public RayIntersection EvalIntersection(RayDifferential ray, ref RayHit rh, RayIntersection isect)
{
var ii = isect ?? (isect = new RayIntersection());
var currentTriangleIndex = (int) rh.Index;
var obj = GetObjectByTriangleIndex(currentTriangleIndex);
ii.Hitpoint = ray.Point(rh.Distance);
ii.BaryCentricPoint = new UV(rh.U, rh.V);
obj.Entity.InterpolateTriangleNormal(currentTriangleIndex, rh.U, rh.V, ref ii.ShadingNormal);
obj.Entity.InterpolateTriUV(currentTriangleIndex, rh.U, rh.V, out ii.TextureCoords);
ii.GeoNormal = scene.sceneData.Triangles[currentTriangleIndex].ComputeNormal(scene.sceneData.GeoData.Vertices);
ii.ComputeDifferential(ray);
return ii;
}
public void ComputeDifferential(RayDifferential ray)
{
if (ray.hasDifferentials)
{
// Estimate screen space change in $\pt{}$ and $(u,v)$
// Compute auxiliary intersection points with plane
var p = new Normal(Hitpoint.x, Hitpoint.y, Hitpoint.z);
float d = -Normal.Dot(ref GeoNormal, ref p);
var rxv = new Vector(ray.rxOrigin.x, ray.rxOrigin.y, ray.rxOrigin.z);
float tx = -(Vector.Dot(ref GeoNormal, ref rxv) + d) / Vector.Dot(ref GeoNormal, ref ray.rxDirection);
if (float.IsNaN(tx))
{
dudx = dvdx = 0f;
dudy = dvdy = 0f;
dpdx = dpdy = new Vector(0f);
return;
}
Point px = ray.rxOrigin + tx * ray.rxDirection;
Vector ryv = new Vector(ref ray.ryOrigin);
float ty = -(Vector.Dot(ref GeoNormal, ref ryv) + d) / Vector.Dot(ref GeoNormal, ref ray.ryDirection);
if (float.IsNaN(ty))
{
dudx = dvdx = 0f;
dudy = dvdy = 0f;
dpdx = dpdy = new Vector(0f);
return;
}
Point py = ray.ryOrigin + ty * ray.ryDirection;
dpdx = px - Hitpoint;
dpdy = py - Hitpoint;
// Compute $(u,v)$ offsets at auxiliary points
// Initialize _A_, _Bx_, and _By_ matrices for offset computation
float[][] A = new float[2][];
float[] Bx = new float[2];
float[] By = new float[2];
int[] axes = new int[2];
if (Math.Abs(GeoNormal.x) > Math.Abs(GeoNormal.y) && Math.Abs(GeoNormal.x) > Math.Abs(GeoNormal.z))
{
axes[0] = 1; axes[1] = 2;
}
else if (Math.Abs(GeoNormal.y) > Math.Abs(GeoNormal.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 (!MathLab.SolveLinearSystem2X2(A, Bx, out dudx, out dvdx))
{
dudx = 0f; dvdx = 0f;
}
if (!MathLab.SolveLinearSystem2X2(A, By, out dudy, out dvdy))
{
dudy = 0f; dvdy = 0f;
}
}
else
{
dudx = dvdx = 0f;
dudy = dvdy = 0f;
dpdx = dpdy = new Vector(0f);
}
}
