I'd like to draw the trail for each of a group of bouncing points, but I can't get it work by using begainShape/endShape. No continuous line segments are created, instead points are still shown as individual points.

I assume the problem is related to the arraylist to store position history ...

Advices are appreciated!

reference for drawing bouncing points: "The Nature of Code" Exercise 2.1
reference for drawing trail from "Form and Code":
http://formandcode.com/code-examples/simulate-particles



code: (pls hit the "p" key after lunching the code to switch to line mode)

1. // keys:
2. // [space] : toggle animation
3. // [p]     : toggle point or line
4. 
   
5. Mover[] movers = new Mover[50];
6. boolean animationToggle = false;
7. boolean displayPt = true;
8. void setup(){
9.   size(700,350);
10.   for(int i=0; i<movers.length; i++){
11.     movers[i] = new Mover(random(0.5,3),
12.                           new PVector(random(0,width), random(0,height/2)),
13.                           color(floor(random(255)),floor(random(255)),floor(random(255)))
14.                          );
15.   }
16. }
17. void draw() {
18.   PVector wind = new PVector(0.03,0);
19.   PVector gravity = new PVector(0,0.4);
20.  
21.   if (animationToggle == true){
22.     //___op1: with tail
23.     //fill(0,10);
24.     //rect(0,0,width,height);
25.     //___op2: no tail
26.     //background(0);
27.    
28.     for(int i=0; i<movers.length; i++){
29.       movers[i].applyForce(wind);
30.       movers[i].applyForce(gravity);
31.       movers[i].update();
32.       movers[i].display();
33.       movers[i].checkEdges();
34.     }
35.   }
36. }
37. class Mover{
38.  
39.   PVector location;
40.   PVector velocity;
41.   PVector acceleration;
42.   float mass;
43.   color c;
44.   ArrayList<PVector> hist; //array list to store position history
45.   int cnt = 0; //counter
46.   Mover(float m_, PVector loc_, color c_) {
47.     location = new PVector(loc_.x, loc_.y);
48.     velocity = new PVector(0,0);
49.     acceleration = new PVector(0,0);
50.     mass = m_;
51.     c = c_;
52.     hist = new ArrayList<PVector>();
53.     hist.add(location);
54.   }
55.  
56.   void applyForce(PVector force){
57.     PVector f = PVector.div(force,mass);
58.     acceleration.add(f);
59.   }
60.  
61.   void update() {
62.     velocity.add(acceleration);
63.     location.add(velocity);
64.     acceleration.mult(0);
65. //    //_____op1: save location every 10 frames
66. //    if (frameCount % 10 == 0 && cnt<hist.size()) {
67. //      hist.add(location);
68. //      cnt++;
69. //    }
70.     //_____op2: save location every frames
71.     hist.add(location);    
72.   }
73.  
74.   void display() {
75.     noStroke();
76.     fill(c);
77.     if (displayPt == true){// draw pt
78.       ellipse(location.x,location.y,mass*10,mass*10);//scale by mass
79.     } else {// draw line
80.       noFill();
81.       stroke(255);
82.       strokeWeight(3);
83.       beginShape();
84.         for (int i=0; i<hist.size(); i++) {
85.           vertex(hist.get(i).x, hist.get(i).y);
86.         }
87.         vertex(location.x, location.y);
88.       endShape();      
89.     }
90.   }
91.   void checkEdges() {
92.     if (location.x > (width-mass*5)) {
93.       location.x = width-mass*5;
94.       velocity.x *= -1;
95.     } else if (location.x < (0-mass*5)) {
96.       velocity.x *= -1;
97.       location.x = mass*5;
98.     }
99.     if (location.y > (height-mass*5)) {
100.       velocity.y *= -1;
101.       location.y = height-mass*5;
102.     }
103.   }
104.  
105. }
106. void keyPressed(){
107.   if ( key == ' ' ) {
108.     animationToggle = (animationToggle == true) ? (false):(true);
109.   } 
110.  
111.   if ( key == 'p' ) {
112.     displayPt = (displayPt == true) ? (false):(true);
113.   }
114. }