box

int d=180, num=250, l=100, v=3;
PVector[] location = new PVector[num];
PVector[] velocity = new PVector[num];
float r=-.25, sz=15;

void setup() {
  size(500, 500, P3D);
  colorMode(HSB, 360, 100, 100);
  smooth(8);
  sphereDetail(30);
  for (int i=0; i<num; i++) {
    location[i] = new PVector(random(-l, l), random(-l, l), random(-l, l));
    velocity[i] = new PVector(random(-v, v), random(-v, v), random(-v, v));
  }
}

void draw() {
  randomSeed(1234);
  background(#000000);
  for (int i=0; i<num; i++) {
    location[i].add(velocity[i]);
  }
  translate(width/2, height/2, -170);
  rotateY(r);
  noFill();
  stroke(#ffffff, 150);
  box(2*d, 2*d, 2*d);
  for (int i=0; i<num; i++) {
    pushMatrix();
    translate(location[i].x, location[i].y, location[i].z);
    if (location[i].x<-d+sz || location[i].x>d-sz) velocity[i].x *= -1;
    if (location[i].y<-d+sz || location[i].y>d-sz) velocity[i].y *= -1;
    if (location[i].z<-d+sz || location[i].z>d-sz) velocity[i].z *= -1;
    noStroke();
    fill(random(180,360), 90, 90);
    //fill(255);
    lights();
    sphere(sz);
    popMatrix();
  }

  r += 0.005;
  //saveFrame("image-###.tif");
  //if (frameCount>130) noLoop();
}