public IntersectionPoint GetIntersectionPoint(Ray ray)
{
float currentMinDistance = float.MaxValue;
IntersectionPoint resultPoint = null;
foreach (var triangle in this.triangles)
{
var point = triangle.Intersect(ray);
if (point != null && point.DistanceToRayOrigin < currentMinDistance)
{
resultPoint = point;
currentMinDistance = point.DistanceToRayOrigin;
}
}
return(resultPoint);
}
private Vector GetContributionFromLightSourceSampling(IntersectionPoint point, Random rand, Vector pathWeight)
{
//Sample Point on LightSource
var lightPoint = data.LightSource.SampleRandomPointOnLightSource(rand);
Vector directionToLight = (lightPoint.Position - point.Position).Normalize();
//Shadow-Ray-Test: Test is the Point on Lightsource visible from 'point'?
var lightVisiblePoint = this.intersectionFinder.GetIntersectionPoint(new Ray(point.Position, directionToLight));
float DistanceForPoint2PointVisibleCheck = 0.0001f; //Magic Number
bool isVisible = lightVisiblePoint != null && (lightVisiblePoint.Position - lightPoint.Position).Length() < DistanceForPoint2PointVisibleCheck;
if (isVisible == false)
{
return(new Vector(0, 0, 0)); //No contribution, if 'point' is located in shadow
}
//Pathcontribution from Lightsource-Sampling
float cosAtPoint = Math.Max(0, Vector.Dot(point.Normal, directionToLight));
float cosAtLight = Math.Max(0, Vector.Dot(lightPoint.Normal, -directionToLight));
float geometryFactor = cosAtPoint * cosAtLight / (lightPoint.Position - point.Position).SqrLength();
float pdfAFromLightSourceSampling = data.LightSource.PdfA; //This is the PdfA for sampling the lightPoint on the Position lightPoint.Position
Vector contributionFromLightSampling = Vector.Mult(pathWeight, DiffuseBrdf.Evaluate(point)) * geometryFactor * data.LightSource.EmissionPerArea / pdfAFromLightSourceSampling;
//Get PdfA from Brdf-Sampling.
float pdfW = DiffuseBrdf.PdfW(point.Normal, directionToLight);
float continuationPdf = Math.Min(1, point.Color.Max());
//This is the PdfA, to hit the LightSource with Brdf-Sampling and hit the Lightsource on the Position lightPoint.Position
//The Factor "cosAtLight / (lightPoint.Position - point.Position).SqrLength()" is the pdfW to PdfA-Conversionfactor.
//This means, you project to Solid Angle Measure from the Brdf to the surface area measure on the Point on the Light
float pdfAFromBrdfSampling = pdfW * continuationPdf * cosAtLight / (lightPoint.Position - point.Position).SqrLength();
//Heare we have used LightSource-Sampling for the Creation of the Point on the LightSource. So we use pdfAFromLightSourceSampling in the numerator
float misFactor = pdfAFromLightSourceSampling / (pdfAFromLightSourceSampling + pdfAFromBrdfSampling);
contributionFromLightSampling *= misFactor;
return(contributionFromLightSampling);
}
private ConnectionData TryToConnectPointWithCamera(IntersectionPoint point, Vector pathWeight, int lightPathsPerIteration)
{
Vector2D pixelPosition = GetPixelPositionForScenePoint(point.Position);
if (pixelPosition != null)
{
//GeometryTerm
Vector cameraToLightPointDirection = (point.Position - data.Camera.Position).Normalize();
float cosAtCamera = Vector.Dot(cameraToLightPointDirection, data.Camera.Forward);
float cosAtPoint = Vector.Dot(-cameraToLightPointDirection, point.Normal);
float geomertryFaktor = (cosAtCamera * cosAtPoint) / (point.Position - data.Camera.Position).SqrLength();
//Brdf (Inputdirection is Direction from preceeding point to 'point' and Outgoingdirection is direction from 'point' to Camera-Point
//In this case its a Diffuse Brdf and no Input- or Outputdirection is needed
Vector brdf = DiffuseBrdf.Evaluate(point);
//If you use Pathtracing and don't divide the Pathweight with the PdfW from the Camera, then you implicite multiply the Pathweight with (1 / CameraPdfW)
//To get with Lightracing the same Results as with Pathtracing, you have to multipli the PathWeight with the cameraPdfW, which is also called PixelFilter
float cameraPdfW = data.Camera.PdfWForPrimaryRayDirectionSampling(cameraToLightPointDirection); //cameraPdfW == PixelFilter
Vector pathContribution = Vector.Mult(pathWeight, brdf) * geomertryFaktor / lightPathsPerIteration * cameraPdfW;
int x = (int)pixelPosition.X;
int y = (int)pixelPosition.Y;
if (x >= 0 && x < width && y >= 0 && y < height)
{
return(new ConnectionData()
{
PixelX = x,
PixelY = y,
PathContribution = pathContribution,
});
}
}
return(null);
}
private Vector EstimateColorWithPathtracingWithNextEventEstimation(int x, int y, Random rand)
{
//This is the sum from all Pathcontributions from all Pathlenghts up to maxPathLength
//This means Contribution(C L) + Contribution(C D L) + Contribution(C D D L) + Contribution(C D D D L) + Contribution(C D D D D L)
//For Each Pathlength-Step, the Contribution from Brdf-Sampling and Lightsource-Sampling is added but only one from this two Sampling-Methods
//will create a Contribution != 0. If you hit the Lightsource, then you only get the BrdfSampling-Contribution. The LightSource-Sampling-Contribution
//will be zero because if your running point is on the light and the light don't reflect any light, then you don't can create any more Lightpoints
//If you are on a Point in the Scene (Not Lightsoure) then only the Contribution from Lightsource-Sampling can be greater zero. The Brdf-Sampling
//Contribution (Pathtracing) will be zero.
Vector contributionSum = new Vector(0, 0, 0);
Ray primaryRay = data.Camera.GetPrimaryRay(x, y);
float cosAtCamera = Vector.Dot(primaryRay.Direction, this.data.Camera.Forward);
Vector pathWeight = new Vector(1, 1, 1) * cosAtCamera;
Ray ray = primaryRay;
float pdfW = data.Camera.PdfWForPrimaryRayDirectionSampling(ray.Direction); //This will store the PdfW and Contination Pdf, which was used for Brdf-Sampling
int maxPathLength = 5;
for (int i = 0; i < maxPathLength; i++)
{
IntersectionPoint point = this.intersectionFinder.GetIntersectionPoint(ray);
if (point == null)
{
break; //Ray leave the scene
}
//Try to add Contribution from Brdf-Sampling (This Brdf-Sampling is also called Pathtracing because you do this for every Pathpoint)
if (point.IsLocatedOnLightSource && Vector.Dot(point.Normal, -ray.Direction) > 0)
{
//This is the PdfA on the LightPoint, if you would use LightSource-Sampling, to reach from lastPoint(ray.Origin) to current point 'point'
float pdfAFromLightSourceSampling = data.LightSource.PdfA;
//This is the PdfA on the LightPoint, which you get from BrdfSampling to reach rom lastPoint(ray.Origin) to current point 'point'
float pdfAFromBrdfSampling = pdfW * Vector.Dot(point.Normal, -ray.Direction) / (ray.Origin - point.Position).SqrLength();
//We have used Brdf-Sampling. So the pdfAFromBrdfSampling is in the numerator
float misFactor = pdfAFromBrdfSampling / (pdfAFromLightSourceSampling + pdfAFromBrdfSampling);
Vector contributionFromBrdfSampling = Vector.Mult(pathWeight, point.Emission) * misFactor;
contributionSum += contributionFromBrdfSampling;
break; //The light don't reflect any light. So stop here with Pathtracing
}
//Try to add Contribution from Lightsource-Sampling (This is the Next Event Estimation-Sampling)
contributionSum += GetContributionFromLightSourceSampling(point, rand, pathWeight);
//Stop with Russia Rollete
float continuationPdf = Math.Min(1, point.Color.Max());
if (rand.NextDouble() >= continuationPdf)
{
break; // Absorbation
}
//Sample Direction and try to hit to lightSource
Vector direction = DiffuseBrdf.SampleDirection(point.Normal, rand);
pdfW = DiffuseBrdf.PdfW(point.Normal, direction) * continuationPdf;
float cosAtPoint = Math.Max(0, Vector.Dot(point.Normal, direction));
pathWeight = Vector.Mult(pathWeight, DiffuseBrdf.Evaluate(point)) * cosAtPoint / pdfW; //New Pathweight after Brdf-Sampling
ray = new Ray(point.Position, direction);
}
return(contributionSum);
}
public static Vector Evaluate(IntersectionPoint point)
{
return(point.Color / (float)Math.PI);
}
public List <Photon> SearchPhotons(IntersectionPoint searchPoint, float searchRadius)
{
float rSqr = searchRadius * searchRadius;
return(this.kdTree.FixedRadiusSearch(searchPoint.Position, searchRadius).Cast <Photon>().Where(x => Vector.Dot(x.Normal, searchPoint.Normal) > 0).ToList());
}
