An Apollonian Gasket is fractal of circles packed within a circle. Its constructed using Descartes theorem . If you have three kissing circles, Descartes’ theorem gives you a fourth. But now we have more circles so we can use the theorem again to get even more. Applying the theorem recursively we can pack more and more circles into the spaces, until the circles are too small to see.

Made with JavaScript and p5.js. You can find an interactive editable version on OpenProcessing