C47: Approximating the Fire Flicker effect using Local Dynamic Radiance Maps

Metzgar,J., Semwal,S.K.

Realistic fire and the flicker effect is a complicated process to
simulate in realtime and little work has been done to simulate this
complicated illumination effect in realtime. Fire is not a
directionally uniform source of light but varies in intensity not only
with time but also with direction. Most realtime applications use a
standard point light source model for local illumination effects and
may use a model to change the light source intensity with time but not
direction. The problem is that point light sources are isotropic, but
many sources of light have anisotropic qualities as well. Radiance
maps and Precomputed Radiance Transfer (PRT) have been used to
increase realism at realtime interactive frame rates. These models
approximate global illumination by applying an environment map
(typically approximated with spherical harmonics) to get their soft
lighting effect. In this paper we present Local Dynamic Radiance Maps
(LDRM) which uses radiance maps in a local illumination model to add
anisotropic behavior to light sources. We implemented a realtime
rendering engine that supports shadow mapping and the physically based
Cook-Torrance model to approximate global illumination. In particular,
we generate dynamic radiance maps using Perlin noise to simulate the
nonlinear radiance of fire and we also implement a rudimentary
Lattice-Boltzmann flame rendering effect. Finally, we show how LDRM
can be applied not just to approximating the fire flicker effect, but
as a general framework for simulating the illumination properties of
other nonlinear light sources.