Normalized Oren-Nayar for BRDF explorer.

NormalizedOrenNayar.brdf

analytic

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

::begin parameters
float roughness 0 1 1
float f0 0 1 0.04
bool fresnel 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 VdotH = dot(V,H);
    float a = roughness*roughness;
    
    float fdiff = 1.05 * (1.0 - f0) * (1.0 - pow(1.0 - LdotN, 5.0)) * (1.0 - pow(1.0 - VdotN, 5.0));
    float A = 1.0 - 0.5 * (a / (a + 0.65));
    float B = 0.45 * (a / (a + 0.09));
    float Bp = LdotV - (VdotN * LdotN);
    float Bm = min(1.0, LdotN / VdotN);
    if (fresnel) {
      return vec3((1.0/PI) * (1.0 - f0) * (fdiff * LdotN * A + B * Bp * Bm));
    }
    
    if (Bp >= 0.0) {
      return vec3((1.0/PI)*(LdotN*A + B*Bp*Bm));
    }
    
    return vec3((1.0/PI)*(LdotN*A + B*Bp));
}

::end shader