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

pixels = W:1024 H:1024

x = from -10.0 to 10.0 W
y = from -10.0 to 10.0 H

t = 5

a = length2(x, y) - t
ca = cos(a)
sa = sin(a)

t = x*ca - y*sa
y = x*sa + y*ca
x = abs(t)
y = abs(y)

u = atan2(x, y)/PI
v = length2(x, y)

k = sqrt(u) + sqrt(v) - sqrt(u + v)

r = k
g = k
b = k
