public Spectrum f(Vector3 <float> woWorld, Vector3 <float> wiWorld, BxDF.BxDFType type = BxDF.BxDFType.All)
{
// Transform the incident and outgoing directions to local BSDF space
var wo = WorldToLocal(woWorld);
var wi = WorldToLocal(wiWorld);
var f = Spectrum.Zero;
// Evaluate each BxDF
var reflect = Vector3 <float> .Dot(wiWorld, ng) * Vector3 <float> .Dot(woWorld, ng) > 0;
foreach (var bxdf in bxdfs)
{
// Two possibilities:
// - wo and wi lie in the same hemisphere: only evaluate reflection
// - wo and wi lie in different hemispheres: only evaluate transmission
if (bxdf.Matches(type) && (
reflect && (bxdf.Type & BxDF.BxDFType.Reflection) > 0 ||
!reflect && (bxdf.Type & BxDF.BxDFType.Transmission) > 0))
{
f += bxdf.f(wo, wi);
}
}
return(f);
}
/// <summary>
/// Choose an incoming direction on the view from a BxDF matching a type
/// and returns its contribution
/// </summary>
/// <param name="leaving">the vector leaving the surface</param>
/// <param name="incoming">the vector arriving at the surface, the function will set it</param>
/// <param name="type">the type of scattering</param>
/// <returns></returns>
public SampledSpectrum Sample(Vector3 leaving, ref Vector3 incoming, BxDF.BxDFType type)
{
/* we randomly choose a BxDF that matches the type */
var matchingBxDFs = _bxdfs.Where(f => type.HasFlag(f.Type)).ToList(); // the list of bxdf matching the type
if (matchingBxDFs.Count == 0)
{
return(SampledSpectrum.Black());
}
// random selection over matching bxdfs
var bxdf =
matchingBxDFs.ElementAt(Math.Min((int)(StaticRandom.NextFloat() * matchingBxDFs.Count), matchingBxDFs.Count - 1));
var leavingLocal = WorldToLocal(ref leaving);
Vector3 incomingLocal;
// we sample the chosen bxdf
var spectrum = bxdf.Sample(leavingLocal, out incomingLocal);
// we transform the incoming ray returned by the sampling to world space
incoming = LocalToWorld(ref incomingLocal);
// is the reflection is not specular, we add contribution from other bxdfs of the same type
if (!bxdf.Type.HasFlag(BxDF.BxDFType.Reflection))
{
spectrum = _bxdfs.Where(b => type.HasFlag(b.Type))
.Aggregate(spectrum, (current, b) => current + b.F(incomingLocal, leavingLocal));
}
return(spectrum);
}
public SampledSpectrum F(Vector3 incoming, Vector3 leaving, BxDF.BxDFType type)
{
var s = SampledSpectrum.Black();
var incomingLocal = WorldToLocal(ref incoming);
var leavingLocal = WorldToLocal(ref leaving);
return(_bxdfs.Where(bxdf => type.HasFlag(bxdf.Type))
.Aggregate(s, (current, bxdf) => current + bxdf.F(incomingLocal, leavingLocal)));
}
public Spectrum Sample_f(Vector3 <float> woWorld, out Vector3 <float> wiWorld, Point2 <float> u, out float pdf, BxDF.BxDFType type, out BxDF.BxDFType sampledType)
{
// Check that there are matching BxDFs
var matchingBxdfs = bxdfs.Count(b => b.Matches(type));
if (matchingBxdfs == 0)
{
pdf = 0;
sampledType = 0;
wiWorld = Vector3 <float> .Zero;
return(Spectrum.Zero);
}
// Randomly pick a matching BxDF with the first dimension of the sample
var n = (int)Math.Min(Math.Floor(u.X * matchingBxdfs), matchingBxdfs - 1);
var pickedBxdf = bxdfs.Where(b => b.Matches(type)).Skip(n).First();
sampledType = pickedBxdf.Type;
// Remap the sample to [0,1]
u.X = u.X * matchingBxdfs - n;
// Sample an incoming direction from the BxDF
var wo = WorldToLocal(woWorld);
var f = pickedBxdf.Sample_f(wo, out Vector3 <float> wi, u, out pdf, out sampledType);
wiWorld = LocalToWorld(wi);
if (pdf == 0)
{
return(Spectrum.Zero);
}
// Compute overall PDF with matching BxDFs
if ((pickedBxdf.Type & BxDFType.Specular) == 0 && matchingBxdfs > 1)
{
foreach (var b in bxdfs.Where(b => b != pickedBxdf && b.Matches(type)))
{
pdf += b.Pdf(wo, wi);
}
}
if (matchingBxdfs > 1)
{
pdf /= matchingBxdfs;
}
// Compute the BDSF value for the sampled incoming direction
if ((pickedBxdf.Type & BxDFType.Specular) == 0 && matchingBxdfs > 1)
{
var reflect = Vector3 <float> .Dot(wiWorld, ng) * Vector3 <float> .Dot(woWorld, ng) > 0;
foreach (var bxdf in bxdfs)
{
if (bxdf.Matches(type) && (
reflect && (bxdf.Type & BxDFType.Reflection) > 0 ||
!reflect && (bxdf.Type & BxDFType.Transmission) > 0))
{
f += bxdf.f(wo, wi);
}
}
}
return(f);
}
public BxDF FirstMatch(BxDF.BxDFType type = BxDF.BxDFType.All)
{
return(bxdfs.FirstOrDefault(b => b.Matches(type)));
}
public int NumComponents(BxDF.BxDFType type = BxDF.BxDFType.All)
{
return(bxdfs.Count(b => b.Matches(type)));
}