https://post-processing.tresjs.org/guide/pmndrs/ascii
https://forum.babylonjs.com/t/ascii-shader-using-glsl-postpr...
https://threejs.org/examples/?q=ascii#webgl_effects_ascii
https://codesandbox.io/p/sandbox/ascii-postprocessing-n628p8...
and the code: https://github.com/kristopolous/ascsee
I just updated it so it compiles on modern systems.
I also found the original version if you like being an archaeologist: https://9ol.es/tmp/gol.c