Particle systems model an object as a cloud of primitive particles that define its volumn.
1.New particles are generated into the system
2.each new particle is assigned its individual attributes
3.any particles that have existed within the system past their prescribed lifetime are extinguished
4.the remaining particles are moved and transformed according to their dynamic attributes and finally
5.an image of the living particles is rendered in a frame buffer.
The motions and transformations of particles could be tied to the solution of a system of partial differential equations, or particle attributes could be assigned on the basis of statictical machanics. We can, therefor, take advantage of models which have been developed in other scientific or engineering disciplines.
A particle system also has a generation shape which defines a region about its origin into which newly born particles are randomly placed. A sphere of radius r, a circle of radius r in the x-y plane of its coordinate system, and a rectangle of length l and width w in the x-y plane of its coordinate system.
The generation shape of particle system also describes the initial direction in which new particles move. In a spherical generation shape, particles move outward away from the origin of the particles system. In a circular or rectangular shape, particles move upward from the x-y plane, but are allowed to vary from the vertical according to an "ejection" angle, which is another parameter.
A particle system has a parameter that specifies the shape of each of the particles it generates.First we assume that particle systems do not intersect with other surface-based modeling primitives.
The other assumption is each particle can be displayed as a point light source. Each particle adds a bit of light to the pixels that it covers. A particle behind another particle is not obscured but rather adds more light to the pixels covered.
Reference:
Particle Systems - A Technique for modeling a class of fuzzy objects
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