fix course mode.

We've been using the environment and Lua globals as "parameters" to treat
broadcasts as "functions called on every object".  That doesn't work with
queued message handling.  It's also a bit confusing; it means there are
"parameters" available only for some messages.  It's cleaner to just make the
information available as a function.

stepmania/src/ScreenGameplay.cpp

@@ -2197,12 +2197,7 @@ void ScreenGameplay::HandleScreenMessage( const ScreenMessage SM )
 
 		int iPlaySongIndex = GAMESTATE->GetCourseSongIndex()+1;
 		iPlaySongIndex %= m_apSongsQueue.size();
-		Lua *L = LUA->Get();
-		m_apSongsQueue[iPlaySongIndex]->PushSelf( L );
-		GAMESTATE->m_Environment->Set( L, "NextSong" );
 		MESSAGEMAN->Broadcast( "NextCourseSong" );
-		GAMESTATE->m_Environment->Unset( L, "NextSong" );
-		LUA->Release( L );
 		m_NextSong.PlayCommand( "Start" );
 		m_NextSong.Reset();
 		m_NextSong.StartTransitioning( SM_LoadNextSong );
@@ -2414,6 +2409,34 @@ void ScreenGameplay::ShowOniGameOver( PlayerNumber pn )
 	m_sprOniGameOver[pn].PlayCommand( "Die" );
 }
 
+Song *ScreenGameplay::GetNextCourseSong() const
+{
+	ASSERT( GAMESTATE->IsCourseMode() );
+
+	int iPlaySongIndex = GAMESTATE->GetCourseSongIndex()+1;
+	iPlaySongIndex %= m_apSongsQueue.size();
+
+	return m_apSongsQueue[iPlaySongIndex];
+}
+
+// lua start
+#include "LuaBinding.h"
+
+class LunaScreenGameplay: public Luna<ScreenGameplay>
+{
+public:
+	LunaScreenGameplay() { LUA->Register( Register ); }
+
+	static int GetNextCourseSong( T* p, lua_State *L ) { p->GetNextCourseSong()->PushSelf(L); return 1; }
+	static void Register( Lua *L )
+	{
+  		ADD_METHOD( GetNextCourseSong )
+		Luna<T>::Register( L );
+	}
+};
+
+LUA_REGISTER_DERIVED_CLASS( ScreenGameplay, ScreenWithMenuElements )
+// lua end
 
 /*
  * (c) 2001-2004 Chris Danford, Glenn Maynard

stepmania/src/ScreenGameplay.h

@@ -44,6 +44,12 @@ public:
 	virtual bool UsesBackground() const { return false; }
 	virtual ScreenType GetScreenType() const { return gameplay; }
 
+	//
+	// Lua
+	//
+	virtual void PushSelf( lua_State *L );
+	Song *GetNextCourseSong() const;
+
 protected:
 	ThemeMetric<CString> PLAYER_TYPE;
 	ThemeMetric<CString> GIVE_UP_TEXT;