if we have wxBG_STYLE_PAINT, we must clear the background ourselves, since on OSX there might be transparent subpanels, fixes #11958

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64055 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/splitter.cpp

@@ -194,6 +194,12 @@ void wxSplitterWindow::SetResizeCursor()
 void wxSplitterWindow::OnPaint(wxPaintEvent& WXUNUSED(event))
 {
     wxPaintDC dc(this);
+#ifdef __WXOSX__
+    // as subpanels might have a transparent background we must erase the background
+    // at least on OSX, otherwise traces of the sash will remain 
+    // test with: splitter sample->replace right window
+    dc.Clear();
+#endif
 
     DrawSash(dc);
 }