Use pre-seeded font caches to avoid mut

src/backlight.rs

@@ -3,7 +3,6 @@ use crate::color::Color;
 use crate::draw::{draw_bar, draw_box, Font, ROBOTO_REGULAR};
 use crate::module::{Input, ModuleImpl};
 
-use std::cell::RefCell;
 use std::fs::OpenOptions;
 use std::io::{Error, ErrorKind};
 use std::io::{Read, Write};
@@ -15,7 +14,7 @@ pub struct Backlight {
     device_path: PathBuf,
     cur_brightness: u64,
     max_brightness: u64,
-    font: RefCell<Font>,
+    font: Font,
     dirty: bool,
 }
 
@@ -87,10 +86,12 @@ impl Backlight {
             device_path: first_device.path(),
             cur_brightness: 0,
             max_brightness: 0,
-            font: RefCell::new(Font::new(&ROBOTO_REGULAR, 24.0)),
+            font: Font::new(&ROBOTO_REGULAR, 24.0),
             dirty: true,
         };
 
+        dev.font.add_str_to_cache("backlight");
+
         dev.update()?;
 
         Ok(dev)
@@ -106,7 +107,7 @@ impl ModuleImpl for Backlight {
     ) -> Result<Vec<(i32, i32, i32, i32)>, Error> {
         buf.memset(bg);
         let c = Color::new(1.0, 1.0, 1.0, 1.0);
-        self.font.borrow_mut().draw_text(
+        self.font.draw_text(
             &mut buf.subdimensions((0, 0, 128, 24))?,
             bg,
             &c,