Particle system is a technique for modeling a class of fuzzy objects, such as fire, clouds, and water. Particle systems model such objects as clouds of primitive particles that define their volumes. Over a period of time, particles are generated into the system, moved and changed within the system, and removed from the system.
Each particle has attributes such as:
For each frame, the position of each particle is computed and updated using:
Other attributes (e.g., velocity, age, and color) of each particle are updated for each frame. When the particle lives larger than its life expectancy, it's killed. New particles may be generated from existing particles.
Particle systems are state dependent. For each frame the system checks the current state of each particle and updates it for the current frame. Because the state at the new frame depends on what happened in the past, the system can update itself properly only in a forward direction. Playing the animation backwards won't update the system correctly. To see how the particle system is behaving, always play the animation in a forward direction.
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