To come to a conclusion of this lenghty thread: There were two problems, view entities not being visible, and view entities not being subject to postprocessing. I hope we can now agree that the first one was just a script problem, but the second one is real.

The reason is that view entities were originally not meant to be part of the scene, they were meant as 3D panel elements. Thus they are not rendered together with the scene, but together with panels.

I'll check if I can change that in some way for postprocessing view entities. But in the mean time, you can easily use level entities for that purpose. Most other engines have no "view entities" anyway and nevertheless support guns, flares, etc. They just use a vec_for_screen function for placing an entity at a screen position. You can easily do the same when you want guns or flares to be subject to postprocessing.

I'm even willing to do that for you - donate some cool sun flare sprites to the community and I'll donate a script that renders them as light or sun flares, including postprocessing. Do we have a deal?