SOURCE

var balls = []

function setup(){
  createCanvas(400, 200)
}

function draw(){
  background(0)
  var r1 = random(10)
  var r2 = random(9, 10)
  
  if(r1 > r2){
    balls.push( new ball() ) 
  }
  
  for(let i=balls.length-1; i>=0; i--){
    balls[i].run();
    if(balls[i].isRemove()){
      balls.splice(i, 1)
    }
  }
  
}


class ball {
  constructor(){
    // 位置向量
    this.location = createVector(random(190, 205), 150);
    
    // x移动时速度向量
    this.velocity = createVector(random(0.4, 0.6))
    
    // x-- or x++
    this.ab = floor(random(1, 3));
    
    // 随机的力
    this.f = random(3, 5);
    
    // color
    this.c = createVector(random(255), random(255), random(255))
  }
  
  run(){
    this.update(this.location, this.velocity)
    this.show(this.location, this.c)
  }
  
  show(l, c){
    stroke(c.x, c.y, c.z)
    noFill()
    ellipse(l.x, l.y, 10, 10)
  }
  
  update(l,v){
    
    if( this.isDown() ){
      
      this.leftORtight(l, v);
      l.y -= this.f;
      
    }else{
      
      this.leftORtight(l, v);
      l.y += -this.f
      
    }
    
    this.f -= 0.16;
  }
  
  leftORtight(l, v){
    if(this.ab < 2){
        l.x += v.x
      }else{
        l.x -= v.x
      }
  }
  
  // 什么时候落下，没有力自然就落下了
  isDown(){
    return this.f >= 0;
  }
  
  // 什么时候清空内存
  isRemove(){
    return this.location.y > height
  }
  
}