public void add(int count,float x, float y) //x y为小人坐标
    {
        add(count, Left_Top,x,y);
        add(count, Left_Bottom,x,y);
        add(count, Right_Top, x,y);
        add(count, Right_Bottom, x,y);
    }
    
    public void add(int count,int dir,float sx, float sy)
    {
        //Random random = new Random();
        for (int i = 0; i < count; i++)
        { 
            int x = 0,y = 0;  //子弹坐标
            double v_x = 0;   //子弹速度
            double v_y = 0;
            double t;
            switch (dir)    //判断从哪个角发出
            {    
                case Left_Top:
                    x = 0; y = 0;
                    t = sx / Math.sqrt(sx * sx + sy * sy);
                    v_x = 3 * t;
                    v_y = -3 * Math.sqrt(1 * t * t);
                    break;
                case Left_Bottom:
                    x = 0; y = 480;
                    sy = 480 - sy;
                    t = sx / Math.sqrt(sx * sx + sy * sy);
                    v_x = 3 * t;
                    v_y = 3 * Math.sqrt(1 * t * t);
                    break;
                case Right_Top:
                    x = 320; y = 0;
                    sx = 320 - sx;
                    t = sx / Math.sqrt(sx * sx + sy * sy);
                    v_x = -3 * t;
                    v_y = -3 * Math.sqrt(1 * t * t);
                    break;
                case Right_Bottom:
                    x = 320; y = 480;
                    sy = 480 - sy;
                    sx = 320 - sx;
                    t = sx / Math.sqrt(sx * sx + sy * sy);
                    v_x = -3 * t;
                    v_y = 3 * Math.sqrt(1 * t * t);
                    break;
                default:
                    break;
            }
            Particle particle = new Particle(v_y, v_x, x, y);
            particleSet.add(particle);
        }
    }