Ultimate Game Design : Building game worlds

Building Game Worlds
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U L T I M A T E G A M E D E S I G N
Developers have many choices to make in building up effects for games. You can create
fire as a sprite animation, flipping individual frames like traditional animation, or
modeling the behavior of fire using a particle system. You must make many trade-offs to
maintain game performance speed. You certainly can’t use elaborate particle systems for
everything just yet. They are simply too tough to compute. Where you can use them, and
where their output can be optimized, they offer dazzling visual possibilities.
Using Particle Emitters
Just like a light or an actor (a character or prop), you can put emitters in a scene. An
emitter emits particles. (Think of a sprinkler on your front lawn as an example of an
emitter.) You define how many particles an emitter will emit. It’s generally best to
start with very low numbers, because emitters are processor-intensive.
Suppose we start with 50–100 particles. Particles can be emitted from a point or from
a surface. For this example, I’ve chosen an omni-oriented point emitter. Figure 3-8 is an
example of a point emitter sitting on top of a cylinder (like a smokestack, for instance).
You can see the result of particles being emitted from this point emitter in all directions
in Figure 3-9. I have set the particles to render or draw as circles so that you can
see them easier. This is a very basic beginning to starting to shape the behavior of
your particles toward your intended effect.
The behavior of particles is influenced and shaped by forces, called fields, applied
on those particles. You can use fields in hundreds of combinations and create many
FIGURE 3-8
Omni-oriented point emitter