Flash supports a scripting language called 'Actionscript' which is intended to be used to create complicated animations, interactions and such like. However, using only one frame, it can be used to construct patterns. Those shown here are static and don't move but by using the same techniques, they could be made to do so. Basically two methods can be used, actually drawing lines and possibly filling them in (similar to the turtle robots we used to play with), or manipulating a simple graphic, such as a square, which is already drawn. Simple scripts can produce quite complicated results with just a few lines of code. To see a fully annotated example - click here.
The thumbnails are too small to see detail - for a larger picture click them.