Approximating the Fire Flicker Effect Using Local Dynamic Radiance Maps

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.