#version 330 core
out vec4 FragColor;
in vec2 TexCoords;
in vec3 WorldPos;
in vec3 Normal;
// material parameters
uniform sampler2D albedoMap;
uniform sampler2D normalMap;
uniform sampler2D metallicMap;
uniform sampler2D roughnessMap;
uniform sampler2D aoMap;
// IBL
uniform samplerCube irradianceMap;
uniform samplerCube prefilterMap;
uniform sampler2D brdfLUT;
// lights
uniform vec3 lightPositions[4];
uniform vec3 lightColors[4];
uniform vec3 camPos;
const float PI = 3.14159265359;
// ----------------------------------------------------------------------------
// Easy trick to get tangent-normals to world-space to keep PBR code simplified.
// Don't worry if you don't get what's going on; you generally want to do normal
// mapping the usual way for performance anyways; I do plan make a note of this
// technique somewhere later in the normal mapping tutorial.
vec3 getNormalFromMap()
{
vec3 tangentNormal = texture(normalMap, TexCoords).xyz * 2.0 - 1.0;
vec3 Q1 = dFdx(WorldPos);
vec3 Q2 = dFdy(WorldPos);
vec2 st1 = dFdx(TexCoords);
vec2 st2 = dFdy(TexCoords);
vec3 N = normalize(Normal);
vec3 T = normalize(Q1*st2.t - Q2*st1.t);
vec3 B = -normalize(cross(N, T));
mat3 TBN = mat3(T, B, N);
return normalize(TBN * tangentNormal);
}
// ----------------------------------------------------------------------------
float DistributionGGX(vec3 N, vec3 H, float roughness)
{
float a = roughness*roughness;
float a2 = a*a;
float NdotH = max(dot(N, H), 0.0);
float NdotH2 = NdotH*NdotH;
float nom = a2;
float denom = (NdotH2 * (a2 - 1.0) + 1.0);
denom = PI * denom * denom;
return nom / denom;
}
// ----------------------------------------------------------------------------
float GeometrySchlickGGX(float NdotV, float roughness)
{
float r = (roughness + 1.0);
float k = (r*r) / 8.0;
float nom = NdotV;
float denom = NdotV * (1.0 - k) + k;
return nom / denom;
}
// ----------------------------------------------------------------------------
float GeometrySmith(vec3 N, vec3 V, vec3 L, float roughness)
{
float NdotV = max(dot(N, V), 0.0);
float NdotL = max(dot(N, L), 0.0);
float ggx2 = GeometrySchlickGGX(NdotV, roughness);
float ggx1 = GeometrySchlickGGX(NdotL, roughness);
return ggx1 * ggx2;
}
// ----------------------------------------------------------------------------
vec3 fresnelSchlick(float cosTheta, vec3 F0)
{
return F0 + (1.0 - F0) * pow(clamp(1.0 - cosTheta, 0.0, 1.0), 5.0);
}
// ----------------------------------------------------------------------------
vec3 fresnelSchlickRoughness(float cosTheta, vec3 F0, float roughness)
{
return F0 + (max(vec3(1.0 - roughness), F0) - F0) * pow(clamp(1.0 - cosTheta, 0.0, 1.0), 5.0);
}
// ----------------------------------------------------------------------------
void main()
{
// material properties
vec3 albedo = pow(texture(albedoMap, TexCoords).rgb, vec3(2.2));
float metallic = texture(metallicMap, TexCoords).r;
float roughness = texture(roughnessMap, TexCoords).r;
float ao = texture(aoMap, TexCoords).r;
// input lighting data
vec3 N = getNormalFromMap();
vec3 V = normalize(camPos - WorldPos);
vec3 R = reflect(-V, N);
// calculate reflectance at normal incidence; if dia-electric (like plastic) use F0
// of 0.04 and if it's a metal, use the albedo color as F0 (metallic workflow)
vec3 F0 = vec3(0.04);
F0 = mix(F0, albedo, metallic);
// reflectance equation
vec3 Lo = vec3(0.0);
for(int i = 0; i < 4; ++i)
{
// calculate per-light radiance
vec3 L = normalize(lightPositions[i] - WorldPos);
vec3 H = normalize(V + L);
float distance = length(lightPositions[i] - WorldPos);
float attenuation = 1.0 / (distance * distance);
vec3 radiance = lightColors[i] * attenuation;
// Cook-Torrance BRDF
float NDF = DistributionGGX(N, H, roughness);
float G = GeometrySmith(N, V, L, roughness);
vec3 F = fresnelSchlick(max(dot(H, V), 0.0), F0);
vec3 numerator = NDF * G * F;
float denominator = 4.0 * max(dot(N, V), 0.0) * max(dot(N, L), 0.0) + 0.0001; // + 0.0001 to prevent divide by zero
vec3 specular = numerator / denominator;
// kS is equal to Fresnel
vec3 kS = F;
// for energy conservation, the diffuse and specular light can't
// be above 1.0 (unless the surface emits light); to preserve this
// relationship the diffuse component (kD) should equal 1.0 - kS.
vec3 kD = vec3(1.0) - kS;
// multiply kD by the inverse metalness such that only non-metals
// have diffuse lighting, or a linear blend if partly metal (pure metals
// have no diffuse light).
kD *= 1.0 - metallic;
// scale light by NdotL
float NdotL = max(dot(N, L), 0.0);
// add to outgoing radiance Lo
Lo += (kD * albedo / PI + specular) * radiance * NdotL; // note that we already multiplied the BRDF by the Fresnel (kS) so we won't multiply by kS again
}
// ambient lighting (we now use IBL as the ambient term)
vec3 F = fresnelSchlickRoughness(max(dot(N, V), 0.0), F0, roughness);
vec3 kS = F;
vec3 kD = 1.0 - kS;
kD *= 1.0 - metallic;
vec3 irradiance = texture(irradianceMap, N).rgb;
vec3 diffuse = irradiance * albedo;
// sample both the pre-filter map and the BRDF lut and combine them together as per the Split-Sum approximation to get the IBL specular part.
const float MAX_REFLECTION_LOD = 4.0;
vec3 prefilteredColor = textureLod(prefilterMap, R, roughness * MAX_REFLECTION_LOD).rgb;
vec2 brdf = texture(brdfLUT, vec2(max(dot(N, V), 0.0), roughness)).rg;
vec3 specular = prefilteredColor * (F * brdf.x + brdf.y);
vec3 ambient = (kD * diffuse + specular) * ao;
vec3 color = ambient + Lo;
// HDR tonemapping
color = color / (color + vec3(1.0));
// gamma correct
color = pow(color, vec3(1.0/2.2));
FragColor = vec4(color , 1.0);
}
HI