#https://www.shadertoy.com/view/Xd23Wm

pixels = W:1024 H:1024

x = from 0 to 8 W
y = from 0 to 8 H

px = mod(x, 1)
py = mod(y, 1)

v = 0.85
k = 0
k = if( (px < 0.6) & (px > 0.4), v, k )
k = if( (py < 0.6) & (py > 0.4), v, k )

r = k
g = k
b = k
