Question from enabling opacity mapping in categorical colors

Hi Paraview,
This is a simple question related to my previous post.
While I applied opacity mapping on this cube, I saw through it.

I understand this means there is no “surface” in the contacting area between sub-cube, which is reasonable. I am just curios if we can set something to make the surface exist (maybe set something for verbose surface?) or is there a way to remove sub-cube like I intended to.

I know threshold filter works, but it is heavy and not flexible. I also tried different options in Backface Representation, but none of them works.

Not as-is with surface representation. What you are looking for is “Masked Cells” which is supported by most type of vtkDataSet. But you must set it on the data.