How can I check if a form is behind another window? - winforms

Question

Is there a property for a form that I can check to know when it is behind another window?
I have an OpenGL based virtual environment running inside a form.
I would like to be able to ignore the mouse when clicking on another window that is on top of this form.
I looked at this thread but the title of the question does not match the answer.

Answer 1

Hans is, as always, right. Pinvoke is your friend here.. I found a solution to my needs in the msdn forum, this method uses a number of WinAPI-calls to determine if a window is overlapped. I did some minor modifications to enable ignoring certain handles. The method returns true as long as another window is overlapping it slightly, you may need to make your own modifications..
private const int GW_HWNDPREV = 3;
[DllImport("user32.dll")]
private static extern IntPtr GetWindow(IntPtr hWnd, int uCmd);
[DllImport("user32.dll", SetLastError = true)]
[return: MarshalAs(UnmanagedType.Bool)]
private static extern bool GetWindowRect(IntPtr hWnd, ref RECT lpRect);
[DllImport("user32.dll")]
private static extern bool IntersectRect(out RECT lprcDst, [In] ref RECT lprcSrc1, [In] ref RECT lprcSrc2);
[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
private static extern bool IsWindowVisible(IntPtr hWnd);
public static bool IsWindowOverlapped(IntPtr hWnd, HashSet<IntPtr> ignoreHandles)
{
if (hWnd == IntPtr.Zero)
return false; //throw new InvalidOperationException("Window does not yet exist");
if (!IsWindowVisible(hWnd))
return false;
HashSet<IntPtr> visited = new HashSet<IntPtr> { hWnd };
//The set is used to make calling GetWindow in a loop stable by checking if we have already
//visited the window returned by GetWindow. This avoids the possibility of an infinate loop.
RECT thisRect = new RECT();
GetWindowRect(hWnd, ref thisRect);
while ((hWnd = GetWindow(hWnd, GW_HWNDPREV)) != IntPtr.Zero && !visited.Contains(hWnd))
{
visited.Add(hWnd);
if (ignoreHandles != null && ignoreHandles.Contains(hWnd))
continue;
RECT testRect, intersection;
testRect = intersection = new RECT();
if (IsWindowVisible(hWnd) && GetWindowRect(hWnd, ref testRect) && IntersectRect(out intersection, ref thisRect, ref testRect))
return true;
}
return false;
}