#https://www.shadertoy.com/view/ls33DN

pixels = W:1024 H:1024

x = from 0 to 20 W
y = from 0 to 20 H

t = sign(cos(length2(ceil(x), ceil(y))*99.0))
x = x*t
x = fract(x)
y = fract(y)
r = cos(min(length2(x, y), length2(x-1, y-1))*44.0)
g = r
b = r
