VDrift lighting, materials, textures

Code:

// Fresnel term F [f0, 1]

// Schlick: F(f0, hv) = f0 + (1 - f0) * (1 - hv)^5

vec3 F(const vec3 f0, const float hv)

{

    return f0 + (vec3(1) - f0) * pow(1 - hv, 5);

}



// Microfacet normal distribution D [0, 1]

// Statistical distribution of surface normals

// ag (width) determines shape, ag -> 0 dirac delta

// GGX: D(nh, ag) = ag^2 / (pi * (nh^2 * (ag^2 - 1) + 1)^2)

float D(const float nh, const float ag)

{

    float ag2 = ag * ag;

    float nh2 = nh * nh;

    float s = (nh2 * (ag2 - 1) + 1);

    float s2 = s * s;

    return ag2 / (PI * s2);

}



// Shadow masking function G [0, 1]

// Needed to maintain energy conservation of D

// ag (width) determines shape, ag -> 0 box function

// GGX: G = G1(nv, ag) * G1(nl, ag) with G1(x, ag) = 2 / (1 + sqrt(ag^2 / x^2 - ag^2 + 1))

float G(const float nv, const float nl, const float ag)

{

    float ag2 = ag * ag;

    float nl2 = nl * nl;

    float nv2 = nv * nv;

    return 2 / ((1 + sqrt(ag2 / nl2 - ag2 + 1)) * 2 / (1 + sqrt(ag2 / nv2 - ag2 + 1)));

}



vec3 BRDF(const vec3 fd, const vec3 f0, const float hv, const float nv, const float nl, const float nh, const float roughness)

{

    return fd / PI + D(nh, roughness) * F(f0, hv) * G(nv, nl, roughness) / (4 * nl * nv)

}

Code:

analytic



::begin parameters

float roughness 0.001 1 .1

float metallic 0.001 1 .1

color color 1 1 1

::end parameters





::begin shader



const float pi = 3.14159265358979323846;



vec3 Fresnel(vec3 f0, float cos_theta)

{

    float b = 1 - cos_theta;

    float b2 = b * b;

    return f0 + (1 - f0) * b2 * b2 * b;

}



vec3 VDriftBRDF(vec3 f0, float r, float nv, float nl, float nh, float vh)

{

    float a = r * r;

    float a2 = a * a;

    float d = nh * nh * (a2 - 1) + 1;

    float r1 = r + 1;

    float k = r1 * r1 / 8;

    vec3 f = Fresnel(f0, vh);

    return f * a2 / (4 * pi * d * d * (nl * (1 - k) + k) * (nv * (1 - k) + k));

}



vec3 BRDF( vec3 L, vec3 V, vec3 N, vec3 X, vec3 Y )

{

    vec3 f0 = mix(vec3(0.04), color, metallic);

    vec3 H = normalize(V + L);

    float nv = max(0.0, dot(N, V));

    float nl = max(0.0, dot(N, L));

    float nh = max(0.0, dot(N, H));

    float vh = max(0.0, dot(V, H));

    return VDriftBRDF(f0, roughness, nv, nl, nh, vh) ;

}



::end shader