C# winform check if control is physicaly visible

Question

Is it possible to determine if at least one pixel of a control can be seen (by a property or maybe using event notification).

NB : I am not looking for the Visible p

Answer 1

Inspired by Hans's answer I've implemented this behavior in this way;

    [DllImport("user32.dll")]
    static extern IntPtr WindowFromPoint(POINT Point);

    [StructLayout(LayoutKind.Sequential)]
    public struct POINT
    {
        public int X;
        public int Y;

        public POINT(int x, int y)
        {
            this.X = x;
            this.Y = y;
        }

        public static implicit operator System.Drawing.Point(POINT p)
        {
            return new System.Drawing.Point(p.X, p.Y);
        }

        public static implicit operator POINT(System.Drawing.Point p)
        {
            return new POINT(p.X, p.Y);
        }
    }

    public static bool IsControlVisibleToUser(this Control control)
    {
        var pos = control.PointToScreen(control.Location);
        var pointsToCheck = new POINT[]
                                {
                                    pos,
                                    new Point(pos.X + control.Width - 1, pos.Y),
                                    new Point(pos.X, pos.Y + control.Height - 1),
                                    new Point(pos.X + control.Width - 1, pos.Y + control.Height - 1),
                                    new Point(pos.X + control.Width/2, pos.Y + control.Height/2)
                                };

        foreach (var p in pointsToCheck)
        {
            var hwnd = WindowFromPoint(p);
            var other = Control.FromChildHandle(hwnd);
            if (other == null)
                continue;

            if (control == other || control.Contains(other))
                return true;
        }

        return false;
    }