IK

int n = 10;
float xpos[] = new float[n];
float ypos[] = new float[n];

// --------------------------------------------------------
void setup() {
  size(500, 500);

  for (int i=0; i<n; i++) {
    xpos[i] = i * 10;
    ypos[i] = i * 10;
  }
}


// --------------------------------------------------------
void draw() {

  background(255);
  xpos[0] = mouseX;
  ypos[0] = mouseY;

  float restLen = 20.0;

  for (int i=1; i<n; i++) {
    float dx = xpos[i] - xpos[i-1];
    float dy = ypos[i] - ypos[i-1];
    float d  = sqrt(dx*dx + dy*dy);
    if (d>0) {
      xpos[i] = xpos[i-1] + (dx * restLen) / d;
      ypos[i] = ypos[i-1] + (dy * restLen) / d;
    }
  }  


  for (int i=1; i<n; i++) {
    noStroke();
    stroke(0);
    line(xpos[i], ypos[i], xpos[i-1], ypos[i-1]);
  }
}