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Simulate fuzzy phenomena with particle systems

Use particle systems to simulate explosion rings, fireworks explosions, vapor trails, and more

By Jeff Friesen, JavaWorld.com, 05/29/06

Computer graphics (CG) is important to the games we play, the movies we watch, the design of our vehicles, and more. CG uses traditional polygon-based techniques to model and render classical geometry (cones, spheres, cubes, etc.). In contrast, the geometry of natural phenomena—such as fire and flowing water—needs a different modeling, rendering, and animation technique: particle systems.

After introducing you to the particle system concept and presenting particle systems in a historical context, this Java Fun and Games installment takes you on a tour of Java-based software that I created to build and play with particle systems. The article then reveals a demo applet that uses this software to simulate explosion rings, fireworks explosions, and vapor trails.

Particle system basics

A particle system is a CG technique that combines modeling, rendering, and animation to simulate fuzzy phenomena (also known as fuzzy objects); examples are various kinds of explosions, flowing water, clouds, fire, meteor trails, snow, sparks, fog, and falling leaves. These phenomena are called fuzzy because, due to the absence of straight edges, they appear blurred when rendered: they are composed of particles.

Particle systems manipulate collections of particles. Each particle has various attributes that affect the particle's behavior, along with where and how (as a point composed of one or more pixels, a line, an image, and so on) the particle is rendered. Common attributes include position, velocity (speed and direction), color, lifetime, age, shape, size, and transparency. Most of these attributes vary their values during the particle's existence:

• Birth: Particles are generated somewhere in the fuzzy object's vicinity. Each of the particle's attributes is given an initial value. This value may be fixed or determined by some stochastic process.
• Life: Various particle attributes (like position and age) tend to vary over time. For an explosion, each particle's color may darken as the particle moves further away from the explosion's center. This signifies an energy decrease (the particle is dying).
• Death: Particles typically have two attributes that determine the length of the particle's life: age and lifetime. Age determines the amount of time the particle has already lived. It typically is initialized to 0 and is measured in animation frames (iterations of an animation loop). Lifetime is the maximum amount of time the particle can live and also is measured in frames. The particle is destroyed when its age reaches its lifetime. Various factors may result in a premature death, including a particle moving out of the viewing area and not returning to that area, and a particle's color fading to black prior to its age reaching its lifetime. In this case, we could assume that a black particle indicates zero energy (think explosion particles).

Particle systems have been in use for several decades. Perhaps their earliest use dates back to 1961-1962. According to "Welcome to PONG-Story," in 1961, three MIT students created a video game called Spacewar for the PDP-1 minicomputer (released by Digital Equipment Corporation in November 1960). This game featured a particle system to simulate explosions.