Processing: Creative Coding and Computational Art

Figure 6-9. Multiple randomized particle lines
I imagine some of you might need a little clarification on parts of this last example.
Although this is a simple program in number of code lines, parts of it are a bit dense.
When you nest a for loop, as in the example, it is important to understand how the loop
executes. The outer for loop initializes i to height/totalRows. This loop will run as long
as i is less than the height of the display window. i will be incremented by the same
amount i is originally initialized to, height/totalRows. On the first iteration of the outer
for loop, the inner for loop runs through an entire loop cycle. In this case, j is initialized
to 1 and also incremented by 1 as long as it remains less than the value of steps. After the
inner loops runs through all its iterations, control goes back to the outer loop, which is
incremented by height/totalRows; and then the process repeats itself, with the inner
loop again going through its entire iterative loop cycle. This process will continue until the
condition in the outer loop no longer evaluates to true (i is no longer less than the height
of the display window). As you might imagine, if you’re not careful, you can pretty easily
create nested loops that take a lot of time to finish.
One other significant point regards how you name your variables in the loops. Within a
code structure bounded by curly braces (for loops, if statements, functions, etc.), variables
declared in the head or body of the structure (or passed in, as in the case of parameters
in the head of a function) have local scope. This is in contrast to variables declared
at the top of a program, which have global scope. Because of local scope, the variable i,
declared in the head of the for loop, only exists between the curly braces of the for loop;
it has no existence outside the loop. That’s why it’s possible to use the same-named
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