In general that would be math or colors. Check out:

• https://forum.processing.org/topic/how-can-i-find-the-area-of-an-overlapped-region-with-processing
• https://forum.processing.org/topic/find-all-shapes-from-2-intersecated-rects

Are the squares straight or rotated?

Hi, Amnon, assuming the squares are straight, how to realize it?

Thanks!

This is actually not as easy as it may seem. You need the correct points and the correct lines. Which is hard because you don't know how the rectangles will intersect. So each point can be lost and each line can be broken. Here is one way to do it.

Code Example

1. PVector p1 = new PVector(300, 300);
2. PVector p2 = new PVector();
3. float w1 = 150;
4. float h1 = 200;
5. float w2 = 200;
6. float h2 = 150;
7.  
8. void setup() {
9.   size(800, 800);
10.   noFill();
11. }
12.  
13. void draw() {
14.   p2.set(mouseX, mouseY, 0);
15.   background(255);
16.   stroke(0);
17.   strokeWeight(1);
18.   rect(p1.x, p1.y, w1, h1);
19.   rect(p2.x, p2.y, w2, h2);
20.  
21.   if (rectCollision(p1, w1, h1, p2, w2, h2)) {
22.     ArrayList <PVector> vecs = new ArrayList <PVector> ();
    
23.     addPoint(vecs, new PVector(p1.x, p1.y));
24.     addPoint(vecs, new PVector(p1.x+w1, p1.y));
25.     addPoint(vecs, new PVector(p1.x+w1, p1.y+h1));
26.     addPoint(vecs, new PVector(p1.x, p1.y+h1));
27.     addPoint(vecs, new PVector(p2.x, p2.y));
28.     addPoint(vecs, new PVector(p2.x+w2, p2.y));
29.     addPoint(vecs, new PVector(p2.x+w2, p2.y+h2));
30.     addPoint(vecs, new PVector(p2.x, p2.y+h2));
31.     addPoint(vecs, new PVector(max(p1.x, p2.x), max(p1.y, p2.y)));
32.     addPoint(vecs, new PVector(min(p1.x+w1, p2.x+w2), max(p1.y, p2.y)));
33.     addPoint(vecs, new PVector(max(p1.x, p2.x), min(p1.y+h1, p2.y+h2)));
34.     addPoint(vecs, new PVector(min(p1.x+w1, p2.x+w2), min(p1.y+h1, p2.y+h2)));
35.    
36.     stroke(0, 0, 255);
37.     strokeWeight(15);
38.     for (PVector v : vecs) {
39.       PVector hnb = neighbour(vecs, v, true);
40.       PVector vnb = neighbour(vecs, v, false);
41.       line(hnb.x, hnb.y, v.x, v.y);
42.       line(vnb.x, vnb.y, v.x, v.y);
43.     }
44.   }
45. }
46.  
47. boolean rectCollision(PVector p1, float w1, float h1, PVector p2, float w2, float h2) {
48.   return !(p1.x > p2.x + w2 || p1.x + w1 < p2.x || p1.y > p2.y + h2 || p1.y + h1 < p2.y);
49. }
50.  
51. void addPoint(ArrayList <PVector> list, PVector v) {
52.   boolean r1 = pointInRect(v, p1, w1, h1);
53.   boolean r2 = pointInRect(v, p2, w2, h2);
54.   if (!r1&&!r2) { list.add(v); }
55. }
56.  
57. boolean pointInRect(PVector v, PVector p, float w, float h) {
58.   return (v.x > p.x && v.x < p.x+w && v.y > p.y && v.y < p.y+h);
59. }
60.  
61. PVector neighbour(ArrayList <PVector> list, PVector p, boolean horizontal) {
62.   ArrayList <PVector> neighbours = new ArrayList <PVector> ();
63.   for (PVector v : list) {
64.     if (v!=p) {
65.       if (horizontal) { if (v.y==p.y) { neighbours.add(v); } }
66.       else { if (v.x==p.x) { neighbours.add(v); } }
67.     }
68.   }
69.   if (neighbours.size()==1) {
70.     return neighbours.get(0);
71.   } else {
72.     PVector v1 = neighbours.get(0);
73.     float d1 = v1.dist(p);
74.     for (int i=1; i<neighbours.size(); i++) {
75.       PVector v2 = neighbours.get(i);
76.       float d2 = v2.dist(p);
77.       if (d2<d1) {
78.         d1 = d2;
79.         v1 = v2;
80.       }
81.     }
82.     return v1;
83.   }
84. }

Thank you very much, Amnon!

This is exactly what I'd like to realize.

I'll read through your code and digest the method you use.