// 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;
}
// private method of li
Spectrum InstantRadiosity::_li( const Ray& r , bool ignoreLe , float* first_intersect_dist ) const
{
// return if it is larger than the maximum depth
if( r.m_Depth > max_recursive_depth )
return 0.0f;
// get intersection from camera ray
Intersection ip;
if( false == scene.GetIntersect( r , &ip ) )
return ignoreLe?0.0f:scene.Le( r );
// eavluate light path less than two vertices
Spectrum radiance = ignoreLe?0.0f:ip.Le( -r.m_Dir );
unsigned light_num = scene.LightNum();
for( unsigned i = 0 ; i < light_num ; ++i )
{
const Light* light = scene.GetLight(i);
radiance += EvaluateDirect( r , scene , light , ip , LightSample(true) , BsdfSample(true) , BXDF_TYPE( BXDF_ALL ) );
}
if( first_intersect_dist )
*first_intersect_dist = ip.t;
// pick a virtual light source randomly
const unsigned lps_id = min( m_nLightPathSet - 1 , (int)(sort_canonical() * m_nLightPathSet) );
list<VirtualLightSource> vps = m_pVirtualLightSources[lps_id];
Bsdf* bsdf = ip.primitive->GetMaterial()->GetBsdf(&ip);
// evaluate indirect illumination
Spectrum indirectIllum;
list<VirtualLightSource>::const_iterator it = vps.begin();
while( it != vps.end() )
{
if( r.m_Depth + it->depth > max_recursive_depth )
{
++it;
continue;
}
Vector delta = ip.intersect - it->intersect.intersect;
float sqrLen = delta.SquaredLength();
float len = sqrt( sqrLen );
Vector n_delta = delta / len;
Bsdf* bsdf1 = it->intersect.primitive->GetMaterial()->GetBsdf(&(it->intersect));
float gterm = AbsDot( n_delta , ip.normal ) * AbsDot( n_delta , it->intersect.normal ) / max( m_fMinSqrDist , sqrLen );
Spectrum f0 = bsdf->f( -r.m_Dir , -n_delta );
Spectrum f1 = bsdf1->f( n_delta , it->wi );
Spectrum contr = gterm * f0 * f1 * it->power;
if( !contr.IsBlack() )
{
Visibility vis(scene);
vis.ray = Ray( it->intersect.intersect , n_delta , 0 , 0.001f , len - 0.001f );
if( vis.IsVisible() )
indirectIllum += contr;
}
++it;
}
radiance += indirectIllum / (float)m_nLightPaths;
if( m_fMinDist > 0.0f )
{
Vector wi;
float bsdf_pdf;
Spectrum f = bsdf->sample_f( -r.m_Dir , wi , BsdfSample( true ) , &bsdf_pdf );
if( !f.IsBlack() && bsdf_pdf != 0.0f )
{
PixelSample ps;
float gather_dist;
Ray gather_ray( ip.intersect , wi , r.m_Depth + 1 , 0.001f , m_fMinDist - 0.001f );
Spectrum li = _li( gather_ray , true , &gather_dist );
if( !li.IsBlack() )
{
float dgterm = AbsDot( wi , ip.normal ) * max( 0.0f , 1.0f - gather_dist * gather_dist / m_fMinSqrDist );
radiance += f * li * dgterm / bsdf_pdf;
}
}
}
return radiance;
}
// radiance along a specific ray direction
Spectrum DirectLight::Li( const Ray& r , const PixelSample& ps ) const
{
if( r.m_Depth > max_recursive_depth )
return 0.0f;
// get the intersection between the ray and the scene
Intersection ip;
// evaluate light directly
if( false == scene.GetIntersect( r , &ip ) )
return scene.Le( r );
Spectrum li = ip.Le( -r.m_Dir );
// eavluate direct light
unsigned light_num = scene.LightNum();
for( unsigned i = 0 ; i < light_num ; ++i )
{
const Light* light = scene.GetLight(i);
li += EvaluateDirect( r , scene , light , ip , LightSample(true) , BsdfSample(true), BXDF_TYPE( BXDF_ALL ) );
}
return li;
}