Color sampleLight(Scene scene, Ray n, Random rand, IShape light)
{
Vector center;
double radius;
switch (light)
{
case Sphere sphere:
radius = sphere.Radius;
center = sphere.Center;
break;
default:
Box box = light.BoundingBox();
radius = box.OuterRadius();
center = box.Center();
break;
}
var point = center;
if (SoftShadows)
{
for (; ;)
{
var x = (rand.NextDouble() * 2) - 1;
var y = (rand.NextDouble() * 2) - 1;
if ((x * x) + (y * y) <= 1)
{
var l = center.Sub(n.Origin).Normalize();
var u = l.Cross(Vector.RandomUnitVector(rand)).Normalize();
var v = l.Cross(u);
point = new Vector();
point = point.Add(u.MulScalar(x * radius));
point = point.Add(v.MulScalar(y * radius));
point = point.Add(center);
break;
}
}
}
// construct ray toward light point
Ray ray = new Ray(n.Origin, point.Sub(n.Origin).Normalize());
// get cosine term
var diffuse = ray.Direction.Dot(n.Direction);
if (diffuse <= 0)
{
return(Color.Black);
}
// check for light visibility
Hit hit = scene.Intersect(ray);
if (!hit.Ok() || hit.Shape != light)
{
return(Color.Black);
}
// compute solid angle (hemisphere coverage)
var hyp = center.Sub(n.Origin).Length();
var opp = radius;
var theta = Math.Asin(opp / hyp);
var adj = opp / Math.Tan(theta);
var d = Math.Cos(theta) * adj;
var r = Math.Sin(theta) * adj;
var coverage = (r * r) / (d * d);
if (hyp < opp)
{
coverage = 1;
}
coverage = Math.Min(coverage, 1);
// get material properties from light
Material material = Material.MaterialAt(light, point);
// combine factors
var m = material.Emittance * diffuse * coverage;
return(material.Color.MulScalar(m));
}
