add ActorUtil::ActorParam helper

stepmania/src/ActorUtil.cpp

@@ -528,6 +528,35 @@ FileType ActorUtil::GetFileType( const CString &sPath )
 	else					return FT_Invalid;
 }
 
+/* Helper: set actor parameters, and return them to their original value when released. */
+ActorUtil::ActorParam::ActorParam( CString sName, CString sValue )
+{
+	m_pOld = new LuaReference;
+	m_sName = sName;
+	Lua *L = LUA->Get();
+	LuaHelpers::Push( sValue, L );
+	ActorUtil::SetParamFromStack( L, m_sName, m_pOld );
+	LUA->Release( L );
+}
+
+ActorUtil::ActorParam::~ActorParam()
+{
+	delete m_pOld;
+	Release();
+}
+
+void ActorUtil::ActorParam::Release()
+{
+	if( m_pOld->IsSet() )
+		return;
+	/* Restore the old value. */
+	Lua *L = LUA->Get();
+	m_pOld->PushSelf( L );
+	ActorUtil::SetParamFromStack( L, m_sName );
+	m_pOld->Unset();
+	LUA->Release( L );
+}
+
 /*
  * (c) 2003-2004 Chris Danford
  * All rights reserved.

stepmania/src/ActorUtil.h

@@ -77,6 +77,17 @@ namespace ActorUtil
 
 	void SetParamFromStack( Lua *L, CString sName, LuaReference *pOld=NULL );
 	void GetParam( Lua *L, const CString &sName );
+
+	struct ActorParam
+	{
+		ActorParam( CString sName, CString sValue );
+		~ActorParam();
+		void Release();
+
+	private:
+		CString m_sName;
+		LuaReference *m_pOld;
+	};
 };
 
 #define SET_XY( actor )			ActorUtil::SetXY( actor, m_sName )

stepmania/src/Screen.cpp

@@ -20,23 +20,9 @@
 void Screen::InitScreen( Screen *pScreen )
 {
 	/* Set the name of the loading screen. */
-	LuaReference Old;
-	{
-		Lua *L = LUA->Get();
-		LuaHelpers::Push( pScreen->GetName(), L );
-		ActorUtil::SetParamFromStack( L, "LoadingScreen", &Old );
-		LUA->Release( L );
-	}
+	ActorUtil::ActorParam LoadingScreen( "LoadingScreen", pScreen->GetName() );
 
 	pScreen->Init();
-
-	/* Restore the old value. */
-	{
-		Lua *L = LUA->Get();
-		Old.PushSelf( L );
-		ActorUtil::SetParamFromStack( L, "LoadingScreen" );
-		LUA->Release( L );
-	}
 }
 
 Screen::Screen( CString sName )