Want to change what it does? Try a lowercase letter, any lowercase letter. They are mostly toggles.
The bottom row of keys changes the shape that's being tiled.
The lefthand side of the middle row controls drawing modes:'a' causes it to draw one layer and stop. 's' stops whatever's going on where it is. 'd' causes it to reinitialize some variables between layers. 'f' causes it to draw the next layer (if it's not stopped, but it's not drawing anything, either). 'g' clears the screen and puts up a new background without changing any parameters. 'h', like a mouse click, wipes everything over and generates mostly-new parameters. (Thus, to get previous modes of operation, you can press 'd' to get the constant variation, or 'a' to get draw one layer and stop.)
j-l change how the shape is laid out. q-y change color or lineweight. 'u' changes the speed, 'i' the number of lines per layer, 'o' whether the lines are linearly or non-linearly scaled, and 'p' the dimensions of the repeat. Good luck with mnemonics.
Source code: squaretile
Built with Processing
Built by Elizabeth Zwicky