Point2 p = pointOnImagePlane;
Vector3 v = new Vector3(
width * (p.x() - 0.5),
height * (0.5 - p.y()),
-1.0);
Ray3 ray = new Ray3(Point3.ORIGIN, v.unit());
Color color = getWhite();
double z = v.x() * v.x() + v.y() * v.y() + 1.0;
double pdf = z * z / (width * height);
return ScatteredRay.diffuse(ray, color, pdf);
}