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//***********************************************************
//This gives us the ability to resize the borderless from any borders instead of just the lower right corner
protected override void WndProc(ref Message m)
{
    const int wmNcHitTest = 0x84;
    const int htLeft = 10;
    const int htRight = 11;
    const int htTop = 12;
    const int htTopLeft = 13;
    const int htTopRight = 14;
    const int htBottom = 15;            
    const int htBottomLeft = 16;
    const int htBottomRight = 17;          

    if (m.Msg == wmNcHitTest)
    {
        int x = (int)(m.LParam.ToInt64() & 0xFFFF);
        int y = (int)((m.LParam.ToInt64() & 0xFFFF0000) >> 16);
        Point pt = PointToClient(new Point(x, y));
        Size clientSize = ClientSize;
        ///allow resize on the lower right corner
        if (pt.X >= clientSize.Width - 16 && pt.Y >= clientSize.Height - 16 && clientSize.Height >= 16)
        {           
            m.Result = (IntPtr)(IsMirrored ? htBottomLeft : htBottomRight);
            return;
        }       
        ///allow resize on the lower left corner
        if (pt.X <= 16 && pt.Y >= clientSize.Height - 16 && clientSize.Height >= 16)
        {
            m.Result = (IntPtr)(IsMirrored ? htBottomRight : htBottomLeft);
            return;
        }
        ///allow resize on the upper right corner
        if (pt.X <= 16 && pt.Y <= 16 && clientSize.Height >= 16)
        {
            m.Result = (IntPtr)(IsMirrored ? htTopRight : htTopLeft);
            return;
        }
        ///allow resize on the upper left corner
        if (pt.X >= clientSize.Width - 16 && pt.Y <= 16 && clientSize.Height >= 16)
        {
            m.Result = (IntPtr)(IsMirrored ? htTopLeft : htTopRight);
            return;
        }
        ///allow resize on the top border
        if (pt.Y <= 16 && clientSize.Height >= 16)
        {
            m.Result = (IntPtr)(htTop);
            return;
        }
        ///allow resize on the bottom border
        if (pt.Y >= clientSize.Height - 16 && clientSize.Height >= 16)
        {
            m.Result = (IntPtr)(htBottom);
            return;
        }
        ///allow resize on the left border
        if (pt.X <= 16 && clientSize.Height >= 16)
        {
            m.Result = (IntPtr)(htLeft);
            return;
        }
        ///allow resize on the right border
        if (pt.X >= clientSize.Width - 16 && clientSize.Height >= 16)
        {
            m.Result = (IntPtr)(htRight);
            return;
        }
    }
    base.WndProc(ref m);
}
//***********************************************************
//***********************************************************
//This gives us the ability to drag the borderless form to a new location
public const int WM_NCLBUTTONDOWN = 0xA1;
public const int HT_CAPTION = 0x2;

[DllImportAttribute("user32.dll")]
public static extern int SendMessage(IntPtr hWnd, int Msg, int wParam, int lParam);
[DllImportAttribute("user32.dll")]
public static extern bool ReleaseCapture();

private void YOURCONTROL_MouseDown(object sender, MouseEventArgs e)
{
    //ctrl-leftclick anywhere on the control to drag the form to a new location 
    if (e.Button == MouseButtons.Left && Control.ModifierKeys == Keys.Control)
    {       
        ReleaseCapture();
        SendMessage(Handle, WM_NCLBUTTONDOWN, HT_CAPTION, 0);
    }  
}
//***********************************************************
//***********************************************************
//This gives us the drop shadow behind the borderless form
private const int CS_DROPSHADOW = 0x20000;
protected override CreateParams CreateParams
{
    get
    {
        CreateParams cp = base.CreateParams;
        cp.ClassStyle |= CS_DROPSHADOW;
        return cp;
    }
}
//***********************************************************