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GPU PRO 3 by Wolfgang Engel

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III
Global Illumination
Effects
The global illumination section is a permanent part of this series of books, under-
lining the importance of realistic shading techniques and, more specifically, global
illumination effects in real-time applications. The section contains three articles
addressing very different phenomena, each using dedicated data structures and
algorithms in order to achieve the desired performance. The techniques range
from screen-space approximations to using splat-based representations and spa-
tial index structures.
The first chapter in this section is “Ray-Traced Approximate Reflections Us-
ing a Grid of Oriented Splats,” by Holger Gruen. In this chapter, Gruen exploits
the features of DX11-class hardware to render approximate ray-traced reflections
in dynamic scene elements. His method creates a 3D grid containing a surface
splat representation on-the-fly and then ray marches the grid to render reflec-
tions in real time. Gruen also outlines further improvements, for example, using
hierarchical grids, for future hardware.
Our next chapter is “Screen-Space Bent Cones: A Practical Approach,” by
Oliver Klehm, Tobias Ritschel, Elmar Eisemann, and Hans-Peter Seidel. Ambi-
ent occlusion computed in screen space is a widely used approach to add realism
to real-time rendered scenes at constant and low cost. Oliver Klehm and his
coauthors describe a simple solution to computing bent normals as a byproduct
of screen-space ambient occlusion. This recovers some directional information of
the otherwise fully decoupled occlusion and lighting computation. The authors
further extend bent normals to bent cones, which not only store the average
direction of incident light, but also the opening angle. When preconvolving dis-
tant lighting, this results in physically more plausible lighting at the speed and
simplicity of ambient occlusion.
The last chapter in this section is “Real-Time Near-Field Global Illumina-
tion Based on a Voxel Model,” by Sinje Thiedemann, Niklas Henrich, Thorsten
Grosch, and Stefan M¨uller. Thiedemann and her colleagues describe a method
for computing one-bounce (near-field) indirect illumination with occlusion in dy-
namic scenes. It is based on a fast texture atlas-based generation of scene vox-
elizations for visibility, and reflective shadow maps (RSM) to sample directly lit
surfaces. The indirect illumination is computed using Monte-Carlo integration
using the voxel representation to find the closest intersection for a secondary ray
180 III Global Illumination Effects
within a user-defined search radius (the near-field). The indirect light is then
obtained from projecting the intersection into the RSM.
—Carsten Dachsbacher

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