Efficient traversal of well-behaved hierarchical trees of extents for ray-tracing complex scenes

Traversal of hierarchial trees of extents (HTE) requires computation of intersections between rays and bounding volumes whose faces are parallel to the cartesian axes. By redefining the HTE so that nonoverlapping bounding volumes are generated, a well-behaved data structure is obtained in which “geometrical coherence” is applied to speed up its traversal. We distinguish two types of bounding volumes: internal boxes contain the ray's origin whileexternal bounding volumes do not contain the ray's origin. To traverse the HTE, we look first to polygons in the internal bounding volumes and deal with external boxes only when no ray-polygon intersection is found in internal nodes. As external nodes in the HTE define pruned subtrees of external bounding volumes, geometrical characteristics of the boxes are exploited for HTE traversal. A coding scheme allows a 6-bit code to determine which faces of a bounding volume need to be tested for intersection. Also, our well-behaved HTE allows for reuse of intersection points at lower levels of the tree.

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