Adobe After Effects CS4 - Manual (Page 692)

686 USING AFTER EFFECTS CS4
Expressions
Last updated 12/21/2009
More Help topics
“ Add, edit, and remove expressions ” on page 647
“ Create a camera layer and change camera settings ” on page 186
Expression example: Flip layer horizontally if facing away from camera
❖ Apply the following expression to the Scale property of a 3D layer:
if (toCompVec([0, 0, 1])[2] > 0 ) value else [-value[0], value[1], value[2]]
More Help topics
“ Add, edit, and remove expressions ” on page 647
“ Create a camera layer and change camera settings ” on page 186
Expression example: Animate scale at each layer marker
❖ Apply the following expression to a Scale property to make a layer wobble at each marker:
n = 0;
t = 0;
if (marker.numKeys > 0){
n = marker.nearestKey(time).index;
if (marker.key(n).time > time) n--;
}
if (n > 0) t = time - marker.key(n).time;
amp = 15;
freq = 5;
decay = 3.0;
angle = freq * 2 * Math.PI * t;
scaleFact = (100 + amp * Math.sin(angle) / Math.exp(decay * t)) / 100;
[value[0] * scaleFact, value[1] / scaleFact];
More Help topics
“ Add, edit, and remove expressions ” on page 647
Expression example: Start or stop wiggle at specific time
You can use any expression in place of the wiggle expression used here, to begin and end the influence of any
expression at a specific time.
• Apply the following expression to a property to wiggle it beginning at time 2 seconds:
timeToStart = 2;
if (time > timeToStart){
wiggle(3,25);
}else{
value;
}
• Apply the following expression to a property to stop wiggling it at time 4 seconds: