Issue with opacity and enabling/disabling visibility of glyphs

Hello everyone!

I am using vtkTensorGlyph for visualizing hundreds of thousands of voxeloid cells and vtkLookUpTable to change the color and the opacity of each glyph. I need to be able of enabling/disabling the visibility of some glyphs. To disable a specific glyph I am setting the alpha value of its rgba tuple to zero, but here I am facing a visualization issue. For alpha=0, the glyph instead of being transparent, it seems to take the color of the background and as a result, the above geometry disappears.

  1. Is there some other way of enabling/disabling dynamically glyphs (or make them transparent)?
  2. Can I adjust the opacity of a glyph another way?

the issue:

Here, we have two different moments of the result in two screenshots. The blue and grey rectangles are glyphs. On the left, both glyphs have alpha=1. On the right, I have set the alpha value of the blue rectangle to zero and a hole seems to appear in the grey rectangle.