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

pixels = W:1024 H:1024

x = from -0.36 to 0.36 H
y = from -0.36 to 0.36 W

size = 0.15
thickness = 0.0021

d = 0.0
alpha = 0.15
cx = 0
cy = 0

[loop start:8
d1 = length2(x-cx, y-cy)
d2 = abs(d1-size)
d = d + thickness/d2
cx = cx + alpha*sign(x-cx)
cy = cy + alpha*sign(y-cy)
size = size*0.40
thickness = thickness*0.775
alpha = alpha*0.5
loop end]

r = d*0.25
g = d*0.35
b = d*0.45


