float theta;
PVector head,tail;
Boolean dragging;
ArrayList ALPHA_PLUSes;
int centreHole;

void setup(){
  size(980,490);
  
  ALPHA_PLUSes = new ArrayList();
  
  tail = new PVector();
  head = new PVector();
  
  dragging = true;
}

void draw(){
  background(0);
  
  //draw nucleus
  pushMatrix();
  translate(width/2,height/2);
  
  noStroke();
  fill(100,0,255);
  ellipse(0,0,20,20);
  
  popMatrix();
  
  //draw arrow  
  if (dragging == true){
    
    theta = atan2(head.x-tail.x,tail.y-head.y);
    
    stroke(255);
    line(tail.x,tail.y,head.x,head.y);
    
    pushMatrix();
    translate(head.x,head.y);
    rotate(theta);
    line(0,0,10,10);
    line(0,0,-10,10);
    popMatrix();
  }
  
  for (int i = ALPHA_PLUSes.size()-1; i>=0; i--) {
    ALPHA_PLUS OBJECT = (ALPHA_PLUS) ALPHA_PLUSes.get(i);
    OBJECT.move();
    OBJECT.display();
    OBJECT.show_trails();
  }
  
  status("Frame Rate: "+str(round(frameRate)));
}

void mousePressed(){
  tail = new PVector(mouseX,mouseY);
  head = new PVector(mouseX,mouseY);
  dragging = true;
}

void mouseDragged(){
  head = new PVector(mouseX,mouseY);
}

void mouseReleased(){
  head.sub(tail);
  head.div(40);
  dragging = false;
  
  ALPHA_PLUSes.add(new ALPHA_PLUS(tail,head));
}