Week 6: code concepts revision

Dr Charles Martin

Semester 2, 2020


assignment 1 is marked and coming back to you soon.

assignment 2 is due on Monday!

COMP1720/6720 Course Survey

31 responses

Are you in Canberra?

Coder vs Artist

Quick Questions:

The webpage is useful: Mean 4.61 (Agree - Strongly Agree)

The online mode is easy for students: Mean 4.06 (Agree - Strongly Agree)

Tutorial sessions are helpful: Mean 3.87 (Neutral - Agree)

Things you like

“I enjoy being able to express my own creative ideas”


“use your imagination and find art”

“lecture format and teaching style :)”

“I enjoy how flexible the assignments are”

“partner collaboration as well as the lab tasks”

“I… find the art focused lectures to be very engaging and interesting”

“I like to show my personality through homework”

Things that are hard

“art part is a bit hard”

“my ideas… are too hard to achieve in p5. I wish I could… fit p5 perfectly”

“I think learning the code while others are already ahead and know it puts me at a disadvantage”

Any suggestions on what could be improved

  • want more samples

  • larger groups instead of pairs

  • feel isolated in labs

  • aesthetics is subjective (?)

  • more instructions, details in the assignments (?)

  • organised area of coding topics (?)

  • website too bright (!)

Partners and Group Work in Labs

  • lots of you enjoy group work

  • some of you would prefer labs to be individual

  • they are designed to be completed in pairs/groups

  • peer learning is an effective way to learn for students at different levels!

  • realistically, students don’t work in groups online unless it’s part of the task (shock!)

What we do

  • prepare labs to offer lot of practice

  • answer every question in the forum

  • keep you accountable for regular engagement

What you can do

  • ask questions in the forums
  • include something you have made in p5 in your pre-labs from now on
  • participate in labs as much as possible; focus on pairs and peer-learning
  • share your work in labs and on the forum
  • take ownership over your learning (fill gaps with videos and books)

code theory recap

painting like a 5yo

first words

  • background()
  • rect()
  • ellipse()
  • fill()
  • stroke()
  • random()

…and more in the reference

you have to be very specific

computers can’t deal with vagueness—it can’t figure out what you mean if you don’t say it clearly

talking to p5 about colour fill(red, green, blue)

talking to p5 about position ellipse(x, y, width, height)

the grid

how does the computer read?

function draw() {
    ellipse(10, 10, 20, 20);
    ellipse(310, 100, 200, 20);

function drawStuff() {
    rect(100, 100, 20, 20);
    fill(0,127, 255);
    rect(300, 200, 200, 120);


setup, draw, draw, draw, draw…

in p5, the order matters

because of the paint canvas metaphor, you can easily paint over something if you get the order wrong!


At this point you have all the tools you need to draw anything in p5!

Everything else is for making structured programs to save you time, save you typing, and to be interactive and dynamic!


a stable name for a value (which might change)

//  name        value
let dogeCount = 15;
let halfRange = width/2;
let randomValue = random(13);

To use variables:

  1. declare: let age; means there’s a variable called “age”
  2. initialise: age = 34 means set the age variable to the number 34
  3. use: when you do refer to the variable in your code, e.g. 2*age

(N.B., sometimes I write let instead of var - both mean “declare” and are almost the same)

Special Variables


These are declared and initialised by p5.js, but are for you to use!

What can we do now?

We can set out sketches with simple maths.

And we can start to be interactive!

representing truth

one little bit of maths…

the boolean type: true and false.

&& (and) || (or) ! (not)

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

conditionals and loops

syntax recap: conditionals

let the_sky_is_blue = false;
if (the_sky_is_blue) {
} else {
if (frameCount > 60) {
    text("you lose!");
} else {
    text("wow, you're so good at this!");

syntax recap: loops

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

What can we do?

  • dynamic sketches

  • make decisions in our code

  • repeat code to save typing!


syntax recap: functions

// name <---parameters--->
   rect(100, 100, 100, 100);

writing your own functions

function polkadot(x, y){
  ellipse(x, y, 20, 20);
function double(x) {
  return x * 2;


syntax recap: arrays

let arrayOfNumbers = [100, 24, -2];
let arrayOfStrings = ["John", "Paul", "George", "Ringo"];
let arrayOfBooleans = [true, false, true, true, false];
let emptyArray = [];

// arrays in arrays
let points = [[0, 5], [50, 100], [0, 200]];

the Array reference is on MDN, but several p5 functions use arrays as well

working with arrays

let arr = [1, 2, 3, 4, 5];

arr[1] = 42 // change the first element

arr.push(9000) // add to the end of an array
arr.unshift(0) // add to the start of an array

arr.pop() // remove from the end of an array
arr.shift() // remove from the start of an array

arr.length // get the length of the array

looping over arrays

let points = [[0, 5], [50, 100], [0, 200]];

for(let i = 0; i < points.length; i = i+1){
  let x = points[i][0];
  let y = points[i][1];
  // do stuff here



objects: a bunch of properties, each of which has a name and a value

a useful way of grouping related bits of data together

syntax recap: objects

let sally = {
  species: "Pikachu",
  level: 1,
  hp: 100,
  owner: "Ash",
  captured: true

get/set property values

// get the current value

// set a new value
sally.species = "Raichu"

remember that sally.species and sally["species"] are the same

arrays, or objects?

sometimes we want arrays, and sometimes we want objects

  • use an object when you have a bunch of related values with different types
  • use an array when you have a bunch of values with the same type

don’t be afraid to have an array of objects (and vice versa)

p5 is making objects (under the bonnet)

for example the color() function

let magenta = color(220,0,220);


what do you think the bubble object might look like?

function drawBubble(bubble) {
    fill(20, 50, 250, 150);
  ellipse(bubble.x, bubble.y, 50, 50);

looping over arrays of objects

// loop over all the bubbles
for(let i = 0; i < bubbles.length; i = i+1){

if it's on fire, don't panic

and check the console

further reading/watching

check out the sketches we’ve done together (link) and extend them!

play p5 reference golf (pick a few random p5 functions and see if you can use them to make something cool)

read this book: Make: Getting Started with p5.js

MDN javascript docs (tutorials, reference)