// ----------------------------------------------------------------------------
// The hierarchy of scrolling classes is a bit complicated because we want to
// put as much functionality as possible in a mix-in class not deriving from
// wxWindow so that other classes could derive from the same base class on all
// platforms irrespectively of whether they are native controls (and hence
// don't use our scrolling) or not.
//
// So we have
//
//                           wxScrollHelperBase
//                                   |
//                                   |
//                                  \|/
//      wxWindow               wxScrollHelper
//       |  \                   /        /
//       |   \                 /        /
//       |    _|             |_        /
//       |     wxScrolledWindow       /
//       |                           /
//      \|/                         /
//   wxControl                     /
//         \                      /
//          \                    /
//           _|                |_
//            wxScrolledControl
//
// ----------------------------------------------------------------------------