In this lesson you learned how to:

• Control particles using creation and runtime expressions.
• Apply a random function to your expression.

For a particle object, you typically create two expressions—a creation expression that initializes an attribute value in the first frame, and a runtime expression that controls the attribute value in subsequent frames. (Creation and runtime expressions exist only for particle objects, not for other types of objects.)

This lesson described how to color stationary particles as a simple way to describe creation and runtime expressions. However, it’s more typical to use particle expressions to:

• Create sophisticated particle motion and life span; for example, the movement and fading of exploding fireworks.
• Create complex colors for emitted particles, for example, rocket exhaust flames.
• Create complex colors and movement of particles following collision with geometry, for example, sparks resulting from fired bullets.

  Creating such effects requires experience and experimentation. Expression writing can be as complex as computer programming. A detailed understanding of expression execution and syntax is essential. You also need to become familiar with the built-in mathematical functions such as the sphrand function introduced in this lesson.

  For further information and related techniques, refer to the Maya Help.