/******************************************************************/
/* 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;
}