Spirograph draws animated Hypotrochoid and Epitrochoid curves.

It was written during a long stint on jury service when I had a lot of time between sessions in court.

You can interact with the drawing by clicking on the curve to pause it. Things to try:

• Change the size of the moving circle
• Change the size of the fixed circle
• Change the pen distance from the center of the moving circle
• Resize the whole curve while keeping the shape
• Modify options using the drop down (arrow top left)

The program can also be run as a screen saver. Simply add the exe to the screen saver folder. Windows will automatically run with the /s switch.

Most difficult part: differentiating the curve to work out the optimal angular increment to maintain a smooth curve even when the pen speed is very high.