Source code in the processing programming language

size(300, 300);
background(0);
float radius = min(width, height) / 2.0;
float cx = width / 2;
float cy = width / 2;
for (int x = 0; x < width; x++) {
  for (int y = 0; y < width; y++) {
    float rx = x - cx;
    float ry = y - cy;
    float s = sqrt(sq(rx) + sq(ry)) / radius;
    if (s <= 1.0) {
      float h = ((atan2(ry, rx) / PI) + 1.0) / 2.0;
      colorMode(HSB);
      color c = color(int(h * 255), int(s * 255), 255);
      set(x, y, c);
    }
  }
}


size(300, 300)
background(0)
radius = min(width, height) / 2.0
cx, cy = width / 2, width / 2
for x in range(width):
        for y in range(height):
            rx = x - cx
            ry = y - cy
            s = sqrt(rx ** 2 + ry ** 2) / radius
            if s <= 1.0:
                h = ((atan2(ry, rx) / PI) + 1.0) / 2.0
                colorMode(HSB)
                c = color(int(h * 255), int(s * 255), 255)
                set(x, y, c) # note set() used as Processing set() not as Python set()