A Mandelbox that generates Kleinian group fractals

[JosLeys]

This is work in progress, I'm not yet fully satisfied with how it works.
Stay tuned.

This was done in Ultrafractal:

[JosLeys]

This is answer to a question from Vladimir who discovered discontinuities in the renders.
These are normal. Due to the mod(y) in the formula one gets layers of objects, as in the first image below.
Within a layer the top and bottom objects are shifted (unless the transformation parameter's imaginary part is zero.
The second image shows a cut in the xy plane. The offset between the objects shows up in multiple places.