// Returns the solid angle subtended by the shape w.r.t. the reference
// point p, given in world space. Some shapes compute this value in
// closed-form, while the default implementation uses Monte Carlo
// integration; the nSamples parameter determines how many samples are
// used in this case.
public virtual double SolidAngle(Point3D p, int nSamples = 512)
{
Interaction it = new Interaction(p, new Normal3D(), new Vector3D(), new Vector3D(0.0, 0.0, 1.0), 0.0,
new MediumInterface());
double solidAngle = 0.0;
for (int i = 0; i < nSamples; ++i)
{
Point2D u = new Point2D(PbrtMath.RadicalInverse(0, i), PbrtMath.RadicalInverse(1, i));
double pdf;
Interaction pShape = Sample(it, u, out pdf);
if (pdf > 0.0 && !IntersectP(new Ray(p, (pShape.P - p).ToVector3D(), 0.999)))
{
solidAngle += 1.0 / pdf;
}
}
return(solidAngle / nSamples);
}
