Learning Processing: A Beginner's Guide to Programming Images ...

214 Learning Processing
13.9
// Draw an ellipse at x,y
noStroke();
fill(0);
ellipse(x + width/2, y + height/2, 16, 16); // Adjust for center of window
// Increment the angle
theta + = 0.01;
}
Exercise 13-5: Using Example 13-5, draw a spiral path. Start in the center and move
outward. Note that this can be done by changing only one line of code and adding one line
of code!
Oscillation
Trigonometric functions can be used for more than geometric calculations associated with right triangles.
Let’s take a look at Figure 13.11, a graph of the sine function where y � sin( x ).
fi g. 13.11
4
2
0
�1π 0 1π
2π
�2
�4
y
You will notice that the output of sine is a smooth curve alternating between –1 and 1 . Th is type of
behavior is known as oscillation , a periodic movement between two points. A swinging pendulum, for
example, oscillates.
We can simulate oscillation in a Processing sketch by assigning the output of the sine function to an
object’s location. Th is is similar to how we used noise( ) to control the size of a circle (see Example 13-4),
only with sin( ) controlling a location. Note that while noise( ) produces a number between 0 and 1.0, sin( )
outputs a range between –1 and 1. Example 13-6 shows the code for an oscillating pendulum .
x