Python Mode

Processing doesn’t include support for the Python programming language by default. In order to enable Python support, you’ll need to install an add-on called Python Mode. You can do this by clicking on the drop-down menu on the right side of the toolbar and selecting Add Mode.... A window with the title Contribution Manager will appear. Click the tab labelled Modes and scroll down until you see Python Mode for Processing 3, then press Install.

After you’ve installed Python Mode, you can switch back and forth between the Python and Java versions of Processing using the drop-down menu in the toolbar. If you find yourself getting strange syntax errors or exceptions when running your program, make sure you have the right mode selected!

Your First Program

You’re now running the Processing Development Environment (or PDE). There’s not much to it. The large area is the Text Editor, and there are two buttons across the top—this is the toolbar. Below the editor is the Message Area, and below that is the Console. The Message Area is used for one-line messages, and the Console is used for more technical details.

ellipse(50, 50, 80, 80)

Example 2-2: Make Circles

Delete the text from the last example, and try this one:

def setup():
  size(480, 120)

def draw():
  if mousePressed:
    fill(0)
  else:
    fill(255)
  ellipse(mouseX, mouseY, 80, 80)

Python is notoriously picky about formatting, so make sure you type the code exactly as shown, indentation and all.

This program creates a window that is 480 pixels wide and 120 pixels high, and then starts drawing white circles at the position of the mouse. When a mouse button is pressed, the circle color changes to black. We’ll explain more about this program later. For now, run the code, move the mouse, and click to see what it does. While the sketch is running, the Run button will change to a square “stop” icon, which you can click to halt the sketch.

Show

If you don’t want to use the buttons, you can always use the Sketch menu, which reveals the shortcut Ctrl-R (or Cmd-R on OS X) for Run. The Present option clears the rest of the screen when the program is run to present the sketch all by itself. You can also use Present from the toolbar by holding down the Shift key as you click the Run button. See Figure 2-2.

Figure 2-2. A Processing sketch is displayed on screen with Run and Present. The Present option clears the entire screen before running the code for a cleaner presentation.

Save and New

The next important command is Save. You can find it under the File menu. By default, your programs are saved to the sketchbook, which is a folder that collects your programs for easy access. Select the Sketchbook option in the File menu to bring up a list of all the sketches in your sketchbook.

It’s always a good idea to save your sketches often. As you try different things, keep saving with different names so that you can always go back to an earlier version. This is especially helpful if—no, when—something breaks. You can also see where the sketch is located on your computer with the Show Sketch Folder command under the Sketch menu.

You can create a new sketch by selecting the New option from the File Menu. This will create a new sketch in its own window.

Share

Processing sketches are made to be shared. The Export Application option in the File menu will bundle your code into a single folder. Export Application creates an application for your choice of OS X, Windows, and/or Linux. This is an easy way to make self-contained, double-clickable versions of your projects. Select if you want the program to be full screen or in a window, and if there is a stop button and background color.

Examples and Reference

Learning how to program involves exploring lots of code: running, altering, breaking, and enhancing it until you have reshaped it into something new. With this in mind, the Processing software download includes dozens of examples that demonstrate different features of the software. To open an example, select Examples from the File menu and double-click an example’s name to open it. The examples are grouped into categories based on their function, such as Form, Motion, and Image. Find an interesting topic in the list and try an example. (The examples are specific to each Processing mode, so make sure you have Python Mode selected before you try to access them.)

The Processing Reference for Python explains every code element with a description and examples. The Processing Reference programs are much shorter (usually four or five lines) and easier to follow than the longer code found in the Examples folder. We recommend keeping the Processing Reference open while you’re reading this book and while you’re programming. It can be navigated by topic or alphabetically, but sometimes it’s fastest to do a text search within your browser window.

The Processing Reference was written with the beginner in mind; we hope that we’ve made it clear and understandable. We’re grateful to the many people who’ve spotted errors over the years and reported them. If you think you can improve a reference entry or you find a mistake, please let us know by clicking on the link at the top of each reference page.