I am sorry, I don't understand your problem.

BTW, the loadImage() outside of setup() might not work...

loadImage outside setup always worked for me.

Ok, in setup i add 2 targets:

1. m.addTarget(100, 100)
2.   .addTarget(700, 700)

First it should move to the first added target, once it's there it should move back. Atm it doesn't move back.

Perhaps because you put your images in the sketch folder instead of the data folder...

if(target.x - pos.x < speed)

Your test is faulty when target.x is on the left of pos.x... It immediately goes to the next-next target. Obvious if you change the print out and add one:

1.     println(target.x + " " + pos.x);
2.     if(target.x - pos.x < speed) { // should take y in account as well
3.       println("Next");
4.       setNextTarget();
5.     }

i absoluted it now, works a bit better.
It can move to the 2nd goal now, after that it's nan.

1. Mirror m;
2. PImage bground;
3. PImage lspot;
4. void setup() {
5.   size(800, 800);
6.  
7.    bground = loadImage("essent.png");
8.  lspot = loadImage("lspot_01.png");
9.  
10.   m = new Mirror(50, 50);
11.  
12.   m.addTarget(100, 100)
13.   .addTarget(700, 700)
14.   .addTarget(300, 600)
15.   .setMaxSpeed(2);
16.   
17.    // frameRate(1);
18.  
19. }
20. void draw() {
21.   tint(255, 10);
22.   image(bground, 0, 0);
23.  
24.   m.update();
25.   m.draw();
26.  
27.   fill(0);
28.   ellipse(100, 100, 5, 5);
29.   ellipse(700, 700, 5, 5);
30.   ellipse(300, 600, 5, 5);
31.  
32. }
33. class Mirror {
34.   PVector pos;
35.   float maxSpeed = 1;
36.  
37.   ArrayList<PVector> targets = new ArrayList<PVector>();
38.   int targetIndex = 0;
39.   int targetDirection = 1;
40.   Mirror() {
41.   }
42.   Mirror(float x, float y) {
43.     pos = new PVector(x, y);
44.   }
45.   Mirror(PVector pos) {
46.     this.pos = pos;
47.   }
48.   // - - - - - - - - - - - - -
49.   Mirror setMaxSpeed(float maxSpeed) {
50.     this.maxSpeed = maxSpeed;
51.     return this;
52.   }
53.   // - - - - - - - - - - - - -
54.   Mirror addTarget(PVector t) {
55.     targets.add(t);
56.     return this;
57.   }
58.  
59.   // - - - - - - - - - - - - -
60.   Mirror addTarget(float x, float y) {
61.     targets.add(new PVector(x, y));
62.     return this;
63.   }
64.   // - - - - - - - - - - - - -
65.  
66.   void setNextTarget() {
67.     targetIndex += targetDirection;
68.     if(targetIndex >= targets.size() || targetIndex < 0) {
69.       targetDirection = -targetDirection;
70.       setNextTarget();
71.     }
72.   }
73.   // - - - - - - - - - - - - -
74.   void update() {
75.    
76.     PVector target = targets.get(targetIndex);
77.    
78.     float xDist = target.x - pos.x;
79.     float yDist = target.y - pos.y;
80.    
81.    
82.    
83.     /*
84.     println("targetIndex "+targetIndex);
85.     println("target.x: "+target.x);
86.     println("pos.x: "+pos.x);
87.     */
88.    // println(xDist+"\t"+yDist);
89.    
90.     float xStep, yStep;
91.    
92.     if(abs(xDist) > abs(yDist)) {
93.       xStep = xDist/ceil(abs(xDist)/maxSpeed);
94.       yStep = yDist/ceil(abs(xDist)/maxSpeed);
95.     } else {
96.       xStep = xDist/ceil(abs(yDist)/maxSpeed);
97.       yStep = yDist/ceil(abs(yDist)/maxSpeed);
98.     }
99.    
100.   //  println(xStep+"\t"+yStep);
101.    
102.     pos.x += xStep;
103.     pos.y += yStep;
104.    
105.     if(abs(target.x - pos.x) < 0.1 && abs(target.y - pos.y) < 0.1) {
106.       setNextTarget();
107.     }
108.    
109.    
110.    
111.   }
112.   // - - - - - - - - - - - - -
113.   void draw() {
114.     // blend(lspot, 0, 0, lspot.width, lspot.height, int(pos.x), int(pos.y), lspot.width, lspot.height, LIGHTEST);
115.     fill(255, 0, 0);
116.     ellipse(pos.x, pos.y, 5, 5);
117.   }
118.   // - - - - - - - - - - - - -
119. }

i'm really tired :(

I found the problem, it's in setNextTarget(),

i go work on it now. I just posted to prevend someone wasting time.

---edit:

solution:

1. void setNextTarget() {
2.     targetIndex += targetDirection;
3.     if(targetIndex == targets.size() || targetIndex < 0) {
4.       targetDirection = -targetDirection;
5.       targetIndex += targetDirection*2;
6.     }
7.    
8.   }