Experimented with this because I wanted to see if I could make regular scenes wacky, and remembered Rob Pieke’s projection plugin in the Renderman docs.
The ‘Droste’ effect is used to produce Escher style results, as explained here
To achieve this I simply distort the rays that the physical (now not so physical) lens shader produces, which is less efficient than just applying this as a post process in comp. However, there are benefits to seeing the effect in the Karma viewport as you work.
I’m hoping to expand on this over the next few weeks when I have time.
I’d like to get the spiral effect working, clean up the code a bit and open source it for everyone else to play with!