int pts[] = nearpoints(1, v@P, 1.0, 2);
vector pos_0 = point(1, 'P', pts[0]);
vector pos_1 = point(1, 'P', pts[1]);
float d_0 = distance(pos_0, v@P);
float d_1 = distance(pos_1, v@P);
float d = d_1 - d_0;d_0 is the distance for driving the growing circles while d is the distance to the cell boundaries.
