Update the multiple_viewports example to show how to use Context::request_repaint_of().

Author: hydra

examples/multiple_viewports/src/main.rs

@@ -1,13 +1,13 @@
 #![cfg_attr(not(debug_assertions), windows_subsystem = "windows")] // hide console window on Windows in release
 #![allow(rustdoc::missing_crate_level_docs)] // it's an example
 
+use eframe::egui;
+use std::sync::atomic::AtomicUsize;
 use std::sync::{
     Arc,
     atomic::{AtomicBool, Ordering},
 };
 
-use eframe::egui;
-
 fn main() -> eframe::Result {
     env_logger::init(); // Log to stderr (if you run with `RUST_LOG=debug`).
     let options = eframe::NativeOptions {
@@ -27,15 +27,18 @@ struct MyApp {
     /// The downside is that their painting is linked with the parent viewport:
     /// if either needs repainting, they are both repainted.
     show_immediate_viewport: bool,
+    immediate_viewport_redraw_counter: usize,
 
     /// Deferred viewports run independent of the parent viewport, which can save
     /// CPU if only some of the viewports require repainting.
     /// However, this requires passing state with `Arc` and locks.
     show_deferred_viewport: Arc<AtomicBool>,
+    deferred_viewport_redraw_counter: Arc<AtomicUsize>,
 }
 
 impl eframe::App for MyApp {
     fn update(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
+        let mut deferred_viewport_refresh_requested = false;
         egui::CentralPanel::default().show(ctx, |ui| {
             ui.label("Hello from the root viewport");
 
@@ -48,6 +51,21 @@ impl eframe::App for MyApp {
             ui.checkbox(&mut show_deferred_viewport, "Show deferred child viewport");
             self.show_deferred_viewport
                 .store(show_deferred_viewport, Ordering::Relaxed);
+
+            deferred_viewport_refresh_requested =
+                ui.button("request refresh of deferred viewport").clicked();
+
+            ui.group(|ui| {
+                ui.label(format!(
+                    "Immediate viewport counter: {}",
+                    self.immediate_viewport_redraw_counter
+                ));
+                ui.label(format!(
+                    "Deferred viewport counter: {}",
+                    self.deferred_viewport_redraw_counter
+                        .load(Ordering::Relaxed)
+                ));
+            })
         });
 
         if self.show_immediate_viewport {
@@ -62,8 +80,14 @@ impl eframe::App for MyApp {
                         "This egui backend doesn't support multiple viewports"
                     );
 
+                    self.immediate_viewport_redraw_counter += 1;
+
                     egui::CentralPanel::default().show(ctx, |ui| {
                         ui.label("Hello from immediate viewport");
+                        ui.label(format!(
+                            "Counter: {}",
+                            self.immediate_viewport_redraw_counter
+                        ));
                     });
 
                     if ctx.input(|i| i.viewport().close_requested()) {
@@ -76,8 +100,16 @@ impl eframe::App for MyApp {
 
         if self.show_deferred_viewport.load(Ordering::Relaxed) {
             let show_deferred_viewport = self.show_deferred_viewport.clone();
+            let counter = self.deferred_viewport_redraw_counter.clone();
+
+            let deferred_viewport_id = egui::ViewportId::from_hash_of("deferred_viewport");
+
+            if deferred_viewport_refresh_requested {
+                ctx.request_repaint_of(deferred_viewport_id);
+            }
+
             ctx.show_viewport_deferred(
-                egui::ViewportId::from_hash_of("deferred_viewport"),
+                deferred_viewport_id,
                 egui::ViewportBuilder::default()
                     .with_title("Deferred Viewport")
                     .with_inner_size([200.0, 100.0]),
@@ -87,8 +119,11 @@ impl eframe::App for MyApp {
                         "This egui backend doesn't support multiple viewports"
                     );
 
+                    let value = counter.fetch_add(1, Ordering::Relaxed);
+
                     egui::CentralPanel::default().show(ctx, |ui| {
                         ui.label("Hello from deferred viewport");
+                        ui.label(format!("Counter: {}", value));
                     });
                     if ctx.input(|i| i.viewport().close_requested()) {
                         // Tell parent to close us.