Check if a control is partially covered by another window

Check if a control is partially covered by another window

You would have to iterate over all windows above yours in Z-order and
check for each window you find if it has the WS_EX_TOPMOST exstyle set
and is visible.
If it has, you have to get its window rectangle (GetWindowRect) and test
if that overlaps your window.

Example:


procedure TForm1.Button1Click(Sender: TObject);
var
  wnd: HWND;

  function IsTopMost(wnd: HWND): Boolean;
  begin
    Result := (GetWindowLong(wnd, GWL_EXSTYLE) and WS_EX_TOPMOST) <> 0;
  end;

  procedure logWindowInfo(wnd: HWND);
  const
    visString: array[Boolean] of string = ('not ', '');
  var
    buffer: array[0..256] of Char;
    r:      TRect;
  begin
    if wnd = 0 then Exit;
    GetClassName(wnd, buffer, SizeOf(buffer));
    with Memo1.Lines do
    begin
      Add(Format(' Window of class %s ', [buffer]));
      GetWindowRect(wnd, r);
      Add(Format(' at (%d,%d):(%d,%d)', [r.Left, r.Top, r.Right, r.Bottom]));
      Add(Format(' Window is %svisible', [visString[IsWindowVisible(wnd)]]));
      Add(Format(' Window is %stopmost', [visString[IsTopmost(wnd)]]));
    end;
  end;

begin
  Memo1.Clear;
  wnd := Handle;
  repeat
    wnd := GetNextWindow(wnd, GW_HWNDPREV);
    LogWindowInfo(wnd);
  until wnd = 0;
  Memo1.Lines.Add('End log.');
end;