Chladni
A singing plate, mapped by the sand on its silent lines
A square plate that sings, mapped by the bright points that gather on the lines which never move — the same way sand walks to the silence on a real vibrating plate. The figure ripples through zero as the plate rings, and sweeping the mode numbers re-solves one figure into the next instead of cutting.
Rendering cost: heavy. A raymarch or escape-time loop per pixel: cap the pixel ratio, or keep it to a card rather than a fullscreen background. How to tune it
Take Chladni with you.
Chladni is free. Sign in and it is yours — the background itself, with your settings already saved in, ready to drop into your site. The account is only somewhere to put the files. No card now, and no card later.
The other 61 come with a licence, $9.99 once.
$0forever
Your preset is in the URL. It survives the trip.