Fabric shader

/*
 *
 * fabric.osl shader by Derek Flood (c)2015
 * from http://docs.sharktacos.com/misc.php?action=help&hid=66
 *
 */

float fresnelReflectionFactor(normal bumped_normal, float ior)
{
    float c = abs(dot(I, bumped_normal));
    float g = ior * ior - 1.0 + c * c;
    if (g > 0.0) {
        g = sqrt (g);
        float A = (g - c) / (g + c);
        float B = (c * (g + c) - 1.0) / (c * (g - c) + 1.0);
        return 0.5 * A * A * (1.0 + B * B);
    }
   
    return 1.0;
}

normal getBumpedNormal(color centerColor, color uColor, color vColor, float inverseBumpAmount)
{
    vector worldTangent = normalize(dPdu);
    vector worldBitangent = normalize(dPdv);
    vector worldNormal = normalize(N);
   
    vector average = vector(0.3333333);
    float center = dot (average, vector(centerColor));
    float ddu = center - dot(average, vector(uColor));
    float ddv = center - dot(average, vector(vColor));
   
    return normalize(ddu * worldTangent + ddv * worldBitangent + inverseBumpAmount * worldNormal);
}

surface fabric
    [[ string description = "artist based fabric material" ]]
(
    /* Diffuse section */   
    color Sheen_color = color(1.0, 1.0, 1.0) [[ string description = "Sheen color can be black for nylon sheen." ]],
    float Sheen_opacity = 1.0 [[ string description = "Determines amount of sheen effect as fibres pick up light at incident angle." ]],
    float Sheen_tint = 0.5 [[ string description = "Tints both the sheen and specular." ]],
    int Sheen_ramp_type = 3
        [[ string widget = "mapper",
        string description = "Six types of interpolation for sheen. 1-3 (linear, exponential and smooth) are sharper, 4-6 (Sigmoid, square root and Fresnel) are softer.",
        string options = "linear:1|exponential:2|Smooth:3|Sigmoid:4|Square_root:5|Fresnel:6" ]],
        
    string Diffuse_color = "",
    float Diffuse_weight = 0.8,
    float Diffuse_roughness = 0.4,
    /* Spec section */
    color Spec_color = 1.0,
    float Spec_amount = 0.5,
    float Spec_glossiness = 0.6,
    float IOR = 1.33 [[ string description = "Determines the strength of Fresnel reflections; fabric generally has low frontal reflections." ]],
    int Subdivs = 8,
    int Trace_reflections = 1
        [[ string widget = "checkBox" ]],
    int Fresnel = 1
        [[ string widget = "checkBox" ]],
   
    /* Anisotropy section */
    float Anisotropy = 0.25,         // Fabric is anisotropic due to weave.
    float Aniso_rotation = 0,
   
    /* Bump section */
    string Bump_texture = "",
    float Bump_amount = 1.0,
    output color result = 1 )
{
    /* Define Bump */
    normal bumped_normal = N;
    if (Bump_amount > 0.0)
    {
        float delta = 0.004;
        color center = texture(Bump_texture, u, v);
        color uColor = texture(Bump_texture, u + delta, v);
        color vColor = texture(Bump_texture, u, v + delta);
   
        bumped_normal = getBumpedNormal(center, uColor, vColor, 1.0 / Bump_amount);
   
    }
   
    /* Define Main color */
        color MainColor = texture (Diffuse_color, u, v, "missingcolor", color(1,0,0));
        MainColor = pow (MainColor, 2.2);
       
    /* Define Edge color */
        color TintBoost = transformc("hsl", MainColor);
        TintBoost[2] = pow (TintBoost[2], 0.2);
        TintBoost[2] = clamp(TintBoost[2],0,1);
        TintBoost = transformc("hsl","rgb", TintBoost);
         
        color EdgeColor =  Sheen_color / 10;
        color TintEdge = EdgeColor * TintBoost;
        EdgeColor = mix (EdgeColor, TintEdge, Sheen_tint);
        EdgeColor = clamp (EdgeColor, 0, 1);
       
    /* Define Spec color */
        color SpecColor = Spec_color;
        color TintedSpec = SpecColor * TintBoost;
        SpecColor = mix (SpecColor, TintedSpec, Sheen_tint);
  
    /* Define Ramp */
   
        float facingRatio = 1 - abs(dot(I, bumped_normal));
       
        if( Sheen_ramp_type == 1) // linear             
            {facingRatio = facingRatio; }
        if( Sheen_ramp_type == 2) // exponential (Down) 
            { facingRatio *= facingRatio;  }  
        if( Sheen_ramp_type == 3) // smooth      
            { facingRatio = smoothstep (0,1, facingRatio ); }
           
        if( Sheen_ramp_type == 4) // sigmoid S-curve
            {
            float Sigmoid = facingRatio / (1 + abs(facingRatio));
            facingRatio = clamp( 2 * Sigmoid, 0, 1);
            }
        if( Sheen_ramp_type == 5) //  square root   
            { facingRatio = sqrt (facingRatio); }
           
        if( Sheen_ramp_type == 6) // fresnel          
            { facingRatio = 2 * fresnelReflectionFactor(bumped_normal, IOR);  }
   
   
    /* Fresnel */
        if (Fresnel)
        { SpecColor *= fresnelReflectionFactor(bumped_normal, IOR); }
        if (Trace_reflections)
        { MainColor *= (1.0 - SpecColor); }
       
    /* BRDF Mixes*/
        color SheenMix = EdgeColor * facingRatio * Sheen_opacity;
        color EdgeMask = mix(1, Sheen_color, (facingRatio * Sheen_opacity) );
        MainColor *= EdgeMask;
        MainColor *= (1.0 - SheenMix);       
           
        closure color sheen_component = SheenMix * diffuse(bumped_normal, "roughness", Diffuse_roughness);
        closure color diffuse_component =  MainColor * Diffuse_weight * diffuse(bumped_normal, "roughness", Diffuse_roughness);
        closure color specular_component = Spec_amount * SpecColor *       
            vray_blinn (bumped_normal, Spec_glossiness, Anisotropy, Aniso_rotation,       
            "subdivs", Subdivs, "trace_reflections", Trace_reflections);       
               
        closure color reflect_component = SpecColor * reflection(bumped_normal, IOR);
        Ci = diffuse_component + specular_component + reflect_component + sheen_component;
}