Week 3: conditionals, iteration and colours

Brent Schuetze

Semester 2, 2023


assignment 1 due this coming Monday 9pm (any questions?)

Remember that the git process you follow for the labs is exactly the same as the process you’ll follow to submit assignment 1!

remember the Git help videos

Course reps

Your course reps are now listed on the Getting Help page.

These fine folks are here to listen to your concerns or issues confidentially, you can contact them over email or on the forum.

Example Assignment 1

Yichen’ Example Assignment 1: Bluebot

ass1 artist statement

Your submission must include a short (max 200 words) artist statement. This is a short document, written in the first person, which explains:

  • What your artwork is.
  • Why it is an artwork.

Tell us what is interesting and artistic about your submission—don’t assume that we can guess. Explain how and why your work is interesting, coherent, and has personality.

  • don’t explain your code line-by-line—instead, think about the overall goals and effect you’re trying to achieve

  • use references to support your statement.


Having references in your references.md is good!. (You must have at least two!)

If I include an image from the internet—should it be in my references? (YES!)

If I include code from p5js.org—should it be in my references? (YES!)

If I am inspired from a book—should it be in my references? (YES!)

If my friend suggested a nice colour—should it be in my references? (YES!)


p5 uses a setup, draw, draw, draw… “draw loop”

variables are a way to give names to values (e.g. numbers, strings, etc.) which might change


the “path” the running program takes through the code

jump around, then jump back (but it’s predictable)


mostly numbers so far: numeric literals (e.g. 42) and number variables (e.g. height, mouseY, frameCount)

but there are other types (as we’ll see)

code theory

two new concepts:




if I run, I can make it to the tram stop in time”

if I have a spare month I’ll read War and Peace

“I’ll start assignment 1 when I’ve finished watching Netflix”

Boolean type

there’s a special data type for representing truth values called Boolean. How is it different?

  • Boolean variables must be either true or false (no other possibilities!)
// here are some boolean variables
let the_sky_is_blue = true;
let the_sea_is_red = false;

Boolean logic

you can also get a Boolean from the result of a logical expression (MDN docs)

  • < (less than)
  • <= (less than or equal to)
  • > (greater than)
  • >= (greater than or equal to)
  • == (equal to, note the double equals sign)
  • != not equal to

Boolean logic

all these variables are also Boolean

let x_is_small = mouseX < 100;
let y_is_big = mouseY >= 500;
let jan_is_happy = !true;

combining Boolean expressions

we can use logic to check multiple things at once:

  • && (and)
  • || (or)

or inverse them:

  • ! (not)

combining Boolean expressions

this allows us to do things like

(the_sky_is_blue && the_sea_is_red)
(the_sky_is_blue || the_sea_is_red)

note: each whole line above evaluates to true or false depending on whether the parts are true or false

using Boolean expressions to make decisions

what if you want your sketch to do one thing some of the time, and another thing the rest of the time?

javascript has an if statement:

if (condition) {
  // do something
} else {
  // do something else

this also has a human-language intuition

if (the_sky_is_blue) {
} else {

let’s have a look at a basic example.

what could Boolean variables be used for?

monitoring some aspect of a program which is either true or false:

  • has something been clicked?
  • is something finished?
  • enhancing readability of your code (e.g. if you create variables called isFinished, sceneStarted, etc.)

JavaScript vs p5: a note about the docs

This is a bit tricky for new coders, the documentation is in two places.

  • language features like if statements (and while/for loops later) are part of the javascript programming language (which is what p5 is written in)

  • the best javascript docs are on the Mozilla Developer Network (MDN) (p5 reference is no good here)

  • I’ll point you to the reference material which is most appropriate


i.e. loops

you’ve already seen a loop—the draw loop

but sometimes you want to do multiple things in a loop within a frame (i.e. a single flow through the draw function)

while loop

the first type of loop we’ll look at is the while loop:

  // do some things while "condition" evaluates to true

does this look familiar?

while loop intuition

a human-language intuition:


let’s have a look at an example

a working example

let count = 0;

// count < 5 is a logical comparison
// (with a true/false answer)
while(count < 5){
    random(width), random(height), // x and y
    10*count, 10*count             // width and height
  count = count + 1;
function setup() {
  createCanvas(windowWidth, windowHeight);

function draw() {

  let x = 0;
  while (x < width) {
    fill(x/2, random(255), 255);
    rect(x, 0, random(10), random(height));
    x += random(10);

looping tips

make sure the Boolean expression will evaluate to false at some stage—otherwise you’ll loop forever!

you probably want to have some variable which you modify in the loop, and then when the modifications are “done” the expression in the while loop should be false

when writing a loop, look at your code: be the computer (think about types & flow)

for loop

the other type of loop in javascript is the for loop

it’s like a while loop, but it has the “modify the loop variable” (e.g. count = count + 1;) part built-in

for (let i = 0; i < 10; i=i+1) {
  // loop code goes here

in this example we called the loop variable i (although you can give it whatever name you like)

differences between for and while loops

let i = 0; 
while (i < 10) {
  // loop code goes here 
for (let i = 0; i < 10; i=i+1) {
  // loop code goes here

code theory recap

Boolean expressions (e.g. mouseX < 500) and if statements let us control the flow: do this or that

loops (for, while) allow us to control the flow: do this over and over again

you’ll get lots of practice in the labs

how to think about colour

How do we keep track of colours?

How do we find colours?

How do we make art with colours in p5?


What is a primary colour?

What is a primary colour?

there are two basic ways to mix colours together

adding (good for shining light out of a screen)

subtracting (good for working with materials that absorb light)

Two bits of p5 to know about:

  • blendMode (ref) changes how colours interact.

  • colorMode (ref) changes how colours are represented.

Newton: White light is made of colours

How do we keep track of these colours?

Newton deduced that white light must be composed of all these colours


Goethe's colour wheel


symmetric colour wheel with associated symbolic qualitites


Tate Collection, UK

Johannes Itten's Colour Wheel (1920s)

Primary, secondary and tertiary

good if you’re a painter!

Munsell System (1910s)

but for scientific notation etc, we need a different approach

Hue, Chroma, Value

Hue, Saturation, Brightness


Color spaces for computer graphics (1978)

Color spaces for computer graphics

SIGGRAPH Comput. Graph.

Joblove, George H. and Greenberg, Donald


What are the point of these colour systems?

Attempts to define what colour is made of.

Newton, Goethe, Itten: Made of combinations of Red, Blue and Yellow (primary colours for subtractive mixing)

Munsell: Made of three independent properties: hue, chroma, and lightness - (perceptually uniform)

Joblove/Greenberg: Defined hue/saturation/brightness as a good standard for computer graphics (see Wikipedia).

Why should you care?

Suppose you have a green colour in RGB, but you want to make it more intense or brighter.

What R, G, and B values should you change to achieve this?

Colour as Art

What if we made art where “colour” is the material?

Olafur Eliasson (b. 1967)

Your rainbow panorama


ARoS Aarhus Kunstmuseum, Denmark


Olafur Eliasson (b. 1967)

Your rainbow panorama


ARoS Aarhus Kunstmuseum, Denmark


Olafur Eliasson (b. 1967)

Your rainbow panorama


ARoS Aarhus Kunstmuseum, Denmark


Olafur Eliasson (b. 1967)

Your rainbow panorama


ARoS Aarhus Kunstmuseum, Denmark


Olafur Eliasson (b. 1967)

Feelings are Facts


Ullens Center for Contemporary Art, Beijing

📷 Studio Olafur Eliasson

created using smoke and lights

interested in the intersection of colour and sound

Roy de Maistre

Rhythmic composition in yellow green minor


Johannes Ittens’s 7 types of contrast

  • hue
  • value (light and dark)
  • temperature
  • complement
  • simultaneous
  • saturation
  • extension

contrast is what happens when you put two or more colours together and it gives off a sort of feeling

From Ittens' 'Elements of Colour', (1961)

From Ittens' 'Elements of Colour', (1961)

finding colours

Online colour palette generators:

http://paletton.com/ (shows complementary colours, triads/tetrads etc)

https://coolors.co/app (generate random palettes which look decent)

http://colormind.io/ (uses AI because… reasons)

let's make some colour art

Let’s explore colour spaces in RGB and HSB!

further reading/watching

Shiffman videos:


while and for loops

MDN javascript docs (have a look at the Tutorials & References menus in the sidebar)