GGX Approximation Diffuse for BRDF Explorer

GGXApproxDiffuse.brdf

analytic

# variables go here...
# only floats supported right now.
# [type] [name] [min val] [max val] [default val]

::begin parameters
float albedo 0 1 1
float roughness 0 1 1
::end parameters

# Then comes the shader. This should be GLSL code
# that defines a function called BRDF (although you can
# add whatever other functions you want too).

::begin shader

const float PI = 3.14159265358979323846;

vec3 BRDF( vec3 L, vec3 V, vec3 N, vec3 X, vec3 Y )
{
    float VdotN = dot(V,N);
    float LdotN = dot(L,N);
    float LdotV = dot(L,V);
    vec3 H = normalize(L+V);
    float NdotH = dot(N,H);
    float a = roughness*roughness;
    
    float facing = 0.5 + 0.5 * LdotV;
    float rough = facing * (0.9 - 0.4 * facing) * ((0.5 + NdotH)/NdotH);
    float Smooth = 1.05 * (1 - pow(1-LdotN, 5)) * (1-pow(1-VdotN, 5));
    float single = 1/PI * mix(Smooth, rough, a);
    float multi = 0.1159 * a;
    float contrib = albedo * (single + albedo*multi);
    return vec3(contrib);
}

::end shader