Extended Morton codes for high performance bounding volume hierarchy construction

We propose an extension to the Morton codes used for spatial sorting of scene primitives. The extended Morton codes increase the coherency of the clusters resulting from the object sorting and work better for non-uniform distribution of scene primitives. In particular, our codes are enhanced by encoding the size of the objects, applying adaptive ordering of the code bits, and using variable bit counts for different dimensions. We use these codes for constructing Bounding Volume Hierarchies (BVH) and show that the extended Morton code leads to higher quality BVH, particularly for the fastest available BVH build algorithms that heavily rely on spatial coherence of Morton code sorting. In turn, our method allows to achieve up to 54% improvement in the BVH quality especially for scenes with a non-uniform spatial extent and varying object sizes. Our method is easy to implement into any Morton code based build algorithm as it involves only a modification of the Morton code computation step.