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Link to this page: bit.ly/p5js-sp

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Welcome and Introduction

Your Teacher

I am Dave Briccetti (bri-’cheddy). I am a professional computer programmer who enjoys teaching programming to kids. I teach at two private schools, at the Lafayette Library occasionally, and I have individuals and small groups come to my house in Lafayette for lessons. If you want to know more about me, look around here on my web site.

When you follow links from this document, holding Shift and Cmd while you click will open the page in a new tab and switch to that tab.

About This Course

JavaScript and p5.js

JavaScript is a popular programming language, especially for programs that run in a web browser.

p5.js is a JavaScript framework for combining animation, graphics, sound and art with programming.

Class Details

Class Format

Our classes consist of:

  • Instruction (Lectures)
  • Exercises, where you practice what you’ve just learned, with specific goals
  • Creative project work, where you apply what you’ve learned in your own way
  • Show and tell, where we share our interesting creations

I usually keep lectures to just a few minutes. During this time I need your focus and full attention. During exercises and creative work, I encourage you to interact with your classmates. Get up, walk around and see what others are doing. Sit where you want, rearranging any time. Just make sure RoomHelper 3000 (see below) knows where you are.


Many of your parents are likely excited about you learning programming at school. They will be curious about what we are doing. Please point them to this page, so they can follow along with us. Show them at home what you are learning in class. Explaining your programs to others can increase your understanding.

When You Finish

When you complete assigned work, there’s always more to do. You can

  • Help others
  • Read the p5.js reference and learn about more features
  • Look at p5.js examples
  • Experiment, and make your own original creations

RoomHelper 3000!

I created this webapp specifically to help with this class. It will help me get to know your names and faces, and to call on you fairly.

The link to RoomHelper 3000 is in the Resources section, above.

Select your name, and the row and column of your computer, and push the Set button.

Multiple Browser Windows

I recommend you put RH3K (RoomHelper 3000) in a small browser window off to one side, and do your work in a larger window.

Computer Programming

Computer programs are instructions for getting a computer to perform a task, such as these:

  • Send a text message
  • Play a game
  • Manage a calendar
  • Drive a car
  • Fly a spacecraft

Types of Computers

Programs run on computers of different sizes and types:

  • mainframes
  • desktops
  • laptops
  • tablets
  • smartphones
  • Arduino and Raspberry Pi


Programs are written using programming languages. Some popular ones are:

  • Java
  • JavaScript
  • C++
  • Python
  • Scala

Building on the Work of Others

Programmers build on the work of other programmers. If we all had to figure out how to make 3D graphics or simulate physical processes (bouncing objects, collisions, gravity, etc.), it would take much longer to create our applications. People who are good at specific areas of programming (graphics, physics, music, etc.) publish their programs for use by others, as packages, libraries, or frameworks. p5.js, for example is a framework created by UCLA Assistant Professor Lauren McCarthy to make it easier for other programmers to make graphics, sound and art.

Some Example Programs for Inspiration

Try running some of my favorite p5.js creations, to get ideas and inspiration:

  1. Cube of Cubes
  2. Cube to Sphere
  3. 3D Clock (change view in CodePen so code is on the left side)
  4. Arpeggio Maker
  5. Metronome
  6. Talking Name Picker

Let’s Get Coding

Let’s create our first p5.js program, using the p5.js Online Editor.

Log in with a Google account. Push the Play button (white triangle) to see what the program does. It should draw a 400×400 gray rectangle. Change that program to look like the following, and then run it.

function setup() {
  createCanvas(400, 400);

function draw() {
  stroke(0, 255, 0);
  line(width / 2, height / 2, mouseX, mouseY);

Unlike with block-based environments like Scratch, in JavaScript you can make simple mistakes that prevent the program from even starting. Pay careful attention to things like parentheses ( ), braces { }, commas, and semicolons ;, and where capital letters are used.

Move the mouse over the rectangle and see what happens. Think about what width, height, mouseX and mouseY mean. What about the three numbers following stroke?

Explanation of the Program

  1. the two-dimensional coordinate system
    • x coordinates indicate the distance in pixels from the left side of the canvas
    • y coordinates indicate the distance in pixels from the top of the canvas
    • the origin is at the top left, in 2D, and in the center in 3D
  2. the red, green, blue (RGB) color model
    • our eyes are sensitive to these three colors
    • often we use numbers from 0 to 255 to specify how much of each color we want
  3. the setup and draw functions
    • setup is called once at the beginning, and usually creates the canvas
    • draw is called repeatedly and rapidly
  4. background
    • fills the entire canvas with the specified color
  5. fill, stroke
    • fill is the interior, and stroke is the outline
  6. mouseX, mouseY
    • where the mouse is
  7. line
    • a function that creates a line, given two pairs of (x, y) coordinates—one for each end

Saving Your Work

p5.js lets you save your work if you log in with Google, or create an account for p5.js. Instead, you can copy your code from the editor web page into a Google Doc or other file on Google Drive.

Challenge 1, Lines from Corners

Back to the p5.js online editor. Change the program so that instead of drawing one green line from the center to the mouse position, it draws two or more lines in different colors from corners. Collaborate with other students if you like.

Explore some of the examples provided by the p5.js editor. File -> Examples. Remember or make a note of some things you’d like to do or learn more about.

Solution to Challenge 1

I’ll code this for you in class. How many of you completed it?

Drawing Shapes

Let’s draw a few shapes. In order to position them on the canvas, we give x and y coordinates. Remember that x is the distance from the left side, and y is the distance from the top. p5.js lets us use width and height to get the canvas dimensions. We can position shapes using fractions of these dimensions. For example, width / 2, height / 2 gives us the coordinates of the center of the canvas. width * 0.25 would give us an x coordinate for 1/4 of the way across from the left edge.

I’ll show you some examples now.

In the p5.js reference, you can learn how to make other 2D “primitives” besides lines, such as triangles, rectangles, and ellipses.

Challenge 2, Face Program

Start with this program. Modify it so it looks like this:

Challenge 2 expected result

What you have to understand in order to do this challenge:

  • rectMode(CENTER) changes things so that when drawing rectangles, you give the location of its center and not of the top left corner
  • strokeWeight(…) sets the thickness of the stroke
  • you can use names for colors. Notice that I changed some colors.
  • since there are two rectangles, you’ll need to duplicate the line of code that makes the one rectangle, and change something in the new line. Shall I show you how to duplicate a line?
  • for the point, you’ll duplicate it twice so you’ll have three points


Here is the actual program I used to make the drawing with two “eyes”. It’s shorter than the code I made in the video.

Bonus Problem

Make your own, original creation.


Star Field

Here’s a pretty cool star field 3D program. It’s complicated, so let’s make a simpler, 2D one together, and maybe come back to this one when you’re more experienced.

Random Points?

Here’s another program with random points. Run it and see what it makes. Can you figure out how it works? We may return to this program later, too.

Simple Star Field

Let’s make a simple 2D star field together. What you’ll learn:

  • There’s a feature of p5.js called the random function that lets us randomly create x, y coordinate pairs and colors
  • We can store colors we want to use in a data structure known as an array, and choose from those colors randomly

Steps in making a star field program:

  1. Create an array of the star colors
  2. Set the background to black, in the setup function
  3. In draw, randomly pick x and y coordinates and a color, and draw a point in that color

Challenge 3, Random Shapes

Make a program that makes shapes (rectangles, ellipses, triangles or lines) appear on the canvas. Choose one or more of the following randomly:

  • Position
  • Size and shape
  • Color (stroke or fill)
  • Stroke weight

Need a tip to get started? Modify the simple Star Field program and use rect instead of point.

Show and Tell

We’ll show some of your programs to the class towards the end of the period.

A Solution

Constants and Variables

Computer programs often need to keep track of things:

  • How much an object is currently rotated
  • The current color of an object
  • When a student will be allowed to send their next chat message (flood control)
  • A game score
  • The name of the player
  • Where on the game map a player is located
  • What the player is carrying (inventory)

Some of these things—a score, for example—are numbers. Others that contain words or symbols, such as a name, are strings. A location in a 2D or 3D world might contain a group of two or three numbers, (x, y) or (x, y, z) coordinates, or latitude, longitude and elevation. An inventory is a collection of zero or more items, the items being strings or some other type. A common collection type in JavaScript is the array.

When you play a computer game and you save the game (or it saves itself automatically), it writes the values of the variables that track where you are in the game from random access memory (RAM) onto more permanent storage—a solid state drive (SSD) or a hard disk drive (HDD). (What’s the difference?)

Let’s play with some variables in a web site that lets us visualize running a program.

3D Graphics

It’s time now to leave the flat world of the (x, y) plane and enter the (x, y, z) three-dimensional space!

The Origin and the Axes

The origin is now in the center of the screen. x is still the horizontal position, and y is still the vertical position. z is the distance away from you, with larger numbers meaning closer to you.

A Rotating Box

I’ll show you a sketch with a rotating box. mouseX controls the rotation speed, and mouseY controls the color.

A Rotating Box, from Scratch

Let’s create a rotating box program, from scratch. Make it with me.

Other 3D Shapes

Let’s look in the reference for how to make other 3D shapes.

Placing Shapes in Different Positions

Unless you request otherwise, shapes you place will appear ot the origin (the center).


You can move objects on any of the three axes, by calling translate. You give translate three numbers: the amounts you want to move on each of the three axes. These numbers can be positive or negative.

Push and Pop

If you place multiple objects in the scene, using translate for each, the translations will interfere with each other. So we isolate the translations by surrounding the drawing we do with them with calls to push and pop. push saves the current transformation state (what things like translate and the rotation functions) do, and pop restores the state to how it was before the push.

Simple Example

This program draws a cube and a cone, using push, translate, and pop.

Cooler Example

This cooler program has four objects, and they all rotate together around the y axis.

Challenge 4, Multiple 3D Shapes Artistic Sketch

Combine two or more shapes (a cylinder and a cube, perhaps). Be creative and artistic in your choice of colors, sizes and shapes.

If you like, have it rotate. You might control various aspects of it with mouseX and mouseY, as I did.

Multiple 3D Objects Using Loops

When placing multiple similar objects in your scene in a regular pattern, you needn’t repeat blocks of code. You can use loops.

Complicated Example

This example makes a field of objects. It uses a loop within a loop. This is meant to show you the power of loops, but let’s not study it just yet.

Simpler Example

This simpler example uses a single loop to make three objects. Let’s study it.

Challenge 5, Multiple 3D Shapes Using One or More Loops

Make a program that creates multiple objects using one or more loops. You can use one of the above programs as a starting point if you like.

Bonus challenge: use a loop within a loop within a loop to translate on x, y, and z.


p5.js has a feature that lets us make sounds.


An oscillator creates a tone at a specific frequency. This code makes a tone at the frequency 440 hz.

Run this “440 Oscillator” program

You can change the 440 to different numbers to hear different frequencies.

Oscillator reference

Controlling Frequency with mouseX

You can change the frequency when the mouse moves.

Mouse frequency example program

Pitch Matching Game

Here is a very cool pitch matching game, using two oscillators.

Tuning and “Beats”

Challenge 6: Do Something Creative with Sound

Use what you’ve learned about p5.Oscillator to make something creative and interesting. Here is an example.

Playing Notes Using MIDI Note Numbers

Let’s study this Multi-Octave Spooky Music program and make spooky Halloween music.