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Random properties
WIP - last updated 21 April 2021
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.
- 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 a pseudorandom number generator. To put simply, different seed number yield difference sequence of random number.
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;
// 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];
*/

// 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

// 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)

// 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
}

// Mass flickering
vel = 50;
seedRandom(0,true);
Math.sin(time*vel+random(index))*100;

// 'Wave flickering'
vel = 50;
seedRandom(0,true);
Math.sin(time*vel+index)*100;
// Combining
bool = 1
;
vel = 50;
seedRandom(0,true);
wave=Math.sin(time*vel+index)*100;
rand =Math.sin(time*vel+random(index))*100;
bool==0 ? wave : rand;

seed = 29;
threshold = linear(time,0,thisComp.duration,0,100); // or Connect to slider to animate switch on & off
seedRandom(seed,true);
randValue = random(0,90);
if(randValue < threshold){
100;} else 0

v2
v1
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)
// Apply on a color property eg. Fill, Shape Fill
seedRandom(1,true);
random([0,0,0,1],[1,1,1,1])
// 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");
- 1.retrieve the absolute index of a layer,
- 2.add a slider that increment by a value at a set interval
- 3.do the mod calculation
// 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");
includes
search
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;

// 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);
var seed = 1;
var seedRandom(seed,true);
var myDelay = random(1,10);
var time - myDelay;
var fps = 1;
x = framesToTime(Math.round(time*fps))
//There probably is a better way but I cannot figured it out right now.
//Apply this to a composition with a image sequence inside
seedRandom(0,true);
t= random(0,72);
framesToTime(t);
- for spriting images,
- refer to CoMotion 2021 title sequence background
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
eg. Matrix katakana
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.- 1.Download Jeff Almasol's script from aescript or redefinery
- 2.Install script via After Effects or putting directly into the Applications folder
- 3.Modify values
- 4.Select layers, and run script file
Last modified 2yr ago