Processing: Creative Coding and Computational Art

PROCESSING: CREATIVE CODING AND COMPUTATIONAL ART
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arc()
An arc is a curve segment of the circumference of a circle. The arc() function allows you
to draw a curve segment by specifying the x and y position of the center of the circle, the
width and height of the circle, and the beginning and ending angles (in radians) describing
the arc rotation. It is helpful to remember that 2 * pi equals a full rotation around a circle.
In the next sketch (shown in Figure 7-21) I create two arcs, each rotating halfway around
the circle. The first arc begins at 0 and goes to pi, and the second begins at pi and ends at
2 * pi (please note that pi is written as PI in Processing):
//concave/convex curve
size(200, 200);
background(255);
int x = width/2, y = height/2;
int w = 100, h = 100;
strokeWeight(4);
smooth();
fill(0);
arc(x, y-h/2, w, h, 0, PI);
noFill();
arc(x, y+h/2, w, h, PI, PI*2);
Figure 7-21. Using Processing’s arc() function
The arc() function is easier to use than it looks. Because it requires six arguments, two of
which are angles, it can seem overly complicated—but it really isn’t. It helps to think of the
arc() function as a partial ellipse() function. In fact, if you really want to, you can use
arc() in place of ellipse(). arc() also has both a fill and a stroke option, just like
ellipse(). Here’s a simple modification to the program that creates two concentric circles
using arc(), as shown in Figure 7-22: