Processing: Creative Coding and Computational Art

If you run this, you should see a 100-by-100-pixel square in the middle of the display
window.
When you write your own function, you need to include Processing’s setup() function, or
you’ll get a compile error when you try to run the sketch. A function begins with a return
type (either void or a legal data type); an identifier (the name of the function); open and
closed parentheses, with any optional declared parameters; and open and closed curly
braces.
Here’s the structure of a function:
return type (void or legal datatype) function name(optional ➥
parameters){
code to execute when function is called;
}
The drawRectangle(float x, float y, float w, float h) function in the preceding
sketch expects four arguments to be passed to it when it’s called, as I specified four
parameters between its parentheses. You’ll notice that I use both the terms parameter and
argument. This can be confusing to new coders (and even some experienced coders); I
prefer to call the values between the parentheses in the function definition parameters,
and the values passed to the function arguments. I know this may sound like an issue of
semantics (or worse), but I find it easier to discuss and teach this stuff by using the two different
terms.
This last example didn’t do much more than Processing’s plain old rect() call. The next
example (see Figure 3-7) makes better use of the drawRectangle() function and also
revisits for loops—yippee!
void setup(){
size(400, 400);
background(255);
for (int i=0; i