Bildsynthese
PBR Materialien

vec3 fresnelSchlick(float cosTheta, vec3 F0) {
  return F0 + (1.0 - F0) * pow(1.0 - cosTheta, 5.0);
} 

float D_GGX(float NoH, float roughness) {
  float alpha = roughness * roughness;
  float alpha2 = alpha * alpha;
  float NoH2 = NoH * NoH;
  float b = (NoH2 * (alpha2 - 1.0) + 1.0);
  return alpha2 / (PI * b * b);
}

float G1_GGX_Schlick(float NdotV, float roughness) {
  //float r = roughness; // original
  float r = 0.5 + 0.5 * roughness; // Disney remapping
  float k = (r * r) / 2.0;
  float denom = NdotV * (1.0 - k) + k;
  return NdotV / denom;
}

float G_Smith(float NoV, float NoL, float roughness) {
  float g1_l = G1_GGX_Schlick(NoL, roughness);
  float g1_v = G1_GGX_Schlick(NoV, roughness);
  return g1_l * g1_v;
}

vec3 microfacetBRDF(in vec3 L, in vec3 V, in vec3 N, 
              in vec3 baseColor, in float metallicness, 
              in float fresnelReflect, in float roughness) {
     
  vec3 H = normalize(V + L); // half vector

  // all required dot products
  float NoV = clamp(dot(N, V), 0.0, 1.0);
  float NoL = clamp(dot(N, L), 0.0, 1.0);
  float NoH = clamp(dot(N, H), 0.0, 1.0);
  float VoH = clamp(dot(V, H), 0.0, 1.0);     
  
  // F0 for dielectics in range [0.0, 0.16] 
  // default FO is (0.16 * 0.5^2) = 0.04
  vec3 f0 = vec3(0.16 * (fresnelReflect * fresnelReflect)); 
  // in case of metals, baseColor contains F0
  f0 = mix(f0, baseColor, metallicness);

  // specular microfacet (cook-torrance) BRDF
  vec3 F = fresnelSchlick(VoH, f0);
  float D = D_GGX(NoH, roughness);
  float G = G_Smith(NoV, NoL, roughness);
  vec3 spec = (D * G * F) / max(4.0 * NoV * NoL, 0.001);
  
  // diffuse
  vec3 rhoD = vec3(1.0) - F; // if not specular, use as diffuse
  rhoD *= 1.0 - metallicness; // no diffuse for metals
  vec3 diff = rhoD * baseColor / PI; 
  
  return diff + spec;
}