OpenGLでDisneyの物理ベースシェーディングを書いてみる

// MeshEntityの作成
  mesh_entities_.emplace_back(mesh, material, glm::vec3(-2.0f, 0.0f, 0.0f),
                              glm::vec3(0.0f), glm::vec3(1.0f));
  mesh_entities_.emplace_back(mesh, material, glm::vec3(0.0f, 0.0f, 0.0f),
                              glm::vec3(0.0f), glm::vec3(1.0f));
  mesh_entities_.emplace_back(mesh, material, glm::vec3(2.0f, 0.0f, 0.0f),
                              glm::vec3(0.0f), glm::vec3(1.0f));

// # Copyright Disney Enterprises, Inc.  All rights reserved.
// #
// # Licensed under the Apache License, Version 2.0 (the "License");
// # you may not use this file except in compliance with the License
// # and the following modification to it: Section 6 Trademarks.
// # deleted and replaced with:
// #
// # 6. Trademarks. This License does not grant permission to use the
// # trade names, trademarks, service marks, or product names of the
// # Licensor and its affiliates, except as required for reproducing
// # the content of the NOTICE file.
// #
// # You may obtain a copy of the License at
// # http://www.apache.org/licenses/LICENSE-2.0
float SchlickFresnel(float cosTheta)
{
  return pow(clamp((1 - cosTheta), 0, 1), 5.0);
}

float D_GTR1(float NdotH, float a)
{
  float a2 = a * a;
  float tmp = 1 + (a2 - 1) * NdotH * NdotH;
  return (a2 - 1) / (PI * log(a2) * tmp);
}

float D_GTR2aniso(float NdotH, float HdotX, float HdotY, float ax, float ay)
{
  float tmp = (HdotX * HdotX) / (ax * ax) + (HdotY * HdotY) / (ay * ay) + NdotH * NdotH;
  return 1 / (PI * ax * ay * tmp * tmp);
}

float G_GGX(float NdotV, float a)
{
  float a2 = a * a;
  float down = NdotV + sqrt(a2 + NdotV * NdotV - a2 * NdotV * NdotV);
  return 1 / down;
}

float G_GGXaniso(float NdotV, float VdotX, float VdotY, float ax, float ay)
{
  float tmp = VdotX * VdotX * ax * ax + VdotY * VdotY * ay * ay + NdotV * NdotV;
  float down = NdotV + sqrt(tmp);
  return 1 / down;
}

vec3 DisneyBRDF(vec3 L, vec3 V, vec3 N, vec3 H, vec3 X, vec3 Y, vec3 baseColor, float subsurface, float metallic, float specular, float specularTint, float roughness, float anisotropic, float sheen, float sheenTint, float clearcoat, float clearcoatGloss)
{
  float NdotL = dot(N, L);
  float NdotV = dot(N, V);
  if (NdotL < 0 || NdotV < 0) return vec3(0);

  float NdotH = dot(N, H);
  float LdotH = dot(L, H);

  float luminance = 0.3 * baseColor.r + 0.6 * baseColor.g + 0.1 * baseColor.b;
  vec3 C_tint = luminance > 0 ? baseColor / luminance : vec3(1);
  vec3 C_spec = mix(specular * 0.08 * mix(vec3(1), C_tint, specularTint), baseColor, metallic);
  vec3 C_sheen = mix(vec3(1), C_tint, sheenTint);

  // diffuse
  float F_i = SchlickFresnel(NdotL);
  float F_o = SchlickFresnel(NdotV);
  float F_d90 = 0.5 + 2 * LdotH * LdotH * roughness;
  float F_d = mix(1.0, F_d90, F_i) * mix(1.0, F_d90, F_o);

  float F_ss90 = LdotH * LdotH * roughness;
  float F_ss = mix(1.0, F_ss90, F_i) * mix(1.0, F_ss90, F_o);
  float ss = 1.25 * (F_ss * (1 / (NdotL + NdotV) - 0.5) + 0.5);

  float FH = SchlickFresnel(LdotH);
  vec3 F_sheen = FH * sheen * C_sheen;

  vec3 BRDFdiffuse = ((1 / PI) * mix(F_d, ss, subsurface) * baseColor + F_sheen) * (1 - metallic);

  // specular
  float aspect = sqrt(1 - anisotropic * 0.9);
  float roughness2 = roughness * roughness;
  float a_x = max(0.001, roughness2 / aspect);
  float a_y = max(0.001, roughness2 * aspect);
  float D_s = D_GTR2aniso(NdotH, dot(H, X), dot(H, Y), a_x, a_y);
  vec3 F_s = mix(C_spec, vec3(1), FH);
  float G_s = G_GGXaniso(NdotL, dot(L, X), dot(L, Y), a_x, a_y) * G_GGXaniso(NdotV, dot(V, X), dot(V, Y), a_x, a_y);

  vec3 BRDFspecular = G_s * F_s * D_s;

  // clearcoat
  float D_r = D_GTR1(NdotH, mix(0.1, 0.001, clearcoatGloss));
  float F_r = mix(0.04, 1.0, FH);
  float G_r = G_GGX(NdotL, 0.25) * G_GGX(NdotV, 0.25);

  vec3 BRDFclearcoat = vec3(0.25 * clearcoat * G_r * F_r * D_r);

  return BRDFdiffuse + BRDFspecular + BRDFclearcoat;
}

  vec3 tangent = normalize(vWorldTangent);
  vec3 bitangent = normalize(cross(N, tangent));
  tangent = normalize(cross(bitangent, N));

  float subsurface = 0.0;
  float specular = 0.5;
  float specularTint = 0.0;
  float sheen = 0.0;
  float sheenTint = 0.5;
  float clearcoat = 0.0;
  float clearcoatGloss = 1.0;

  float subsurface = 0.0;
  float specular = 0.5;
  float specularTint = 0.0;
  float sheen = 0.0;
  float sheenTint = 0.5;
  // float clearcoat = 0.0;
  float clearcoat = 1.0;
  float clearcoatGloss = 0.95;