learnxinyminutes-docs/processing.html.markdown

---
language: "Processing"
filename: learnprocessing.pde
contributors:
    - ["Phone Thant Ko", "http://github.com/phonethantko"]
---
## Introduction

Processing is a programming language for creation of digital arts and multimedia content, allowing non-programmers to
learn fundamentals of computer programming in a visual context.  
While the language is based on Java language,
its syntax has been largely influenced by both Java and Javascript syntaxes. [See more here](https://processing.org/reference/)  
The language is statically typed, and also comes with its official IDE to compile and run the scripts.

```processing
/* ---------
   Comments
   ---------
*/

// Single-line comment starts with //

/*
   Since Processing is based on Java,
   the syntax for its comments are the same as Java (as you may have noticed above)!
   Multi-line comments are wrapped as seen here.
*/

/* ---------------------------------------
   Writing and Running Processing Programs
   ---------------------------------------
 */

// In Processing, your program's entry point is a function named setup() with a void return type.
// Note! The syntax looks strikingly similar to that of C++.
void setup() {
  // This prints out the classic output "Hello World!" to the console when run.
  println("Hello World!"); // Another language with a semi-column trap, ain't it?
}

// Normally, we put all the static codes inside the setup() method as the name suggest since it only runs once.
// It can range from setting the background colours, setting the canvas size.
background(color); // setting the background colour
size(width,height,[renderer]); // setting the canvas size with optional parameter defining renderer
// You will see more of them throughout this document.

// If you want to run the codes indefinitely, it has to be placed in draw() method.
// draw() must exist if you want the code to run continuously and obviously, there can only be one draw() method.
int i = 0;
void draw() {
  // This block of code loops forever until stopped
  print(i);
  i++; // Increment Operator!
}

// Now that we know how to write the working script and how to run it,
// we will proceed to explore what data types and collections are supported in Processing.

/* ------------------------
   Datatypes & collections
   ------------------------
*/

// According to Processing References, Processing supports 8 primitive datatypes as follows.

boolean booleanValue = true; // Boolean
byte byteValueOfA = 23; // Byte
char charValueOfA = 'A'; // Char
color colourValueOfWhiteM = color(255, 255, 255); // Colour (Specified using color() method)
color colourValueOfWhiteH = #FFFFFF; // Colour (Specified using hash value)
int intValue = 5; // Integer (Number without decimals)
long longValue = 2147483648L; // "L" is added to the number to mark it as a long
float floatValue = 1.12345; // Float (32-bit floating-point numbers)
double doubleValue = 1.12345D; // Double (64-bit floating-point numbers)

// NOTE!
// Although datatypes "long" and "double" work in the language,
// processing functions do not use these datatypes, therefore
// they need to be converted into "int" and "float" datatypes respectively,
// using (int) and (float) syntax before passing into a function.

// There is a whole bunch of default composite datatypes available for use in Processing.
// Primarily, I will brief through the most commonly used ones to save time.

// String
// While char datatype uses '', String datatype uses "" - double quotes.
String sampleString = "Hello, Processing!";
// String can be constructed from an array of char datatypes as well. We will discuss array very soon.
char source = {'H', 'E', 'L', 'L', 'O'};
String stringFromSource = new String(source); // HELLO
// As in Java, strings can be concatenated using the "+" operator.
print("Hello " + "World!"); // Hello World!

// Array
// Arrays in Processing can hold any datatypes including Objects themselves.
// Since arrays are similar to objects, they must be created with the keyword "new".
int[] intArray = new int[5];
int[] intArrayWithValues = {1, 2, 3}; // You can also populate with data.

// ArrayList
// Functions are similar to those of array; arraylists can hold any datatypes.
// The only difference is arraylists resize dynamically,
// as it is a form of resizable-array implementation of the Java "List" interface.
ArrayList<Integer> intArrayList = new ArrayList<Integer>();

// Object
// Since it is based on Java, Processing supports object-oriented programming.
// That means you can basically define any datatypes of your own and manipulate them to your needs.
// Of course, a class has to be defined before for the object you want.
// Format --> ClassName InstanceName
SomeRandomClass myObject // then instantiate later
//or
SomeRandomClass myObjectInstantiated = new SomeRandomClass();

// Processing comes up with more collections (eg. - Dictionaries and Lists) by default,
// for the simplicity sake, I will leave them out of discussion here.

/* ------------
   Maths
   ------------
*/

// Arithmetic
1 + 1 // 2
2 - 1 // 0
2 * 3 // 6
3 / 2 // 1
3.0 / 2 // 1.5
3.0 % 2 // 1.0

// Processing also comes with a set of functions that simplify mathematical operations.
float f = sq(3); // f = 9.0
float p = pow(3, 3); // p = 27.0
int a = abs(-13) // a = 13
int r1 = round(3.1); // r1 = 3
int r2 = round(3.7); // r2 = 4
float sr = sqrt(25); // sr = 5.0

// Vectors
// Processing provides an easy way to implement vectors in its environment using PVector class.
// It can describe a two or three dimensional vector and
// comes with a set of methods which are useful for matrices operations.
// You can find more information on PVector class and its functions here.
// (https://processing.org/reference/PVector.html)

// Trigonometry
// Processing also supports trigonometric operations by supplying a set of functions.
// sin(), cos(), tan(), asin(), acos(), atan() and also degrees() and radians() for convenient conversion.
// However, those functions take angle in radians as the parameter so it has to be converted beforehand.
float one = sin(PI/2); // one = 1.0
// As you may have noticed, there exists a set of constants for trigonometric uses;
// PI, HALF_PI, QUARTER_PI and so on...

/* -------------
   Control Flow
   -------------
*/

// Conditional Statements
// If Statements - The same syntax as if statements in Java.
if (author.getAppearance().equals("hot")) {
  print("Narcissism at its best!");
} else {
  // You can check for other conditions here.
  print("Something is really wrong here!");
}
// A shortcut for if-else statements can also be used.
int i = 3;
String value = (i > 5) ? "Big" : "Small"; // "Small"

// Switch-case structure can be used to check multiple conditions more concisely.
int value = 2;
switch(value) {
  case 0:
    print("Nought!"); // This doesn't get executed.
    break; // Jumps to the next statement
  case 1:
    print("Getting there..."); // This again doesn't get executed.
    break;
  case 2:
    print("Bravo!"); // This line gets executed.
    break;
  default:
    print("Not found!"); // This line gets executed if our value was some other value.
    break;
}

// Iterative statements
// For Statements - Again, the same syntax as in Java
for(int i = 0; i < 5; i ++){
  print(i); // prints from 0 to 4
}

// While Statements - Again, nothing new if you are familiar with Java syntax.
int j = 3;
while(j > 0) {
  print(j);
  j--; // This is important to prevent from the code running indefinitely.
}

// loop()| noLoop() | redraw() | exit()
// These are more of Processing-specific functions to configure program flow.
loop(); // allows the draw() method to run forever while
noLoop(); // only allows it to run once.
redraw(); // runs the draw() method once more.
exit(); // This stops the program. It is useful for programs with draw() running continuously.
```
## Drawing with Processing
Since you will have understood the basics of the language by now, we will now look into the best part of Processing; DRAWING.

```processing
/* ------
   Shapes
   ------
*/

// 2D Shapes

// Point
point(x, y); // In 2D space
point(x, y, z); // In 3D space
// Draws a point in the coordinate space.

// Line
line(x1, y1, x2, y2); // In 2D space
line(x1, y1, z1, x2, y2, z2); // In 3D space
// Draws a line connecting two points defined by (x1, y1) and (x2, y2).

// Triangle
triangle(x1, y1, x2, y2, x3, y3);
// Draws a triangle connecting three points defined by coordinate paramters.

// Rectangle
rect(a, b, c, d, [r]); // With optional parameter defining the radius of all corners
rect(a, b, c, d, [tl, tr, br, bl]); // With optional set of parameters defining radius of each corner
// Draws a rectangle with {a, b} as a top left coordinate and c and d as width and height respectively.

// Quad
quad(x, y, x2, y2, x3, y3, x4, y4);
// Draws a quadrilateral with parameters defining coordinates of each corner point.

// Ellipse
ellipse(x, y, width, height);
// Draws an eclipse at point {x, y} with width and height specified.

// Arc
arc(x, y, width, height, start, stop, [mode]);
// While the first four parameters are self-explanatory,
// start and end defined the angles the arc starts and ends (in radians).
// Optional parameter [mode] defines the filling;
// PIE gives pie-like outline, CHORD gives the chord-like outline and OPEN is CHORD without strokes

// Curves
// Processing provides two implementation of curves; using curve() and bezier().
// Since I plan to keep this simple I won't be discussing any further details.
// However, if you want to implement it in your sketch, here are the references:
// (https://processing.org/reference/curve_.html)(https://processing.org/reference/bezier_.html)

// 3D Shapes

// 3D space can be configured by setting "P3D" to the renderer parameter in size() method.
size(width, height, P3D);
// In 3D space, you will have to translate to the particular coordinate to render the 3D shapes.

// Box
box(size);  // Cube with same length defined by size
box(w, h, d); // Box with width, height and depth separately defined

// Sphere
sphere(radius); // Its size is defined using the radius parameter
// Mechanism behind rendering spheres is implemented by tessellating triangles.
// That said, how much detail being rendered is controlled by function sphereDetail(res)
// More information here: (https://processing.org/reference/sphereDetail_.html)

// Irregular Shapes
// What if you wanted to draw something that's not made available by Processing's functions?
// You can use beginShape(), endShape(), vertex(x,y) to define shapes by specifying each point.
// More information here: (https://processing.org/reference/beginShape_.html)

/* ---------------
   Transformations
   ---------------
*/

// Transformations are particularly useful to keep track of the coordinate space
// and the vertices of the shapes you have drawn.
// Particularly, matrix stack methods; pushMatrix(), popMatrix() and translate(x,y)
pushMatrix(); // Saves the current coordinate system to the stack
// ... apply all the transformations here ...
popMatrix(); // Restores the saved coordinate system
// Using them, the coordinate system can be preserved and visualized without causing any conflicts.

// Translate
translate(x, y); // Translates to point{x, y} i.e. - setting origin to that point
translate(x, y, z); // 3D counterpart of the function

// Rotate
rotate(angle); // Rotate the amount specified by the angle parameter
// It has 3 3D counterparts to perform rotation, each for every dimension,
// namely: rotateX(angle), rotateY(angle), rotateZ(angle)

// Scale
scale(s); // Scale the coordinate system by either expanding or contracting it.

/* --------------------
   Styling and Textures
   --------------------
*/



/* -------
   Imports
   -------
*/

// The power of Processing can be further visualized when we import libraries and packages into our sketches.
// Import statement can be written as below at the top of the source code.
import processing.something.*;

```
Processing is easy to learn and is particularly useful to create multimedia contents (even in 3D) without
having to type a lot of codes. It is so simple that you can read through the code and get a rough idea of
the program flow.  
However, that does not apply when you introduce external libraries, packages and even your own classes.
(Trust me! Processing projects can get really large)  

## What's Next?

Here, I have compiled some useful resources:  

 - [Processing Website](http://processing.org)
 - [Processing Sketches](http://openprocessing.org)