Problem with transparency with VTK >= 8.0 on Linux

Support
1

Hi, I have an issue with rendering transparent objects with any version of VTK from 8.0 onwards (tested up to 9.0.0). I’m running CentOS 7 inside VirtualBox, and glxinfo reports:

OpenGL version string: 3.3 (Compatibility Profile) Mesa 18.3.4
OpenGL renderer string: llvmpipe (LLVM 7.0, 256 bits)

This is the code that I’m using to test, which I picked up online from somewhere:

import vtk

def main():
    cubeSource = vtk.vtkCubeSource()
    cubeMapper = vtk.vtkPolyDataMapper()
    cubeMapper.SetInputConnection(cubeSource.GetOutputPort())
    
    cubeActor = vtk.vtkActor()
    cubeActor.GetProperty().SetOpacity(0.5)
    cubeActor.SetMapper(cubeMapper)
    
    sphereSource = vtk.vtkSphereSource()
    sphereMapper = vtk.vtkPolyDataMapper()
    sphereMapper.SetInputConnection(sphereSource.GetOutputPort());
    
    sphereActor = vtk.vtkActor()
    sphereActor.GetProperty().SetColor(0.5,1,0.5);
    sphereActor.SetMapper(sphereMapper);
    
    renderer = vtk.vtkRenderer()
    renderer.AddActor(cubeActor);
    renderer.AddActor(sphereActor);
    
    renderWindow = vtk.vtkRenderWindow()
    renderWindow.AddRenderer(renderer);
    
    interactor = vtk.vtkRenderWindowInteractor()
    interactor.SetRenderWindow(renderWindow);
    renderer.SetBackground(0,0,0);
    renderWindow.Render();
    
    interactor.Start();

if __name__ == '__main__':
    main()

So the code creates a sphere inside a transparent box. Result on Windows:
image
Result on Linux:
image

I’ve tried enabling depth peeling, it makes no different from what I can tell. The box also isn’t shown even if it’s the only actor on the scene. Is there anything else I can test, or any extra info I can provide? The code works as expected with VTK 7.1.1.

Thanks.

1 Like
2

You could try to set this in your environment …

MESA_GL_VERSION_OVERRIDE=4.5
3

Hi Andreas, thanks for the reply. The problem persists with that change too, and from my understanding the currently reported version (3.3) should be enough for VTK.

4

Another flag to try could be
LIBGL_ALWAYS_INDIRECT=1

5

This one segfaults with:

ERROR: In ../Rendering/OpenGL2/vtkOpenGLRenderWindow.cxx, line 741
vtkXOpenGLRenderWindow (0x5606d38c1640): GLEW could not be initialized: Missing GL version

This happens even if I set both variables (LIBGL_ALWAYS_INDIRECT and MESA_GL_VERSION_OVERRIDE)

6

As an update, I got someone to run the sample on a machine (non-remote) with different hardward/libs:

OpenGL renderer string: Radeon RX 5500 XT (NAVI14, DRM 3.35.0, 5.4.0-29-generic, LLVM 9.0.1)
OpenGL core profile version string: 4.6 (Core Profile) Mesa 20.0.4
OpenGL core profile shading language version string: 4.60

In this setup the rendering works as expected. It works even if there they force software rendering via LIBGL_ALWAYS_SOFTWARE=1 GALLIUM_DRIVER=llvmpipe python main.py. Here’s the output from glxinfo in this case:

OpenGL vendor string: VMware, Inc.
OpenGL renderer string: llvmpipe (LLVM 9.0.1, 128 bits)
OpenGL core profile version string: 3.3 (Core Profile) Mesa 20.0.4

The main difference that I can see is that in this latest report the Mesa version is 20.0.4, while in my original case it is 18.3.4. Is there a minimum Mesa version for VTK, or versions that are known to present issues?

Thanks!