GPU Pro 6

2. Rendering Vector Displacement-Mapped Surfaces in a GPU Ray Tracer 469

Top-level BVH

Middle-level BVH

Bottom-level BVH

VD

654

12

0

3

Mesh 0

xform 0

Mesh 1

xform 1

Mesh 1

xform 2

Mesh 2

xform 3

Figure 2.6. Three-level hierarchy. A leaf of the top-level BVH stores an object, which

is a middle-level BVH and transform. A leaf of the middle-level BVH stores primitives

such as a triangle, a quad, or a VD patch. There is a bottom-level BVH that is built

on the fly during the rendering for a leaf storing a VD patch.

AABB of a quad using the value. Although this results in a loose-fitted AABB,

which makes ray tracing less efficient than when tight AABBs are computed, it

makes ...