Particle Systems

Particle systems are an extremely hot topic in game design and simulation at present (see Figure 10.10 for an example). A particle system is basically a collection of small objects (particles) that obey some model of physics. Particle systems are real attention getters and are commonly used for effects such as explosions, fire, and gas trails. Moreover, in visualization, particle systems are often exactly what we are trying to model in the first place. In Figure 10.10, the particle system models the gaseous explosions and is based on a complex mathematical model developed by astrophysicists.

One aspect of a dynamical system is a certain amount of evolving randomness and possibly a fate for each particle. For example, part of what makes a realistic looking fire model is that the flames flicker in a fashion that isn't totally predictable. An explosion also contains a certain level of randomness and, further, the sparks and hot cinders tend to change state over the time course of the model. These examples clearly fall into the realm of particle systems.

A major challenge to building a particle system is abandoning the approach of having a unique transform and appearance for every particle. Any particle will contain a whole family of properties that describe things such as its position, velocity, color, life span, gravity, and wind force. All these properties will be dynamic (that is, the color of a burning ember will glow and slowly turn to black). For a system with thousands of particles, keeping track of and computing these properties will be a large job. Transparency is another property widely used in this type of modeling.

Often the approach is to have two interacting systems. The first represents the particle itself and the second is a particle manager.