sdf_noise.gdshaderinc

// http://iquilezles.org/www/articles/smin/smin.htm
float smin( float a, float b, float k )
{
    float h = max(k-abs(a-b),0.0);
    return min(a, b) - h*h*0.25/k;
}

// http://iquilezles.org/www/articles/smin/smin.htm
float smax( float a, float b, float k )
{
    float h = max(k-abs(a-b),0.0);
    return max(a, b) + h*h*0.25/k;
}

// https://iquilezles.org/www/articles/fbmsdf/fbmsdf.htm
float sph( vec3 i, vec3 f, vec3 c )
{
    // random radius at grid vertex i+c (please replace this hash by
    // something better if you plan to use this for a real application)
    vec3  p = 17.0*fract( (i+c)*0.3183099+vec3(0.11,0.17,0.13) );
    float w = fract( p.x*p.y*p.z*(p.x+p.y+p.z) );
    float r = 0.7*w*w;
    // distance to sphere at grid vertex i+c
    return length(f-c) - r;
}

// https://iquilezles.org/www/articles/fbmsdf/fbmsdf.htm
float sdBase( in vec3 p )
{
    vec3 i = floor(p);
    vec3 f = fract(p);
    return min(min(min(sph(i,f,vec3(0,0,0)),
    sph(i,f,vec3(0,0,1))),
    min(sph(i,f,vec3(0,1,0)),
    sph(i,f,vec3(0,1,1)))),
    min(min(sph(i,f,vec3(1,0,0)),
    sph(i,f,vec3(1,0,1))),
    min(sph(i,f,vec3(1,1,0)),
    sph(i,f,vec3(1,1,1)))));
}

// https://iquilezles.org/www/articles/fbmsdf/fbmsdf.htm
float sdFbm( 
    in vec3 p, 
    in int detail, 
    in float rough, 
    in float inflate, 
    in float smooth_fac, 
    in float d)
{
    float s = 1.0;
    for( int i=0; i < min(int(detail), 12); i++ )
    {
        float n = s*sdBase(p);

        n = smax(n,d - inflate*s, smooth_fac*s );
        d = smin(n,d      , smooth_fac*s );

        p = mat3(vec3( 0.00, 1.60, 1.20),
                 vec3(-1.60, 0.72,-0.96),
                 vec3(-1.20,-0.96, 1.280))*p;
        s = rough*s;
    }
    return d;
}