Processing: Creative Coding and Computational Art

Continuous mode
In continuous mode, users build upon what they’ve learned in basic mode, with the edition
of code structures called functions and classes. As you recall, functions are the main building
blocks used in procedural programming, and are simply groupings of lines of code that
execute only when they are explicitly called. Classes are much more complicated structures
than functions, and are utilized in OOP. I’ll cover classes in detail in Chapter 8. In
basic mode, code is executed linearly (line by line). Functions and classes, on the other
hand, allow code to be executed nonlinearly. These structures are only executed when
they are explicitly called, not when they are initially read into memory.
In continuous mode, two basic Processing functions are provided, which allow you to add
your own custom structures (functions or classes). The two functions are as follows:
void setup(){
}
void draw(){
}
The setup() function is called only once, at the start of the program. This is the place
where you normally initialize variables that will be used later in the program. Adding the
setup() function to your sketch allows you to add your own additional custom functions
and classes. The draw() function adds animation capabilities to your sketch and has a
built-in loop, more accurately called a thread or timer. By default, adding the draw() function
to your sketch causes any code between the curly braces of this structure to continuously
execute. There are a number of ways of controlling this behavior, which I’ll cover in
Chapter 11. You can also read more about Processing’s draw() function in Appendix A.
The following sketch example is built in continuous mode and uses two custom functions,
fadeScreen() and paintOutlines(). The sketch is a little drawing program. I’ve added
comments throughout the sketch to explain the program flow, although I don’t necessarily
expect you to fully grasp the code. The sketch allows you to draw by moving and also
dragging the mouse (holding down the mouse button as you move the mouse). A screenshot
of the output of the sketch is shown in Figure 5-11.
/*
Drawing Shapes
Ira Greenberg, November 2, 2005
*/
//declare global variables
float radiusX, radiusY;
//controls rate of screen fade
int screenFadeValue = 20;
//controls maximum size of shape
int sizeMax = 30;
THE PROCESSING ENVIRONMENT
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