public Spectrum SpecularTransmit(
RayDifferential ray,
SurfaceInteraction isect,
Scene scene,
Sampler sampler,
int depth)
{
Vector3D wo = isect.Wo;
double pdf;
Point3D p = isect.P;
Normal3D ns = isect.ShadingN;
Bsdf bsdf = isect.Bsdf;
Spectrum f = bsdf.Sample_f(wo, out Vector3D wi, sampler.Get2D(), out pdf,
out BxdfType sampledType, BxdfType.Transmission | BxdfType.Specular);
Spectrum L = Spectrum.Create(0.0);
if (pdf > 0.0 && !f.IsBlack() && wi.AbsDot(ns) != 0.0)
{
// Compute ray differential _rd_ for specular transmission
RayDifferential rd = new RayDifferential(isect.SpawnRay(wi));
if (ray.HasDifferentials)
{
rd.HasDifferentials = true;
rd.RxOrigin = p + isect.Dpdx.ToPoint3D();
rd.RyOrigin = p + isect.Dpdy.ToPoint3D();
double eta = bsdf.Eta;
Vector3D w = -wo;
if (wo.Dot(ns) < 0.0)
{
eta = 1.0 / eta;
}
Normal3D dndx = isect.ShadingDndu * isect.Dudx +
isect.ShadingDndv * isect.Dvdx;
Normal3D dndy = isect.ShadingDndu * isect.Dudy +
isect.ShadingDndv * isect.Dvdy;
Vector3D dwodx = -ray.RxDirection - wo,
dwody = -ray.RyDirection - wo;
double dDNdx = dwodx.Dot(ns) + wo.Dot(dndx);
double dDNdy = dwody.Dot(ns) + wo.Dot(dndy);
double mu = eta * w.Dot(ns) - wi.Dot(ns);
double dmudx =
(eta - (eta * eta * w.Dot(ns)) / wi.Dot(ns)) * dDNdx;
double dmudy =
(eta - (eta * eta * w.Dot(ns)) / wi.Dot(ns)) * dDNdy;
rd.RxDirection =
wi + eta * dwodx - (mu * dndx + dmudx * ns).ToVector3D();
rd.RyDirection =
wi + eta * dwody - (mu * dndy + dmudy * ns).ToVector3D();
}
L = f * Li(rd, scene, sampler, depth + 1) * wi.AbsDot(ns) / pdf;
}
return(L);
}
/// <inheritdoc />
public override Spectrum Li(RayDifferential ray, Scene scene, Sampler sampler, int depth = 0)
{
Spectrum L = Spectrum.Create(0.0);
// Find closest ray intersection or return background radiance
if (!scene.Intersect(ray, out SurfaceInteraction isect))
{
foreach (var light in scene.Lights)
{
L += light.Le(ray);
}
return(L);
}
// Compute emitted and reflected light at ray intersection point
// Initialize common variables for Whitted integrator
Normal3D n = isect.ShadingN;
Vector3D wo = isect.Wo;
// Compute scattering functions for surface interaction
isect.ComputeScatteringFunctions(ray);
if (isect.Bsdf == null)
{
return(Li(new RayDifferential(isect.SpawnRay(ray.Direction)), scene, sampler, depth));
}
// Compute emitted light if ray hit an area light source
L += isect.Le(wo);
// Add contribution of each light source
foreach (var light in scene.Lights)
{
Spectrum Li =
light.Sample_Li(isect, sampler.Get2D(), out Vector3D wi, out double pdf, out VisibilityTester visibility);
if (Li.IsBlack() || pdf == 0.0)
{
continue;
}
Spectrum f = isect.Bsdf.f(wo, wi);
if (!f.IsBlack() && visibility.Unoccluded(scene))
{
L += f * Li * wi.AbsDot(n) / pdf;
}
}
if (depth + 1 < _maxDepth)
{
// Trace rays for specular reflection and refraction
L += SpecularReflect(ray, isect, scene, sampler, depth);
L += SpecularTransmit(ray, isect, scene, sampler, depth);
}
return(L);
}
public Spectrum SpecularReflect(
RayDifferential ray,
SurfaceInteraction isect,
Scene scene,
Sampler sampler,
int depth)
{
// Compute specular reflection direction _wi_ and BSDF value
Vector3D wo = isect.Wo;
BxdfType type = BxdfType.Reflection | BxdfType.Specular;
Spectrum f = isect.Bsdf.Sample_f(wo, out Vector3D wi, sampler.Get2D(), out double pdf, out BxdfType sampledType, type);
// Return contribution of specular reflection
Normal3D ns = isect.ShadingN;
if (pdf > 0.0 && !f.IsBlack() && wi.AbsDot(ns) != 0.0)
{
// Compute ray differential _rd_ for specular reflection
RayDifferential rd = new RayDifferential(isect.SpawnRay(wi));
if (ray.HasDifferentials)
{
rd.HasDifferentials = true;
rd.RxOrigin = isect.P + isect.Dpdx.ToPoint3D();
rd.RyOrigin = isect.P + isect.Dpdy.ToPoint3D();
// Compute differential reflected directions
Normal3D dndx = isect.ShadingDndu * isect.Dudx +
isect.ShadingDndv * isect.Dvdx;
Normal3D dndy = isect.ShadingDndu * isect.Dudy +
isect.ShadingDndv * isect.Dvdy;
Vector3D dwodx = -ray.RxDirection - wo,
dwody = -ray.RyDirection - wo;
double dDNdx = dwodx.Dot(ns) + wo.Dot(dndx);
double dDNdy = dwody.Dot(ns) + wo.Dot(dndy);
rd.RxDirection =
wi - dwodx + 2.0 * (wo.Dot(ns) * dndx + dDNdx * ns).ToVector3D();
rd.RyDirection =
wi - dwody + 2.0 * (wo.Dot(ns) * dndy + dDNdy * ns).ToVector3D();
}
return(f * Li(rd, scene, sampler, depth + 1) * wi.AbsDot(ns) /
pdf);
}
else
{
return(Spectrum.Create(0.0));
}
}
/// <inheritdoc />
public override Spectrum We(Ray ray, out Point2D pRaster2)
{
// Interpolate camera matrix and check if $\w{}$ is forward-facing
CameraToWorld.Interpolate(ray.Time, out Transform c2w);
double cosTheta = ray.Direction.Dot(c2w.ExecuteTransform(new Vector3D(0.0, 0.0, 1.0)));
if (cosTheta <= 0.0)
{
pRaster2 = null;
return(Spectrum.Create(0.0));
}
// Map ray $(\p{}, \w{})$ onto the raster grid
Point3D pFocus = ray.AtPoint((LensRadius > 0.0 ? FocalDistance : 1.0) / cosTheta);
Point3D pRaster = RasterToCamera.ExecuteTransform(c2w.Inverse().ExecuteTransform(pFocus));
//Point3D pRaster = Inverse(RasterToCamera)(Inverse(c2w.Inverse)(pFocus));
// Return raster position if requested
pRaster2 = new Point2D(pRaster.X, pRaster.Y);
// Return zero importance for out of bounds points
Bounds2I sampleBounds = Film.GetSampleBounds();
if (pRaster.X < sampleBounds.MinPoint.X || pRaster.Z >= sampleBounds.MaxPoint.X ||
pRaster.Y < sampleBounds.MinPoint.Y || pRaster.Y >= sampleBounds.MaxPoint.Y)
{
return(Spectrum.Create(0.0));
}
// Compute lens area of perspective camera
double lensArea = LensRadius != 0.0 ? (Math.PI * LensRadius * LensRadius) : 1.0;
// Return importance for point on image plane
double cos2Theta = cosTheta * cosTheta;
return(Spectrum.Create(1.0 / (_a * lensArea * cos2Theta * cos2Theta)));
}
