Swirl
Swirl produces the classic black & white hypnotic spiral effect, with additional options.

Center Sets the center of the Swirl.
Density Controls the density of the Swirl. Extreme values can produce Moiré patterns, but they will be antialiased.
Bulge Adds extra dimension to the Swirl.
Angle Rotates the Swirl.
Reverse Reverse the direction of the Swirl