Method set_pre_bg

src/script.rs:113–115

(&mut self, pre_bg: Option<Command>)

            commands: Vec::new(),
            current_block: 0,
            read_block: 0,
            current_bgm: String::new(),
            pre_voice: None,
            timeline: Timeline::default(),
            clear: HashSet::new(),
            choices: HashMap::new(),