eframe: several windows in series (#1919)

* Add example of opening several eframe windows in series

* Reuse the same winit event loop

* Ignore events to the wrong window

* Run run_return again

Cargo.toml

@@ -12,19 +12,7 @@ members = [
     "emath",
     "epaint",
 
-    "examples/confirm_exit",
-    "examples/custom_3d_glow",
-    "examples/custom_3d_three-d",
-    "examples/custom_font",
-    "examples/custom_font_style",
-    "examples/custom_window_frame",
-    "examples/download_image",
-    "examples/file_dialog",
-    "examples/hello_world",
-    "examples/puffin_profiler",
-    "examples/retained_image",
-    "examples/screenshot",
-    "examples/svg",
+    "examples/*",
 ]
 
 [profile.dev]

eframe/src/native/run.rs

@@ -72,7 +72,20 @@ trait WinitApp {
     fn on_event(&mut self, event: winit::event::Event<'_, RequestRepaintEvent>) -> EventResult;
 }
 
-fn run_and_return(mut event_loop: EventLoop<RequestRepaintEvent>, mut winit_app: impl WinitApp) {
+/// Access a thread-local event loop.
+///
+/// We reuse the event-loop so we can support closing and opening an eframe window
+/// multiple times. This is just a limitation of winit.
+fn with_event_loop(f: impl FnOnce(&mut EventLoop<RequestRepaintEvent>)) {
+    use std::cell::RefCell;
+    thread_local!(static EVENT_LOOP: RefCell<EventLoop<RequestRepaintEvent>> = RefCell::new(winit::event_loop::EventLoopBuilder::with_user_event().build()));
+
+    EVENT_LOOP.with(|event_loop| {
+        f(&mut *event_loop.borrow_mut());
+    });
+}
+
+fn run_and_return(event_loop: &mut EventLoop<RequestRepaintEvent>, mut winit_app: impl WinitApp) {
     use winit::platform::run_return::EventLoopExtRunReturn as _;
 
     tracing::debug!("event_loop.run_return");
@@ -100,6 +113,14 @@ fn run_and_return(mut event_loop: EventLoop<RequestRepaintEvent>, mut winit_app:
                 ..
             }) => EventResult::RepaintAsap,
 
+            winit::event::Event::WindowEvent { window_id, .. }
+                if window_id != winit_app.window().id() =>
+            {
+                // This can happen if we close a window, and then reopen a new one,
+                // or if we have multiple windows open.
+                EventResult::Wait
+            }
+
             event => winit_app.on_event(event),
         };
 
@@ -131,6 +152,13 @@ fn run_and_return(mut event_loop: EventLoop<RequestRepaintEvent>, mut winit_app:
     tracing::debug!("eframe window closed");
 
     winit_app.save_and_destroy();
+
+    drop(winit_app);
+
+    // Needed to clean the event_loop:
+    event_loop.run_return(|_, _, control_flow| {
+        control_flow.set_exit();
+    });
 }
 
 fn run_and_exit(
@@ -424,12 +452,15 @@ mod glow_integration {
         native_options: &epi::NativeOptions,
         app_creator: epi::AppCreator,
     ) {
-        let event_loop = glutin::event_loop::EventLoopBuilder::with_user_event().build();
-        let glow_eframe = GlowWinitApp::new(&event_loop, app_name, native_options, app_creator);
-
         if native_options.run_and_return {
-            run_and_return(event_loop, glow_eframe);
+            with_event_loop(|event_loop| {
+                let glow_eframe =
+                    GlowWinitApp::new(event_loop, app_name, native_options, app_creator);
+                run_and_return(event_loop, glow_eframe);
+            });
         } else {
+            let event_loop = winit::event_loop::EventLoopBuilder::with_user_event().build();
+            let glow_eframe = GlowWinitApp::new(&event_loop, app_name, native_options, app_creator);
             run_and_exit(event_loop, glow_eframe);
         }
     }
@@ -684,12 +715,15 @@ mod wgpu_integration {
         native_options: &epi::NativeOptions,
         app_creator: epi::AppCreator,
     ) {
-        let event_loop = winit::event_loop::EventLoopBuilder::with_user_event().build();
-        let wgpu_eframe = WgpuWinitApp::new(&event_loop, app_name, native_options, app_creator);
-
         if native_options.run_and_return {
-            run_and_return(event_loop, wgpu_eframe);
+            with_event_loop(|event_loop| {
+                let wgpu_eframe =
+                    WgpuWinitApp::new(event_loop, app_name, native_options, app_creator);
+                run_and_return(event_loop, wgpu_eframe);
+            });
         } else {
+            let event_loop = winit::event_loop::EventLoopBuilder::with_user_event().build();
+            let wgpu_eframe = WgpuWinitApp::new(&event_loop, app_name, native_options, app_creator);
             run_and_exit(event_loop, wgpu_eframe);
         }
     }

examples/serial_windows/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "serial_windows"
+version = "0.1.0"
+authors = ["Emil Ernerfeldt <emil.ernerfeldt@gmail.com>"]
+license = "MIT OR Apache-2.0"
+edition = "2021"
+rust-version = "1.61"
+publish = false
+
+
+[dependencies]
+eframe = { path = "../../eframe" }

examples/serial_windows/README.md

@@ -0,0 +1,8 @@
+Demonstrates how to open several windows after each other.
+
+NOTE: this doesn't work on Mac due to <https://github.com/rust-windowing/winit/issues/2431>.
+See also <https://github.com/emilk/egui/issues/1918>.
+
+```sh
+cargo run -p serial_windows
+```

examples/serial_windows/src/main.rs

@@ -0,0 +1,53 @@
+#![cfg_attr(not(debug_assertions), windows_subsystem = "windows")] // hide console window on Windows in release
+
+use eframe::egui;
+
+fn main() {
+    if cfg!(target_os = "macos") {
+        eprintln!("WARNING: this example does not work on Mac! See https://github.com/emilk/egui/issues/1918");
+    }
+
+    let options = eframe::NativeOptions {
+        run_and_return: true,
+        ..Default::default()
+    };
+
+    eprintln!("Starting first window…");
+    eframe::run_native(
+        "First Window",
+        options.clone(),
+        Box::new(|_cc| Box::new(MyApp::default())),
+    );
+
+    std::thread::sleep(std::time::Duration::from_secs(2));
+
+    eprintln!("Starting second window…");
+    eframe::run_native(
+        "Second Window",
+        options.clone(),
+        Box::new(|_cc| Box::new(MyApp::default())),
+    );
+
+    std::thread::sleep(std::time::Duration::from_secs(2));
+
+    eprintln!("Starting third window…");
+    eframe::run_native(
+        "Third Window",
+        options,
+        Box::new(|_cc| Box::new(MyApp::default())),
+    );
+}
+
+#[derive(Default)]
+struct MyApp {}
+
+impl eframe::App for MyApp {
+    fn update(&mut self, ctx: &egui::Context, frame: &mut eframe::Frame) {
+        egui::CentralPanel::default().show(ctx, |ui| {
+            if ui.button("Close").clicked() {
+                eprintln!("Pressed Close button");
+                frame.quit();
+            }
+        });
+    }
+}