eframe: Remove warm-starting (#3574)

This was an ill-supported feature with little benefit or use.

crates/eframe/src/epi.rs

@@ -212,18 +212,6 @@ pub trait App {
     fn persist_egui_memory(&self) -> bool {
         true
     }
-
-    /// If `true` a warm-up call to [`Self::update`] will be issued where
-    /// `ctx.memory(|mem| mem.everything_is_visible())` will be set to `true`.
-    ///
-    /// This can help pre-caching resources loaded by different parts of the UI, preventing stutter later on.
-    ///
-    /// In this warm-up call, all painted shapes will be ignored.
-    ///
-    /// The default is `false`, and it is unlikely you will want to change this.
-    fn warm_up_enabled(&self) -> bool {
-        false
-    }
 }
 
 /// Selects the level of hardware graphics acceleration.

crates/eframe/src/native/epi_integration.rs

@@ -4,10 +4,7 @@ use winit::event_loop::EventLoopWindowTarget;
 
 use raw_window_handle::{HasRawDisplayHandle as _, HasRawWindowHandle as _};
 
-use egui::{
-    DeferredViewportUiCallback, NumExt as _, ViewportBuilder, ViewportId, ViewportIdPair,
-    ViewportInfo,
-};
+use egui::{DeferredViewportUiCallback, NumExt as _, ViewportBuilder, ViewportId};
 use egui_winit::{EventResponse, WindowSettings};
 
 use crate::{epi, Theme};
@@ -206,28 +203,6 @@ impl EpiIntegration {
         });
     }
 
-    pub fn warm_up(
-        &mut self,
-        app: &mut dyn epi::App,
-        window: &winit::window::Window,
-        egui_winit: &mut egui_winit::State,
-    ) {
-        crate::profile_function!();
-        let saved_memory: egui::Memory = self.egui_ctx.memory(|mem| mem.clone());
-        self.egui_ctx
-            .memory_mut(|mem| mem.set_everything_is_visible(true));
-
-        let mut raw_input = egui_winit.take_egui_input(window, ViewportIdPair::ROOT);
-        raw_input.viewports =
-            std::iter::once((ViewportId::ROOT, ViewportInfo::default())).collect();
-        self.pre_update();
-        let full_output = self.update(app, None, raw_input);
-        self.post_update();
-        self.pending_full_output.append(full_output); // Handle it next frame
-        self.egui_ctx.memory_mut(|mem| *mem = saved_memory); // We don't want to remember that windows were huge.
-        self.egui_ctx.clear_animations();
-    }
-
     /// If `true`, it is time to close the native window.
     pub fn should_close(&self) -> bool {
         self.close

crates/eframe/src/native/run.rs

@@ -1151,12 +1151,6 @@ mod glow_integration {
                 .expect("viewport doesn't exist")
         }
 
-        fn viewport_mut(&mut self, viewport_id: ViewportId) -> &mut Viewport {
-            self.viewports
-                .get_mut(&viewport_id)
-                .expect("viewport doesn't exist")
-        }
-
         fn window(&self, viewport_id: ViewportId) -> Rc<Window> {
             self.viewport(viewport_id)
                 .window
@@ -1488,7 +1482,7 @@ mod glow_integration {
 
             let app = {
                 let window = glutin.window(ViewportId::ROOT);
-                let mut app = app_creator(&epi::CreationContext {
+                let cc = epi::CreationContext {
                     egui_ctx: integration.egui_ctx.clone(),
                     integration_info: integration.frame.info().clone(),
                     storage: integration.frame.storage(),
@@ -1497,18 +1491,9 @@ mod glow_integration {
                     wgpu_render_state: None,
                     raw_display_handle: window.raw_display_handle(),
                     raw_window_handle: window.raw_window_handle(),
-                });
-
-                if app.warm_up_enabled() {
-                    let viewport = glutin.viewport_mut(ViewportId::ROOT);
-                    integration.warm_up(
-                        app.as_mut(),
-                        &window,
-                        viewport.egui_winit.as_mut().unwrap(),
-                    );
-                }
-
-                app
+                };
+                crate::profile_scope!("app_creator");
+                app_creator(&cc)
             };
 
             let glutin = Rc::new(RefCell::new(glutin));
@@ -2124,15 +2109,11 @@ mod wgpu_integration {
                 raw_display_handle: window.raw_display_handle(),
                 raw_window_handle: window.raw_window_handle(),
             };
-            let mut app = {
+            let app = {
                 crate::profile_scope!("user_app_creator");
                 app_creator(&cc)
             };
 
-            if app.warm_up_enabled() {
-                integration.warm_up(app.as_mut(), &window, &mut egui_winit);
-            }
-
             let mut viewport_from_window = HashMap::default();
             viewport_from_window.insert(window.id(), ViewportId::ROOT);
 

crates/eframe/src/web/app_runner.rs

@@ -153,17 +153,6 @@ impl AppRunner {
         self.painter.canvas_id()
     }
 
-    pub fn warm_up(&mut self) {
-        if self.app.warm_up_enabled() {
-            let saved_memory: egui::Memory = self.egui_ctx.memory(|m| m.clone());
-            self.egui_ctx
-                .memory_mut(|m| m.set_everything_is_visible(true));
-            self.logic();
-            self.egui_ctx.memory_mut(|m| *m = saved_memory); // We don't want to remember that windows were huge.
-            self.egui_ctx.clear_animations();
-        }
-    }
-
     pub fn destroy(mut self) {
         log::debug!("Destroying AppRunner");
         self.painter.destroy();

crates/eframe/src/web/web_runner.rs

@@ -58,8 +58,7 @@ impl WebRunner {
 
         let follow_system_theme = web_options.follow_system_theme;
 
-        let mut runner = AppRunner::new(canvas_id, web_options, app_creator).await?;
-        runner.warm_up();
+        let runner = AppRunner::new(canvas_id, web_options, app_creator).await?;
         self.runner.replace(Some(runner));
 
         {