/* \brief Illuminates a given point in the scene.
*
* Given a point and two random samples (e.g., for position on area lights),
* this method returns direction from point to light, distance,
* pdf of having chosen this direction (e.g., 1 / area).
* Optionally also returns pdf of emitting particle in this direction,
* and cosine from lights normal (helps with PDF of hitting the light,
* but set to 1 for point lights).
*
* Returns radiance.
*/
public abstract RgbSpectrum Illuminate(
ref SceneSphere aSceneSphere,
ref Vector aReceivingPosition,
ref UV aRndTuple,
out Vector oDirectionToLight,
out float oDistance,
out float oDirectPdfW,
out float oEmissionPdfW,
out float oCosAtLight);
/* \brief Emits particle from the light.
*
* Given two sets of random numbers (e.g., position and direction on area light),
* this method generates a position and direction for light particle, along
* with the pdf.
*
* Can also supply pdf (w.r.t. area) of choosing this position when calling
* Illuminate. Also provides cosine on the light (this is 1 for point lights etc.).
*
* Returns "energy" that particle carries
*/
public abstract RgbSpectrum Emit(
ref SceneSphere aSceneSphere,
ref UV aDirRndTuple,
ref UV aPosRndTuple,
out Vector oPosition,
out Vector oDirection,
out float oEmissionPdfW,
out float oDirectPdfA,
out float oCosThetaLight);
public override RgbSpectrum Illuminate(
ref SceneSphere aSceneSphere,
ref Vector aReceivingPosition,
ref UV aRndTuple,
out Vector oDirectionToLight,
out float oDistance,
out float oDirectPdfW,
out float oEmissionPdfW,
out float oCosAtLight)
{
UV uv = new UV();
MC.UniformSampleTriangle(aRndTuple.U, aRndTuple.V, ref uv.U, ref uv.V);
Vector lightPoint = p0 + e1*uv.U + e2*uv.V;
oDirectionToLight = lightPoint - aReceivingPosition;
float distSqr = oDirectionToLight.Length;
oDistance = MathLab.Sqrt(distSqr);
oDirectionToLight = oDirectionToLight/oDistance;
var invDir = -oDirectionToLight;
var norm = mFrame.Normal();
float cosNormalDir = Vector.Dot(ref norm, ref invDir);
// too close to, or under, tangent
if (cosNormalDir < Consts.EPS_COSINE)
{
oCosAtLight = float.MinValue;
oDirectPdfW = 0f;
oEmissionPdfW = 0f;
return RgbSpectrum.ZeroSpectrum();
}
oDirectPdfW = mInvArea*distSqr/cosNormalDir;
oCosAtLight = cosNormalDir;
oEmissionPdfW = mInvArea*cosNormalDir*MathLab.INVPI;
return mIntensity;
}
/* \brief Returns radiance for ray randomly hitting the light
*
* Given ray direction and hitpoint, it returns radiance.
* Can also provide area pdf of sampling hitpoint in Illuminate,
* and of emitting particle along the ray (in opposite direction).
*/
public abstract RgbSpectrum GetRadiance(
ref SceneSphere aSceneSphere,
ref Vector aRayDirection,
ref Vector aHitPoint,
out float oDirectPdfA,
out float oEmissionPdfW);
public override RgbSpectrum GetRadiance(ref SceneSphere aSceneSphere, ref Vector aRayDirection, ref Vector aHitPoint, out float oDirectPdfA, out float oEmissionPdfW)
{
throw new NotImplementedException();
}
public override RgbSpectrum Emit(ref SceneSphere aSceneSphere, ref UV aDirRndTuple, ref UV aPosRndTuple, out Vector oPosition, out Vector oDirection, out float oEmissionPdfW, out float oDirectPdfA, out float oCosThetaLight)
{
throw new NotImplementedException();
}
public override RgbSpectrum Illuminate(ref SceneSphere aSceneSphere, ref Vector aReceivingPosition, ref UV aRndTuple, out Vector oDirectionToLight, out float oDistance, out float oDirectPdfW, out float oEmissionPdfW, out float oCosAtLight)
{
throw new NotImplementedException();
}
public override RgbSpectrum GetRadiance(
ref SceneSphere aSceneSphere,
ref Vector aRayDirection,
ref Vector aHitPoint,
out float oDirectPdfA,
out float oEmissionPdfW)
{
var n = mFrame.Normal();
var wo = -aRayDirection;
float cosOutL = Math.Max(0f, Vector.Dot(ref n, ref wo));
if (Math.Abs(cosOutL) < MathLab.Epsilon)
{
oDirectPdfA = 0f;
oEmissionPdfW = 0f;
return RgbSpectrum.ZeroSpectrum();
}
oDirectPdfA = mInvArea;
oEmissionPdfW = Utils.CosHemispherePdfW((Normal) mFrame.Normal(), -aRayDirection);
oEmissionPdfW *= mInvArea;
return mIntensity;
}
public override RgbSpectrum Emit(
ref SceneSphere aSceneSphere,
ref UV aDirRndTuple,
ref UV aPosRndTuple,
out Vector oPosition,
out Vector oDirection,
out float oEmissionPdfW,
out float oDirectPdfA,
out float oCosThetaLight)
{
UV uv = new UV();
MC.UniformSampleTriangle(aPosRndTuple.U, aPosRndTuple.V, ref uv.U, ref uv.V);
oPosition = p0 + e1*uv.U + e2*uv.V;
Vector localDirOut = Utils.SampleCosHemisphereW(aDirRndTuple, out oEmissionPdfW);
oEmissionPdfW *= mInvArea;
// cannot really not emit the particle, so just bias it to the correct angle
localDirOut.z = Math.Max(localDirOut.z, Consts.EPS_COSINE);
oDirection = mFrame.ToWorld(ref localDirOut);
oDirectPdfA = mInvArea;
oCosThetaLight = localDirOut.z;
return mIntensity*localDirOut.z;
}
