Lazier rendering, less background work

src/main.rs

@@ -36,14 +36,14 @@ fn main() -> Result<(), Error> {
     let mut ui = ui::Root::new(&mut state, &open_buffers);
 
     Terminal::with(move |term| {
+        let mut needs_render = true;
         loop {
-            // Render the state to the screen
+            // Wait for a while, or until an event occurs
-            term.update(|fb| ui.render(&state, fb));
-
-            // Wait for a while
             term.wait_at_least(Duration::from_millis(250));
 
             while let Some(ev) = term.get_event() {
+                needs_render = true; // TODO: Don't always rerender?
+
                 // Resize events are special and need handling by the terminal
                 if let TerminalEvent::Resize(cols, rows) = ev {
                     term.set_size([cols, rows]);
@@ -59,7 +59,12 @@ fn main() -> Result<(), Error> {
                 }
             }
 
-            state.tick();
+            state.tick(&mut needs_render);
+
+            // Render the state to the screen
+            if needs_render {
+                term.update(|fb| ui.render(&state, fb));
+            }
         }
     })
 }

src/state.rs

@@ -867,16 +867,23 @@ impl Buffer {
         }
     }
 
-    pub fn tick(&mut self) {
+    pub fn tick(&mut self, needs_render: &mut bool) {
         if let Some(path) = &self.path {
             let stale = std::fs::metadata(path)
                 .and_then(|m| m.modified())
-                .map(|lm| lm > self.opened_at.expect("state buffer must have open time"));
+                .map_or(true, |lm| {
-            match (stale, self.unsaved) {
+                    lm > self.opened_at.expect("state buffer must have open time")
-                (Ok(false), _) => {}
+                });
-                (Ok(true), true) => self.diverged = true,
+            if stale {
-                (Ok(true), false) => self.reload(),
+                if self.unsaved {
-                (Err(_), _) => {}
+                    if !self.diverged {
+                        self.diverged = true;
+                        *needs_render = true;
+                    }
+                } else {
+                    self.reload();
+                    *needs_render = true;
+                }
             }
         }
 
@@ -985,10 +992,10 @@ impl State {
         }
     }
 
-    pub fn tick(&mut self) {
+    pub fn tick(&mut self, needs_render: &mut bool) {
         self.tick += 1;
         for b in self.buffers.values_mut() {
-            b.tick();
+            b.tick(needs_render);
         }
     }