The problem in VTK may be different.  Do you know how the
> polygonal surfaces are being drawn?  Vertex arrays?  Display
> lists?  Immediate mode?  GL_TRIANGLES, GL_TRIANGLE_STRIP, etc?

I'm pretty certain it's triangle strips.

The following section of vtk causes the problem.

  // extract the skin
  vtkContourFilter *skinExtractor = vtkContourFilter::New();
  skinExtractor->SetInput(v16->GetOutput());
  skinExtractor->SetValue(0, 500);

  vtkStripper *stripper = vtkStripper::New();
  stripper->SetInput(skinExtractor->GetOutput());
  
  vtkPolyDataMapper *skinMapper = vtkPolyDataMapper::New();
  skinMapper->SetInput(stripper->GetOutput());
  skinMapper->ScalarVisibilityOff();
  vtkActor *skin = vtkActor::New();
  skin->SetMapper(skinMapper);

but if I skip the stripper (which should convert to triangle strips),

  vtkContourFilter *skinExtractor = vtkContourFilter::New();
  skinExtractor->SetInput(v16->GetOutput());
  skinExtractor->SetValue(0, 500);

  vtkPolyDataMapper *skinMapper = vtkPolyDataMapper::New();
  skinMapper->SetInput(skinExtractor->GetOutput());
  skinMapper->ScalarVisibilityOff();
  vtkActor *skin = vtkActor::New();
  skin->SetMapper(skinMapper);

The image displays correctly. So it's most likely a problem with
Mesa's triangle strip rendering. I don't think it's VTK's triangle
stripper since NVidia's GL displays it correctly.

Dave