Graphics Reference
In-Depth Information
Each path contributes
to coefficients of active
voxels it intersects.
Figure 8.61
In tracing a light path through the voxel grid, the radiance is added to the spherical harmon-
ics representation of directional radiance distribution of the voxel. (From [Moon et al. 08]
c
2008 ACM, Inc. Included here by permission.)
into each voxel the light path hits by projecting its value onto spherical harmonic
basis functions. The value is recorded as a
scattering matrix
representing the
scattering function of the hair; the values stored in the grid are therefore just
the SH coefficients (Section 7.2.5). After the lighting simulation is complete, the
SH coefficients are smoothed to reduce noise.
In the rendering phase (
Figure 8.62
)
, rays are traced from the eye. At the
intersection with a hair fiber, the scattered radiance is obtained from the SH rep-
resentation in the voxel. The scattering at the fiber is computed by multiplying
the SH coefficients by the scattering matrix. Before this can be done, the SH co-
ordinate system must be rotated to match the orientation of the fiber. This has to
be done separately during the rendering phase, because each voxel may contain
Rotate
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Evaluate
Figure 8.62
Rendering a point on a hair fiber using the spherical harmonics representation in the voxel
requires rotating the SH basis to the hair fiber axis direction. From there, the scattering
computation reduces to a matrix multiplication. (From [Moon et al. 08] c
2008 ACM,
Inc. Included here by permission.)
