Link.pde

// // The Link class is used for handling constraints between particles.
// class Link {
//   float restingDistance;
//   float stiffness;
  
//   Particle p1;
//   Particle p2;
  
//   // the scalars are how much "tug" the particles have on each other
//   // this takes into account masses and stiffness, and are set in the Link constructor
//   float scalarP1;
//   float scalarP2;
  
//   // if you want this link to be invisible, set this to false
//   boolean drawThis = true;
  
//   Link (Particle which1, Particle which2, float restingDist, float stiff) {
//     p1 = which1; // when you set one object to another, it's pretty much a reference. 
//     p2 = which2; // Anything that'll happen to p1 or p2 in here will happen to the paticles in our array
    
//     restingDistance = restingDist;
//     stiffness = stiff;
    
//     // although there are no differences in masses for the curtain, 
//     // this opens up possibilities in the future for if we were to have a fabric with particles of different weights
//     float im1 = 1 / p1.mass; // inverse mass quantities
//     float im2 = 1 / p2.mass;
//     scalarP1 = (im1 / (im1 + im2)) * stiffness;
//     scalarP2 = (im2 / (im1 + im2)) * stiffness;
//   }
  
//   void constraintSolve () {
//     // calculate the distance between the two particles
//     PVector delta = PVector.sub(p1.position, p2.position);  
//     float d = sqrt(delta.x * delta.x + delta.y * delta.y);
//     float difference = (restingDistance - d) / d;
    
//     // if the distance is more than curtainTearSensitivity, the cloth tears
//     // it would probably be better if force was calculated, but this works
//     if (d > curtainTearSensitivity) 
//       p1.removeLink(this);
    
//     // P1.position += delta * scalarP1 * difference
//     // P2.position -= delta * scalarP2 * difference
//     p1.position.add(PVector.mult(delta, scalarP1 * difference));
//     p2.position.sub(PVector.mult(delta, scalarP2 * difference));
//   }

//   void draw () {
//     if (drawThis)
//       line(p1.position.x, p1.position.y, p2.position.x, p2.position.y);
//   }
// }