Add a separate underlay layer. This should be used for adding actors

instead of modifying background, since changing the background per-
screen breaks the "persist background" logic in ScreenManager.

stepmania/src/ScreenWithMenuElements.cpp

@@ -80,6 +80,12 @@ ScreenWithMenuElements::ScreenWithMenuElements( CString sClassName ) : Screen( s
 	m_textHelp->SetTips( asHelpTips );
 	this->AddChild( m_textHelp );
 
+	m_sprUnderlay.Load( THEME->GetPathB(m_sName,"underlay") );
+	m_sprUnderlay->SetName("Underlay");
+	m_sprUnderlay->SetDrawOrder( DRAW_ORDER_BEFORE_EVERYTHING );
+	SET_XY_AND_ON_COMMAND( m_sprUnderlay );
+	this->AddChild( m_sprUnderlay );
+	
 	m_sprOverlay.Load( THEME->GetPathB(m_sName,"overlay") );
 	m_sprOverlay->SetName("Overlay");
 	SET_XY_AND_ON_COMMAND( m_sprOverlay );

stepmania/src/ScreenWithMenuElements.h

@@ -26,6 +26,7 @@ public:
 	void ResetTimer();
 
 protected:
+	AutoActor			m_sprUnderlay;
 	AutoActor			m_autoHeader;
 	Sprite				m_sprStyleIcon;
 	MemoryCardDisplay	m_MemoryCardDisplay[NUM_PLAYERS];