C#自訂控制項背景色透明的方法

I struggled for ages with the problem of having controls show through a control that was painted on top of them.  It seems that ControlStyles.SupportsTransparentBackColor just allowed the control to pick up the container's background colour/image and wouldn't prevent the control from hiding any controls that were underneath it. I eventually found an answer so I thought I would post it here.  This code example of a Pointer class, will take an alpha-blended png in the constructor and allow all the controls behind it to show through the transparent or semi-transparent pixels in the png, even when the pointer's location is changed ...

public class Pointer : Control{    public Pointer(Image image)        : base()    {        Image = image;        SetStyle(ControlStyles.SupportsTransparentBackColor          | ControlStyles.UserPaint          | ControlStyles.AllPaintingInWmPaint          | ControlStyles.Opaque, true);        BackColor = Color.Transparent;    }    protected override void OnLocationChanged(EventArgs e)    {        // pick up the container's surface again.         Visible = false;        Visible = true;    }    protected override CreateParams CreateParams    {        get        {            CreateParams cp = base.CreateParams;            cp.ExStyle |= 0x00000020; //WS_EX_TRANSPARENT             return cp;        }    }    private Image image;    public Image Image    {        get        {            return image;        }        set        {            image = value;            Size = image.Size;        }    }    protected override void OnPaint(PaintEventArgs pe)    {        base.OnPaint(pe);        pe.Graphics.DrawImage(image, 0, 0);    }}