/******************************************************************/
/* This file is part of the homework assignments for CSCI-427/527 */
/* at The College of William & Mary and authored by Pieter Peers. */
/* No part of this file, whether altered or in original form, can */
/* be distributed or used outside the context of CSCI-427/527 */
/* without consent of either the College of William & Mary or */
/* Pieter Peers. */
/******************************************************************/
#include <cmath>
#include "constants.h"
#include "phongBrdf.h"
#include "coordinateTransform.h"
//////////////////
// Constructors //
//////////////////
phongBrdf::phongBrdf(const color& albedo, float sharpness)
{
_albedo = albedo;
_sharpness = sharpness;
}
phongBrdf::phongBrdf(const phongBrdf& src)
{
_albedo = src._albedo;
_sharpness = src._sharpness;
}
///////////////
// Operators //
///////////////
phongBrdf& phongBrdf::operator=(const phongBrdf& src)
{
_assign(src);
return *this;
}
/////////////
// Methods //
/////////////
color phongBrdf::shade(const vec3d& in, const vec3d& out) const
{
// sanity check (below horizon)
if(in.z < 0.0f || out.z < 0.0f) return color(0.0f);
// compute reflected direction (simplies when n=(0,0,1))
vec3d reflected(-in.x, -in.y, in.z);
// evaluate phong
return _albedo * std::pow(std::max( reflected.dot(out), 0.0f), _sharpness);
}
color phongBrdf::reflectance(const vec3d& in, const vec3d& out) const
{
// use shade evaluation times a normalization factor to ensure
// conservation of enegery.
return shade(in, out) * (_sharpness + 2.0f) / (2.0f * PI);
}
brdfSample phongBrdf::sample(const vec3d& in, float r1, float r2) const
{
// sanity check
if(in.z < 0.0f) return brdfSample();
// compute reflected direction
vec3d reflected(-in.x, -in.y, in.z);
// sample hemisphere around reflected direction.
vec3d out( sqrt( 1.0f - pow(r1, 2.0f / (_sharpness + 1.0f)) ) * cos(2.0f * PI * r2),
sqrt( 1.0f - pow(r1, 2.0f / (_sharpness + 1.0f)) ) * sin(2.0f * PI * r2),
pow(r1, 1.0f / (_sharpness + 1.0f)) );
// transform to global coord
coordinateTransformation trans(reflected);
out = trans.transformDirection(out);
// compute pdf
float pdf = 0.0f;
if(out.z >= 0.0f)
pdf = (_sharpness + 1.0f) / (2.0f * PI) * pow(reflected.dot(out), _sharpness);
// Done.
return brdfSample(out, pdf, this->reflectance(in, out));
}
bool phongBrdf::isSpecular(void) const
{
// Consider low roughness to be diffuse.
// Use 5.0f as an arbitrary threshold.
return (_sharpness > 5.0f);
}
bool phongBrdf::isDiffuse(void) const
{
return !isSpecular();
}
float phongBrdf::reflectivity(void) const
{
// Done.
return (_albedo.r + _albedo.g + _albedo.b) / 3.0f;
}
/////////////////////
// Private Methods //
/////////////////////
void phongBrdf::_assign(const phongBrdf& src)
{
_albedo = src._albedo;
_sharpness = src._sharpness;
}
void phongBrdf::_swap(phongBrdf& src)
{
swap(_albedo, src._albedo);
std::swap(_sharpness, src._sharpness);
}
void phongBrdf::_print(std::ostream& s) const
{
s << "Phong BRDF: albedo=" << _albedo << ", sharpness=" << _sharpness;
}
