So much fun from 16 x 16-tixy.land
The function is limited to 32 characters but even so that gives you a lot of possibilities. Most patterns are dynamic, changing as you watch. It’s quite fascinating. The pattern shown in the screen shot is from Math.tan(t*(100-y*x)/9). and the actual url (including the code is)
The %28 etc are the HTML encoding of (, while %29 is ) and %2f is /.
You can edit any function on the page so try substituting sin, cos instead of tan. Also abs works as well.