(L) [2012/07/13] [ost
by sajis997] [Spherical Light Sampling for direct lighting only] Wayback!Hi
I am not sure if you i get your questions . Which rays distance to attenuate ?
I am elaborating the algorithm that i am doing to implement the direct illumination and the questions you asked will hopefully be answered through the discussion.
Code: [LINK # Select all]Color PathTracer::computeDirectIllumination(const Intersection &intersection)
{
//declare the color to store the radiance
//from the direct illumination
Color outputColor;
//pointer to the area light
AreaLight *areaLight;
Color incomingRadiance,BRDF;
Vector3D lightVec;
Vector3D lightNormal;
float incidentAngle;
Intersection shadowIntersection;
Ray shadowRay;
bool shadowHit = false;
//get the number of area lights in the scene
unsigned int numberOfLights = mScene->getNumberOfAreaLights();
unsigned int samples = getNumberOfSamples();
for(unsigned int shadowRays = 0; shadowRays < samples ; shadowRays++)
{
for(unsigned int i = 0; i < numberOfLights;++i)
{
//get the area light - i in the scene
areaLight = mScene->getAreaLight(i);
//get the shadow ray for the area light
//we get a new shadow ray for each sample over the light source
shadowRay = intersection.getShadowRay(areaLight);
//check if the shadow ray intersect the scene
//we also store the shadow hit information to check the lights material
shadowHit = mScene->intersect(shadowRay,shadowIntersection);
//we calculate the outgoing radiance under two options
//if the shadow ray do not hit any intersectables between the inersection point in the scene and light sample point
//OR if the shadow ray hit a intersectable that happen to be the light source
if(!shadowHit || (shadowHit && shadowIntersection.mMaterial->emissive()))
{
//calculate the light vector - the irradiance - wio
//getWorldPosition() gets the sample point within the sphere
lightVec = areaLight->getWorldPosition() - intersection.mPosition;
lightVec.normalize();
//the light normal is already calculated while calculating the light's
//world position in the previous step
lightNormal = areaLight->getSampleNormal();
//get the dot product between the negated light normal and light vector
float ndotd = std::max(-lightNormal.dot(lightVec),0.0f);
//the emissive radiance from the light source
//which does not depend over ray's incident direction
//it is the emissive color * scaling factor
incomingRadiance = areaLight->getRadiance();
//length squared between the light sample point and intersection point
float d2 = lightVec.length2();
incidentAngle = std::max(lightVec.dot(intersection.mNormal),0.0f);
//get the BRDF
BRDF = intersection.mMaterial->evalBRDF(intersection,lightVec);
//accumulate the color for all the lights
outputColor += (BRDF * incomingRadiance * incidentAngle * ndotd)/(areaLight->getPDF() * d2);
}
}
outputColor /= samples;
}
return outputColor;
}
I think i am calculating the light vector and attentuating its contribution by 1/d2.
I am also calculating the hit angle and how to attentuate the hit angle ?
If you need any more explanation please do mention .
Regards
Sajjad
(L) [2012/07/20] [ost
by sajis997] [Spherical Light Sampling for direct lighting only] Wayback!Thanks for the hints.
I think i have reached a bit closer to the solution . But i am still having some arti-facts over the luminaire and some of the areas around it.
Please check it here:
[LINK http://www.student.itn.liu.se/~sajis997/cornellscenearea4.png]
Any idea what might have caused it? I am following the Peter Shirley's book "realistic ray tracing" and some of the concepts described over there about sampling the spherical luminarie is not clear to me and this is why i think i am doing something wrong. I believe that some one in the forum have already had gone through the book .
Lets go to Chapter 13 : Explicit Direct Lighting. And then to 13.2 - Sampling a spherical luminaire
At the end of the first paragraph it is written - "We now use a coordinate system defined with x at the origin, and a right-handed orthonormal basis with"
What does it mean by x at the origin ? To me x is the first intersection point where we are calculating the radiance value , right ?
In my case i am defining the sphere center at (0,0,0) and then transforming the origin by world transformation to the scene and then calculating the w as mentioned in the book, v = w X n and u = v X w.
This is how i am defining the orthonormal basis
I shall looking forward to more suggestion over this issue.
Regards
Sajjad