Processing: Creative Coding and Computational Art

Figure 13-14. Extrusion Example sketch
In reality, my example is a pretty cheap version of extrusion, since I used Processing’s
box() command, which created the rectangle in 3D space, allowing me to just interactively
change the value of the depth argument in the box() call. If I had started with a “real” rectangle,
I would have had to deal with adding and attaching new geometry to have enough
vertices (at least eight) to make a box. Notice in the example that when you drag the
mouse up, the rectangle becomes a solid box, but when you drag it down, the box exterior
seems to become strangely transparent. This occurrence isn’t a quantum paradox, but one
of the clever ways 3D is optimized for our still slow computers. Since we normally aren’t
interested in the inside of a form (the part we can’t see), 3D engines tend not to waste
processing power rendering that information. Thus, in 3D, polygons are usually singlesided.
So, when the mouse is dragged down and the box collapses in on itself, the inside
surfaces become the outside surfaces; however, since the inside faces are invisible, you can
see through them to the original outside surfaces, which are now inside the box—oy vey!
Lest you think I got off too easy borrowing Processing’s box() function in the last extrusion
example, I’ll follow it up with a better one. Using the keyboard, you can control the length
of the extrusion and the number of segments. You can also set the rendering as wireframe,
hollow shaded, or filled solid. The left and right arrows control extrusion length, the up
and down arrows control the addition/deletion of segments, the S key toggles between
solid shaded and hollow shaded, and the W key toggles between wireframe and shaded.
All the surfaces are double-sided, allowing you to see both the inside and outside of the
box when in hollow shaded mode. I included three screenshots generated by the sketch,
shown in Figures 13-15 through 13-17.
/* Better Extrusion Example
Arrow keys control segments (up/down)
and extrusion length (left/right)
's' key controls solid rendering
'w' key controls wireframe rendering
*/
// begin as a flat cube
int segments = 1;
int pts = 8;
float rectWidth = 150, rectHeight = 100;
float extrudeLength;
3D
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