<meta name="generator" content=

"HTML Tidy for Mac OS X (vers 31 October 2006 - Apple Inc. build 15.12), see www.w3.org">

<title></title>

<h1>Processing Overview</h1>

<table width="656">

<tr>

<td>

<p class="license">This tutorial is for Python Mode in

Processing 2+. If you see any errors or have comments,

please <a href=

"https://github.com/jdf/processing-py-site/issues?state=open">

let us know</a>. This tutorial is adapted from the book,

<a href=

"http://www.processing.org/learning/books/#fry">Visualizing

Data</a> by Ben Fry, O'Reilly 2007. Copyright &copy; 2008

Ben Fry. All rights reserved.</p>

<p>&nbsp;</p>

<p>Processing is a simple programming environment that was

created to make it easier to develop visually oriented

applications with an emphasis on animation and providing

users with instant feedback through interaction. The

developers wanted a means to &ldquo;sketch&rdquo; ideas in

code. As its capabilities have expanded over the past

decade, Processing has come to be used for more advanced

production-level work in addition to its sketching role.

Originally built as a domain-specific extension to Java

targeted towards artists and designers, Processing has

evolved into a full-blown design and prototyping tool used

for large-scale installation work, motion graphics, and

complex data visualization.<br>

<br>

Python Mode for Processing is an extension to Processing,

allowing you to write Processing programs in the Python

programming language (instead of the Java-like Processing

programming language). Program elements in Processing are

fairly simple, regardless of which language you're learning

to program in. If you're familiar with Python, it's best to

forget that Processing has anything to do with it for a

while, until you get the hang of how the API works.<br>

<br>

The latest version of Processing can be downloaded at

<a href=

"http://processing.org/download"><em>http://processing.org/download</em></a><br>

<br>

An important goal for the project was to make this type of

programming accessible to a wider audience. For this

reason, Processing is free to download, free to use, and

open source. But projects developed using the Processing

environment and core libraries can be used for any purpose.

This model is identical to GCC, the GNU Compiler

Collection. GCC and its associated libraries (e.g. libc)

are open source under the GNU Public License (GPL), which

stipulates that changes to the code must be made available.

However, programs created with GCC (examples too numerous

to mention) are not themselves required to be open

source.<br>

<br>

Python Mode for Processing consists of:</p>

<ul>

<li>The Processing Development Environment (PDE). This is

the software that runs when you double-click the

Processing icon. The PDE is an Integrated Development

Environment (IDE) with a minimalist set of features

designed as a simple introduction to programming or for

testing one-off ideas.</li>

<li>A collection of functions (also referred to as

commands or methods) that make up the &ldquo;core&rdquo;

programming interface, or API, as well as several

libraries that support more advanced features such as

sending data over a network, reading live images from a

webcam, and saving complex imagery in PDF format.</li>

<li>The Python Mode add-on, which makes it possible to

write programs in Python that look and behave like

Processing programs and have access the Processing

API.</li>

<li>An active online community, based at <a href=

"http://processing.org"><em>http://processing.org</em></a>.</li>

</ul><br>

For this reason, references to &ldquo;Processing&rdquo; can

be somewhat ambiguous. Are we talking about the API, the

language, the development environment, or the web site?

We'll be careful in this text when referring to each.

<h3>Sketching with Processing</h3>

<p>A Processing program is called a <em>sketch</em>. The

idea is to make programming feel more like scripting, and

adopt the process of scripting to quickly write code.

Sketches are stored in the <em>sketchbook</em>, a folder

that's used as the default location for saving all of your

projects. Sketches that are stored in the sketchbook can be

accessed from File &rarr; Sketchbook. Alternatively, File

&rarr; Open... can be used to open a sketch from elsewhere

on the system.<br>

<br>

Advanced programmers need not use the PDE, and may instead

choose to use its libraries with the Python environment of

choice. However, if you're just getting started, it's

recommended that you use the PDE for your first few

projects to gain familiarity with the way things are done.

To better address our target audience, the conceptual model

(how programs work, how interfaces are built, and how files

are handled) is somewhat different from other programming

environments.<br></p>

<h3>Hello world</h3>

<p>The Processing equivalent of a "Hello World" program is

simply to draw a line:<br></p>

<pre>

<span style="color: #006699;">line</span>(15, 25, 70, 90)

Enter this example and press the Run button, which is an

icon that looks like the Play button from any audio or

video device. Your code will appear in a new window, with a

gray background and a black line from coordinate (15, 25)

to (70, 90). The (0, 0) coordinate is the upper left-hand

corner of the display window. Building on this program to

change the size of the display window and set the

background color, type in the code below:<br>

<br>

<pre>

<span style="color: #006699;">size</span>(400, 400)

<span style="color: #006699;">background</span>(192, 64, 0)

<span style="color: #006699;">stroke</span>(255)

<span style="color: #006699;">line</span>(150, 25, 270, 350)

This version sets the window size to 400 x 400 pixels, sets

the background to an orange-red, and draws the line in

white, by setting the stroke color to 255. By default,

colors are specified in the range 0 to 255. Other

variations of the parameters to the <tt>stroke()</tt>

function provide alternate results:<br>

<br>

<pre>

stroke(255) # sets the stroke color to white

stroke(255, 255, 255) # identical to the line above

stroke(255, 128, 0) # bright orange (red 255, green 128, blue 0)

stroke("#FF8000") # bright orange as a web color

stroke(255, 128, 0, 128) # bright orange with 50% transparency

The same alternatives work for the <tt>fill()</tt>

function, which sets the fill color, and the

<tt>background()</tt> function, which clears the display

window. Like all Processing functions that affect drawing

properties, the fill and stroke colors affect all geometry

drawn to the screen until the next fill and stroke

functions.<br>

<br>

<h3>Hello mouse</h3>

<p>A program written as a list of statements (like the

previous examples) is called a <em>static</em> sketch. In a

static sketch, a series of functions are used to perform

tasks or create a single image without any animation or

interaction. Interactive programs are drawn as a series of

frames, which you can create by adding functions titled

<tt>setup()</tt> and <tt>draw()</tt> as shown in the code

below. These are built-in functions that are called

automatically.<br>

<br></p>

<pre>

<span style="color: #33997E;">def</span> <span style=

"color: #006699;"><b>setup</b></span>():

<span style="color: #006699;">size</span>(400, 400)

<span style="color: #006699;">stroke</span>(255)

<span style="color: #006699;">background</span>(192, 64, 0)

<span style="color: #33997E;">def</span> <span style=

"color: #006699;"><b>draw</b></span>():

<span style="color: #006699;">line</span>(150, 25, <span style=

"color: #D94A7A;">mouseX</span>, <span style=

"color: #D94A7A;">mouseY</span>)

The <tt>setup()</tt> block runs once, and the

<tt>draw()</tt> block runs repeatedly. As such,

<tt>setup()</tt> can be used for any initialization; in

this case, setting the screen size, making the background

orange, and setting the stroke color to white. The

<tt>draw()</tt> block is used to handle animation. The

<tt>size()</tt> function must always be the first line

inside <tt>setup()</tt>.<br>

<br>

Because the <tt>background()</tt> function is used only

once, the screen will fill with lines as the mouse is

moved. To draw just a single line that follows the mouse,

move the <tt>background()</tt> function to the

<tt>draw()</tt> function, which will clear the display

window (filling it with orange) each time <tt>draw()</tt>

runs.<br>

<br>

<pre>

<span style="color: #33997E;">def</span> <span style=

"color: #006699;"><b>setup</b></span>():

<span style="color: #006699;">size</span>(400, 400)

<span style="color: #006699;">stroke</span>(255)

<span style="color: #33997E;">def</span> <span style=

"color: #006699;"><b>draw</b></span>():

<span style="color: #006699;">background</span>(192, 64, 0)

<span style="color: #006699;">line</span>(150, 25, <span style=

"color: #D94A7A;">mouseX</span>, <span style=

"color: #D94A7A;">mouseY</span>)

Static programs are most commonly used for extremely simple

examples, or for scripts that run in a linear fashion and

then exit. For instance, a static program might start, draw

a page to a PDF file, and exit.<br>

<br>

Most programs will use the <tt>setup()</tt> and

<tt>draw()</tt> blocks. More advanced mouse handling can

also be introduced; for instance, the

<tt>mousePressed()</tt> function will be called whenever

the mouse is pressed. In the following example, when the

mouse is pressed, the screen is cleared via the

<tt>background()</tt> function:<br>

<br>

<pre>

<span style="color: #33997E;">def</span> <span style=

"color: #006699;"><b>setup</b></span>():

<span style="color: #006699;">size</span>(400, 400)

<span style="color: #006699;">stroke</span>(255)

<span style="color: #33997E;">def</span> <span style=

"color: #006699;"><b>draw</b></span>():

<span style="color: #006699;">line</span>(150, 25, <span style=

"color: #D94A7A;">mouseX</span>, <span style=

"color: #D94A7A;">mouseY</span>)

<span style="color: #33997E;">def</span> <span style=

"color: #D94A7A;">mousePressed</span>():

<span style="color: #006699;">background</span>(192, 64, 0)

<!--More about static versus active mode programs can be found in the Programming Modes section of the reference, which can be viewed from Help &rarr; Environment, or online at <a href="http://processing.org/reference/environment/"><em>http://processing.org/reference/environment</em></a><br />-->

<!-- commenting out for now

<h3>Creating images from your work</h3>

<p>If you don't want to distribute the actual project, you

might want to create images of its output instead. Images

are saved with the <tt>saveFrame()</tt> function. Adding

<tt>saveFrame()</tt> at the end of <tt>draw()</tt> will

produce a numbered sequence of TIFF-format images of the

program's output, named <em>screen-0001.tif</em>,

<em>screen-0002.tif</em>, and so on. A new file will be

saved each time <tt>draw()</tt> runs &mdash; watch out,

this can quickly fill your sketch folder with hundreds of

files. You can also specify your own name and file type for

the file to be saved with a function like:</p>

<pre>

saveFrame("output.png")

To do the same for a numbered sequence, use # (hash marks)

where the numbers should be placed:<br>

<br>

<pre>

saveFrame("output-####.png")

For high quality output, you can write geometry to PDF

files instead of the screen, as described in the later

section about the <tt>size()</tt> function.<br>

<h3>Examples and reference</h3>

<p>While many programmers learn to code in school, others

teach themselves and learn on their own. Learning on your

own involves looking at lots of other code: running,

altering, breaking, and enhancing it until you can reshape

it into something new. With this learning model in mind,

the Processing software download includes hundreds of

examples that demonstrate different features of the

environment and API.<br>

<br>

The examples can be accessed from the File &rarr; Examples

menu. They're grouped into categories based on their

function (such as Motion, Typography, and Image) or the

libraries they use (PDF, Network, and Video).<br>

<br>

Find an interesting topic in the list and try an example.

You'll see functions that are familiar, e.g.

<tt>stroke()</tt>, <tt>line()</tt>, and

<tt>background()</tt>, as well as others that have not yet

been covered.

<!-- FIXME: include this again after reference works in IDE

<h3>More about size()</h3>

<p>The <tt>size()</tt> function sets the global variables

width and height. For objects whose size is dependent on

the screen, always use the width and height variables

instead of a number. This prevents problems when the size()

line is altered.</p>

<pre>

<span style="color: #006699;">size</span>(400, 400)

<span style=

"color: #666666;"># The wrong way to specify the middle of the screen</span>

<span style="color: #006699;">ellipse</span>(200, 200, 50, 50);

<span style=

"color: #666666;"># Always the middle, no matter how the size() line changes</span>

<span style="color: #006699;">ellipse</span>(<span style=

"color: #D94A7A;">width</span>/2, <span style=

"color: #D94A7A;">height</span>/2, 50, 50);

In the earlier examples, the <tt>size()</tt> function

specified only a width and height for the window to be

created. An optional parameter to the <tt>size()</tt>

function specifies how graphics are rendered. A renderer

handles how the Processing API is implemented for a

particular output function (whether the screen, or a screen

driven by a high-end graphics card, or a PDF file). The

default renderer does an excellent job with high-quality 2D

vector graphics, but at the expense of speed. In

particular, working with pixels directly is slow. Several

other renderers are included with Processing, each having a

unique function. At the risk of getting too far into the

specifics, here's a description of the other possible

drawing modes to use with Processing.<br>

<br>

<pre>

size(400, 400, P2D)

The P2D renderer uses OpenGL for faster rendering of

two-dimensional graphics, while using Processing's simpler

graphics APIs and the Processing development environment's

easy application export.<br>

<br>

<pre>

size(400, 400, P3D)

The P3D renderer also uses OpenGL for faster rendering. It

can draw three-dimensional objects and two-dimensional

object in space as well as lighting, texture, and

materials.<br>

<br>

<pre>

size(400, 400, PDF, "output.pdf")

The PDF renderer draws all geometry to a file instead of

the screen. To use PDF, in addition to altering your size()

function, you must select Import Library, then PDF from the

Sketch menu. This is a cousin of the default renderer, but

instead writes directly to PDF files.<br>

<br>

<h3>Loading and displaying data</h3>

<p>One of the unique aspects of the Processing API is the

way files are handled. The <tt>loadImage()</tt> and

<tt>loadStrings()</tt> functions each expect to find a file

inside a folder named <em>data</em>, which is a

subdirectory of the sketch folder.<br>

<br>

File handling functions include <tt>loadStrings()</tt>,

which reads a text file into an array of String objects,

and <tt>loadImage()</tt> which reads an image into a PImage

object, the container for image data in Processing.<br>

<br></p>

<pre>

<span style=

"color: #666666;"># Examples of loading a text file and a JPEG image</span>

<span style=

"color: #666666;"># from the data folder of a sketch.</span>

lines = <span style=

"color: #006699;">loadStrings</span>(<span style=

"color: #7D4793;">"something.txt"</span>)

img = <span style="color: #006699;">loadImage</span>(<span style=

"color: #7D4793;">"picture.jpg"</span>)

The <tt>loadStrings()</tt> function returns an array of

Python string objects, which is assigned to a variable

named <tt>lines</tt>; it will presumably be used later in

the program under this name. The reason

<tt>loadStrings</tt> creates an array is that it splits the

<em>something.txt</em> file into its individual lines. The

following function returns a <tt>PImage</tt> object, which

is assigned to a variable named <tt>img</tt>.<br>

<br>

To add a file to the data folder of a Processing sketch,

use the Sketch &rarr; Add File menu option, or drag the

file into the editor window of the PDE. The data folder

will be created if it does not exist already.<br>

<br>

To view the contents of the sketch folder, use the Sketch

&rarr; Show Sketch Folder menu option. This opens the

sketch window in your operating system's file browser.<br>

<h3>Libraries add new features</h3>

<p>A <em>library</em> is a collection of code in a

specified format that makes it easy to use within

Processing. Libraries have been important to the growth of

the project, because they let developers make new features

accessible to users without needing to make them part of

the core Processing API.<br>

<br>

Several core libraries come with Processing. These can be

seen in the Libraries section of the online reference (also

available from the Help menu from within the PDE.) These

libraries can be seen at <a href=

"http://processing.org/reference/libraries/"><em>http://processing.org/reference/libraries/</em></a><br>

<br>

One example is the PDF Export library. This library makes

it possible to write PDF files directly from Processing.

These vector graphics files can be scaled to any size and

output at very high resolutions.<br>

<br>

To use the PDF library in a Python Mode project, choose

Sketch &rarr; Import Library &rarr; pdf. This will add the

following line to the top of the sketch:</p>

<pre>

add_library('pdf')

This line instructs Processing to use the indicated library

when running the sketch.<br>

<br>

Now that the PDF library is imported, you may use it to

create a file. For instance, the following line of code

creates a new PDF file named <em>lines.pdf</em> that you

can draw to.<br>

<br>

<pre>

beginRecord(PDF, "lines.pdf")

Each drawing function such as <tt>line()</tt> and

<tt>ellipse()</tt> will now draw to the screen as well as

to the PDF.<br>

<br>

Other libraries provide features such as reading images

from a camera, sending and receiving MIDI and OSC commands,

sophisticated 3D camera control, and access to MySQL

databases.<br>

<h3>Sketching and scripting</h3>

<p>Processing sketches are made up of one or more tabs,

with each tab representing a piece of code. The environment

is designed around projects that are a few pages of code,

and often three to five tabs in total. This covers a

significant number of projects developed to test and

prototype ideas, often before embedding them into a larger

project or building a more robust application for broader

deployment.<br>

<br>

Processing assembles our experience in building software of

this kind (sketches of interactive works or data-driven

visualization) and simplifies the parts that we felt should

be easier, such as getting started quickly, and insulating

new users from issues like those associated with setting up

complicated programming frameworks.<br></p>

<h3>Don't start by trying to build a cathedral</h3>

<p>If you're already familiar with programming, it's

important to understand how Processing differs from other

development environments and languages. The Processing

project encourages a style of work that builds code

quickly, understanding that either the code will be used as

a quick sketch, or ideas are being tested before developing

a final project. This could be misconstrued as software

engineering heresy. Perhaps we're not far from

&ldquo;hacking,&rdquo; but this is more appropriate for the

roles in which Processing is used. Why force students or

casual programmers to learn about graphics contexts,

threading, and event handling functions before they can

show something on the screen that interacts with the mouse?

The same goes for advanced developers: why should they

always need to start with the same two pages of code

whenever they begin a project?<br>

<br>

In another scenario, the ability to try things out quickly

is a far higher priority than sophisticated code structure.

Usually you don't know what the outcome will be, so you

might build something one week to try an initial

hypothesis, and build something new the next based on what

was learned in the first week. To this end, remember the

following considerations as you begin writing code with

Processing:</p>

<ul>

<li>Be careful about creating unnecessary structures in

your code. As you learn about encapsulating your code

into classes, it's tempting to make ever-smaller classes,

because data can always be distilled further. Do you need

classes at the level of molecules, atoms, or quarks? Just

because atoms go smaller doesn't mean that we need to

work at a lower level of abstraction. If a class is half

a page, does it make sense to have six additional

subclasses that are each half a page long? Could the same

thing be accomplished with a single class that is a page

and a half in total?</li>

<li>Consider the scale of the project. It's not always

necessary to build enterprise-level software on the first

day. Explore first: figure out the minimum code necessary

to help answer your questions and satisfy your

curiosity.</li>

</ul>The argument is not to avoid continually rewriting,

but rather to delay engineering work until it's

appropriate. The threshold for where to begin engineering a

piece of software is much later than for traditional

programming projects because there is a kind of

<em>art</em> to the early process of quick iteration.<br>

<br>

Of course, once things are working, avoid the urge to

rewrite for its own sake. A rewrite should be used when

addressing a completely different problem. If you've

managed to hit the nail on the head, you should refactor to

clean up function names and class interactions. But a full

rewrite of already finished code is almost always a bad

idea, no matter how "ugly" it may seem.<br>

<p>&nbsp;</p>

<p class="license">This tutorial is for Python Mode in

Processing 2+. If you see any errors or have comments,

please <a href=

"https://github.com/jdf/processing-py-site/issues?state=open">

let us know</a>. This tutorial is adapted from the book,

<a href=

"http://www.processing.org/learning/books/#fry">Visualizing

Data</a> by Ben Fry, O'Reilly 2007. Copyright &copy; 2008

Ben Fry. All rights reserved.</p>

</td>

</tr>

</table>