private Vector3 SampleLight(Shape Shape, Vector3 Hit, Vector3 ViewDirection, Vector3 Normal, Vector2 UV, Vector3 SampleDirection, LobeType SampledLobe, Vector3 BSDFAttenuation)
{
//If this is not diffuse or there are no lights, no direct lighting calculation needs to be done
if (SampledLobe != LobeType.DiffuseReflection || World.Lights.Count == 0)
{
return(Vector3.Zero);
}
//Pick a light
World.PickLight(out Shape Light, out double LightPickPDF);
Vector3 Emission = Light.Material.GetProperty("emission", UV).Color;
Vector3 TotalDirectLighting = Vector3.Zero;
//Sample BSDF
if (BSDFAttenuation != Vector3.Zero)
{
//Visibility check
World.Raycast(new Ray(Hit + SampleDirection * 0.001, SampleDirection), out Shape BSDFShape, out Vector3 BSDFHit, out Vector3 BSDFNormal, out Vector2 BSDFUV);
if (BSDFShape == Light)
{
//Calculate light pdf for bsdf sample
double LightPDF = Math.Pow((Hit - BSDFHit).Length(), 2) / (Vector3.Dot(BSDFNormal, Vector3.Normalize(Hit - BSDFHit)) * Light.Area());
//Calculate bsdf pdf for bsdf sample
Shape.Material.PDF(ViewDirection, Normal, UV, SampleDirection, SampledLobe, out double ScatterPDF);
//Weighted sum of the 2 sampling strategies for this sample
TotalDirectLighting += BSDFAttenuation * Emission * Util.BalanceHeuristic(ScatterPDF, LightPDF) / ScatterPDF;
}
}
//Sample light directly
Vector3 LightSample = Light.Sample() - Hit;
double Distance = LightSample.Length();
LightSample.Normalize();
//Visibility check
World.Raycast(new Ray(Hit + LightSample * 0.001, LightSample), out Shape LightShape, out Vector3 LightHit, out Vector3 LightNormal, out Vector2 LightUV);
if ((LightHit - Hit).Length() >= Distance - 0.001)
{
//Calculate light pdf for light sample,
double LightPDF = Math.Pow(Distance, 2) / (Vector3.Dot(LightNormal, -LightSample) * Light.Area());
//Calculate bsdf pdf for light sample
Shape.Material.Evaluate(ViewDirection, Normal, UV, LightSample, SampledLobe, out BSDFAttenuation);
Shape.Material.PDF(ViewDirection, Normal, UV, LightSample, SampledLobe, out double ScatterPDF);
//Weighted sum of the 2 sampling strategies for this sample
if (BSDFAttenuation != Vector3.Zero)
{
TotalDirectLighting += BSDFAttenuation * Emission * Util.BalanceHeuristic(LightPDF, ScatterPDF) / LightPDF;
}
}
return(TotalDirectLighting / LightPickPDF);
}