Previously, changing themes attempted to preserve Lua data by

serializing data and tables while reinstantiating Lua.  That's
ugly, and can't serialize some things (eg. functions).

Instead, when changing themes, shut down the high-level objects
and unregister as much as we can from Lua, change the theme,
then reregister things.  This doesn't clean the slate as much;
globals won't be erased, etc.

A better way would be to clear everything that uses Lua
(delete singletons), then reload it all.  Singleton creation is
a bit of a mess currently so that would break a lot, and we
don't want to reload songs.

stepmania/src/GameLoop.cpp

@@ -115,6 +115,44 @@ static void CheckFocus()
 	}
 }
 
+/* On the next update, change themes, and load sNewScreen. */
+static RString g_sNewTheme;
+static RString g_sNewScreen;
+void GameLoop::ChangeTheme( const RString &sNewTheme, const RString &sNewScreen )
+{
+	g_sNewTheme = sNewTheme;
+	g_sNewScreen = sNewScreen;
+}
+
+#include "StepMania.h" // XXX
+namespace
+{
+	void DoChangeTheme()
+	{
+		SAFE_DELETE( SCREENMAN );
+		TEXTUREMAN->DoDelayedDelete();
+
+		/* Clear theme metrics, so ThemeMetric<apActorCommand>s are cleared. */
+		THEME->ClearSubscribers();
+
+		THEME->SwitchThemeAndLanguage( g_sNewTheme, THEME->GetCurLanguage(), PREFSMAN->m_bPseudoLocalize );
+		PREFSMAN->m_sTheme.Set( g_sNewTheme );
+
+		/* Apply the new window title, icon and aspect ratio. */
+		StepMania::ApplyGraphicOptions();
+
+		SCREENMAN = new ScreenManager();
+
+		StepMania::ResetGame();
+		SCREENMAN->ThemeChanged();
+		SCREENMAN->SetNewScreen( g_sNewScreen );
+
+		g_sNewTheme = RString();
+		g_sNewScreen = RString();
+	}
+
+}
+
 void GameLoop::RunGameLoop()
 {
 	/* People may want to do something else while songs are loading, so do
@@ -124,6 +162,9 @@ void GameLoop::RunGameLoop()
 
 	while( !ArchHooks::UserQuit() )
 	{
+		if( !g_sNewTheme.empty() )
+			DoChangeTheme();
+
 		/*
 		 * Update
 		 */