// p.x and p.y are current coordinates

// v.x and v.y is a velocity at point p

vec2 get_velocity(vec2 p) {

  vec2 v = vec2(0., 0.);

​

  // change this to get a new vector field

  v.x = 0.1 * p.y;

  v.y = -0.2 * p.y;

​

  return v;

}