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Pen Plotter Portrait “Bruce” – Breakdown

 

Bruce

 

 

Beard Close Up

Beard Generator

Below is a screen capture of the beard generator application I created in openFrameworks.  Parameters could be adjust to control the appearance of the beard, such as max length, max curliness, gravity, etc.

Generative Beard Growth

I drew some guide lines in Illustrator so I would know the general shape of the beard. Imported the lines into OF and made a grid of hairs and watched them wander, curl and grow.

Beard Outline

One issue with the pen plotter is the lack of clipping. Which can be seen in the above gif. The lines eventually just form a dark mass of curlies. The plotter receives commands that construct lines and outlines, so I had to write some clipping code so that each hair would look more like a tendril. The output after clipping below.

bruceBeardWithClipping

Braid Generator

Now onto the braids. Instead of creating the braids entirely programmatically, I wanted finer control of their appearance. So I created three “braid pieces” in Illustrator. They are in green, pink and yellow. I designed them to be repeatable, nestling in nicely with their neighbors.

 

Braid Pieces

Each piece has four points of reference, as shown by the orange circles. They helped me determine the width and height of the braid and the offset of the lines to the center axis. I used the local x distance from the center axis to rotate the line points around a curve using the normal along the curve.

braid1braid2braid3

This position rotation is applied to every point in every line of each piece. The results of using many braid pieces along curved paths are depicted below.

 

Braid Generator

 


HP7475 Pen Plotter with OpenFrameworks

HP7475 Pen Plotter Printing from OpenFrameworks
I recently purchased a HP7475 Pen Plotter from ebay for about $110 with shipping. I love that this printer uses physical pens that are dragged on paper to make marks. The marks have the inconsistencies that arise when drawing with a pen on paper and they are beautiful.
The first step was talking with the printer from my MacBook. This printer was initially released in 1983. Several people have detailed steps about sending printer commands from a modern computer.
http://notes.variogr.am/post/29262500593/1980s-pen-plotters-of-the-future
http://grandahl.net/feed/?p=19
http://www.tobiastoft.com/posts/an-intro-to-pen-plotters
Chiplotle!

The printer uses a language called HPGL that is rather straight forward. The above links provide several different ways to communicate with the printer. I want to use OpenFrameworks to communicate with the printer and the above methods seem overly complicated to achieve this. Add-on time!
The original manual is online and there is a cheat sheet for some of the printer commands.
I wrote ofxHPGL to communicate with the printer and it’s rather straightforward. The serial buffer on the printer is super tiny, so there is a sleep millis in there so that the buffer doesn’t overflow. If the printer starts acting weird, that is usually the issue.