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// One spring - version 1.2

// This script attaches a spring between the 2 layers shown in the popups.
// Layer 1 keeps its original motion, while layer 2 is attached by a spring to it.

//      LAYER                                               PROPERTY                     CHANNEL
//      ------                                              ----------                     --------
// 1: Layer that moves                               doesn't matter               doesn't matter
// 2: Layer attached to #1 by a spring        doesn't matter               doesn't matter


if (time() == start_time) {
   rest_length = 10;							// rest length of spring in pixels
   damp = 0.95;										// Damping (0 = infinite friction, 1 = none)

   p1 = value(pop_layer(1), position);
   p2 = value(pop_layer(2), position);

   last_p1 = tmap(time() - step_time, value(pop_layer(1), position));
   last_p2 = tmap(time() - step_time, value(pop_layer(2), position)); 

   v1 = (p1 - last_p1);
   v2 = (p2 - last_p2);
} else {
  p1 = value(pop_layer(1), position);

   delta = p2 - p1;
   n_delta = normalize(delta);

   a = 2 * n_delta * (length(delta) - rest_length) * step_time;

	v2 = (v2 - a) * damp;
  v1 = (v1 + a) * damp;

   p1 = p1 + v1;
   p2 = p2 + v2;
}
value(pop_layer(2), position) = p2;