add GraphicsWindow::GetHwnd

stepmania/src/archutils/Win32/GraphicsWindow.cpp

@@ -413,6 +413,11 @@ void GraphicsWindow::Update()
 	}
 }
 
+HWND GraphicsWindow::GetHwnd()
+{
+	return g_hWndMain;
+}
+
 /*
  * (c) 2004 Glenn Maynard
  * All rights reserved.

stepmania/src/archutils/Win32/GraphicsWindow.h

@@ -25,6 +25,8 @@ void RecreateGraphicsWindow( const RageDisplay::VideoModeParams &p );
 	RageDisplay::VideoModeParams GetParams();
 	HDC GetHDC();
 	void Update();
+
+	HWND GetHwnd();
 };
 
 #endif