Adobe After Effects CS4 - Manual (Page 669)

663 USING AFTER EFFECTS CS4
Expressions
Last updated 12/21/2009
Argument type: vec1 and vec2 are Arrays.
Returns the dot (inner) product of the vector arguments.
cross(vec1, vec2) Return type: Array [2 or 3].
Argument type: vec1 and vec2 are Arrays [2 or 3].
Returns the vector cross product of vec1 and vec2. Refer to a math reference or JavaScript guide for more information.
normalize(vec) Return type: Array.
Argument type: vec is an Array.
Normalizes the vector so that its length is 1.0. Using the normalize method is a short way of performing the operation
div(vec, length(vec)) .
length(vec) Return type: Number.
Argument type: vec is an Array.
Returns the length of vector vec.
length(point1, point2) Return type: Number.
Argument type: point1 and point2 are Arrays.
Returns the distance between two points. The point2 argument is optional. For example, length(point1, point2)
is the same as length(sub(point1, point2)) .
For example, add this expression to the Focus Distance property of a camera to lock the focal plane to the camera's
point of interest so that the point of interest is in focus:
length(position, pointOfInterest)
lookAt(fromPoint, atPoint) Return type: Array [3].
Argument type: fromPoint and atPoint are Arrays [3].
The argument fromPoint is the location in world space of the layer you want to orient. The argument atPoint is the
point in world space you want to point the layer at. The return value can be used as an expression for the Orientation
property, making the z axis of the layer point at atPoint. This method is especially useful for cameras and lights. If you
use this expression on a camera, turn off auto-orientation. For example, this expression on the Orientation property
of a spot light makes the light point at the anchor point of layer number 1 in the same composition:
lookAt(position, thisComp.layer(1).position)
Random Numbers methods (expression reference)
Note: The wiggle method—which is used to randomly vary a property value—is in the Property attributes and methods
category. (See “
Property attributes and methods (expression reference) ” on page 677.)
seedRandom(offset, timeless=false) Return type: none.
Argument type: offset is a Number, timeless is a Boolean.
The random and gaussRandom methods use a seed value that controls the sequence of numbers. By default, the seed
is computed as a function of a unique layer identifier, the property within the layer, the current time, and an offset
value of 0. Call
seedRandom to set the offset to something other than 0 to create a different random sequence.
Use true for the timeless argument to not use the current time as input to the random seed. Using true for the timeless
argument allows you to generate a random number that doesn’t vary depending on the time of evaluation.