// generate sample in two dimension
void RegularSampler::Generate2D( float* sample , unsigned num , bool accept_uniform ) const
{
Sort_Assert( sample != 0 );
unsigned n = (unsigned)sqrt((float)num);
Sort_Assert( n * n == num );
unsigned dn = 2 * n;
for( unsigned i = 0 ; i < n ; ++i )
{
unsigned offset = dn * i;
for( unsigned j = 0 ; j < dn ; j+=2 )
{
// fall back to random sampling if uniform sampling is not accepted.
// For certain cases, like sampling brdf and light, uniform sampling is not acceptable
if( !accept_uniform )
{
sample[offset+j] = sort_canonical();
sample[offset+j+1] = sort_canonical();
continue;
}
sample[offset+j] = ( (float)j/2 + 0.5f ) / (float)n ;
sample[offset+j+1] = ( (float)i + 0.5f ) / (float)n ;
}
}
}
// 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);
}
}
}
}
// generate sample in two dimension
void RandomSampler::Generate2D( float* sample , unsigned num , bool accept_uniform ) const
{
Sort_Assert( sample != 0 );
int count = 2 * num;
for( int i = 0 ; i < count ; i += 2 )
{
sample[i] = sort_canonical();
sample[i+1] = sort_canonical();
}
}
// sample a ray from light
void Square::sample_l( const LightSample& ls , Ray& r , Vector& n , float* pdf ) const
{
float u = 2 * ls.u - 1.0f;
float v = 2 * ls.v - 1.0f;
r.m_fMin = 0.0f;
r.m_fMax = FLT_MAX;
r.m_Ori = transform( Point( radius * u , 0.0f , radius * v ) );
r.m_Dir = transform( UniformSampleHemisphere( sort_canonical() , sort_canonical() ) );
n = transform.invMatrix.Transpose()( Vector( 0.0f , 1.0f , 0.0f ) );
if( pdf ) *pdf = 1.0f / ( SurfaceArea() * TWO_PI );
}
// generate sample in one dimension
void RandomSampler::Generate1D( float* sample , unsigned num , bool accept_uniform ) const
{
Sort_Assert( sample != 0 );
for( unsigned i = 0 ; i < num ; ++i )
sample[i] = sort_canonical();
}
// generate sample in one dimension
void StratifiedSampler::Generate1D( float* sample , unsigned num , bool accept_uniform ) const
{
Sort_Assert( sample != 0 );
for( unsigned i = 0 ; i < num ; ++i )
sample[i] = ( (float)i + sort_canonical() ) / (float)num ;
}
// generate sample in two dimension
void StratifiedSampler::Generate2D( float* sample , unsigned num , bool accept_uniform ) const
{
Sort_Assert( sample != 0 );
unsigned n = (unsigned)sqrt((float)num);
Sort_Assert( n * n == num );
unsigned dn = 2 * n;
for( unsigned i = 0 ; i < n ; ++i )
{
unsigned offset = dn * i;
for( unsigned j = 0 ; j < dn ; j+=2 )
{
sample[offset+j] = ( (float)j/2 + sort_canonical() ) / (float)n ;
sample[offset+j+1] = ( (float)i + sort_canonical() ) / (float)n ;
}
}
}
// generate sample in one dimension
void RegularSampler::Generate1D( float* sample , unsigned num , bool accept_uniform ) const
{
Sort_Assert( sample != 0 );
for( unsigned i = 0 ; i < num ; ++i )
{
// fall back to random sampling if uniform sampling is not accepted.
// For certain cases, like sampling brdf and light, uniform sampling is not acceptable
if( !accept_uniform )
sample[i] = sort_canonical();
else
sample[i] = ( (float)i + 0.5f ) / (float)num ;
}
}
// 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;
}
// 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;
}
