Processing: Creative Coding and Computational Art

PROCESSING: CREATIVE CODING AND COMPUTATIONAL ART
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Returning to the original speed settings, speedX = 2, speedY = 2.5, what could you do if
you wanted to double the speed of the object, but not alter its direction? You could multiply
both values by 2. This would cause the object to move faster, but still along the same
path. So what happened? I know this may seem pathetically simple, but the underlying
concepts are very important for what we’ll be doing (and not as simple as they may initially
seem).
When you double the speed settings, the object’s speed obviously increases, but the ratio
of the two speeds remains the same, keeping the object moving in the same direction. This
ratio relates to the slope of the line defining the movement of the object. You may recall
that slope is calculated as the change in y (∆y) over the change in x (∆x)—or the rise over
the run.
Thus, speed and direction can be thought of as two separate quantities; you can alter an
object’s speed while still maintaining its current direction. (It would be pretty hard to drive
a car safely if we couldn’t do this.) Mathematically, there is a convenient way of expressing
all this, namely in a structure called a vector.
I’ve mentioned vectors earlier in the book, and we’ll delve deeper into them in the final
chapters (on 3D) as well. A vector, for our current purposes, is a quantity that describes
both speed and direction, more commonly known as velocity.
In the next example, the two parts of the vector (direction and speed) are coded as separate
variables, to help illustrate their relationship. The sketch moves five rectangles in the
same direction, but at differing speeds.
float directionX = .56, directionY = .83;
float[] speeds = {.75, 1.3, 2.2, .92, 1.5};
float[] x = new float[5], y = new float[5];
void setup(){
size(400, 400);
noStroke();
fill(128);
smooth();
}
void draw(){
background(255);
for (int i=0; i