What's p5.js?

p5.js is JavaScript (JS) library, which is used for creating graphic and interactive experiences for artists and developers. The code is written directly in JS, and it gets executed like any other JS file that is included on a website. It requires an empty HTML file that links to the p5.js library and your sketch file in the header. 

p5.js based on the core principles of Processing, but there are some differences in the language syntax. 

Using p5.js

For the purpose of the course we are going to use Openprocessing.org. It's an online platform, where anyone can create and share visual-based, open source projects. The big advantage of open processing is that the users can like and comment other sketches, follow other users and create themed collections. 

Alternative Editors

p5.js has its own web-based editor which compiles the code on the go and displays it directly in the browser.

Processing IDE, which has to be put in p5.js mode in order to compile the JS code. It consists of three main parts. 

1. The text editor, where you can write (or paste in) the code.

2. Message area and Console/Errors window. The Message area which displays the errors and is useful to see if you e.g., miss a semicolon. The Console/Errors window displays warnings, but can be also used to output text for debugging.

3. The final part is the Display window. This is where you can see the results of our code after it is compiled, by pressing the Run button in the upper left corner. 

The third option is to use one of the text editors e.g. Sublime, Atom, Visual Studio Code and run p5.js directly on your computer. For that, you would need to download a complete p5.js library and run the code on a local server. For more experienced developers, p5.js can also be used in any web application using npm and the "instance mode" of p5.js

References:

In order to understand the examples and to write your own programs, you will be using references, i.e. artefacts that describe a programming language.

Basic Sketch Structure

Every p5.js program consists of setup() and draw() function. Setup() runs when the program starts and it's used to set the initial environment properties, such as the size of the canvas in the browser window. Draw() executes the code inside the block until the program is stopped or noLoop() is called. We will learn more about how functions work in the p5.js Writing our own Functions.

function setup() {
  createCanvas(300,300);
  // setup stuff
}

function draw() {
  // draw stuff
}

You will notice there are some special symbols used here, and everything is organised in a specific structure. The syntax of a programming language defines how all these things should be used. We will get to know what all these symbols do in the following examples.

Example 1 : Graphic output

This example shows how to draw graphics directly to an output window. 

function setup(){
	createCanvas(300,300); // define canvas size 
	stroke(255,255,255); // define line colour 
}

function draw() {
	background(0); // define background colour 
	strokeWeight(1); // line thickness 
	line(100,10,100,150); // draw a line 
	line(150,10,150,200);
	line(200,10,200,250);
	fill(0,0,0); // define fill colour 
	strokeWeight(5); // line thickness 
	ellipse(100,150,50,50); // draw an ellipse
	ellipse(150,200,50,50); // draw an  ellipse
	noFill(); // turn of fill
	ellipse(200,250,50,50); // draw an  ellipse
}

Example 2 : Complex Forms

This example shows you how to change line attributes and how to draw more complex shapes using the beginShape() and endShape() functions.

function setup() {
	createCanvas(300,300); // define canvas size 
	stroke(255); // define line colour 
	strokeWeight(8); // line thickness
	strokeJoin(MITER); // this is the default
 	//strokeJoin(BEVEL);
 	//strokeJoin(ROUND);
	noFill();
}

function draw() {
	background(0); // define background colour 
	beginShape();
 	vertex(50,50);
 	vertex(200,50);
 	vertex(200,200);
 	vertex(50,200);
 	vertex(50,100);
 	vertex(150,100);
 	vertex(150,150);
	endShape();
}

Example 3: Colors and Transparency

Colours are defined with 3 values, the so-called RGB values. The colour consists of three components (red + green + blue) and is determined by additive colour mixing. The value of each colour can range from 0-255.

This range of numbers results from the fact that each colour value represents an 8-bit value. Therefore, true colour can be represented with 24-bit (3 * 8-bit = RGB).

Forms can also be transparent, using the alpha channel. The colour is simply extended by a 4th parameter (RGBA). Smaller alpha values are more transparent than greater ones.

function setup() {
	createCanvas(300,300);
	noStroke();
}

function draw() {
	background(0);
	fill(210,200,200);
	ellipse(125,150,50,50);
	stroke(150,10,10);
	fill(100,100,90,200);
	beginShape();
 	vertex(50,50);
 	vertex(125,150);
 	vertex(200,50);
 	vertex(200,200);
 	vertex(50,200);
 	vertex(50,50);
	endShape();
}

Exercise 1:

Experiment with the examples by adding or combined new drawing commands (Arc, Point, Triangle, etc.). Look through the references page to find more.