Bidirectional path tracing in OptiX

While there are a lot of unidirectional GPU path tracers in the wild, bidirectional path tracers running purely on the GPU are still very uncommon. BDPT helps in speeding up convergence in scenes with lots of indirect lighting, such as the alleys in Sponza and interior scenes and also makes caustics appear much faster than unidirectional path tracers. In late 2010, there was a fantastic demo by Dietger van Antwerpen (former Brigade developer) showing Kelemen-style Metropolis light transport on top of a bidirectional GPU path tracer (see http://raytracey.blogspot.com/2010/12/real-time-metropolis-light-transport-on.html) and this guy seems to have found a way to make it work on the GPU with OptiX: 

http://heart-touching-graphics.blogspot.com/2012/02/bidirectional-path-tracing-using-nvidia.html

 Should be interesting to see further results.