refactor RunMode: move it from backend to the demo App

This simplifies the egui_glium and egui_web backends substantially,
reduces the scope of RunMode to a single file, and
removes duplicated code.

Basically: this is how I should have written it from the beginning.

Author: emilk

demo_glium/src/main.rs

@@ -1,11 +1,11 @@
 #![deny(warnings)]
 #![warn(clippy::all)]
 
-use egui_glium::{storage::FileStorage, RunMode};
+use egui_glium::storage::FileStorage;
 
 fn main() {
     let title = "Egui glium demo";
     let storage = FileStorage::from_path(".egui_demo_glium.json".into());
     let app: egui::DemoApp = egui::app::get_value(&storage, egui::app::APP_KEY).unwrap_or_default();
-    egui_glium::run(title, RunMode::Reactive, storage, app);
+    egui_glium::run(title, storage, app);
 }

demo_web/src/lib.rs

@@ -6,7 +6,7 @@ use wasm_bindgen::prelude::*;
 /// This is the entry-point for all the web-assembly.
 #[wasm_bindgen]
 pub fn start(canvas_id: &str) -> Result<(), wasm_bindgen::JsValue> {
-    let backend = egui_web::WebBackend::new(canvas_id, egui_web::RunMode::Reactive)?;
+    let backend = egui_web::WebBackend::new(canvas_id)?;
     let app = Box::new(egui::DemoApp::default());
     let runner = egui_web::AppRunner::new(backend, app)?;
     egui_web::run(runner)?;

egui/src/app.rs

@@ -19,29 +19,12 @@ pub trait App {
     fn on_exit(&mut self, _storage: &mut dyn Storage) {}
 }
 
-// TODO: replace with manually calling `egui::Context::request_repaint()` each frame.
-/// How the backend runs the app
-#[derive(Clone, Copy, Debug, Eq, PartialEq)]
-pub enum RunMode {
-    /// Repaint the UI all the time (at the display refresh rate of e.g. 60 Hz).
-    /// This is good for games where things are constantly moving.
-    /// This can also be achieved with `RunMode::Reactive` combined with calling `egui::Context::request_repaint()` each frame.
-    Continuous,
-
-    /// Only repaint when there are animations or input (mouse movement, keyboard input etc).
-    /// This saves CPU.
-    Reactive,
-}
-
 pub struct WebInfo {
     /// e.g. "#fragment" part of "www.example.com/index.html#fragment"
     pub web_location_hash: String,
 }
 
 pub trait Backend {
-    fn run_mode(&self) -> RunMode;
-    fn set_run_mode(&mut self, run_mode: RunMode);
-
     /// If the app is running in a Web context, this returns information about the environment.
     fn web_info(&self) -> Option<WebInfo> {
         None

egui/src/demos/app.rs

@@ -4,6 +4,49 @@ use crate::{app, color::*, containers::*, demos::*, paint::*, widgets::*, *};
 
 // ----------------------------------------------------------------------------
 
+/// How often we repaint the demo app by default
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+enum RunMode {
+    /// This is the default for the demo.
+    ///
+    /// If this is selected, Egui is only updated if are input events
+    /// (like mouse movements) or there are some animations in the GUI.
+    ///
+    /// Reactive mode saves CPU.
+    ///
+    /// The downside is that the UI can become out-of-date if something it is supposed to monitor changes.
+    /// For instance, a GUI for a thermostat need to repaint each time the temperature changes.
+    /// To ensure the UI is up to date you need to call `egui::Context::request_repaint()` each
+    /// time such an event happens. You can also chose to call `request_repaint()` once every second
+    /// or after every single frame - this is called `Continuous` mode,
+    /// and for games and interactive tools that need repainting every frame anyway, this should be the default.
+    Reactive,
+
+    /// This will call `egui::Context::request_repaint()` at the end of each frame
+    /// to request the backend to repaint as soon as possible.
+    ///
+    /// On most platforms this will mean that Egui will run at the display refresh rate of e.g. 60 Hz.
+    ///
+    /// For this demo it is not any reason to do so except to
+    /// demonstrate how quickly Egui runs.
+    ///
+    /// For games or other interactive apps, this is probably what you want to do.
+    /// It will guarantee that Egui is always up-to-date.
+    Continuous,
+}
+
+/// Default for demo is Reactive since
+/// 1) We want to use minimal CPU
+/// 2) There are no external events that could invalidate the UI
+///    so there are no events to miss.
+impl Default for RunMode {
+    fn default() -> Self {
+        RunMode::Reactive
+    }
+}
+
+// ----------------------------------------------------------------------------
+
 /// Demonstrates how to make an app using Egui.
 ///
 /// Implements `egui::app::App` so it can be used with
@@ -12,6 +55,8 @@ use crate::{app, color::*, containers::*, demos::*, paint::*, widgets::*, *};
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
 #[cfg_attr(feature = "serde", serde(default))]
 pub struct DemoApp {
+    #[cfg_attr(feature = "serde", serde(skip))] // go back to `Continuous` mode each time we start
+    run_mode: RunMode,
     previous_web_location_hash: String,
     open_windows: OpenWindows,
     demo_window: DemoWindow,
@@ -172,16 +217,15 @@ impl DemoApp {
         ui.separator();
 
         ui.horizontal(|ui| {
-            let mut run_mode = backend.run_mode();
+            let run_mode = &mut self.run_mode;
             ui.label("Run mode:");
-            ui.radio_value("Continuous", &mut run_mode, app::RunMode::Continuous)
+            ui.radio_value("Continuous", run_mode, RunMode::Continuous)
                 .tooltip_text("Repaint everything each frame");
-            ui.radio_value("Reactive", &mut run_mode, app::RunMode::Reactive)
+            ui.radio_value("Reactive", run_mode, RunMode::Reactive)
                 .tooltip_text("Repaint when there are animations or input (e.g. mouse movement)");
-            backend.set_run_mode(run_mode);
         });
 
-        if backend.run_mode() == app::RunMode::Continuous {
+        if self.run_mode == RunMode::Continuous {
             ui.add(
                 label!("Repainting the UI each frame. FPS: {:.1}", backend.fps())
                     .text_style(TextStyle::Monospace),
@@ -232,6 +276,11 @@ impl app::App for DemoApp {
             .map(|info| info.web_location_hash.as_str())
             .unwrap_or_default();
         self.ui(ui, web_location_hash);
+
+        if self.run_mode == RunMode::Continuous {
+            // Tell the backend to repaint as soon as possible
+            ui.ctx().request_repaint();
+        }
     }
 
     #[cfg(feature = "serde_json")]

egui_glium/src/backend.rs

@@ -6,7 +6,7 @@ use crate::{
 };
 
 pub use egui::{
-    app::{App, Backend, RunMode, Storage},
+    app::{App, Backend, Storage},
     Srgba,
 };
 
@@ -16,30 +16,20 @@ const WINDOW_KEY: &str = "window";
 pub struct GliumBackend {
     frame_times: egui::MovementTracker<f32>,
     quit: bool,
-    run_mode: RunMode,
     painter: Painter,
 }
 
 impl GliumBackend {
-    pub fn new(run_mode: RunMode, painter: Painter) -> Self {
+    pub fn new(painter: Painter) -> Self {
         Self {
             frame_times: egui::MovementTracker::new(1000, 1.0),
             quit: false,
-            run_mode,
             painter,
         }
     }
 }
 
 impl Backend for GliumBackend {
-    fn run_mode(&self) -> RunMode {
-        self.run_mode
-    }
-
-    fn set_run_mode(&mut self, run_mode: RunMode) {
-        self.run_mode = run_mode;
-    }
-
     fn cpu_time(&self) -> f32 {
         self.frame_times.average().unwrap_or_default()
     }
@@ -62,12 +52,7 @@ impl Backend for GliumBackend {
 }
 
 /// Run an egui app
-pub fn run(
-    title: &str,
-    run_mode: RunMode,
-    mut storage: FileStorage,
-    mut app: impl App + 'static,
-) -> ! {
+pub fn run(title: &str, mut storage: FileStorage, mut app: impl App + 'static) -> ! {
     let event_loop = glutin::event_loop::EventLoop::new();
     let mut window = glutin::window::WindowBuilder::new()
         .with_decorations(true)
@@ -98,7 +83,7 @@ pub fn run(
 
     // used to keep track of time for animations
     let start_time = Instant::now();
-    let mut runner = GliumBackend::new(run_mode, Painter::new(&display));
+    let mut runner = GliumBackend::new(Painter::new(&display));
     let mut clipboard = init_clipboard();
 
     event_loop.run(move |event, _, control_flow| {
@@ -120,13 +105,10 @@ pub fn run(
 
             *control_flow = if runner.quit {
                 glutin::event_loop::ControlFlow::Exit
-            } else if runner.run_mode() == RunMode::Continuous {
+            } else if output.needs_repaint {
                 display.gl_window().window().request_redraw();
                 glutin::event_loop::ControlFlow::Poll
             } else {
-                if output.needs_repaint {
-                    display.gl_window().window().request_redraw();
-                }
                 glutin::event_loop::ControlFlow::Wait
             };
 

egui_web/src/backend.rs

@@ -1,7 +1,7 @@
 use crate::*;
 
 pub use egui::{
-    app::{App, Backend, RunMode, WebInfo},
+    app::{App, Backend, WebInfo},
     Srgba,
 };
 
@@ -12,20 +12,18 @@ pub struct WebBackend {
     painter: webgl::Painter,
     frame_times: egui::MovementTracker<f32>,
     frame_start: Option<f64>,
-    run_mode: RunMode,
     last_save_time: Option<f64>,
 }
 
 impl WebBackend {
-    pub fn new(canvas_id: &str, run_mode: RunMode) -> Result<Self, JsValue> {
+    pub fn new(canvas_id: &str) -> Result<Self, JsValue> {
         let ctx = egui::Context::new();
         load_memory(&ctx);
         Ok(Self {
             ctx,
             painter: webgl::Painter::new(canvas_id)?,
             frame_times: egui::MovementTracker::new(1000, 1.0),
             frame_start: None,
-            run_mode,
             last_save_time: None,
         })
     }
@@ -83,14 +81,6 @@ impl WebBackend {
 }
 
 impl Backend for WebBackend {
-    fn run_mode(&self) -> RunMode {
-        self.run_mode
-    }
-
-    fn set_run_mode(&mut self, run_mode: RunMode) {
-        self.run_mode = run_mode;
-    }
-
     fn web_info(&self) -> Option<WebInfo> {
         Some(WebInfo {
             web_location_hash: location_hash().unwrap_or_default(),

egui_web/src/lib.rs

@@ -229,7 +229,7 @@ pub struct AppRunnerRef(Arc<Mutex<AppRunner>>);
 fn paint_and_schedule(runner_ref: AppRunnerRef) -> Result<(), JsValue> {
     fn paint_if_needed(runner_ref: &AppRunnerRef) -> Result<(), JsValue> {
         let mut runner_lock = runner_ref.0.lock();
-        if runner_lock.web_backend.run_mode() == RunMode::Continuous || runner_lock.needs_repaint {
+        if runner_lock.needs_repaint {
             runner_lock.needs_repaint = false;
             let (output, paint_jobs) = runner_lock.logic()?;
             runner_lock.paint(paint_jobs)?;

example_glium/src/main.rs

@@ -4,7 +4,7 @@
 #![warn(clippy::all)]
 
 use egui::{Slider, Window};
-use egui_glium::{storage::FileStorage, RunMode};
+use egui_glium::storage::FileStorage;
 
 /// We derive Deserialize/Serialize so we can persist app state on shutdown.
 #[derive(Default, serde::Deserialize, serde::Serialize)]
@@ -39,7 +39,7 @@ fn main() {
     let title = "My Egui Window";
     let storage = FileStorage::from_path(".egui_example_glium.json".into()); // Where to persist app state
     let app: MyApp = egui::app::get_value(&storage, egui::app::APP_KEY).unwrap_or_default(); // Restore `MyApp` from file, or create new `MyApp`.
-    egui_glium::run(title, RunMode::Reactive, storage, app);
+    egui_glium::run(title, storage, app);
 }
 
 fn my_save_function() {