Processing: Creative Coding and Computational Art

PROCESSING: CREATIVE CODING AND COMPUTATIONAL ART
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and so forth typically utilize a line screen, composed of dots that lay a dot pattern down
when they print. The frequency of the line screen is measured in lines per inch, or LPI. As
long as the line screen is fine enough, the dot pattern is not noticeable. However, tighter
line screens also require papers that bleed less and can hold the distinct dot pattern. There
is a formula you can use to calculate required dpi, based on the line screen frequency and
image size. A simpler rule, however, is to just double the frequency of the line screen to
determine image dpi. So for grainy newspaper printing, a line screen frequency might be
85 LPI, but for a coffee table art book, the frequency might be 200 LPI; thus the image
would need to be around 170 dpi and 400 dpi, respectively. You would also need to make
sure that your image was at the actual printing size at that resolution. That being said, I
recommend that when you land that huge print job, you discuss the image and printing
resolution issues with the printer.
Vector graphics
Vector graphics are typically used for simple illustrations, logos, and images that require
distinct and precise contours. Computer text is vector-based, normally just wrapped in a
text-based object that includes certain methods for editing the text. In vector-based
graphics applications like Illustrator, FreeHand, and Flash, you can create outlines from
text objects, or break them apart and get down to the vector information. Vector graphics
are made up of vertices (points) and strokes. The lines can be straight or curved, and are
generated mathematically. Straight lines are simple linear equations, like y = 4x + 3. In
Processing, you don’t need to worry about the math; you can simply use the line function
to generate a line:
line(x1, y1, x2, y2)
The first two coordinates in the function are the starting point and the last two coordinates
are the line’s endpoint. Processing and Java utilize internal drawing methods that
handle the algebra and draw the line. Curves are a little more complex and require higherdegree
polynomials (don’t scream). The preceding linear equation is a first-degree polynomial,
so a second-degree would just have x to the 2nd power. For example, y = 2x 2 +
3x – 4 is a simple second-degree polynomial, also called a quadratic equation. (Is this ringing
some dusty old bells?) So I’m bugging you with all this math because second-degree
(quadratic) and third-degree (cubic) polynomials are used to generate the smooth curves
that are made with the common Bézier pen tools found in all major graphics applications.
But again, all you have to do is put in the points and Processing will crank out the math
and curves; it is actually a little more complicated than that, but not much. I’ll discuss the
actual implementation in the next few chapters.
The pixels contained within the bounds of the vector shapes do not need to be stored in
memory as they would for raster graphics, because the shapes, including color fills and
strokes, are calculated during runtime (when the program runs). Because vector graphics
are just plots of a set of vertices, they can be moved or transformed very easily. It is no
sweat for the computer to take in the list of coordinates and perform some calculations
on the data and redraw the shapes with the updated vertices. However, since the vertices