Blur skybox

I want to know how to blur the skybox.

We have implemented a Bokeh blur in F3D: https://gitlab.kitware.com/f3d/f3d/-/blob/master/src/vtkF3DRenderPass.cxx#L235

This is a great way to emphasize the dataset and this should be moved to VTK at some point.

I test it, is blur the background, but is too slow.

You can reduce the number of samples.