Or you could just start with ASCII... I was discussing how shaders work with a friend and wound up hacking together a sort of "shadertoy" that runs in Emacs last night. Scroll to end of file to see examples...

https://hg.sr.ht/~oofoe/shademacs/browse/sdf.el?rev=tip

  (shade 10 2 (lambda (x y) x))  ; Horizontal ramp.
  ;; @ # & % * = + : - · 
  ;; @ # & % * = + : - ·