C# 透明控件（WinForm）

 public partial class tspControl : UserControl
    {
        public tspControl()
        {
            InitializeComponent();
            SetStyle(ControlStyles.SupportsTransparentBackColor
              | ControlStyles.UserPaint
              | ControlStyles.AllPaintingInWmPaint
              | ControlStyles.Opaque, true);
            this.BackColor = Color.Transparent;
        }       

        private Image img;
        public Image Image
        {
            get
            {
                return img;
            }
            set
            {
                img = value;
            }
        }

        protected override void OnLocationChanged(EventArgs e)
        {
            //base.OnLocationChanged(e);
            Visible = false;
            Visible = true;
        }

        protected override CreateParams CreateParams
        {
            get
            {
                //return base.CreateParams;
                CreateParams cp = base.CreateParams;
                cp.ExStyle |= 0x00000020; //WS_EX_TRANSPARENT
                return cp;
            }
        }
        protected override void OnPaint(PaintEventArgs pe)
        {
            if (img != null)
            {
                base.OnPaint(pe);
                pe.Graphics.DrawImage(img, 0, 0);
            }
            else
            {

            }
        }
    }

//注：如果是手动改变图片，最好在刷新一下界面(this.Refresh()；)，记着图片要是透明的才能实现透明
把上面的控件添加到窗体上，下面的方法是改为这个控件上和图片使图片的Color.White透明，如果控件上的Image为NULL，则全透明，
private void btn_OpenImg_Click(object sender, EventArgs e)
        {
            OpenFileDialog opf = new OpenFileDialog();
            if (opf.ShowDialog() == DialogResult.OK)
            {
                Bitmap bit=new Bitmap(opf.FileName);
                bit.MakeTransparent(Color.White);
                tspControl1.Image = bit;
                this.Refresh();
            }
        }