public Color3 Diffuse(Intersection intersection)
{
float killChance = 0;
if (_russianRoulette)
{
killChance = GetKillChance(intersection.Material.Color);
if (_rng.TestChance(killChance))
{
return(Color4.Black);
}
}
//random reflected ray
Vector3 rDir;
if (_cosineDist)
{
rDir = _rng.CosineDistributed(intersection.SurfaceNormal);
}
else
{
rDir = _rng.RandomVectorOnHemisphere(intersection.SurfaceNormal);
}
var reflected = Ray.CreateFromIntersection(intersection, rDir, goesIntoMaterial: true);
//brdf of material
var brdf = intersection.Material.CalculateColor(intersection) / MathHelper.Pi;
//irradiance
var nDotR = Vector3.Dot(intersection.SurfaceNormal, rDir);
var Ei = _scene.Sample(reflected, _rng, true) * nDotR;
Color3 Ld = Color4.Black;
//use next event estimation?
if (_nee)
{
if (_scene.SurfaceLights.Count > 0)
{
//sample light directly - next event estimation
var ranLight = _scene.SurfaceLights.GetRandom(_rng.R); //get random light
Ld = SampleLightDirectly(ranLight, brdf, intersection) * _scene.SurfaceLights.Count * ranLight.Brightness;
}
}
Color3 result;
if (_cosineDist)
{
//probability density function
var pdf = nDotR / MathHelper.Pi;
result = brdf * Ei / pdf + Ld;
}
else
{
result = MathHelper.TwoPi * brdf * Ei + Ld;
}
return(result / (1 - killChance));
}
