Just started to get into processing and I've hit a bit of stumbling block. I'm trying to create a menu where you select an image and information appear, but as of now I'm just having difficulty making a white shape over one of the images change its opacity when I hover over the certain image. If I run the shape section without the image code it works perfectly but when I integrate it either nothing happens (when noLoop is on) or one of the images fades to black (when loop is on). Very confused and I've hit a  block in trying to solve the problem. 

This may be a really simple problem but it's got me stumped, thanks anyone who can guide me on this. 

1. 
   
2. PImage a, b;
3. int x = 0;
4. int y = 250;
5. int w = 500;
6. int h = 250;
7. 
   
8. void setup() {
9.   size(500, 500);
10.   b = loadImage("rathmines.jpg");
11.   a = loadImage("jamesjoyce.jpg");
12.   noLoop();
13. }
14. 
    
15. void draw() {
16.   background(255);
17.   loop();
18.   if (mouseX > x && mouseX < x + w && mouseY > y && mouseY < y + h) {
19. 
    
20.     fill(0);
21.   } 
22.   else {
23. 
    
24.     fill(175);
25.   }
26.   rect(x, y, w, h);
27.   noLoop();
28.   a.resize(0, 600);
29.   image(a, -10, 230);
30.   image(b, 0, -170);
31.   line(0, height/2, width, height/2);
32. }