Global illumination algorithms use rays to transfer the light in the scene. A ray connects
two points that are mutually visible from each other. Although it seems intuitive to transfer
the light into both directions along the ray, only a few algorithms have
taken advantage of bi-directional rays so far, which can increase the samples for minimal additional cost.
In this paper we propose a non-diffuse global illumination algorithm that exploits this promising alternative.
The algorithm is easy to implement but robust and is able to render complex scenes within a few tens of second.