vogelDisc function
VogelDisc from shadow.glsl — S3.
Implementation
VogelTap vogelDisc(int i, int n, double turn) {
final r = math.sqrt((i + 0.5) / n);
final theta = i * 2.3999632 + turn;
return VogelTap(x: r * math.cos(theta), y: r * math.sin(theta));
}