Structure #003, Step 10
The screen is not refreshing every frame, and the lines now accumulate in the image surface. Because only black lines are drawn, the screen continually darkens. The final version of the software is different only in the change of the lines' value from white (when they are short) to black (as they grow).
Implemented in Processing in 2004 by Casey Reas, ported to p5.js in 2016