set the loading screen, so actors can use it as an input variable

stepmania/src/Actor.cpp

@@ -196,9 +196,14 @@ void Actor::LoadFromNode( const CString& sDir, const XNode* pNode )
 	{
         if( pChild->m_sName == "Input" )
         {
-			/* Parameters are set as globals by ActorUtil::LoadFromNode.
+			/*
+			 * Parameters are set as globals by ActorUtil::LoadFromNode and
+			 * Screen::InitScreen.
 			 * If parameters are specified here, save them to the actor.  Accessing
-			 * parameters as globals directly is deprecated. */
+			 * parameters as globals directly is deprecated.  (However, it's still
+			 * the only way to access them when self isn't available, such as from
+			 * RunAtExpressionS.)
+			 */
 			CString sName;
 			if( !pChild->GetAttrValue( "Name", sName ) )
 				RageException::Throw( ssprintf("Input node in '%s' is missing the attribute 'Name'", sDir.c_str()) );

stepmania/src/Screen.cpp

@@ -17,6 +17,32 @@
 #define PERSIST_SCREENS				THEME->GetMetric (m_sName,"PersistScreens")
 #define GROUPED_SCREENS				THEME->GetMetric (m_sName,"GroupedScreens")
 
+void Screen::InitScreen( Screen *pScreen )
+{
+	/* Set the name of the loading screen, so Actor::LoadFromNode can
+	 * access it. */
+	LuaReference Old;
+	{
+		Lua *L = LUA->Get();
+		lua_getglobal( L, "LoadingScreen" );
+		Old.SetFromStack( L );
+
+		LuaHelpers::Push( pScreen->GetName(), L );
+		lua_setglobal( L, "LoadingScreen" );
+		LUA->Release( L );
+	}
+
+	pScreen->Init();
+
+	/* Restore the old value. */
+	{
+		Lua *L = LUA->Get();
+		Old.PushSelf( L );
+		lua_setglobal( L, "LoadingScreen" );
+		LUA->Release( L );
+	}
+}
+
 Screen::Screen( CString sName )
 {
 	SetName( sName );

stepmania/src/Screen.h

@@ -17,7 +17,7 @@ void RegisterScreenClass( const CString& sClassName, CreateScreenFn pfn );
 
 // Each Screen class should have a REGISTER_SCREEN_CLASS in its CPP file.
 #define REGISTER_SCREEN_CLASS( className ) \
-	static Screen* Create##className( const CString &sName ) { Screen *pRet = new className( sName ); pRet->Init(); return pRet; } \
+	static Screen* Create##className( const CString &sName ) { Screen *pRet = new className( sName ); Screen::InitScreen( pRet ); return pRet; } \
 	struct Register##className { \
 		Register##className() { RegisterScreenClass( #className,Create##className); } \
 	}; \
@@ -34,6 +34,8 @@ enum ScreenType
 class Screen : public ActorFrame
 {
 public:
+	static void InitScreen( Screen *pScreen );
+
 	Screen( CString sName );	// enforce that all screens have m_sName filled in
 	virtual ~Screen();