public Color3 Dielectric(Intersection intersection)
{
var n1 = intersection.Ray.Medium.RefractiveIndex;
var n2 = intersection.Material.RefractiveIndex;
float n = n1 / n2;
var ray = intersection.Ray;
var normal = intersection.SurfaceNormal;
float cost = Vector3.Dot(normal, -ray.Direction);
float k = 1 - n * n * (1 - cost * cost);
if (k < 0)
{
//internal reflection
return(Specular(intersection));
}
var T = n * ray.Direction + normal * (n * cost - (float)Math.Sqrt(k));
var refracted = Ray.CreateFromIntersection(intersection, T, float.MaxValue, true);
float R0 = (n1 - n2) / (n1 + n2);
R0 *= R0;
var a = 1 - cost;
float Fr = R0 + (1 - R0) * a * a * a * a * a;
float Ft = 1 - Fr;
var transparency = new Vector3(1);
if (intersection.InsidePrimitive)
{
var absorbance = intersection.Ray.Medium.Color * intersection.Ray.Medium.Absorbance * -intersection.Distance;
transparency = new Vector3(
(float)Math.Exp(-absorbance.R),
(float)Math.Exp(-absorbance.G),
(float)Math.Exp(-absorbance.B));
}
//go inside
if (_rng.RandomFloat() < Ft)
{
return(transparency * _scene.Sample(refracted, _rng, false));
}
//reflect outside
return(transparency * Specular(intersection));
}
private Color3 SampleLightDirectly(ISurfaceLight light, Color3 brdf, Intersection intersection)
{
var rPoint = light.GetRandomPoint(_rng, intersection); //get random point on light
var l = rPoint.Location - intersection.Location; //vector to light
var dist = l.LengthFast;
l.Normalize();
var lightRay = Ray.CreateFromIntersection(intersection, l, dist); //ray to light
var nlightDotL = Vector3.Dot(rPoint.Normal, -l); //light normal dot light
var nDotL = Vector3.Dot(intersection.SurfaceNormal, l); //normal dot light
if (nDotL > 0 && nlightDotL > 0 && !IntersectionHelper.DoesIntersect(lightRay, _scene.Objects, light))
{
var solidAngle = (nlightDotL * light.Area) / (dist * dist); //light area on hemisphere
return(light.Color * solidAngle * brdf * nDotL);
}
return(Color4.Black);
}
public Color3 DirectIllumination(Intersection intersection)
{
var totalIntensity = 0.0f;
foreach (var light in _scene.PointLights)
{
var lightVector = light.Position - intersection.Location;
var invLightDistance2 = 1 / lightVector.LengthSquared;
var shadowRay = Ray.CreateFromIntersection(intersection, lightVector, lightVector.LengthFast);
if (IntersectionHelper.DoesIntersect(shadowRay, _scene.Objects) && !(intersection.IntersectsWith is DebugSphere)) //todo debug
{
continue;
}
var intensity = Vector3.Dot(intersection.SurfaceNormal, shadowRay.Direction);
totalIntensity += Math.Max(intensity, 0) * invLightDistance2 * light.Intensity;
}
return(totalIntensity * intersection.Material.CalculateColor(intersection.Location));
}
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));
}
