Relayout UserInterface on resize in iced_winit

native/src/user_interface.rs

@@ -388,6 +388,23 @@ where
         }
     }
 
+    /// Relayouts and returns a new  [`UserInterface`] using the provided
+    /// bounds.
+    ///
+    /// [`UserInterface`]: struct.UserInterface.html
+    pub fn relayout(self, bounds: Size, renderer: &mut Renderer) -> Self {
+        Self::build(
+            self.root,
+            bounds,
+            Cache {
+                base: self.base,
+                overlay: self.overlay,
+                bounds: self.bounds,
+            },
+            renderer,
+        )
+    }
+
     /// Extract the [`Cache`] of the [`UserInterface`], consuming it in the
     /// process.
     ///

winit/src/application.rs

@@ -9,12 +9,14 @@ use crate::{
     Clipboard, Color, Command, Debug, Error, Executor, Mode, Proxy, Runtime,
     Settings, Size, Subscription,
 };
+
+use iced_futures::futures;
+use iced_futures::futures::channel::mpsc;
 use iced_graphics::window;
 use iced_native::program::Program;
 use iced_native::{Cache, UserInterface};
 
-use iced_futures::futures;
-use iced_futures::futures::channel::mpsc;
+use std::mem::ManuallyDrop;
 
 /// An interactive, native cross-platform application.
 ///
@@ -214,8 +216,9 @@ async fn run_instance<A, E, C>(
     let mut state = State::new(&application, &window);
 
     let surface = compositor.create_surface(&window);
-    let mut physical_size = state.physical_size();
+    let physical_size = state.physical_size();
 
+    let mut viewport_version = state.viewport_version();
     let mut swap_chain = compositor.create_swap_chain(
         &surface,
         physical_size.width,
@@ -224,7 +227,7 @@ async fn run_instance<A, E, C>(
 
     let clipboard = Clipboard::new(&window);
 
-    let mut user_interface = std::mem::ManuallyDrop::new(build_user_interface(
+    let mut user_interface = ManuallyDrop::new(build_user_interface(
         &mut application,
         Cache::default(),
         &mut renderer,
@@ -267,8 +270,7 @@ async fn run_instance<A, E, C>(
                     debug.draw_finished();
                 } else {
                     let cache =
-                        std::mem::ManuallyDrop::into_inner(user_interface)
-                            .into_cache();
+                        ManuallyDrop::into_inner(user_interface).into_cache();
 
                     for message in messages.drain(..) {
                         debug.log_message(&message);
@@ -288,14 +290,13 @@ async fn run_instance<A, E, C>(
                     // Update window
                     state.synchronize(&application, &window);
 
-                    user_interface =
-                        std::mem::ManuallyDrop::new(build_user_interface(
-                            &mut application,
-                            cache,
-                            &mut renderer,
-                            state.logical_size(),
-                            &mut debug,
-                        ));
+                    user_interface = ManuallyDrop::new(build_user_interface(
+                        &mut application,
+                        cache,
+                        &mut renderer,
+                        state.logical_size(),
+                        &mut debug,
+                    ));
 
                     debug.draw_started();
                     primitive = user_interface
@@ -310,17 +311,31 @@ async fn run_instance<A, E, C>(
             }
             event::Event::RedrawRequested(_) => {
                 debug.render_started();
+                let current_viewport_version = state.viewport_version();
 
-                let current_physical_size = state.physical_size();
+                if viewport_version != current_viewport_version {
+                    let physical_size = state.physical_size();
+                    let logical_size = state.logical_size();
+
+                    debug.layout_started();
+                    user_interface = ManuallyDrop::new(
+                        ManuallyDrop::into_inner(user_interface)
+                            .relayout(logical_size, &mut renderer),
+                    );
+                    debug.layout_finished();
+
+                    debug.draw_started();
+                    primitive = user_interface
+                        .draw(&mut renderer, state.cursor_position());
+                    debug.draw_finished();
 
-                if physical_size != current_physical_size {
                     swap_chain = compositor.create_swap_chain(
                         &surface,
                         physical_size.width,
                         physical_size.height,
                     );
 
-                    physical_size = current_physical_size;
+                    viewport_version = current_viewport_version;
                 }
 
                 let new_mouse_interaction = compositor.draw(

winit/src/application/state.rs

@@ -12,6 +12,7 @@ pub struct State<A: Application> {
     background_color: Color,
     scale_factor: f64,
     viewport: Viewport,
+    viewport_version: usize,
     cursor_position: winit::dpi::PhysicalPosition<f64>,
     modifiers: winit::event::ModifiersState,
     application: PhantomData<A>,
@@ -39,6 +40,7 @@ impl<A: Application> State<A> {
             background_color,
             scale_factor,
             viewport,
+            viewport_version: 0,
             // TODO: Encode cursor availability in the type-system
             cursor_position: winit::dpi::PhysicalPosition::new(-1.0, -1.0),
             modifiers: winit::event::ModifiersState::default(),
@@ -54,6 +56,10 @@ impl<A: Application> State<A> {
         &self.viewport
     }
 
+    pub fn viewport_version(&self) -> usize {
+        self.viewport_version
+    }
+
     pub fn physical_size(&self) -> Size<u32> {
         self.viewport.physical_size()
     }
@@ -91,6 +97,8 @@ impl<A: Application> State<A> {
                     size,
                     window.scale_factor() * self.scale_factor,
                 );
+
+                self.viewport_version = self.viewport_version.wrapping_add(1);
             }
             WindowEvent::ScaleFactorChanged {
                 scale_factor: new_scale_factor,
@@ -103,6 +111,8 @@ impl<A: Application> State<A> {
                     size,
                     new_scale_factor * self.scale_factor,
                 );
+
+                self.viewport_version = self.viewport_version.wrapping_add(1);
             }
             WindowEvent::CursorMoved { position, .. } => {
                 self.cursor_position = *position;