public void ComputeDifferentials(RayDifferential ray)
{
if (ray.hasDifferentials)
{
// Estimate screen space change in $\pt{}$ and $(u,v)$
// Compute auxiliary intersection points with plane
double d = -Geometry.Dot(nn, new Vector(p.x, p.y, p.z));
Vector rxv = new Vector(ray.rxOrigin.x, ray.rxOrigin.y, ray.rxOrigin.z);
double tx = -(Geometry.Dot(nn, rxv) + d) / Geometry.Dot(nn, ray.rxDirection);
if (Double.IsNaN(tx))
{
dudx = dvdx = 0.0d;
dudy = dvdy = 0.0d;
dpdx = dpdy = new Vector(0, 0, 0);
return;
}
Point px = ray.rxOrigin + tx * ray.rxDirection;
Vector ryv = new Vector(ray.ryOrigin.x, ray.ryOrigin.y, ray.ryOrigin.z);
double ty = -(Geometry.Dot(nn, ryv) + d) / Geometry.Dot(nn, ray.ryDirection);
if (Double.IsNaN(ty))
{
dudx = dvdx = 0.0d;
dudy = dvdy = 0.0d;
dpdx = dpdy = new Vector(0, 0, 0);
return;
}
Point py = ray.ryOrigin + ty * ray.ryDirection;
dpdx = px - p;
dpdy = py - p;
// Compute $(u,v)$ offsets at auxiliary points
// Initialize _A_, _Bx_, and _By_ matrices for offset computation
double[,] A = new double[2, 2];
double[] Bx = new double[2];
double[] By = new double[2];
int[] axes = new int[2];
if (Math.Abs(nn.x) > Math.Abs(nn.y) && Math.Abs(nn.x) > Math.Abs(nn.z))
{
axes[0] = 1; axes[1] = 2;
}
else if (Math.Abs(nn.y) > Math.Abs(nn.z))
{
axes[0] = 0; axes[1] = 2;
}
else
{
axes[0] = 0; axes[1] = 1;
}
// Initialize matrices for chosen projection plane
A[0, 0] = dpdu[axes[0]];
A[0, 1] = dpdv[axes[0]];
A[1, 0] = dpdu[axes[1]];
A[1, 1] = dpdv[axes[1]];
Bx[0] = px[axes[0]] - p[axes[0]];
Bx[1] = px[axes[1]] - p[axes[1]];
By[0] = py[axes[0]] - p[axes[0]];
By[1] = py[axes[1]] - p[axes[1]];
if (!Utility.SolveLinearSystem2x2(A, Bx, out dudx, out dvdx))
{
dudx = 0.0d; dvdx = 0.0d;
}
if (!Utility.SolveLinearSystem2x2(A, By, out dudy, out dvdy))
{
dudy = 0.0d; dvdy = 0.0d;
}
}
else
{
dudx = dvdx = 0.0d;
dudy = dvdy = 0.0d;
dpdx = dpdy = new Vector(0, 0, 0);
}
}
public BSSRDF GetBSSRDF(RayDifferential ray)
{
dg.ComputeDifferentials(ray);
BSSRDF bssrdf = primitive.GetBSSRDF(dg, ObjectToWorld);
return bssrdf;
}
