this effect is accomplished by alternating these two grayscale ramps in a checker pattern btw:
"▁▂▃▄▅▆▇█"
"▏▎▍▌▋▊▉█"

I made a shadertoy version of it if anyone wants to play around with it https://www.shadertoy.com/view/4f2fDc

@aeva thank u yes i do