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diff --git a/hw6/src/phongBrdf.cpp b/hw6/src/phongBrdf.cpp
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+/******************************************************************/
+/* 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;
+}