Signed distance without volumes

int pr;
vector uvw;
float d = xyzdist(1, v@P, pr, uvw);

vector pos = primuv(1, 'P', pr, uvw);
vector dir = normalize(v@P - pos);
vector nml = primuv(1, 'N', pr, uvw);

float s = sign(dot(dir, nml) + 0.01);

f@sd = s * d;