Add opt-in support for the 'puffin' profiler in eframe (#1483)

examples/README.md

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+Examples of how to use [`eframe`](https://github.com/emilk/egui/tree/master/eframe) and [`egui`](https://github.com/emilk/egui/).

examples/puffin_profiler/Cargo.toml

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+[package]
+name = "puffin_profiler"
+version = "0.1.0"
+authors = ["Emil Ernerfeldt <emil.ernerfeldt@gmail.com>"]
+license = "MIT OR Apache-2.0"
+edition = "2021"
+rust-version = "1.60"
+publish = false
+
+
+[dependencies]
+eframe = { path = "../../eframe", features = ["puffin"] }
+puffin = "0.13"
+puffin_http = "0.10"

examples/puffin_profiler/README.md

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+Example how to use the [puffin profiler](https://github.com/EmbarkStudios/puffin) with an `eframe` app.
+
+
+```sh
+cargo run -p puffin_profiler &
+
+cargo install puffin_viewer
+puffin_viewer --url 127.0.0.1:8585
+```

examples/puffin_profiler/src/main.rs

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+#![cfg_attr(not(debug_assertions), windows_subsystem = "windows")] // hide console window on Windows in release
+
+use eframe::egui;
+
+fn main() {
+    start_puffin_server(); // NOTE: you may only want to call this if the users specifies some flag or clicks a button!
+
+    let options = eframe::NativeOptions::default();
+    eframe::run_native(
+        "My egui App",
+        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| {
+            ui.heading("Example of how to use the puffin profiler with egui");
+            ui.separator();
+
+            let cmd = "cargo install puffin_viewer && puffin_viewer --url 127.0.0.1:8585";
+
+            ui.label("To connect, run this:");
+            ui.horizontal(|ui| {
+                ui.monospace(cmd);
+                if ui.small_button("📋").clicked() {
+                    ui.output().copied_text = cmd.into();
+                }
+            });
+
+            ui.separator();
+
+            ui.label("Note that this app runs in 'reactive' mode, so you must interact with the app for new profile events to be sent. Waving the mouse over this window is enough.");
+
+            if ui
+                .button(
+                    "Click to sleep a bit. That should be visible as a spike in the profiler view!",
+                )
+                .clicked()
+            {
+                puffin::profile_scope!("sleep");
+                std::thread::sleep(std::time::Duration::from_millis(50));
+            }
+        });
+    }
+}
+
+fn start_puffin_server() {
+    puffin::set_scopes_on(true); // tell puffin to collect data
+
+    match puffin_http::Server::new("0.0.0.0:8585") {
+        Ok(puffin_server) => {
+            eprintln!("Run:  cargo install puffin_viewer && puffin_viewer --url 127.0.0.1:8585");
+
+            // We can store the server if we want, but in this case we just want
+            // it to keep running. Dropping it closes the server, so let's not drop it!
+            #[allow(clippy::mem_forget)]
+            std::mem::forget(puffin_server);
+        }
+        Err(err) => {
+            eprintln!("Failed to start puffin server: {}", err);
+        }
+    };
+}