I was dreaming about this all my life:
create a 3D sphere in a box moving there and be reflected by the walls.

Thanks to processing I finally was able to do this. Thank you.

That's maybe the starting point for a 3D pong game (which already exists, I know...).

1. //
2. // vars ====================================================
3. // Creating an array of objects.
4. Mover[] movers = new Mover[1];
5. // main functions ========================================
6. void setup() {
7.   // automatic init
8.   size(displayWidth, displayHeight, OPENGL );
9.   fill(204);
10.   movers[0] = new Mover();
11.   //
12.   sphereDetail(15);
13. } // function
14. void draw() {
15.   // automatically loops
16.   background ( 0, 0, 54 );
17.   lights();
18.   // camera
19.   camera( 110, 150, 430, // eyeX, eyeY, eyeZ   
20.   150, 150, -100, // centerX, centerY, centerZ      
21.   0.0, 1.0, 0.0 );       // upX, upY, upZ  
22.   // Big Game Box
23.   BigGameBox ();
24.   int i = 0;
25.   movers[i].update();
26.   movers[i].checkEdges();
27.   movers[i].display();
28. } // function
29. // ------------------------------------------------------------
30. void BigGameBox () {
31.   noStroke();
32.   fill(122);
33.   // left wall 
34.   beginShape ();
35.   vertex (0, 0, 0);
36.   vertex (0, 0, -300); 
37.   vertex (0, 300, -300);   
38.   vertex (0, 300, 0 );   
39.   endShape(CLOSE);
40.   fill(22);
41.   // Wall in the back
42.   beginShape ();
43.   vertex (0, 0, -300); 
44.   vertex (0, 300, -300);   
45.   vertex (300, 300, -300 );   
46.   vertex (300, 0, -300);   
47.   endShape(CLOSE);
48.   fill(222);
49.   // Right wall
50.   beginShape ();
51.   vertex (300, 300, -300 );   
52.   vertex (300, 0, -300);   
53.   vertex (300, 0, 0);     
54.   vertex (300, 300, 0);       
55.   endShape(CLOSE);
56.   fill(254);
57.   // floor
58.   beginShape ();
59.   vertex (0, 300, 0 );   
60.   vertex (300, 300, 0);   
61.   vertex (300, 300, -300);     
62.   vertex (0, 300, -300);       
63.   endShape(CLOSE);
64.   fill(2);
65.   // ceiling
66.   beginShape ();
67.   vertex (0, 0, 0 );   
68.   vertex (300, 0, 0);   
69.   vertex (300, 0, -300);     
70.   vertex (0, 0, -300);       
71.   endShape(CLOSE);
72. }
73. // ------------------------------------------------------------
74. class Mover {
75.   // the sphere
76.   PVector location;
77.   PVector velocity;
78.   // PVector acceleration;
79.   float topspeed;
80.   int radius = 30;
81.   Mover() {
82.     location = new PVector (100, 60, -100); //  (random(width),random(height));
83.     velocity = new PVector(3, 3, 10);
84.     topspeed = 4;
85.   }
86.   void update() {
87.     velocity.limit(topspeed);
88.     location.add(velocity);
89.   }
90.   void display() {
91.     fill(175);
92.     SphereParameters(location.x, location.y, location.z, radius);
93.   }
94.   void checkEdges() {
95.     // We still sometimes need to refer to the individual components of a PVector
96.     // and can do so using the dot syntax (location.x, velocity.y, etc.)
97.     if (location.x+radius > 300) {
98.       velocity.x = abs(velocity.x) * -1;
99.     }
100.     else if (location.x-radius <= 0) {
101.       velocity.x = abs ( velocity.x );
102.     }
103.     //
104.     if (location.y+radius > 300) {
105.       velocity.y = abs ( velocity.y ) * -1;
106.     }
107.     else if (location.y-radius < 0) {
108.       velocity.y = abs ( velocity.y );
109.     }
110.     //
111.     if (location.z-radius < -300) {
112.       velocity.z = abs ( velocity.z ) ;
113.     }
114.     else if (location.z+radius > -10) {
115.       velocity.z = - abs ( velocity.z );
116.     }
117.   }
118.   //
119.   void SphereParameters ( float x, float y, float z,
120.   float w ) {
121.     // Position and size of a sphere
122.     noStroke();
123.     pushMatrix();
124.     translate ( x, y, z );
125.     sphere ( w );
126.     popMatrix();
127.   } // function
128.   //
129. }// class
130. //