Workshop: Introduction to Creative Coding

• Week 1 - Coordinates, shapes and colour
• Week 2 - Animation, conditionals & random numbers
• Week 3 - Iteration, arrays, objects and pixel arrays
• Week 4 - Other inputs and APIs

Week 1 - Coordinates, shapes and colour

Outcomes

• Set up development environment
• Understand the principles of locating points on screen
• Drawing shapes
• Understanding additive colour and using RGB colour space
• Use browser-based tools for debugging and logging
• Animate shape or colour using variables

What is p5.js?

During this series of workshops you will be using a library called p5.js to learn the fundamentals of programming. The p5.js project is the most recent part of a complex history of open-source, creative coding libraries going back to the early 2000s. It is supported by the Processing Foundation, which is a not-for-profit organisation that emerged from the creative coding library Processing.

From a technical perspective, p5.js is simply a JavaScript library. A library is a collection of code put together to simplify a task or a collection of tasks. In this case p5.js provides a lot of functionality that makes it easy to draw shapes, colours and handle user interaction within a web page.

This video from Daniel Shiffman is a good introduction to p5.js and the creative coding platforms that preceded it:

Supporting code

The code for this workshop is hosted on Github, which is a web-based repository for hosting and versioning code.

Download the code and unzip it on your desktop.

A p5.js project

In this exercise you will set up a p5.js project using the Atom text editor, then examine the different files and run the code in a browser. The code to support this section is located in the following directory and is available to view on Github:

/00_empty_project/

Topics

• p5.js project structure
• What is a sketch?
• What do the setup() and draw() functions do?
• Adding your project to Atom
• Using the browser debugging tools

A p5.js project

Below is the structure of a p5.js project, which is essentially a web project made up of HTML and JavaScript files.

/00_empty_project/
  ├── index.html
  ├── libraries
  │   └── p5
  │       └── p5.min.js
  └── sketch.js

index.html

p5.js is a JavaScript library designed for drawing to a web page. For JavaScript code to run in a browser it needs to be included in a HTML file. The index.html file is the 'entry point' for the browser to access our project code. Note the use of the <script> tag to import two JavaScript files (line 7 & 8).

The first JavaScript file (libraries/p5/p5.min.js) is the p5.js library containing a vast amount of code that we can use without having to fully understand.

The second JavaScript file (sketch.js) is where we write our own code.

sketch.js

Below is the minimum required code for a p5.js sketch. This is simply an empty template for us to start coding and will not produce any visual results.

To summarise, we now know that when the browser loads the index.html file, it will import the p5.js library and the sketch.js file, and then execute the code we have written.

setup() and draw()

Within the sketch we have two functions: setup() and draw(). p5.js calls/runs these functions for us in a particular order. The setup function runs first and only once. The draw function then runs repeatedly until the web page is closed.

Debugging

When coding in any language and with any level of experience or expertise, you will almost always encounter bugs. Writing code is often a trial and error process. Therefore, to be productive programmers we need debug our code in order to identify and fix problems. This means using tools to show us where errors in our code occur whilst it is being executed in its runtime environment.

p5.js is written in JavaScript and therefore the environment for running our code will be the browser. There are developer tools built into all the major browsers that van be used for debugging. For now, we recommend using Chrome so we are all using the same tools throughout the workshop. Chrome has an easy to use and fully featured set of developer tools also known as DevTools.

• Take a look at Chrome's instructions on how to use the DevTools, in particular the Accessing the DevTools section
• A more involved introduction to developer tools from HTML5Rocks.
• p5.js has a very good Field Guide to Debugging. It explains that debugging is a creative problem solving task and stresses the importance of taking time to observing the problem in order to understand it.

Exercise

• Add the 00_empty_project directory to Atom
• Open index.html in a browser
• Use the developer tools to see logged messages

Coordinates and Shapes

In this exercise you will learn how to locate and target positions (i.e. pixels) on screen for drawing. We will also learn how to use some basic functions of p5.js for making primitive shapes. The code to support this section is located in the following directory and is available to view on Github:

/01_coordinates_and_shapes/

Topics

• Comments
• Using p5.js functions
• Drawing some simple shapes
• Locating points on the screen using Cartesian Coordinates

Comments

When writing code it is a good idea to sometimes write notes to yourself or other coders to explain what the code is meant to be doing. The way we do this is by adding comments. Comments can be added in two ways:

1. Single line comment
   Using the double forward slash (//) at the beginning of the line instructs the browser to ignore that entire line.

// This rectangle is the button that starts the game.
rect(20, 100, 50, 100);

2. Block quotes
   A forward slash and an asterisk (/*) will start the comment block and the reverse, an asterisk and a forward slash (*/), will end it. The browser will ignore everything in between, which can be multiple lines of notes.

/*
This is a reminder that the code below is not complete yet. 
It might be improved by taking this code and making it into 
a function of its own.
*/

You will see comments used in this exercise to ignore lines of code that are incomplete or contain errors.

p5.js drawing functions

We will address functions in more detail later but here is a brief explanation. A function is multiple lines of code that achieve a specific task. These are grouped together and given a name so that they can be used again and again.

Later on we will write our own functions but, for now, we will use some functions that are provided by the p5.js library.

• createCanvas(800, 450)
  This is called inside setup() to create a drawing area of a certain width and height – in this example the canvas is 800 pixels wide and 400 pixels high.

• rect( 50, 100, 200, 40 )
  This function draws a rectangle 50 pixels from the left of the canvas (x), 100 pixels from the top (y). The width of the rectangle will be 200 pixels and the height will be 40 pixels.

Cartesian Coordinates

To understand how to position elements on screen we need to go back to school. When drawing to a screen on the majority of programming languages will use a version of the Cartesian Coordinate system.

It was a system developed in the 17th Century by René Descartes for locating unique points on a mathematical representation of a 2D plane using numerical pairs; e.g. (50, 100), (251, 122). This revolutionised the fields of geometry and algebra centuries before the first computer screens.

For our purposes, the numerical pairs represent the number of pixels counting from left to right (x) and top to bottom (y). For most, the diagram on the left will be familiar for plotting points on a graph:

(image credit: https://processing.org/tutorials/pixels/)

The only difference between plotting points on a graph and on a screen using code is that (in nearly all languages) we plot points on a screen starting from the top left corner rather than the centre. You need an x value (horizontal position) and a y value (vertical position) in order to specify a pixel position on screen.

Using coordinates in functions

In our code we call the following function:

rect( 50, 100, 200, 40 );

The function accepts 4 arguments that define the position and shape of the rectangle:

rect( x, y, width, height);

Therefore the result of this will be the following:

Each function in the library can take different arguments depending on its purpose. For example, when defining a line we do not specify the width and height because lines are 1 dimensional (they have zero or negligible height). Instead, a line is better defined by a start and end position on our screen; two sets of Cartesian Coordinates:

line(x1, y1, x2, y2);

Below is a diagram showing how this using the cartesian coordinates system.

(image credit: https://processing.org/tutorials/pixels/)

You will not be expected to instinctively know what arguments to give to a particular function like line() or rect(). When using libraries written by someone else, it is common for the authors to provide online documentation describing each of the functions.

Documentation

We know from our sketch that the rect() function accepts a minimum of 4 arguments: x, y, width and height. Without being told, how do we know what these parameters mean? And what about other functions like triangle() or quad()?

To find out, we check the online documentation provided by the authors of the library or programming language. You can search online for the function you are using and the documentation will give you all the information you need to use it, typically with some useful examples. We can check the reference for p5.js, and specifically the page that explains the line function.

Exercise

• Add the 01_coordinates_and_shapes directory to Atom
• Open index.html in a browser
• Change the position, width and height of the rectangle
• Draw a line
• Draw an ellipse, triangle, or quad

Colour

The code to support this section is located in the following directory and is available to view on Github:

/02_colour_stroke_fill/

RGB Colour Space

When defining a colour in code, we need to describe it numerically using a 'colour space'. The most common colour space used in computing is RGB (Red, Green, Blue). Those with experience of graphical software such as Photoshop will be familiar with the colour selector that shows you the RGB values as your move around the colour palette:

An RGB colour can be understood by thinking of it as all possible colours in the visible spectrum that can be made from combinations of red, green, and blue light. By defining the intensity of each of the three colours that are mixed together, it's possible to pick from over 16 million different colours. Arguably more than the human eye can see.

In practical terms, we specify the individual amounts of red, green, and blue using values between 0 and 255.

For example, this describes the colour red:

255, 0, 0     <---- RED

This describes green:

0, 255, 0     <---- GREEN

And this describes the orange colour used on this website:

255, 152, 0     <---- ORANGE

Additive colour

In contrast to subtractive colour models, such as CMYK used for paints and print, the RGB colour space is additive. When you mix the primary paints or pigments together the resulting colour will become increasingly dark, working its way towards black. With colour displayed on a computer monitor or mobile device, adding red, green and blue together will provide white.

If you want to know all there is to know about colour theory then read Joseph Alber's amazing book, Interaction of Colors.

Using colour functions

In the p5.js library there are functions provided for controlling the colour of the fill and stroke of shapes.

• fill(r, g, b)
  This determines the main body of colour inside a shape.
• stroke(r, g, b)
  This defines the colour of the line that surrounds the shape.

Here are some examples of giving three arguments (r,g and b) to the fill and stroke functions:

1. fill( 255, 0, 0 ) // red shape fill
2. fill( 255, 255, 0 ) // yellow shape fill
3. stroke( 0, 0, 255 ) // blue outline
4. stroke( 255, 0, 255 ) // magenta outline

Grayscale

Another feature of these functions is the ability to use them to define grayscale values. Passing a single argument between 0 and 255 will result in a colour between black and white:

1. fill(0) // black shape fill
2. fill(255) // white shape fill
3. stroke(150) // grey outline

Order is important

When calling these functions you are defining the fill and stroke colour for all the shapes you draw after that line of code. So it is important to pay attention to the order in which you use them.

Exercise

The code below draws a selection of shapes around the canvas. They are all coloured white, gray or black. Your task is to add some colour to this situation.

• Add the 02_colour_stroke_fill directory to Atom
• Open index.html in a browser
• Change the fill and stroke colour for each shape

Simple Interaction and variables

The code to support this section is located in the following directory and is available to view on Github:

/03_simple_interaction/

p5.js defines some variables that we can use in our code about the properties of the sketch and also user inputs (e.g. mouse and keyboard). We can use these to make our code easier to maintain, more flexible, and to possibly add some basic interactions.

What is a variable?

A variable is how we store useful values in code. The types of things we can store depends on the programming language being used, but common examples are numbers and text.

Think of a variable as a container or box. The value is the thing inside the box, and the label on the front of the box is the name we use to identify it.

var myNumber = 5;
var myText = "hello";

In reality, the variable's container is a small section of memory on your computer.

p5.js provided variables

After you've called the createCanvas(width, height) function, p5.js automatically stores the specified dimensions as variables named width and height that can be used throughout your sketch. For example, you can use those variables to calculate and draw something in the exact centre of the canvas:

rect(width/2, height/2, 20, 20);

Special variables, such as mouseX and mouseY are made available by p5.js. These are extremely useful if we want to make sketches that respond to the user's mouse input. These two variables contain the x and y coordinates of the user's mouse at that precise moment. We can use changing values to modify our drawing and create something more dynamic.

Exercise

• Add the 03_simple_interaction directory to Atom
• Open index.html in a browser
• Change the provided code so that a shape follows the mouse around the canvas

Week 1 Assignment

For the next workshop, I would like you to make a portrait (self or other) using what you've learned from week 1. You should use the following functions and variables:

• rect()
• ellipse()
• triangle()
• fill()
• stroke()
• mouseX / mouseY

I would like you to use Codepen to submit your work. Codepen is an online code editor for web based technologies (HTML, CSS & JavaScript) as well as a platform for sharing your code. I have created a template for you to use that already includes the p5.js libraries:

http://codepen.io/pen?template=zKLpKw

Follow the link above and then edit the code in the JS panel. Click Save and you will have created a 'pen' with a unique URL (see below). Submit the Codepen URL to our Slack channel before the next workshop.

Week 2 - Animation, conditionals & random numbers

Outcomes

• Understand variables and how to use them
• Understand functions and how to use them
• Using conditional statements to control code flow
• Using variables for animation
• Using random numbers
• Mapping values from one range to another

Supporting code

The code for this workshop is hosted on Github, which is a web-based repository for hosting and versioning code.

Download the code and unzip it on your desktop.

During this workshop session we will be using the following project directories:

04_using_variables/
05_animation/
06_conditionals/
07_random/
08_random_recursive_tree/
09_map_weather_api/
10_map_hsb_colours/

Variables

Firstly let's take another look at variables in a bit more detail. A variable is simply a way of storing information in the computer's memory. Let's dive right in with an example...

var rectWidth = 5;

Let's break down the above statement:

1. var - This is how the browser knows you are 'declaring' a new variable
2. rectWidth - This is the name of the variable, which we can refer to later in our code. What you call a variable is up to you but there are some conventions.
3. 5 - The value which we want to store in the computer's memory

Read more about variables in JavaScript

Using variables

/04_using_variables/

Now that our variable rectWidth is stored in memory, we can access it using its name to return the stored value.

var rectWidth = 5;
var rectHeight = 7;
var rectArea = rectWidth * rectHeight; 
console.log(rectArea); // This will write 35 to the console.

In this example, a new variable rectHeight is declared and assigned a value of 7. On the third line both the previous variable values are retrieved from memory and multiplied using the multiply operator (*). This is immediately stored in the rectArea variable before finally being logged to the console.

Here is what happens line by line:

1. Store the number 5 in a variable named rectWidth
2. Store the number 7 in a variable named rectHeight
3. Multiply the values in rectWidth and rectHeight, storing the result in a variable named rectArea
4. Log the value of rectArea

Exercise

• Add the 04_using_variables directory to Atom
• Open index.html in a browser
• Open and look at the console in the browser's developer tools
• Remove the comments at the beginning of line 20 and reload your browser

Animation using variables

The code to support this section is located in the following directory and is available to view on Github:

/05_animation/

In this exercise a variable will is used to store, retrieve and increase a value. This value will represent the position of a shape drawn to the canvas.

Here is a portion of the code extracted from the provided example:

var positionX = 0;

/*
[code excluded]
*/

function draw(){
  // Set the background to black every frame
  background(0);

  // Draw a rectangle that moves along the X axis
  rect(positionX, height/2, 10, 10);

  // Increase the value stored in positionX
  positionX = positionX + 1;
}

As you can see a variable called positionX is declared and assigned a value of 0. Importantly this variable is declared outside of the function where it is later used. The variable is declared in the global scope (more on this later) making it accessible throughout the entire application (i.e. globally).

Exercise

• Add the 05_animation directory to Atom
• Open index.html in a browser
• Use the conditional if statement to reset the square to position 0.
• Increase the speed of the rectangle
• Move the rectangle on the X and Y axis

Conditionals

The code to support this section is located in the following directory and is available to view on Github:

/06_conditionals/

A conditional statement is used to control which code is executed based on certain pre-determined conditions. This process is one method of controlling the flow of our application.

If statements

Conditional statements are written in code using the if keyword. In fact, conditional statements are often referred to as if statements. Below is an example of how a conditional statement is formed using the if keyword:

if (condition) {
  // code that runs if the condition is true
}

By replacing the condition above with other statements we can start to control what parts of our code are executed under which conditions.

You can think of this as a very simple flow diagram or decision tree. If condition A is TRUE then the code block runs, however if it's FALSE the code is ignored.

Is the statement true or false?

When writing a condition, commonly known as a conditional statement, the truth of the statement is being evaluated or checked. In the following examples this happens by comparing two values. These values can be variables, literal values or a combination of the two.

"Hello, World"
12
3.141592

Here are some practical examples of if statements that use both variables and literal values. Between each set of brackets is a statement comparing two values. Those comparisons will return a value of true or false, which determines if the code within should be executed or ignored.

if( userName == "bob" ){
   // Any code in here will run when userName is equal to ('==') "bob"
}

if( durationHours > 12 ){
  // Any code in here will run when durationHours is greater than (`>`) 12
}

if( rectArea <= 35 ){
  // Any code in here will run when rectArea is less than OR equal to ('<=') 35
}

Comparison operators

In conditional statements, a comparison operator sits between the two values and is used to determine whether the statement is true or false. Below is a list of conditional statements using different comparison operators.

If the statement is true then the code within the conditional will run. Here are some more practical examples:

value1 == value2
userName == "bob" 
playerScore >= 10 
"west" == windDirection
juneTemperature > mayTemperature

Let's break down one of the above conditions:

1. userName
   A variable – as the word 'variable' suggests, we expect it may change.
2. ==
   A comparison operator checking for equality – checks if the value on the left is equal to the value on the right.
3. "bob"
   A string literal – written explicitly and therefore will not change.

Since variables can change value throughout the execution of code, the comparison to a static value causes code to run only during particular conditions.

If variables are named well you can start to read through the logical steps of your application by reading the code as human language:

if the userName is equal to "bob"
  then do something

Exercise

• Add the 06_conditionals directory to Atom
• Open index.html in a browser
• Modify the code inside the first conditional to make the ball bounce off the right side of the canvas
• Use another conditional to make the ball bounce off both sides of the canvas
• Change the colour, size, speed of the ball when it bounces off the wall
• Move up and down instead of left and right

Using random numbers

The code to support this section is located in the following directory and is available to view on Github:

/07_random/

Most programming languages provide functions for generating random numbers. This can be very useful in providing some variations to deterministic behaviour of code.

In p5.js there is a function for generating a random number between a minimum and maximum value:

random(min, max);

The min and max arguments set the minimum and maximum values that can be returned from that function.

random(0, 10);
random(120, 180)
random(15, 22);

You can also use a variable as one of the arguments:

random(0, width);
random(0, height);

The random() function can be used to set properties of shapes in our sketch such as position, size or colour.

In the following example the positionX and positionY variables are assigned values that are half of the width and half of the height of the canvas respectively. This will place the ellipse in the centre of the canvas when the code runs.

var positionX;
var positionY;

function setup() {
  createCanvas(800, 450);
  // Assign a value to the variables
  positionX = width/2;
  positionY = height/2;
}

function draw() {
  // Use the value within the variables.
  ellipse(positionX, positionY, 10, 10);
}

Here is an example of how to use the random function to change the starting position of the ellipse to a random position on the canvas on every execution of the code.

var positionX;
var positionY;

function setup() {
  createCanvas(800, 450);
  // Assign a value to the variables
  positionX = random(0, width); // Random number between 0 & 800
  positionY = random(0, height); // Random number between 0 & 450
}

function draw() {
  // Use the value within the variables.
  ellipse(positionX, positionY, 10, 10);
}

Exercise

• Add the 07_random directory to Atom
• Open index.html in a browser
• Change the X and Y positions of the ellipse using random() on every frame
• Change another feature of the shape with random (size, colour, etc)

Randomness and probability

The code to support this section is located in the following directory and is available to view on Github:

/08_random_recursive_tree/

• Add the 08_random_recursive_tree directory to Atom
• Open index.html in a browser and you will see something similar to this:

This is an example of using randomness and probability to produce organic forms. Take a look through the code and you will see some lines such as this:

// Create a random numbers between 0 and 1
var r = random(0, 1.0);

// 98% chance this will happen
if (r > 0.02) {
  [code excluded here]  
}
// 2% chance this will happen
else {
  [code excluded here]
}

You can see that by using random numbers and conditional statements you can quite easily create systems that have interesting and unexpected results within the limits of probability.

This code also uses a very powerful technique called recursion, which is beyond the scope of this workshop. Essentially the code is self-referential and therefore within very few lines of code can create complex outputs.

Mapping values

The code to support this section is located in the following directory and is available to view on Github:

/09_map_weather_api/

A common programming task – particularly when visualising information – is to take a value that is changing within one range and mapping that onto a different range.

As an example, let's think about visualising the current temperature (a changing value) by drawing a thermostat.

We know that the value is going to be in this approximate range of 0 to 50 °C and the size of the red thermostat indicator is a shape with a height between 0 and 200 pixels:

Let's assume we have retrieved the current temperature in degrees centigrade, for example through a weather API.

If the temperature is 50°C, the height of the red bar would be 200 pixels; if the temperature is 0°C, the height would be 0 pixels; and if the temperature is 25°C (half way point of the range), the height would be 100 pixels (half the height).

Using the map function

Within p5.js there the map function performs the calculations that translates one range onto another. The map() function takes 5 arguments:

map(value, fromMin, fromMax, toMin, toMax); 

So using the example of the thermostat, we would convert the current temperature stored in a variable called temperature using the following:

map(temperature, 0, 50, 0, 200);

And here are some examples from above using literal integer values:

map( 25, 0, 50, 0, 200 ) // returns 100
map( 10, 0, 50, 0, 200 ) // returns 40
map( 35, 0, 50, 0, 200 ) // returns 140

Exercise

• Add the 09_map_weather_api directory to Atom
• Open index.html in a browser
• Look through the code and find where the map() function is used
• Change the city in the preload function to see the API results from other places

HSB Colour

The code to support this section is located in the following directory and is available to view on Github:

/10_map_hsb_colours/

Using the RGB colour space we can produce as the specific colours we need. However, in order to manipulate or generate colours, the RGB colour space doesn't offer the best tools. For this we can use the HSB colour space or Hue, Saturation and Brightness. It is sometimes also known as as HSL (lightness) or HSV (value).

Within this model the hue defines the colour we see, which is the wavelength of light being produced. The saturation defines how intense or vivid the colour is. The way the colour is desaturated is by the addition of grey: 100% saturation means there is no grey and 0% saturation will result in a medium grey. The brightness determines the amount of black or white that's mixed with the hue.

Here are the RGB and HSB colour spaces visualised:

Changing colour mode

In p5.js you can change the colour space from RGB to HSB using the following.

colorMode(HSB);

The colorMode function can also take 3 more arguments:

colorMode(HSB, 360, 100, 100);

These last 3 arguments represent the range of values we can pass as arguments into the colour functions such as fill() and stroke().

In RGB colour mode, the range is by default:

But in HSB mode, the hue is usually between 0 and 360 whilst the saturation and brightness are between 0 and 100.

The saturation and brightness are essentially represented as a percentage (0 to 100%) of their most extreme condition, which is the least saturated and the most bright.

But why is the hue value between 0 and 360? As mentioned the HSB colour is visualised as a cylinder (or sometimes as a cone) and the hue is represented as the perimeter of the circle that sits at the top of the 3D shape. Therefore the 360 is the angle in degrees around that circle.

Image credit: www.runemadsen.com

Exercise

Using the HSB colour space we can create easily create colour schemes that have a mathematical relationship to each other. A simple example is choosing a particular hue and saturation and then adjusting the brightness. However you can also choose selections of hue based on their relationship around the 360 degrees of the colour wheel.

Analogous	Complementary
Triadic	Tetradic

All of these examples are from the Rune Madesen's lecture on colour as part of his Printing Code module at ITP. The online resources from this are extremely useful.

In the provided example, the mouseX value is being mapped from one range (0 to width) onto another (0 to 360):

Therefore as the mouse moves across the canvas the mapped value travels between 0 and 360. This is then used to set the hue of the fill colour showing the full spectrum of colour.

var colour = map(mouseX, 0, width, 0, 360);
var columnWidth = width/3;

fill(colour, 100, 100);
rect(columnWidth*0, 0, columnWidth, height);

fill(colour, 80, 70);
rect(columnWidth*1, 0, columnWidth, height);

fill(colour, 60, 40);
rect(columnWidth*2, 0, columnWidth, height);

• Add the 10_map_hsb_colours directory to Atom
• Open index.html in a browser
• Explore different values for brightness and saturation
• Create colour schemes with hues that have are related on the colour wheel, e.g. analogous, triadic, etc.

Functions

Functions are used to define a process that can be constructed of one or more lines of code. They are often used to organise and structure code by the intended outcome or behaviour.

Here are a few benefits to using functions:

1. Keep code organised
2. Make code easily reusable
3. Breaking down a task into smaller pieces (decomposition)
4. Making problems in the code easier to identify and troubleshoot (seperation of concerns)

Using functions

Making use of functions is broken down into two parts. First, the function behaviour needs to be defined, i.e. the code needs to be written. Secondly, the function needs to be called (also known as 'executed').

Define the function behaviour

Below are 4 lines of code contained within a function that perform the task of calculating the area of a shape. This is where the function is being defined.

function calculateArea() {
  var width = 5;
  var height = 7;
  var area = width * height;
  console.log(area);
}

Let's break down the unfamiliar parts of the above code:

1. function
   This is how the browser knows you are declaring a new function.
2. calculateArea()
   'calculateArea' is the name of the function, which we can use to refer to later in our code. What you call a function is up to you but there are some conventions.
3. { }
   These are curly brackets or curly braces. They start and end the content of the function. All code written between these two brackets is the behaviour of the function.

Call the function

The above code will do nothing until we call the function elsewhere in our code.

calculateArea(); // Logs 35

Function parameters

A common use of a function is to make our code more reusable. One way of making our functions more reusable is by adding parameters.

function calculateArea( width, height ) {
  var area = width * height;
  console.log(area);
}

Assignment

Part 1

Create a sketch that includes:

• one or more elements that changes over time.
• one or more elements that is controlled by mouse or keyboard
• one or more element that is random() in nature

Work can again be submitted using Codepen. Here is the URL for the p5.js template:
http://codepen.io/pen?template=zKLpKw

Please submit the Codepen URL the day before our next workshop.

And here is a short guide on using Codepen:

Part 2

When you submit your URL I would like you to also submit a question about what we've been covering (or have missed) over the last two weeks. For example:

• What does a certain error message mean?
• How do I create a colour with an alpha channel?
• Are there any other colorModes?
• What is the highest framerate?

Week 3 - Iteration, arrays, objects and pixel arrays

Outcomes

• Iteration using while and for loops
• Understand and using arrays
• Using loops and arrays together
• Understanding and using JavaScript objects
• Understanding how colour data is stored in pixel arrays
• Accessing the webcam

Supporting code

The code for this workshop is hosted on Github, which is a web-based repository for hosting and versioning code.

Download the code and unzip it on your desktop.

During this workshop session we will be using the following project directories:

11_iteration_and_loops/
12_iteration_02/
13_loops_and_arrays/
14_pixel_array/
15_image_pixel_array/
16_webcam_capture/

Local web server

So far during this series of workshops testing your code has involved opening the index.html file in your browser, which results in an absolute file path in the browser address bar (see below). You can see this indicated by the file:// protocol followed by the absolute file path to the index.html file:

For some examples you will need to run a local HTTP web server that serves the files in a project. If you have Node.js already installed you can run the following command to install an HTTP web server:

sudo npm install -g http-server

If you receive an error from the above command it's likely that you do not have Node.js installed. In which case visit the Node.js homepage and download/install the LTS version and repeat the command above.

Once you have installed the HTTP web server you will need to change directory (cd) into the project directory on the command line and run the server:

cd ~/Desktop/intro-to-programming-2017/15_image_pixel_array/
http-server

If successful you will see messages in the command line similar to this:

You can then copy and paste one of the URLs into you browser:

Iteration: while and for loops

/11_iteration_and_loops/
/12_iteration_02/

Sometimes it is necessary to repeat a task over and over on the same data in order to achieve a desired outcome. This is known as an iterative process and each step is an iteration.

The most common application for iteration is to create, check, or modify a collection of variables.

In the previous workshop, we were introduced to the idea of conditionals. We saw that an if statement can be used to branch code, but this is only performed once.

If we want to perform a conditional operation repeatedly, we need to use a different statement – the while loop.

The example below will draw six circles onto the canvas. Note that the circles are identical, apart from the x coordinate.

function setup() {
  createCanvas(400, 300);
}

function draw() {
  background(128);
  ellipse(50, 225, 20, 20);
  ellipse(100, 225, 20, 20);
  ellipse(150, 225, 20, 20);
  ellipse(200, 225, 20, 20);
  ellipse(250, 225, 20, 20);
  ellipse(300, 225, 20, 20);
  ellipse(350, 225, 20, 20);
}

We can simplify this code by using a while loop.

function setup() {
  createCanvas(400, 300);
}

function draw() {
  background(128);
  var x = 50;
  while (x <= 350) {
    ellipse(x, 225, 20, 20);
    x = x + 50;
  }
}

What's happening in the above example line-by-line:

1. var x = 50;
   Here we create a temporary variable to help us iterate. In this case an integer, initially set to 50.
2. while (x <= 350) {
   This starts the while loop. As long as the condition inside the parentheses remains true, the code that follows the curly brace will be repeatedly executed (forever!)
3. ellipse(x, 225, 20, 20);
   We draw a circle. The y-position, height, and width are identical for each; the x-positon is set using the current value of our temporary variable.
4. x = x + 50;
   The value of the temporary variable is increased by 50.

As soon as the condition inside the parentheses returns false, the while loop exits and code execution continues.

Although this is a very common code pattern, it's unusual to see while loops actually used in code. This is because most programming languages provide us with a more useful variant – the for loop.

A for loop is written slightly differently from a while loop. The parentheses contain three statements separated by semicolons, rather than a simple test.

function setup() {
  createCanvas(400, 300);
}

function draw() {
  background(128);
  for (var x = 50; x <= 350; x = x + 50) {
    ellipse(x, 225, 20, 20);
  }
}

What's happening inside the parentheses:

1. for (var x = 50; x <= 350; x = x + 50) {
   A temporary variable is declared and initialised in the first statement.
2. for (var x = 50;x <= 350; x = x + 50) {
   The second statement contains the condition that is checked. If this returns false the loop exits.
3. for (var x = 50; x <= 350;x = x + 50) {
   The final statement contains code that is to be executed after each successful loop.

Even in these basic examples, it's clear to see that loops help us avoid repetition and reduce the number of lines of code we write.

Exercise

• Add the 12_iteration_02/ directory to Atom
• Open index.html in a browser
• Change the RGBA values of the pixels inside the nested for loop
• Try using the random() function to set the colour values
• Try using the x and y variables to set the colour values

JavaScript Arrays

Arrays are essentially ordered lists of things and each item in that list can be accessed individually. The array itself is a type of variable and it stores other variables inside. The stored variables can be used in the same way as you use any other variable.

Here is a simple array:

var sizes = [ 20, 350, 80, 210 ];

What's important about an array is the order of the items within. To access any individual item of data stored inside the variable, we need to reference the item's position, commonly referred to as the array index. Crucially, the index of an array starts at zero:

console.log(sizes[0]);  // logs: 20

And therefore the index of the last item in the array would be one less than total number of items. In our example above we have 4 items, so the final item is accessed using the index 3:

console.log(sizes[3]);  // logs: 210

JavaScript arrays are particularly useful since you can store any type of data inside, including integers, strings, objects and—perhaps confusingly—other arrays. Here is an example of an array containing a list of strings:

var technicians = [ "Delia", "Will", "Adam", "Gareth", "Tom" ];

And, as above, we can access the strings using the array variable technicians and counting along the list starting from zero:

console.log( technicians[0] ); // "Delia"
console.log( technicians[2] ); // "Adam"
console.log( technicians[4] ); // "Tom"

Try this for yourself using this CodePen.

Loops and arrays

/13_loops_and_arrays/

When we have only a few items in our arrays, it is not a lot of additional code to access each of them explicitly using their index:

ellipse(x, y, sizes[0]);
ellipse(x, y, sizes[1]);
ellipse(x, y, sizes[2]);
ellipse(x, y, sizes[3]);

But even this is repeating code unnecessarily. And when we start to hold hundreds or thousands of items in our array, it would become unmanageable to write out the code above.

To unleash the full potential of arrays, they can be combined with looping structures such as for loops. As we have seen already, the for loop can be used to run a piece of code a number of times, incrementing an index variable on each execution:

for( var i = 0; i < 4; i++ ){
  console.log( i );
}

A further useful feature of arrays is that they have an internal property that contains the current length of the array:

var sizes = [ 20, 350, 80, 210 ];
console.log(sizes.length);        // logs 4

The length property can be used within our for loop to determine how many times the loop runs the code before stopping. In the case of our sizes array above, the loop would continue to execute as long as the i variable is less than (<) the number of items in the array.

This is a very common design pattern.

for( var i = 0; i < sizes.length; i++ ){
  console.log( i ); 
}

What is happening here?

1. The variable i is set as 0
2. The statement i < sizes.length is tested
3. If the condition is true the code inside runs
4. ...and the variable i is increased by 1
5. Go back to point 2 and repeat until false

The code would run 4 times and log 0, 1, 2 and 3.

Now we have a loop that runs as many times as there are items in the array. Crucially, inside that loop, the variable i is incremented by 1. Each time it increments by 1 we can use it to access the value in the array at that index:

for( var i = 0; i < sizes.length; i++ ){
  console.log( sizes[i] );
}

If we recall that the first item in an array uses the index zero, we can see why our i variable is initialised as 0 rather than 1.

Within our for loop we are now running code that accesses each of the items in the array in the correct order.

See this code executed in CodePen.

JavaScript Objects

In JavaScript most things you encounter are actually objects. The strings, arrays and even functions are objects at the most basic level. This is because they can all contain properties and functions inside them.

Here, for example, the variable message has a property called length that returns the length of the string:

var message1 = "what is an object";
console.log(message1.length); // 15

More examples on CodePen.

These are objects within internal properties and functions that are provided by the JavaScript engine inside the browser. We do not need write the code for these objects as it already exists.

However, creating your own objects is a very handy way to encapsulate related functions and variables, and also act as data containers. We can also use this technique to model things in a more helpful way.

Let take a look at the variables needed to draw a circle and then how we would move those variables inside an object. Here we define three variables:

var x = 50;
var y = 100;
var size = 20;
ellipse( x, y, size );

And here are the same three variables inside an object:

var circle = {
  x    : 50,
  y    : 100,
  size : 20
};

The first thing to note is that the object starts and ends with curly braces; the same way that we start and end functions and if statements.

Pay careful attention to the differences between declaring variables inside and outside of an object. Variables stored inside objects are called properties and each property has a value. The major difference in syntax is that properties and values are separated by a colon (:) instead of an equals sign (=).

x    : 50,  // Note the colon ':' separator...

And each of the property/value pairs are separated by a comma (,), not a semi-colon (;). The exception to this is rule is the last pair for which the comma is optional

x    : 50,  // ...and each pair separated by a comma
y    : 100, 
size : 20   // except the last, which is optional

So now that the data that defines our circle is contained within an object how do we access that data? To access a property of an object the dot syntax is used. For example to access the x value:

circle.x

So to rewrite our code above using an object:

var circle = {
  x    : 50,
  y    : 100,
  size : 20
};

ellipse( circle.x, circle.y, circle.size );

See a simple example of this on CodePen.

Here is an example on CodePen of the above circle sketch created using a constructor function. This is a simple example of using Object Oriented Programming in JavaScript.

Pixel array

/14_pixel_array/

Previously we have discussed that our p5.js canvas is made up of individual pixels. Each of them can be located using an X coordinate between 0 and the width and a Y value between 0 and the height. Also known as Cartesian coordinates.

So how many pixels are there in a canvas of 600 pixels in width and 500 pixels in height:

600 x 500 = 300000 pixels

We have also discussed that each pixel is made up of three values: red, green and blue. Well, there is actually a fourth value, which we haven't discussed in a great detail called alpha. This sets the transparency value of the pixel. So for every pixel on the p5.js/HTML canvas there are 4 pieces of information:

red, green, blue, alpha

So in total for our canvas of 600 x 500 we have this many pieces of information:

300000 (pixels) x 4 (colour value) = 1200000

All of this information is stored in one large linear array, which we can easily access and manipulate. However arrays are simply lists so they do not have a concept of which index relates to which X and Y coordinate on our screen.

If we want to access a particular pixel we do not refer to it as, for example, the 29th pixel (the last pixel in our example above). We are more likely to reference it using the X and Y coordinates. So how do we get from an X and Y coordinate to access and manipulate the 4 colour values within the pixel array?

In the image above the red dot represents a pixel on screen that we want to target in the pixel array to access or change the 4 colour values.

If we were to count the grey boxes you can see that before we reach the red dot we have 2 full rows, which equates to (y * width). Then we count in (or add) x positions. The formula to calculate this for any x and y value is therefore:

x + (y * width)

So far so good. However now we know that the number of the pixel in the canvas but for every pixel there are 4 values in the array. Therefore to calculate the first of four positions in the array that contains the RGBA values for our pixel we simply multiple by 4. In our above example we have calculated the pixel position to be the 16th:

16 (pixel position) * 4 (colour values) = 64 (array index)

So now we know that the four positions in the array that represent our pixel are 64, 65, 66 and 67. We can therefore write the following code to manually set the colour of that pixel:

function draw() {
  loadPixels();
 

  pixels[64] = 255;    // red
  pixels[65] = 255;    // green
  pixels[66] = 255;    // blue
  pixels[67] = 255;    // alpha

  updatePixels();
}

But that is not very reusable code and we would have to manually calculate the index again every time we wanted to address a new pixel. What would be much better is to put all of those calculations into variables so we can simply change the X & Y value with ease:

function draw() {
  loadPixels();

  var x = 40;
  var y = 20;
  var index = ( x + (y * width) ) * 4;

  pixels[index] = 255;      // red
  pixels[index+1] = 255;    // green
  pixels[index+2] = 255;    // blue
  pixels[index+3] = 255;    // alpha

  updatePixels();
}

Using the above code we can address a particular pixel and then access the colours within the pixel array.

Try changing the X and Y values on this CodePen. You may need to look closely or zoom in to see the single coloured pixel.

So we now can access individual pixels based on their X & Y coordinates, what if we wanted to modify all the pixels. We can do this by using a nested for loop to iterate along every pixel on the X and Y axis. A nested for loop is one loop within another:

// Loop through every pixel on the X axis...
for ( var x = 0; x < width; x++ ) {
  // ...and for each X, loop through every pixels on the Y axis
  for ( var y = 0; y < height; y++ ) {
     // Every (x, y) coordinate is looped here:
     var index = (x + y * width) * 4;
     pixels[index] = 255;     // red
     pixels[index+1] = 0;     // green
     pixels[index+2] = 0;     // blue
     pixels[index+3] = 255;   // alpha
  }
}

In this example above every pixel is set to full red, no green, no blue and full transparency.

Exercise

• Add the 12_pixel_array directory to Atom
• Open index.html in a browser
• Change the RGBA values of the pixels inside the nested for loop
• Try using the random() function to set the colour values
• Try using the x and y variables to set the colour values

Image pixel data

/15_image_pixel_array/

So far we have been manipulating the pixel colour values of an empty canvas; or more precisely a canvas full of a single colour. The exact same process is possible but instead of manipulating an empty canvas we can manipulate image data loaded in from an external file.

The data that represents an image is also made up of individual pixels (this is called a raster graphic and therefore within p5.js we access the image pixel data in the exact same way as we have already been accessing pixels in an array. Here is an example of this using a loaded image:

var img;

function preload() {
  img = loadImage("images/maxernst.jpg");
}

function mouseDragged(){
  var index = (mouseX + mouseY * width)*4;

  img.loadPixels();
  var r = img.pixels[index];
  var g = img.pixels[index+1];
  var b = img.pixels[index+2];
  var a = img.pixels[index+3];

  fill(r, g, b, a);
  ellipse(mouseX, mouseY, 40, 40);
}

You will notice a new function being used called preload(). This is a handy function provided by p5.js that ensures that images or external data such as API data are finished loading before calling the setup() and draw() functions:

Inside the preload function we give a relative path as an argument to the loadImage() function. The results of this are stored in a global variable img.

var img;

function preload() {
  img = loadImage("images/maxernst.jpg");
}

Then later in our draw() function we can access the pixel array as a property of the img object. We do this using the dot syntax. Here I am setting the first pixels colour to green:

img.pixel[0] = 0;
img.pixel[1] = 255;
img.pixel[2] = 0;

Exercise

• Add the 13_pixel_array directory to Atom
• Set up a local web server and run it within the 13_pixel_array directory.
• Open the URL provided by the local web server in a browser.
• Click and drag the mouse around the canvas to see the pixel colours being rendered in circles
• Uncomment the lines in the nested for loop and play with the rgba values:

img.pixels[index] = r;
img.pixels[index+1] = g;
img.pixels[index+2] = b;
img.pixels[index+3] = a;

Webcam capturing

The code to support this section is located in the following directory and is available to view on Github:

/16_webcam_capture/

Using p5.js accessing the webcam is quite straightforward. It takes just a few lines of code:

var capture;

function setup() {
  createCanvas(400, 300);
  pixelDensity(1);

  // Create video capture object.
  capture = createCapture(VIDEO);
  capture.size(width, height);
}

function draw() {
  clear();
  // Draw capture to the canvas.
  image(capture, 0, 0, width, height);
}

Behind the scenes the createCapture() function does a few clever things. Firstly it causes the browser to ask the user if they want their camera to be opened and used. This is a security provision to ensure nefarious programmers cannot access webcams without permission. Secondly it creates a HTML Video element in the browser and places it next to our p5.js canvas. We can then use the image data from inside that HTML Video object to draw into our canvas.

See this in action on CodePen.

However this leaves us with two copies of the webcam video. That is why we call capture.hide() in all the following examples.

What is extremely useful about this object stored in the capture variable is that the pixels inside it can be treated exactly the same as the pixel array and image pixel array examples.

clear();
capture.loadPixels();
for ( var x = 0; x < width; x++ ) {
  for ( var y = 0; y < height; y++ ) {
    // Get the pixel at x and y position
    var index = (x + y * width) * 4;
    capture.pixels[index] = 255;     // red
    // capture.pixels[index+1] = 0;   // green
    // capture.pixels[index+2] = 0;   // blue
    // capture.pixels[index+3] = 0;   // alpha  
  }
}
capture.updatePixels();
image(capture, 0, 0, width, height);

In this example above every pixels has had it's red value cranked up to maximum giving the captured image a distinctly red tint.

Within the exercise code you will also find a call to the saveCanvas() function being used within the keyPressed() function:

function keyPressed(){
  if (keyCode == RETURN) {
    saveCanvas("webcam", "jpg");
  }
}

This 4 lines of code allows the webcam image to be saved and downloaded as a JPG when the return key is pressed.

Exercise

• Add the 16_webcam_capture directory to Atom
• Set up a local web server and run it within the 16_webcam_capture directory.
• Open the URL provided by the local web server in a browser.
• Hit the enter key to download a frame of the webcam video
• Uncomment the lines in the nested for loop and play with the rgba values:

capture.pixels[index] = 255;     // red
capture.pixels[index+1] = 255;   // green
capture.pixels[index+2] = 255;   // blue
capture.pixels[index+3] = 255;   // alpha

Week 4 - Other inputs and APIs

Outcomes

• Independently researching new features of p5.js using the documentation
• Using inputs to control behaviour of your sketch
• Understanding the concept of web-based APIs and basic use
• In groups create a sketch that uses either at least one input (learnt today) or APIs to create an interactive sketch

Local web server

So far during this series of workshops testing your code has involved opening the index.html file in your browser, which results in an absolute file path in the browser address bar (see below). You can see this indicated by the file:// protocol followed by the absolute file path to the index.html file:

For some examples you will need to run a local HTTP web server that serves the files in a project. If you have Node.js already installed you can run the following command to install an HTTP web server:

sudo npm install -g http-server

If you receive an error from the above command it's likely that you do not have Node.js installed. In which case visit the Node.js homepage and download/install the LTS version and repeat the command above.

Once you have installed the HTTP web server you will need to change directory (cd) into the project directory on the command line and run the server:

cd ~/Desktop/intro-to-programming-2017/15_image_pixel_array/
http-server

If successful you will see messages in the command line similar to this:

You can then copy and paste one of the URLs into you browser:

Other Inputs

So far you have used the input for mouse position to affect the visual output in your sketch.

There are a range of other inputs we can use to create dynamic / interactive sketches:

• Click
• Keyboard
• Touch / Drag
• Rotation

Experiment with these other inputs using the p5.js reference. Search for ‘Events’ section in the reference.

APIs

/19_api_playground/

Here are a list of APIs you can use for this example:

APIs

OPEN

• Blockchain (Documentation):
  https://blockchain.info/latestblock
  
  
• Most Recent Earthquakes:
  http://apis.is/earthquake/is
  
  
• Icelandic Open Data (Documentation):

1. http://apis.is/cyclecounter
2. http://apis.is/horses?id=IS1987187700
3. http://apis.is/ship?search=engey
   
   

• MusicBrainz:
  http://musicbrainz.org/ws/2/artist/5b11f4ce-a62d-471e-81fc-a69a8278c7da?inc=aliases&fmt=json
  
  
• Exchange Rates (Documentation):
  https://api.fixer.io/latest?symbols=USD,GBP

REQUIRES API KEY

• Weather (Documentation):
  http://api.apixu.com/v1/current.json?key=YOUR_API_KEY_HERE&q=London
  
  

• Population Statistics (Documentation):
  http://inqstatsapi.inqubu.com/?api_key=YOUR_API_KEY_HERE&countries=us&data=population&years=1980:1990
  
  

• NASA Near Eath Objects (Documentation):
  https://api.nasa.gov/neo/rest/v1/feed?start_date=2016-12-24&end_date=2016-12-25&api_key=YOUR_API_KEY_HERE