/******************************************************************/
/* 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 "diffuseBrdf.h"

//////////////////
// Constructors //
//////////////////
diffuseBrdf::diffuseBrdf(const color& albedo)
{
  _albedo = albedo;
}


diffuseBrdf::diffuseBrdf(const diffuseBrdf& src)
{
  _albedo = src._albedo;
}


///////////////
// Operators //
///////////////
diffuseBrdf& diffuseBrdf::operator=(const diffuseBrdf& src)
{
  _assign(src);
  return *this;
}


/////////////
// Methods //
/////////////
color diffuseBrdf::shade(const vec3d& in, const vec3d& out) const
{
  if(in.z < 0.0f || out.z < 0.0f) return color();
  else return _albedo * in.z;
}


color diffuseBrdf::reflectance(const vec3d& in, const vec3d& out) const
{
  if(in.z < 0.0f || out.z < 0.0f) return color(0.0f);
  return _albedo / PI;
}


brdfSample diffuseBrdf::sample(const vec3d& in, float r1, float r2) const
{
  // check if below surface.
  if(in.z < EPSILON) return brdfSample();

  // sample hemisphere proportional to the cosine
  vec3d out( cos(2.0f * PI * r1) * sqrt(std::max(1.0f - r2, 0.0f)),
	     sin(2.0f * PI * r1) * sqrt(std::max(1.0f - r2, 0.0f)),
	     sqrt(r2) );

  // set pdf
  float pdf = out.z / PI;

  // Done.
  return brdfSample(out, 
		    out.z / PI,                     // PDF proportional to cosine
		    _albedo / PI                    // reflectance
		    );
}


bool diffuseBrdf::isSpecular(void) const
{
  return false;
}


bool diffuseBrdf::isDiffuse(void) const
{
  return true;
}


float diffuseBrdf::reflectivity(void) const
{
  return (_albedo.r + _albedo.g + _albedo.b) / 3.0f;
}


/////////////////////
// Private Methods //
/////////////////////
void diffuseBrdf::_assign(const diffuseBrdf& src)
{
  _albedo = src._albedo;
}


void diffuseBrdf::_swap(diffuseBrdf& src)
{
  swap(_albedo, src._albedo);
}

void diffuseBrdf::_print(std::ostream& s) const
{
  s << "Diffuse BRDF: albedo=" << _albedo;
}