9.5.2

378 • CHAPTER 7
OBJECTS MENU • PARTICLES • 379
The particle stream can also contain mixed random particle objects (e.g. a variety of different birds).
Simply drag the different objects into an emitter. These particles are then emitted in the same
proportion. You can also use a metaball to achieve otherwise difcult effects, such as bubbling
liquids. If the particles from an emitter are to be melded together into a metaball, the emitter must
be a child of the metaball.
The particles move in a straightforward fashion until they arrive within the range of a modier. Then
they are diverted, slowed down, rotated, etc. These modiers work, by default, in the Z direction of
their coordinate system (e.g. the wind blows in this direction); if this is not the case, it will be explicitly
pointed out in the text below. Modiers can be embedded in other modiers (i.e. nested). Thus a
Turbulence modier within a Wind modier results in very realistic smoke effects.
Almost all the properties of an emitter and the modiers can be animated. Why not animate the
strength of wind for realistic gusts?
 Particle effects will only be displayed accurately when played at a constant
rate in the Timeline. If you go backwards in time or move more than one frame
forward then strange things may happen on the screen. These strange effects
happen because the new position of a particle is calculated from the previous
position. Therefore you should always reset the time slider to the starting
position when adding new modiers to the particle system.
 When playing back you should enable the Animation > Frame Rate > All
Frames option, or click on the Animation toolbar’s Options icon and enable
All Frames. In order to get an accurate display using the Timeline animation
controls, you must single-step through the animation to make sure that no
frames are skipped. This doesn’t matter when the scene is nally rendered
with the raytracer, since the scene will then be calculated frame by frame from
start to end.
 When using a light for particles, disable the light’s shadow casting, otherwise
the many shadow will slow down rendering greatly.
You cannot use emitters as particles.
 You’ll nd two particle system examples at the end of this chapter, one for
light sources as particles, the other for metaballs as particles.