Accurate CRT Simulation
In the analogtv.c source code, by Trevor Blackwell (part of XScreenSaver) is this comment [1]:    A maxim of technology is that failures reveal underlying
    mechanism. A good way to learn how something works is to
    push it to failure. The way it fails will usually tell you
    a lot about how it works.

To mimic the image on a 1970s-era colour TV, XScreenSaver uses an accurate DSP simulation of all the analogue circuitry, including bandwidth limits, noise, and distortion. A gigahertz processor is just capable of keeping up with this.[1] In XScreenSaver: a collection of free screen savers for X11 and MacOS by Jamie Zawinski [2].Edit: if you want to read the source code---highly recommended!---retype the address below by hand or you'll become acquainted with jwz's countermeasures.[2] https://www.jwz.org/xscreensaver/xscreensaver-5.34.tar.gz