Im  trying to make a micro-game where squares are falling from the sky and you have to avoid them and get to the top. if you make it to the top, an image will appear congratulating you. If you run into another square, however, an image will appear telling you you lost. I can't figure out how to code the collision though. Any ideas?

2. /* preload="grid.jpg" */
3. /* preload="sheen.jpg" */
4. /* preload="losing.jpg" */
5. 
   
6. PImage losing;
7. PImage sheen;
8. PImage grid;
9. int[] rectX = {10, 36, 63, 185, 210, 250, 340, 375, 300, 400, 460, 460, 475, 520, 555, 600, 625, 655, 725, 150, 770, 680};
10. int[] rectY = {10, 690, 320, 28, 165, 730, 385, 75, 610, 15, 280, 565, 700, 35, 360, 200, 450, 630, 350, 400, 30, 700};
11. int rectSize = 25;
12. int playerX = 400;
13. int playerY = 775;
14. int edge = 2;
15. int inner = edge;
16. 
    
17. void setup() {
18.   losing = loadImage("losing.jpg");
19.   sheen = loadImage("sheen.jpg");
20.   grid = loadImage("grid.jpg");
21.   size(800,800);
22.   image(grid, 0, 0);
23.   
24. }
25.   
26.   void draw() {
27.   fill(255); //player avatar & glow effect
28.   strokeWeight(2);
29.   stroke(134,250,255);
30.   filter(BLUR);
31.   rect(playerX,playerY,20,20);
32.   playerX = constrain(playerX, inner, width - inner);
33.   playerY = constrain(playerY, inner, height - inner);
34.   
35. 
    
36. 
    
37.   
38.   fill(0); //AI avatars
39.   strokeWeight(3);
40.   stroke(255,145,6);
41.   for(int i = 0; i < rectX.length; i++){
42.   rect(rectX[i], rectY[i], rectSize, rectSize);
43.  rectY[i]+=25;
44.    rectY[i]%=height;
45.      if(playerY < 5){
46.   image(sheen,0,0);
47.   } 
48. 
    
49.   }
50.   }
51. 
    
52.   
53.   
54. void keyPressed() {
55.   if (keyCode == UP) {
56.     playerY = playerY - 7;
57.   }  
58.     if (keyCode == RIGHT) {
59.     playerX = playerX + 7;
60.   }  
61.     if (keyCode == LEFT) {
62.     playerX = playerX - 7;
63.   }  
64.     if (keyCode == DOWN) {
65.     playerY = playerY + 7;
66.   }   
67. }