/// <summary>
/// Generates a ray from a position in the image into the scene
/// </summary>
/// <param name="filmPos">
/// Position on the film plane: integer pixel coordinates and fractional position within
/// </param>
/// <param name="rng">
/// Random number generator used to sample additional decisions (lens position for depth of field)
/// </param>
/// <returns>The sampled camera ray and related information like PDF and contribution</returns>
public override CameraRaySample GenerateRay(Vector2 filmPos, RNG rng)
{
Debug.Assert(Width != 0 && Height != 0);
// Transform the direction from film to world space.
// The view space is vertically flipped compared to the film.
var view = new Vector3(2 * filmPos.X / Width - 1, 1 - 2 * filmPos.Y / Height, 0);
var localDir = Vector3.Transform(view, viewToCamera);
var dirHomo = Vector4.Transform(new Vector4(localDir, 0), cameraToWorld);
var dir = new Vector3(dirHomo.X, dirHomo.Y, dirHomo.Z);
// Compute the camera position
var pos = Vector3.Transform(new Vector3(0, 0, 0), cameraToWorld);
var ray = new Ray {
Direction = Vector3.Normalize(dir), MinDistance = 0, Origin = pos
};
// Sample depth of field
float pdfLens = 1;
if (lensRadius > 0)
{
var lensSample = rng.NextFloat2D();
var lensPos = lensRadius * SampleWarp.ToConcentricDisc(lensSample);
// Intersect ray with focal plane
var focalPoint = ray.ComputePoint(focalDistance / ray.Direction.Z);
// Update the ray
ray.Origin = new Vector3(lensPos, 0);
ray.Direction = Vector3.Normalize(focalPoint - ray.Origin);
pdfLens = 1 / (MathF.PI * lensRadius * lensRadius);
}
return(new CameraRaySample {
Ray = ray,
Weight = RgbColor.White,
Point = new SurfacePoint {
Position = Position, Normal = Direction
},
PdfRay = SolidAngleToPixelJacobian(pos + dir) * pdfLens,
PdfConnect = pdfLens
});
}
