I have some scripts that uses clippingplanes and their data and often see that Rhino knows about the fill surfaces, yet they are not visible in the display mode.
Check this:
Here I have given the CLIPPING PLANE a red material:
See how the objects on the “ground” in the middle of the screen has fills when I extract the surfaces, but not when I use the display mode clipping plane fill option?
Oh, and for the observant reader: As you can see in the bottom image the wall section of the building is lacking some fills that the OpenGL view at top has, but these too are there:
Apparently OpenGL struggles to know IF the surfaces are to be drawn or clipped.
IMO everything ON the clippingplane should be drawn, and MAYBE this is related to why we see some fills and not all in OpenGL too. I don’t know, just thinking out loud.
PS! I also did a check to see if any of the related objects were flipped inside out, and they were not. Flipping all extracted fill surfaces did not change anything either. Just so you know.