Ray Tracing is a graphics rendering method that uses rays to trace the path of light in a computer model. To accelerate the processing of rays, scenes are typically compiled into smaller spatial boxes using a tree structure and rays then traverse the tree structure to determine relevant spatial boxes. This allows computations involving rays and scene objects to be limited to only objects close to the ray and does not require processing all elements in the computer model.

We present a ray traversal pipeline designed to accelerate ray tracing traversal algorithms using a combination of currently used programmable graphics processors and a new fixed hardware pipeline. Our fixed hardware pipeline performs an initial traversal operation that quickly identifies a smaller sized, fixed granularity spatial bounding box from the original scene. This spatial box can then be traversed further to identify subsequently smaller spatial bounding boxes using any user-defined acceleration algorithm. We show that our pipeline allows for an expected level of user programmability, including development of custom data structures, and can support a wide range of processor architectures. The performance of our pipeline is evaluated for ray traversal and intersection stages using a kd-tree ray tracing algorithm and a custom simulator modeling a generic streaming processor architecture. Experimental results show that our pipeline reduces the number of executed instructions on a graphics processor for the traversal operation by 2.15X for visible rays. The memory bandwidth required for traversal is also reduced by a factor of 1.3X for visible rays.