# Random properties

WIP - last updated 21 April 2021

## Abstract

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 a pseudorandom 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;``````
``````// '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;``````

### Random pop on

``````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``````

Tutorial: Randomly Reveal Layers & Emojis with Expressions, NSC

``````var seed = 1;
var seedRandom(seed,true);

var startTime = 0; // specify when fade starts
var delay = random(0,1); // random delay

linear(time, startTime + delay, startTime + delay + fadeDur, 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])``````

### 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"); ``````
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

### Random cycling color from a palette

``````// user variables
var mySpeed = posterizeTime(3);
var colorNull = thisComp.layer("controls");

// calculate num of color controls
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;``````

## 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);``````

``````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);``````
• for spriting images,

• refer to CoMotion 2021 title sequence background

## Source text & strings

### Generating non-repeating random numbers

``````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``````

### 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.