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

I somewhat finished the answer by Hans Passant. The function below tests for all four corners of the form.

        /// 

    /// determines if a form is on top and really visible.
    /// a problem you ran into is that form.invalidate returns true, even if another form is on top of it. 
    /// this function avoids that situation
    /// code and discussion:
    /// https://stackoverflow.com/questions/4747935/c-sharp-winform-check-if-control-is-physicaly-visible
    /// 
    /// 
    /// 
    public bool ChildReallyVisible(Control child)
    {
        bool result = false;

        var pos = this.PointToClient(child.PointToScreen(Point.Empty));

        result = this.GetChildAtPoint(pos) == child;
        //this 'if's cause the condition only to be checked if the result is true, otherwise it will stay false to the end
        if(result)
        {
            result = (this.GetChildAtPoint(new Point(pos.X + child.Width - 1, pos.Y)) == child);
        }
        if(result)
        {
            result = (this.GetChildAtPoint(new Point(pos.X, pos.Y + child.Height - 1)) == child);
        }
        if(result)
        {
            result = (this.GetChildAtPoint(new Point(pos.X + child.Width - 1, pos.Y + child.Height - 1)) == child) ;
        }
        return result;
    }