Game Development Reference
THE EXPRESSION CONTROLS
The Expression Controls category of effects contains what is
perhaps the oddest group of effects. Other than the effects in the
Audio category, most effects make some kind of visual change.
The Expression Controls effects are used to control expressions,
which are used to control the values of layer properties. In effect,
they control the controllers.
One of the big limitations of expressions is that they cannot
be animated. Let's say you wanted to simulate an earthquake
by applying a Wiggle expression to the Point of Interest value on
your camera layer. Once you applied the expression, the wig-
gling would last for the entire duration of the layer (or, the com-
position, whichever ended fi rst). Enter the Expression Controls
effects, which can be used in conjunction with expressions to
create animations. In this case, we could create a null layer and
apply the camera controlling expression control effect to the null.
As we'll also see, these Expression Control effects can also be used
simply as a visual controller for expressions to make them easier
to work with.
Because all the Expression Controls effects are applied and
function in a similar manner, let's take a look at how expressions
can be controlled with them. Then we'll look briefl y at what each
Expression Controls effect can be used for.
Create a new After Effects project, then a new composition at
the NSTC DV size. Then create a new solid (any color) at the comp
size. Go to the Animation menu at the top of the interface and
select Apply Animation Preset. Navigate to the Animation Presets
folder in the exercise fi les that came with this topic and select the
chads fi re—campfi re.ffx preset. This is a simple fi re pattern cre-
ated with the Fractal Noise effect (Chapter 12) and colored with
Colorama (Chapter 6) (Fig. 8.1).
In the Timeline panel, select the solid layer and press UU (that's
the letter U two times fast). This will reveal all the properties