One of the most useful things you can do with Expressions is randomizing layer properties. Some properties include transform properties (position, rotation, scale, or opacity), color, or even Time Remap. Learning to randomize properties is a good beginner exercise to raise one's comprehension of Javascript Expression. In this page, we will cover different ways to randomize properties.
Understanding Random functions
random()
random(minValue, maxValue)
seedRandom(seed, timeless=false)
Core skills: randomize values, arrays, color
What is a seed?
A random seed (or seed state, or just seed) is a number (or vector) used to initialize apseudorandom number generator. To put simply, different seed number yield difference sequence of random number.
Position
Wiggle
wiggle(20,50);
// wiggle x axis
x = wiggle(20,50)[0];
y = value[1];
pos = [x,y]
// wiggle y axis
x = value[0[;
y = wiggle(20,50);
pos = [x,y]
// getting wiggle increment values only
inc = wiggle(20,50)-50;
positioning
// randomize between a range
seedRandom(1,true);
x = random(300,1920);
y = random(500,1080);
[x,y];
// using arrays and variable
seed = 20;
min = [25,25,-1900];
max = [thisComp.width,thisComp.height,50]
seedRandom(seed,true);
random(min,max);
/* This is same as this
x= random(min[0],max[0]);
y= random(min[1],max[1]);
z= random(min[2],max[2]);
[x,y,z];
*/
Opacity
Flickering / Strobe
// VARIABLES
minSeg = 1.5; //minimum interval (must be > 0)
maxSeg = 2.5; //maximum interval (must be > minSeg)
// flickering duration
minFlicker = .5; //must be less than minSeg
maxFlicker = 1; // must be less than minSeg
flickerDur = random(minFlicker,maxFlicker);
//initial conditions
segEndTime = 0;
i = 1;
// Continuous loop: create a fixed random segment value and add to segEndTime
while (time >= segEndTime){
i += 1;
seedRandom(i,true);
segEndTime = segEndTime + random(minSeg,maxSeg);
}
// Switch back to use the current time as input to the random seed.
seedRandom(1,false);
// As time > threshold, flicker
if (time > segEndTime - flickerDur){random(0,100) }else{ 100 }
// Source: http://www.motionscript.com/expressions-lab-ae65/swinging-light.html
// Also see: http://www.motionscript.com/mastering-expressions/random-3.html
Wiggle
// control = thisComp.layer("control"); // connect to null layer with sliders
freq = 1;
amp = 100;
octave = 1;
amp_mult = 3;
wiggle(freq, amp, octave, amp_mult, time)
Wiggle with flicker
// control = thisComp.layer("control"); // connect to null layer with sliders
freq = 1;
amp = 100;
octave = 1;
amp_mult = 3;
opacity = wiggle(freq, amp, octave, amp_mult, time)
// VARIABLES
minSeg = control.effect("minSeg")("Slider"); //minimum interval (must be > 0)
maxSeg = control.effect("maxSeg")("Slider");; //maximum interval (must be > minSeg)
// flickering duration
minFlicker = control.effect("minFlicker")("Slider");; //must be less than minSeg
maxFlicker = control.effect("maxFlicker")("Slider");; // must be less than minSeg
flickerDur = random(minFlicker, maxFlicker);
//initial conditions
segStartTime = 0;
segEndTime = 0;
i = 1;
// Continuous loop: create a fixed random segment value and add to segEndTime
while (time >= segEndTime) {
i += 1;
seedRandom(i, true);
segStartTime = segEndTime;
segEndTime = segEndTime + random(minSeg, maxSeg);
}
// Switch back to use the current time as input to the random seed.
seedRandom(1, false);
// As time moves threshold, flicker
if (time > segEndTime - flickerDur) {
random(0, 100)
} else {
opacity
}
Using sine function
// Mass flickering
vel = 50;
seedRandom(0,true);
Math.sin(time*vel+random(index))*100;
var seed = 1;
var seedRandom(seed,true);
var startTime = 0; // specify when fade starts
var delay = random(0,1); // random delay
var fadeDur = framesToTime(20); // duration of fade
linear(time, startTime + delay, startTime + delay + fadeDur, 0, 100)
seed = 1;
seedRandom(seed,true);
startTime = random(0,1); // random start time
dur = framesToTime(20); // duration of fade
linear(time, startTime, startTime + dur, 0, 100)
Random Color
RGB color
// Apply on a color property eg. Fill, Shape Fill
seedRandom(1,true);
random([0,0,0,1],[1,1,1,1])
From a color palette
Sequential cycling color from a palette
// user variables
var vel = 2 ;
var numCol = 5;
//main
var inc = Math.floor(time * vel) + index; // counter
var n = inc % numCol + 1; // keep the num between 1 & numCol value
// reference a null with colors controls only
thisComp.layer("controls").effect(n)("Color");
retrieve the absolute index of a layer,
add a slider that increment by a value at a set interval
do the mod calculation
Random cycling color from a palette
// user variables
var mySpeed = posterizeTime(3);
var colorNull = thisComp.layer("controls");
// calculate num of color controls
var numFx = colorNull("ADBE Effect Parade").numProperties;
var numCol = 0;
for (i = 1; i <= numFx; i++) {
if (colorNull.effect(i).name.includes("Color")) {
numCol += 1;
}
}
// main
var n = Math.ceil(random(numCol));
thisComp.layer("controls").effect(n)("Color");
Get num of color controls
var colorNull = thisLayer("ADBE Effect Parade");
var numFx = colorNull.numProperties;
var numCol = 0;
for (i = 1; i <= numFx; i++) {
if (thisLayer.effect(i).includes("Color")) {
numCol += 1;
}
}
numCol;
var numFx = thisLayer("ADBE Effect Parade").numProperties;
var numCol = 0;
for (i = 1; i <= numFx; i++) {
if (thisLayer.effect(i).name.search("Color") >= 0) {
numCol += 1;
}
}
numCol;
Time Remapping / Playback
Random frame playback
// Source Dan Ebbert
fr = 12; // frame rate;
numFrames = 8;
seedRandom(index,true);
seg = Math.floor(time*fr);
f = Math.floor(random(numFrames));
for (i = 0; i < seg; i++)
f = (f + Math.floor(random(1,numFrames)))%numFrames;
framesToTime(f);
Random delayed/advanced layer playback
var seed = 1;
var seedRandom(seed,true);
var myDelay = random(1,10);
var time - myDelay;
Play one frame at a time (without 'float time')
var fps = 1;
x = framesToTime(Math.round(time*fps))
//There probably is a better way but I cannot figured it out right now.
Random still frame (Good for spriting)
//Apply this to a composition with a image sequence inside
seedRandom(0,true);
t= random(0,72);
framesToTime(t);
var nums = [1,2,3,4,5,6,7,8,9,10],//all numbers to be randomized
ranNums = [],
i = nums.length,
j = 0;
while (i--) {
j = Math.floor(Math.random() * (i+1));
ranNums.push(nums[j]);
nums.splice(j,1);
}
ranNums
Using text animators
Binary
From a specific set of characters or words
eg. Matrix katakana
Building a Randomizing rig or preset
Core skills: randomize time, Spriting, building controls, conditional randomizing with modulo operator (alternate colors)
Keep in After Effects scripting, the random function only returns a random number between 0 to 1. What this means is that you cannot do use random(20,30) to generate a random value between 20 and 30. You have to write a function for that, which you can reference here.
Randomizing with AE scripts
Download Jeff Almasol's script from aescript or redefinery
Install script via After Effects or putting directly into the Applications folder
