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diff --git a/hw6/src/diffuseBrdf.cpp b/hw6/src/diffuseBrdf.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 "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;
+}