May be of interest:
Posts from Double Negative, the VFX company that did Interstellar:
Blackhole: <a href="http://dneg.com/dneg_vfx/blackhole/" rel="nofollow">http://dneg.com/dneg_vfx/blackhole/</a>
Wormhole: <a href="http://dneg.com/dneg_vfx/wormhole/" rel="nofollow">http://dneg.com/dneg_vfx/wormhole/</a>
I did once the same thing[1] with canvas. However, this demo warps the whole picture instead of circular region which seems unnatural. Other than that, you did great job.<p>[1] <a href="http://cihadturhan.com/lab/gravitional-lensing/" rel="nofollow">http://cihadturhan.com/lab/gravitional-lensing/</a>
Came across this some time back: <a href="http://blender.stackexchange.com/a/23574" rel="nofollow">http://blender.stackexchange.com/a/23574</a>