Wireframe black artefact (OSMesa, Intel chipset)
Black artefacts are visible when rendering a quad as wireframe on different hardware.
This has been reproduced with OSMesa and Intel UHD Graphics 630.
vtkResliceCursorWidget tests are impacted after forcing the representation of the widget to wireframe in order to workaround #18441. (See !8879 (merged)) It only happens when the cursor is perfectly aligned with the camera view up. Moving the cursor a bit brings the color back.
Similar issues can be reproduce with a simple quad rendered as wireframe.
Please note:
- it only affect quads (vtkResliceCursorActor above is not using lines, but quads with a normal orthogonal to the camera direction).
- it seems to be caused by a wrong computation of
normalVCVSOutput
in vtkOpenGLPolyDataMapper.