The addition of global illumination can dramatically increase the realism achievable when rendering virtual environments.  In particular with interactive applications we expect the environment to reflect changes in the scene due to global lighting effects instead of it being just a static backdrop.  However, a sufficiently fast and accurate computation of global illumination at interactive rates has been difficult even with recent approaches based on realtime ray tracing.

The OpenRT real-time ray tracing engine implements a highly scalable approach to interactive global illumination. It fully recomputes a high-quality solution for each frame and thus offers immediate feedback even for dynamic scenes, achieving more than 20 frames per second for simple scenes.  Compared to previous systems we increased the raw performance by a factor of up to eight and removed the bottlenecks that were limiting scalability. The system now scales linearly in quality and available computing resources, tested with up to 48 CPUs in a commodity PC-cluster. Due to its logarithmic scaling property with respect to scene complexity it even supports lighting simulation in complex scenes with more than 50 million triangles.  This scalability allows applications to perform flexible performance trade-offs.  We also argue that the realism achievable through interactive global illumination will make it a standard feature of future 3D graphics systems once the required computing resources are readily available.