feat(config): add window update_mode option

config/ratty.toml

@@ -3,6 +3,8 @@ width = 960
 height = 620
 opacity = 0.8
 # scale_factor = 1.0
+# update_mode = "Continuous"  # Use "LowPower" to redraw only after input or terminal output.
+# frame_interval_ms = 33      # Minimum milliseconds between LowPower redraws.
 
 [terminal]
 default_cols = 104

src/config.rs

@@ -136,6 +136,11 @@ pub struct WindowConfig {
     pub scale_factor: Option<f32>,
     /// Window opacity from `0.0` to `1.0`.
     pub opacity: f32,
+    /// How the window schedules redraws while focused.
+    pub update_mode: UpdateModeConfig,
+    /// Minimum time between redraws while focused, in milliseconds.
+    /// Only applies when `update_mode` is `LowPower`.
+    pub frame_interval_ms: u64,
 }
 
 impl Default for WindowConfig {
@@ -145,10 +150,24 @@ impl Default for WindowConfig {
             height: 620,
             scale_factor: None,
             opacity: 1.0,
+            update_mode: UpdateModeConfig::Continuous,
+            frame_interval_ms: 33,
         }
     }
 }
 
+/// How the window schedules redraws while focused.
+#[derive(Debug, Clone, Copy, Deserialize, Default)]
+pub enum UpdateModeConfig {
+    /// Redraw continuously, regardless of input.
+    #[serde(rename = "Continuous")]
+    #[default]
+    Continuous,
+    /// Redraw in response to events, rate-limited to `frame_interval_ms`.
+    #[serde(rename = "LowPower")]
+    LowPower,
+}
+
 /// Terminal grid configuration.
 #[derive(Debug, Clone, Deserialize)]
 #[serde(default)]

src/main.rs

@@ -5,15 +5,16 @@ use bevy::prelude::*;
 use bevy::render::RenderPlugin;
 use bevy::render::settings::{WgpuSettings, WgpuSettingsPriority};
 use bevy::window::{PrimaryWindow, WindowCreated, WindowResizeConstraints, WindowResolution};
-use bevy::winit::{WINIT_WINDOWS, WinitSettings};
+use bevy::winit::{UpdateMode, WINIT_WINDOWS, WinitSettings};
 use clap::Parser;
+use std::time::Duration;
 
 #[cfg(target_os = "windows")]
 use winit::platform::windows::{IconExtWindows, WindowExtWindows};
 use winit::window::Icon;
 
 use ratty::cli::Cli;
-use ratty::config::AppConfig;
+use ratty::config::{AppConfig, UpdateModeConfig};
 use ratty::paths::runtime_asset_root;
 use ratty::plugin::TerminalPlugin;
 use ratty::runtime::{RuntimeOptions, TerminalRuntime};
@@ -66,10 +67,19 @@ fn main() -> anyhow::Result<()> {
         .insert_resource(runtime)
         .insert_resource(terminal)
         .insert_non_send(AppWindowIcon { icon: window_icon })
-        // Always update continuously, focused or not. Bevy's default switches
-        // unfocused windows to a reactive mode, which would delay background
-        // PTY output.
-        .insert_resource(WinitSettings::continuous())
+        // Unfocused windows always update continuously. Bevy's default switches
+        // them to a reactive mode, which would delay background PTY output.
+        // While focused, `update_mode` picks between updating continuously and
+        // updating reactively at a capped frame rate to reduce idle CPU usage.
+        .insert_resource(match app_config.window.update_mode {
+            UpdateModeConfig::Continuous => WinitSettings::continuous(),
+            UpdateModeConfig::LowPower => WinitSettings {
+                focused_mode: UpdateMode::reactive_low_power(Duration::from_millis(
+                    app_config.window.frame_interval_ms,
+                )),
+                unfocused_mode: UpdateMode::Continuous,
+            },
+        })
         .add_plugins(
             DefaultPlugins
                 .set(WindowPlugin {