color_wheel.sf

#!/usr/bin/ruby

#
## https://rosettacode.org/wiki/Color_wheel
#

require('Imager')

var (width, height) = (300, 300)
var center = Complex(width/2 , height/2)

var img = %O|Imager|.new(
                      xsize => width,
                      ysize => height,
                     )

for y = ^height, x = ^width {
    var vector = (center - x - y.i)
    var magnitude = (vector.abs * 2 / width)
    var direction = ((Num.pi + atan2(vector.real, vector.imag)) / Num.tau)
    img.setpixel(
        x     => x,
        y     => y,
        color => Hash(hsv => [360*direction, magnitude, magnitude < 1 ? 1 : 0])
    )
}

img.write(file => 'color_wheel.png')