OSL???
(everybody forget that we have OSL!!)
void rng_seed(output int rng, int seed)
{
int chash = seed;
if (chash == 0) chash = 1;
rng = chash * 891694213;
}
float rng_uniform(output int rng)
{
float res = rng / float(2147483647) * 0.5 + 0.5;
rng *= 891694213;
return res;
}
void to_unit_disk(float x, float y, output float x_out, output float y_out)
{
float r, phi;
float a = 2.0 * x - 1.0;
float b = 2.0 * y - 1.0;
if(a > -b) {
if(a > b) {
r = a;
phi = M_PI_4 *(b/a);
}
else {
r = b;
phi = M_PI_4 *(2.0 - a/b);
}
}
else {
if(a < b) {
r = -a;
phi = M_PI_4 *(4.0 + b/a);
}
else {
r = -b;
if(b != 0.0) phi = M_PI_4 *(6.0 - a/b);
else phi = 0.0;
}
}
x_out = r * cos(phi);
y_out = r * sin(phi);
}
void make_orthonormals(vector N, output vector a, output vector b)
{
if(N[0] != N[1] || N[0] != N[2]) a = cross(vector(1, 1, 1), N);
else a = cross(vector(-1, 1, 1), N);
a = normalize(a);
b = cross(N, a);
}
vector sample_cos_hemisphere(vector N, float randu, float randv)
{
vector T, B;
make_orthonormals(N, T, B);
to_unit_disk(randu, randv, randu, randv);
float costheta = sqrt(max(1.0 - randu * randu - randv * randv, 0.0));
return randu * T + randv * B + costheta * N;
}
shader MinThickness(
float Distance = 0.2,
int Samples = 1,
output float Fac = 0)
{
int i, rng;
float f, randu, randv, ray_t = 0;
float mindst=Distance;
vector ray_P, ray_R;
f = fmod(cellnoise(P*123456.0), 1.0);
rng_seed(rng, int(f * 2147483647));
for(i = 0; i < Samples; i++) {
randu = rng_uniform(rng);
randv = rng_uniform(rng);
ray_P = P;
ray_R = sample_cos_hemisphere(-N, randu, randv);
if(trace(ray_P, ray_R, "maxdist", Distance)) {
getmessage("trace", "hitdist", ray_t);
ray_t/=Distance*dot(-N, ray_R);
mindst=min(mindst, ray_t);
}
}
Fac=pow(M_E, -mindst)/Distance;
}
Now all one have to do is to use this node to mix colors, change densities, or whatever.