Split wxPanel in wxPanelBase and platform-specific files.

So far we have only wxMSW-specific implementation (and also a trivial
wxUniv-specific one) but it's still tidier to have all platform-specific code
in separate files, especially as we're going to have more of it for wxMSW
soon.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67251 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/panel.cpp

@@ -0,0 +1,46 @@
+///////////////////////////////////////////////////////////////////////////////
+// Name:        src/msw/panel.cpp
+// Purpose:     Implementation of wxMSW-specific wxPanel class.
+// Author:      Vadim Zeitlin
+// Created:     2011-03-18
+// RCS-ID:      $Id: wxhead.cpp,v 1.11 2010-04-22 12:44:51 zeitlin Exp $
+// Copyright:   (c) 2011 Vadim Zeitlin <vadim@wxwidgets.org>
+// Licence:     wxWindows licence
+///////////////////////////////////////////////////////////////////////////////
+
+// ============================================================================
+// declarations
+// ============================================================================
+
+// ----------------------------------------------------------------------------
+// headers
+// ----------------------------------------------------------------------------
+
+// for compilers that support precompilation, includes "wx.h".
+#include "wx/wxprec.h"
+
+#ifdef __BORLANDC__
+    #pragma hdrstop
+#endif
+
+#ifndef WX_PRECOMP
+    #include "wx/panel.h"
+#endif // WX_PRECOMP
+
+// ============================================================================
+// implementation
+// ============================================================================
+
+bool wxPanel::HasTransparentBackground()
+{
+    for ( wxWindow *win = GetParent(); win; win = win->GetParent() )
+    {
+        if ( win->MSWHasInheritableBackground() )
+            return true;
+
+        if ( win->IsTopLevel() )
+            break;
+    }
+
+    return false;
+}