// Preprocess
void InstantRadiosity::PreProcess()
{
m_pVirtualLightSources = new list<VirtualLightSource>[m_nLightPathSet];
for( int k = 0 ; k < m_nLightPathSet ; ++k )
{
for( int i = 0 ; i < m_nLightPaths ; ++i )
{
// pick a light first
float light_pick_pdf;
const Light* light = scene.SampleLight( sort_canonical() , &light_pick_pdf );
// sample a ray from the light source
float light_emission_pdf = 0.0f;
float light_pdfa = 0.0f;
Ray ray;
float cosAtLight = 1.0f;
Spectrum le = light->sample_l( LightSample(true) , ray , &light_emission_pdf , &light_pdfa , &cosAtLight );
Spectrum throughput = le * cosAtLight / ( light_pick_pdf * light_emission_pdf );
int current_depth = 0;
Intersection intersect;
while( true )
{
if (false == scene.GetIntersect(ray, &intersect))
break;
VirtualLightSource ls;
ls.power = throughput;
ls.intersect = intersect;
ls.wi = -ray.m_Dir;
ls.depth = ++current_depth;
m_pVirtualLightSources[k].push_back( ls );
float bsdf_pdf;
Vector wo;
Bsdf* bsdf = intersect.primitive->GetMaterial()->GetBsdf(&intersect);
Spectrum bsdf_value = bsdf->sample_f(ls.wi, wo, BsdfSample(true), &bsdf_pdf, BXDF_ALL);
if( bsdf_pdf == 0.0f )
break;
// apply russian roulette
float continueProperbility = min( 1.0f , throughput.GetIntensity() );
if( sort_canonical() > continueProperbility )
break;
throughput /= continueProperbility;
// update throughput
throughput *= bsdf_value * ( AbsDot(wo, intersect.normal) / bsdf_pdf );
// update next ray
ray = Ray(intersect.intersect, wo, 0, 0.001f);
}
}
}
}
// return the radiance of a specific direction
// note : there are one factor makes the method biased.
// there is a limitation on the number of vertexes in the path
Spectrum PathTracing::Li( const Ray& ray , const PixelSample& ps ) const
{
Spectrum L = 0.0f;
Spectrum throughput = 1.0f;
int bounces = 0;
Ray r = ray;
while(true)
{
Intersection inter;
// get the intersection between the ray and the scene
// if it's a light , accumulate the radiance and break
if( false == scene.GetIntersect( r , &inter ) )
{
if( bounces == 0 )
return scene.Le( r );
break;
}
if( bounces == 0 ) L+=inter.Le(-r.m_Dir);
// make sure there is intersected primitive
Sort_Assert( inter.primitive != 0 );
// evaluate the light
Bsdf* bsdf = inter.primitive->GetMaterial()->GetBsdf(&inter);
float light_pdf = 0.0f;
LightSample light_sample = (bounces==0)?ps.light_sample[0]:LightSample(true);
BsdfSample bsdf_sample = (bounces==0)?ps.bsdf_sample[0]:BsdfSample(true);
const Light* light = scene.SampleLight( light_sample.t , &light_pdf );
if( light_pdf > 0.0f )
L += throughput * EvaluateDirect( r , scene , light , inter , light_sample ,
bsdf_sample , BXDF_TYPE(BXDF_ALL) ) / light_pdf;
// sample the next direction using bsdf
float path_pdf;
Vector wi;
BXDF_TYPE bxdf_type;
Spectrum f;
BsdfSample _bsdf_sample = (bounces==0)?ps.bsdf_sample[1]:BsdfSample(true);
f = bsdf->sample_f( -r.m_Dir , wi , _bsdf_sample , &path_pdf , BXDF_ALL , &bxdf_type );
if( f.IsBlack() || path_pdf == 0.0f )
break;
// update path weight
throughput *= f * AbsDot( wi , inter.normal ) / path_pdf;
if( throughput.GetIntensity() == 0.0f )
break;
if( bounces > 4 )
{
float continueProperbility = min( 0.5f , throughput.GetIntensity() );
if( sort_canonical() > continueProperbility )
break;
throughput /= continueProperbility;
}
r.m_Ori = inter.intersect;
r.m_Dir = wi;
r.m_fMin = 0.001f;
++bounces;
// note : the following code makes the method biased
// 'path_per_pixel' could be set very large to reduce the side-effect.
if( bounces >= max_recursive_depth )
break;
}
return L;
}
