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要旨:
Real-time shading using general (e.g., anisotropic) BRDFs has so far been
limited to a few point or directional light sources. We extend such shading to
smooth, area lighting using a low-order spherical harmonic basis for the
lighting environment. We represent the 4D product function of BRDF times the
cosine factor (dot product of the incident lighting and surface normal vectors)
as a 2D table of spherical harmonic coefficients. Each table entry represents,
for a single view direction, the integral of this product function times
lighting on the hemisphere expressed in spherical harmonics. This reduces the
shading integral to a simple dot product of 25 component vectors, easily
evaluatable on PC graphics hardware. Non-trivial BRDF models require rotating
the lighting coefficients to a local frame at each point on an object,
currently forming the computational bottleneck. Real-time results can be
achieved by fixing the view to allow dynamic lighting or vice versa. We also
generalize a previous method for precomputed radiance transfer to handle
general BRDF shading. This provides shadows and interreflections that respond
in real-time to lighting changes on a preprocessed object of arbitrary material
(BRDF) type.
