vtkCompositePolyDataMapper2 with alpha blending
Since !5745 (merged), we can use composite mapper with alpha blending to show heterogeneous opacities, not just all-opaque or all-translucent.
However I have an issue when I add a 0D polydata into the composite: the cube looks like it was rendered in an opaque pass? See below, left is without the 0D, right is with the 0D.
Notice how only the cube is affected. I also noticed the issue with a 1D block but could not isolate a minimal example out of it.
This is with a vtk build after a fresh pull this morning. I also tested with 8.2.1 and backported the fix for composite+alpha blending and have the same issue. I assumed that this strange behavior is linked to this fix.
Here is the script. Change the flag l.52 to trigger the problematic render: composite_alpha.py