class Node {
   float x,y;
   float dx, dy;
   boolean fixed;
   String label;
   
   Node(String label){
     this.label = label;
     x = random(width);
     y = random(height);
   }
   
   void relax(){
     float ddx = 0;
     float ddy = 0;
     
     for (int j=0; j< nodeCount; j++){
       Node n = nodes[j];
       if(n != this){
         float vx = x -n.x;
         float vy = y -n.y;
         float lensq = vx *vx +vy *vy;
         if (lensq==0){
           ddx += random(1);
           ddy += random(1);
         } else if(lensq <100*100){
           ddx += vx / lensq;
           ddy += vy / lensq;
         }
       }
     }
     
     float dlen = mag(ddx, ddy) / 2;
     if (dlen >0){
       dx+= ddx /dlen;
       dy+= ddy /dlen;
     }
   }
   
   void update(){
     if(!fixed){
       x += constrain(dx, -5, 5);
       y += constrain(dy, -5, 5);
       
       x = constrain(x, 0, width);
       y = constrain(y, 0, height);
     }
     dx /= 2;
     dy /= 2;
   }
   
   void draw(){
     if (selection == this){
       fill(selectColor);
     }else if(fixed){
       fill(fixedColor);
     }else{
       fill(nodeColor);
     }
     
     stroke(0);
     strokeWeight(0.5);
     
     rectMode(CORNER);
     float w = textWidth(label) +10;
     float h = textAscent() + textDescent() + 4;
     rect(x- w/2, y-h/2, w, h);
     
     fill(0);
     textAlign(CENTER, CENTER);
     text(label, x, y);
   }
}