Processing.js

Processing.js

Original author(s)	John Resig
Developer(s)	Processing Foundation
Initial release	2008 (2008)
Stable release	1.4.8 / March 25, 2014 (2014-03-25)
Repository	https://github.com/jeresig/processing-js
Written in	JavaScript
Size	61 KB (gzipped) / 209 KB (production) / 754 KB (development)
Type	Web application framework
License	MIT
Website	processingjs.org

Processing.js is a JavaScript port of Processing, a programming language designed to write visualisations, images, and interactive content. It allows web browsers to display animations, visual applications, games and other graphical rich content without the need for a Java applet or Flash plugin.

Processing.js was originally created to allow existing Processing developers and existing code to work unmodified on web. Processing.js uses JavaScript to render 2D and 3D content on the HTML canvas element, and is supported by browsers that have implemented this element (the latest versions of Mozilla Firefox, Opera, Internet Explorer, Safari and Google Chrome).

The development of Processing.js was begun by John Resig and then picked up by students at Seneca College after its initial release in 2008. A team of students finished the port of Processing.js, fixing more than 900 bugs, shipping 12 releases, and creating a vibrant community in the process. The project was done through a partnership between the Mozilla Foundation and Seneca College, led by David Humphrey, Al MacDonald, and Corban Brook. The students continue to maintain the project today.

Versions

• 1.4.0
  The first version of Processing.js released in July 2010.
• 1.4.1
  This version resolved bugs present in prior version.The key events for focusing the mouse are handled with global keyEvent instructions which execute only when they receive focus. The versions are exclusively for development and production with API option.
• Latest Upcoming Version(2.1)
  Processing.org will be launching a series of "alpha" releases as they prepare for 2.0. Alpha means unstable and that function names and APIs will continue to change (mostly in PShape, XML, and other new bits like JSON and Table). It might be a bit like driving a sports car but with the hood removed and one of the tires might occasionally blow out. There will be beta releases. After the alpha releases which restricts the APIs changing, but the bugs might still be around. You'll have a proper set of tires and a hood, but you might still need a coat of paint and a radio.

Changes made in latest release: (2.1)

• Libraries of OpenGL are built into core,no need of installing separate library.
• Modified version of GSVideo library is used instead of java.
• It allows one to choose two modes of platform for executing like Android or JavaScript by selecting from a drop down list in the main window.
• Movie Maker class has been removed in that place an item tool which converts frames into video is added.
• For reading XMl and loading separate loadXMl is added and getXXXAttribute is now changed to getXXX.
• Exception handling is made as choice for advanced users.
• A new Table class is added which made easy to deal with punctuation in spreadsheets like comma,delimiter.

IDE

The Processing.js code is designed to be used with standalone text editors, or it may be built into an integrated development environment (IDE).

Following are the IDEs which support Processing.js:

• Sketchpad puts processing on Etherpad, allowing authors to simultaneously edit a text document, and see all of the participants' edits in real-time, with the ability to display each author's text in their own color.
• The Processing.js code can be edited in Processing helper tool.
• Even the code can be designed by using Eclipse by importing packages using GitHub.

iPhone use

There exists an integration of the Processing.js library and a Javascript application framework for iPhone, called iProcessing.

Processing syntax

Processing.js syntax is almost identical to that of the Processing language, in that a setup() function is used to define general visualization properties like canvas size, frame rate and other variables, and a draw() function controls the behavior of each frame in the animation.

The Processing.js library can be included in head section of a web page as a single JavaScript file:

<html>
<head>
  <script type="text/javascript" src="processing.js"></script>
</head>

A canvas element is declared inside the body, with a data-processing-sources attribute, specifying the location of an external file holding the Processing code:

<canvas data-processing-sources="example.pde"></canvas>

Any extension can be used in the external file, for example, the .pde extension used by the Processing language sketch files.

/* example.pde */

// The statements in the setup() function 
// execute once when the program begins
void setup() 
{
  size(200, 200);  // Sets the canvas size to 200 by 200 pixels
  stroke(255);     // Set line drawing color to monochrome white
  frameRate(30);   // Set up draw() to be called 30 times per second
}

float y = 100;

// The statements in draw() are executed until the 
// program is stopped. The function is called as many
// times per second as the frameRate. If no explicit
// rate is set, this is 45 times per second.
void draw() 
{ 
  background(0);   // Set the background to monochrome black
  y = y - 1; 
  if (y < 0) { y = height; } 
  line(0, y, width, y);  // draw a horizontal line at height y
}

Processing language has two ways of rendering a 2D or 3D in order to understand underlying graphic. It uses Java for 2D, and OpenGL for 3D. This code demonstrates the rendering . The size() function provide choice to choose 2D or 3D. To create a 2D sketch that is 100 by 100 pixels. size(100, 100, P2D);
To draw a 3D sketch OpenGL is used: size(100, 100, OPENGL);

Challenges

• calling color() function with out of range values produces unpredictable results
• It is recommended to use hexadecimal values for colors #FFFFFF
• overhead of handling dummy Method overriding for every method we use
• Variables declared in Processing.js require more care than Processing
• More chance of bugs when converting from Processing to Processing.js explicit typecasting is needed, otherwise it produces random results

The sample code below shows explicit casting of the integer datatype.

// before
int g = mouseX / j;

// after
int g = (int)(mouseX / j);

p5.js

Lauren McCarthy has created p5.js, a native JavaScript alternative and successor to Processing.js that has the official support of the Processing Foundation. McCarthy also teaches an introductory course to p5.js on Kadenze.

See also

• D3.js
• JavaScript InfoVis Toolkit
• Processing (programming language)

References

External links

• Official website
• Processing for the Web (POW) project
• Studio Sketchpad, a browser-based IDE for Processing.js
• Computer Science at Khan Academy
• Processing homepage
• Different ways of executing
• GSvideo for playback music