public override (Ray, RgbColor, float) SampleRay(Vector2 primaryPos, Vector2 primaryDir)
{
// Sample a direction from the scene to the background
var dirSample = SampleDirection(primaryDir);
// Sample a point on the unit disc
var unitDiscPoint = SampleWarp.ToConcentricDisc(primaryPos);
// And transform it to the scene spanning disc orthogonal to the selected direction
Vector3 tangent, binormal;
ShadingSpace.ComputeBasisVectors(dirSample.Direction, out tangent, out binormal);
var pos = SceneCenter + SceneRadius * (dirSample.Direction // offset outside of the scene
+ tangent * unitDiscPoint.X // remap unit disc x coordinate
+ binormal * unitDiscPoint.Y); // remap unit disc y coordinate
// Compute the pdf: uniform sampling of a disc with radius "SceneRadius"
float discJacobian = SampleWarp.ToConcentricDiscJacobian();
float posPdf = discJacobian / (SceneRadius * SceneRadius);
// Compute the final result
var ray = new Ray {
Origin = pos, Direction = -dirSample.Direction, MinDistance = 0
};
var weight = dirSample.Weight / posPdf;
var pdf = posPdf * dirSample.Pdf;
return(ray, weight, pdf);
}
public override float RayPdf(Vector3 point, Vector3 direction)
{
float dirPdf = DirectionPdf(-direction);
float discJacobian = SampleWarp.ToConcentricDiscJacobian();
float posPdf = discJacobian / (SceneRadius * SceneRadius);
return(posPdf * dirPdf);
}
