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January 18, 2013 AT 11:00 am

Raspberry Pi Python Adventures #piday #raspberrypi @Raspberry_Pi

Pi-A-Sketch

Here’s a great tutorial from Raspberry Pi Python Adventures that shows how to write code to control motors to create all sorts of geometry in the Pi-A-Sketch project! Via RaspberryPi.org:

Are you guys ready to look at the entrails of the Python? We are going to review the code for the Pi-A-Sketch. Liz already published the URL for the Pi-A-Sketch code on the raspberrypi.org site, but just in case, here it is again:

piasketch.py (bitbucket)

…Initially, I wanted a function to draw a line, and a function to draw a circle. That meant that I would have to write the guts of:

def line(x, y):
    pass

def circle(radius):
    pass

Right away I knew that I would need to do something based on Bresenham’s line drawing algorithm. Horizontal lines are trivial (turn one motor), and so are vertical lines (turn the other motor). Perfect diagonals are also easy to accomplish, since it is just a matter of turning both motors at the same time, for each step. Based on the direction of the steps, 4 different diagonal directions can be done.

Yet, with Bresenham’s algorithm, you can do a line of any slope. In order to save time, I was not going to do special case handling, and just do everything with his algorithm….

Read more.


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