Merge branch 'master' into remove-vertex-indexing

11 files changed, 603 insertions, 139 deletions

diff --git a/runtime/Cargo.toml b/runtime/Cargo.toml
index d19aedd3..8089d545 100644
--- a/runtime/Cargo.toml
+++ b/runtime/Cargo.toml
@@ -12,6 +12,7 @@ keywords.workspace = true
 
 [features]
 debug = []
+multi-window = []
 
 [dependencies]
 iced_core.workspace = true
diff --git a/runtime/src/command.rs b/runtime/src/command.rs
index cd4c51ff..f70da915 100644
--- a/runtime/src/command.rs
+++ b/runtime/src/command.rs
@@ -4,8 +4,11 @@ mod action;
 pub use action::Action;
 
 use crate::core::widget;
+use crate::futures::futures;
 use crate::futures::MaybeSend;
 
+use futures::channel::mpsc;
+use futures::Stream;
 use std::fmt;
 use std::future::Future;
 
@@ -40,14 +43,24 @@ impl<T> Command<T> {
 
     /// Creates a [`Command`] that performs the action of the given future.
     pub fn perform<A>(
-        future: impl Future<Output = T> + 'static + MaybeSend,
-        f: impl FnOnce(T) -> A + 'static + MaybeSend,
-    ) -> Command<A> {
-        use iced_futures::futures::FutureExt;
+        future: impl Future<Output = A> + 'static + MaybeSend,
+        f: impl FnOnce(A) -> T + 'static + MaybeSend,
+    ) -> Command<T> {
+        use futures::FutureExt;
 
         Command::single(Action::Future(Box::pin(future.map(f))))
     }
 
+    /// Creates a [`Command`] that runs the given stream to completion.
+    pub fn run<A>(
+        stream: impl Stream<Item = A> + 'static + MaybeSend,
+        f: impl Fn(A) -> T + 'static + MaybeSend,
+    ) -> Command<T> {
+        use futures::StreamExt;
+
+        Command::single(Action::Stream(Box::pin(stream.map(f))))
+    }
+
     /// Creates a [`Command`] that performs the actions of all the given
     /// commands.
     ///
@@ -106,3 +119,23 @@ impl<T> fmt::Debug for Command<T> {
         command.fmt(f)
     }
 }
+
+/// Creates a [`Command`] that produces the `Message`s published from a [`Future`]
+/// to an [`mpsc::Sender`] with the given bounds.
+pub fn channel<Fut, Message>(
+    size: usize,
+    f: impl FnOnce(mpsc::Sender<Message>) -> Fut + MaybeSend + 'static,
+) -> Command<Message>
+where
+    Fut: Future<Output = ()> + MaybeSend + 'static,
+    Message: 'static + MaybeSend,
+{
+    use futures::future;
+    use futures::stream::{self, StreamExt};
+
+    let (sender, receiver) = mpsc::channel(size);
+
+    let runner = stream::once(f(sender)).filter_map(|_| future::ready(None));
+
+    Command::single(Action::Stream(Box::pin(stream::select(receiver, runner))))
+}
diff --git a/runtime/src/command/action.rs b/runtime/src/command/action.rs
index 6c74f0ef..cb0936df 100644
--- a/runtime/src/command/action.rs
+++ b/runtime/src/command/action.rs
@@ -18,6 +18,11 @@ pub enum Action<T> {
     /// [`Future`]: iced_futures::BoxFuture
     Future(iced_futures::BoxFuture<T>),
 
+    /// Run a [`Stream`] to completion.
+    ///
+    /// [`Stream`]: iced_futures::BoxStream
+    Stream(iced_futures::BoxStream<T>),
+
     /// Run a clipboard action.
     Clipboard(clipboard::Action<T>),
 
@@ -52,10 +57,11 @@ impl<T> Action<T> {
         A: 'static,
         T: 'static,
     {
-        use iced_futures::futures::FutureExt;
+        use iced_futures::futures::{FutureExt, StreamExt};
 
         match self {
             Self::Future(future) => Action::Future(Box::pin(future.map(f))),
+            Self::Stream(stream) => Action::Stream(Box::pin(stream.map(f))),
             Self::Clipboard(action) => Action::Clipboard(action.map(f)),
             Self::Window(window) => Action::Window(window.map(f)),
             Self::System(system) => Action::System(system.map(f)),
@@ -74,10 +80,13 @@ impl<T> fmt::Debug for Action<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
             Self::Future(_) => write!(f, "Action::Future"),
+            Self::Stream(_) => write!(f, "Action::Stream"),
             Self::Clipboard(action) => {
                 write!(f, "Action::Clipboard({action:?})")
             }
-            Self::Window(action) => write!(f, "Action::Window({action:?})"),
+            Self::Window(action) => {
+                write!(f, "Action::Window({action:?})")
+            }
             Self::System(action) => write!(f, "Action::System({action:?})"),
             Self::Widget(_action) => write!(f, "Action::Widget"),
             Self::LoadFont { .. } => write!(f, "Action::LoadFont"),
diff --git a/runtime/src/lib.rs b/runtime/src/lib.rs
index 29e94d65..03906f45 100644
--- a/runtime/src/lib.rs
+++ b/runtime/src/lib.rs
@@ -26,6 +26,9 @@ pub mod system;
 pub mod user_interface;
 pub mod window;
 
+#[cfg(feature = "multi-window")]
+pub mod multi_window;
+
 // We disable debug capabilities on release builds unless the `debug` feature
 // is explicitly enabled.
 #[cfg(feature = "debug")]
diff --git a/runtime/src/multi_window.rs b/runtime/src/multi_window.rs
new file mode 100644
index 00000000..cf778a20
--- /dev/null
+++ b/runtime/src/multi_window.rs
@@ -0,0 +1,6 @@
+//! A multi-window application.
+pub mod program;
+pub mod state;
+
+pub use program::Program;
+pub use state::State;
diff --git a/runtime/src/multi_window/program.rs b/runtime/src/multi_window/program.rs
new file mode 100644
index 00000000..591b3e9a
--- /dev/null
+++ b/runtime/src/multi_window/program.rs
@@ -0,0 +1,32 @@
+//! Build interactive programs using The Elm Architecture.
+use crate::core::text;
+use crate::core::window;
+use crate::core::{Element, Renderer};
+use crate::Command;
+
+/// The core of a user interface for a multi-window application following The Elm Architecture.
+pub trait Program: Sized {
+    /// The graphics backend to use to draw the [`Program`].
+    type Renderer: Renderer + text::Renderer;
+
+    /// The type of __messages__ your [`Program`] will produce.
+    type Message: std::fmt::Debug + Send;
+
+    /// Handles a __message__ and updates the state of the [`Program`].
+    ///
+    /// This is where you define your __update logic__. All the __messages__,
+    /// produced by either user interactions or commands, will be handled by
+    /// this method.
+    ///
+    /// Any [`Command`] returned will be executed immediately in the
+    /// background by shells.
+    fn update(&mut self, message: Self::Message) -> Command<Self::Message>;
+
+    /// Returns the widgets to display in the [`Program`] for the `window`.
+    ///
+    /// These widgets can produce __messages__ based on user interaction.
+    fn view(
+        &self,
+        window: window::Id,
+    ) -> Element<'_, Self::Message, Self::Renderer>;
+}
diff --git a/runtime/src/multi_window/state.rs b/runtime/src/multi_window/state.rs
new file mode 100644
index 00000000..49f72c39
--- /dev/null
+++ b/runtime/src/multi_window/state.rs
@@ -0,0 +1,280 @@
+//! The internal state of a multi-window [`Program`].
+use crate::core::event::{self, Event};
+use crate::core::mouse;
+use crate::core::renderer;
+use crate::core::widget::operation::{self, Operation};
+use crate::core::{Clipboard, Size};
+use crate::user_interface::{self, UserInterface};
+use crate::{Command, Debug, Program};
+
+/// The execution state of a multi-window [`Program`]. It leverages caching, event
+/// processing, and rendering primitive storage.
+#[allow(missing_debug_implementations)]
+pub struct State<P>
+where
+    P: Program + 'static,
+{
+    program: P,
+    caches: Option<Vec<user_interface::Cache>>,
+    queued_events: Vec<Event>,
+    queued_messages: Vec<P::Message>,
+    mouse_interaction: mouse::Interaction,
+}
+
+impl<P> State<P>
+where
+    P: Program + 'static,
+{
+    /// Creates a new [`State`] with the provided [`Program`], initializing its
+    /// primitive with the given logical bounds and renderer.
+    pub fn new(
+        program: P,
+        bounds: Size,
+        renderer: &mut P::Renderer,
+        debug: &mut Debug,
+    ) -> Self {
+        let user_interface = build_user_interface(
+            &program,
+            user_interface::Cache::default(),
+            renderer,
+            bounds,
+            debug,
+        );
+
+        let caches = Some(vec![user_interface.into_cache()]);
+
+        State {
+            program,
+            caches,
+            queued_events: Vec::new(),
+            queued_messages: Vec::new(),
+            mouse_interaction: mouse::Interaction::Idle,
+        }
+    }
+
+    /// Returns a reference to the [`Program`] of the [`State`].
+    pub fn program(&self) -> &P {
+        &self.program
+    }
+
+    /// Queues an event in the [`State`] for processing during an [`update`].
+    ///
+    /// [`update`]: Self::update
+    pub fn queue_event(&mut self, event: Event) {
+        self.queued_events.push(event);
+    }
+
+    /// Queues a message in the [`State`] for processing during an [`update`].
+    ///
+    /// [`update`]: Self::update
+    pub fn queue_message(&mut self, message: P::Message) {
+        self.queued_messages.push(message);
+    }
+
+    /// Returns whether the event queue of the [`State`] is empty or not.
+    pub fn is_queue_empty(&self) -> bool {
+        self.queued_events.is_empty() && self.queued_messages.is_empty()
+    }
+
+    /// Returns the current [`mouse::Interaction`] of the [`State`].
+    pub fn mouse_interaction(&self) -> mouse::Interaction {
+        self.mouse_interaction
+    }
+
+    /// Processes all the queued events and messages, rebuilding and redrawing
+    /// the widgets of the linked [`Program`] if necessary.
+    ///
+    /// Returns a list containing the instances of [`Event`] that were not
+    /// captured by any widget, and the [`Command`] obtained from [`Program`]
+    /// after updating it, only if an update was necessary.
+    pub fn update(
+        &mut self,
+        bounds: Size,
+        cursor: mouse::Cursor,
+        renderer: &mut P::Renderer,
+        theme: &<P::Renderer as iced_core::Renderer>::Theme,
+        style: &renderer::Style,
+        clipboard: &mut dyn Clipboard,
+        debug: &mut Debug,
+    ) -> (Vec<Event>, Option<Command<P::Message>>) {
+        let mut user_interfaces = build_user_interfaces(
+            &self.program,
+            self.caches.take().unwrap(),
+            renderer,
+            bounds,
+            debug,
+        );
+
+        debug.event_processing_started();
+        let mut messages = Vec::new();
+
+        let uncaptured_events = user_interfaces.iter_mut().fold(
+            vec![],
+            |mut uncaptured_events, ui| {
+                let (_, event_statuses) = ui.update(
+                    &self.queued_events,
+                    cursor,
+                    renderer,
+                    clipboard,
+                    &mut messages,
+                );
+
+                uncaptured_events.extend(
+                    self.queued_events
+                        .iter()
+                        .zip(event_statuses)
+                        .filter_map(|(event, status)| {
+                            matches!(status, event::Status::Ignored)
+                                .then_some(event)
+                        })
+                        .cloned(),
+                );
+                uncaptured_events
+            },
+        );
+
+        self.queued_events.clear();
+        messages.append(&mut self.queued_messages);
+        debug.event_processing_finished();
+
+        let commands = if messages.is_empty() {
+            debug.draw_started();
+
+            for ui in &mut user_interfaces {
+                self.mouse_interaction =
+                    ui.draw(renderer, theme, style, cursor);
+            }
+
+            debug.draw_finished();
+
+            self.caches = Some(
+                user_interfaces
+                    .drain(..)
+                    .map(UserInterface::into_cache)
+                    .collect(),
+            );
+
+            None
+        } else {
+            let temp_caches = user_interfaces
+                .drain(..)
+                .map(UserInterface::into_cache)
+                .collect();
+
+            drop(user_interfaces);
+
+            let commands = Command::batch(messages.into_iter().map(|msg| {
+                debug.log_message(&msg);
+
+                debug.update_started();
+                let command = self.program.update(msg);
+                debug.update_finished();
+
+                command
+            }));
+
+            let mut user_interfaces = build_user_interfaces(
+                &self.program,
+                temp_caches,
+                renderer,
+                bounds,
+                debug,
+            );
+
+            debug.draw_started();
+            for ui in &mut user_interfaces {
+                self.mouse_interaction =
+                    ui.draw(renderer, theme, style, cursor);
+            }
+            debug.draw_finished();
+
+            self.caches = Some(
+                user_interfaces
+                    .drain(..)
+                    .map(UserInterface::into_cache)
+                    .collect(),
+            );
+
+            Some(commands)
+        };
+
+        (uncaptured_events, commands)
+    }
+
+    /// Applies widget [`Operation`]s to the [`State`].
+    pub fn operate(
+        &mut self,
+        renderer: &mut P::Renderer,
+        operations: impl Iterator<Item = Box<dyn Operation<P::Message>>>,
+        bounds: Size,
+        debug: &mut Debug,
+    ) {
+        let mut user_interfaces = build_user_interfaces(
+            &self.program,
+            self.caches.take().unwrap(),
+            renderer,
+            bounds,
+            debug,
+        );
+
+        for operation in operations {
+            let mut current_operation = Some(operation);
+
+            while let Some(mut operation) = current_operation.take() {
+                for ui in &mut user_interfaces {
+                    ui.operate(renderer, operation.as_mut());
+                }
+
+                match operation.finish() {
+                    operation::Outcome::None => {}
+                    operation::Outcome::Some(message) => {
+                        self.queued_messages.push(message);
+                    }
+                    operation::Outcome::Chain(next) => {
+                        current_operation = Some(next);
+                    }
+                };
+            }
+        }
+
+        self.caches = Some(
+            user_interfaces
+                .drain(..)
+                .map(UserInterface::into_cache)
+                .collect(),
+        );
+    }
+}
+
+fn build_user_interfaces<'a, P: Program>(
+    program: &'a P,
+    mut caches: Vec<user_interface::Cache>,
+    renderer: &mut P::Renderer,
+    size: Size,
+    debug: &mut Debug,
+) -> Vec<UserInterface<'a, P::Message, P::Renderer>> {
+    caches
+        .drain(..)
+        .map(|cache| {
+            build_user_interface(program, cache, renderer, size, debug)
+        })
+        .collect()
+}
+
+fn build_user_interface<'a, P: Program>(
+    program: &'a P,
+    cache: user_interface::Cache,
+    renderer: &mut P::Renderer,
+    size: Size,
+    debug: &mut Debug,
+) -> UserInterface<'a, P::Message, P::Renderer> {
+    debug.view_started();
+    let view = program.view();
+    debug.view_finished();
+
+    debug.layout_started();
+    let user_interface = UserInterface::build(view, size, cache, renderer);
+    debug.layout_finished();
+
+    user_interface
+}
diff --git a/runtime/src/overlay/nested.rs b/runtime/src/overlay/nested.rs
index 062ccc72..4256efb7 100644
--- a/runtime/src/overlay/nested.rs
+++ b/runtime/src/overlay/nested.rs
@@ -4,7 +4,9 @@ use crate::core::mouse;
 use crate::core::overlay;
 use crate::core::renderer;
 use crate::core::widget;
-use crate::core::{Clipboard, Event, Layout, Point, Rectangle, Shell, Size};
+use crate::core::{
+    Clipboard, Event, Layout, Point, Rectangle, Shell, Size, Vector,
+};
 
 /// An overlay container that displays nested overlays
 #[allow(missing_debug_implementations)]
@@ -33,19 +35,18 @@ where
         &mut self,
         renderer: &Renderer,
         bounds: Size,
-        position: Point,
+        _position: Point,
+        translation: Vector,
     ) -> layout::Node {
         fn recurse<Message, Renderer>(
             element: &mut overlay::Element<'_, Message, Renderer>,
             renderer: &Renderer,
             bounds: Size,
-            position: Point,
+            translation: Vector,
         ) -> layout::Node
         where
             Renderer: renderer::Renderer,
         {
-            let translation = position - Point::ORIGIN;
-
             let node = element.layout(renderer, bounds, translation);
 
             if let Some(mut nested) =
@@ -55,7 +56,7 @@ where
                     node.size(),
                     vec![
                         node,
-                        recurse(&mut nested, renderer, bounds, position),
+                        recurse(&mut nested, renderer, bounds, translation),
                     ],
                 )
             } else {
@@ -63,7 +64,7 @@ where
             }
         }
 
-        recurse(&mut self.overlay, renderer, bounds, position)
+        recurse(&mut self.overlay, renderer, bounds, translation)
     }
 
     /// Draws the [`Nested`] overlay using the associated `Renderer`.
diff --git a/runtime/src/user_interface.rs b/runtime/src/user_interface.rs
index dae9e0ac..3594ac18 100644
--- a/runtime/src/user_interface.rs
+++ b/runtime/src/user_interface.rs
@@ -5,7 +5,9 @@ use crate::core::mouse;
 use crate::core::renderer;
 use crate::core::widget;
 use crate::core::window;
-use crate::core::{Clipboard, Element, Layout, Point, Rectangle, Shell, Size};
+use crate::core::{
+    Clipboard, Element, Layout, Point, Rectangle, Shell, Size, Vector,
+};
 use crate::overlay;
 
 /// A set of interactive graphical elements with a specific [`Layout`].
@@ -199,7 +201,8 @@ where
             let bounds = self.bounds;
 
             let mut overlay = manual_overlay.as_mut().unwrap();
-            let mut layout = overlay.layout(renderer, bounds, Point::ORIGIN);
+            let mut layout =
+                overlay.layout(renderer, bounds, Point::ORIGIN, Vector::ZERO);
             let mut event_statuses = Vec::new();
 
             for event in events.iter().cloned() {
@@ -253,8 +256,12 @@ where
                     overlay = manual_overlay.as_mut().unwrap();
 
                     shell.revalidate_layout(|| {
-                        layout =
-                            overlay.layout(renderer, bounds, Point::ORIGIN);
+                        layout = overlay.layout(
+                            renderer,
+                            bounds,
+                            Point::ORIGIN,
+                            Vector::ZERO,
+                        );
                     });
                 }
 
@@ -448,7 +455,12 @@ where
             .map(overlay::Nested::new)
         {
             let overlay_layout = self.overlay.take().unwrap_or_else(|| {
-                overlay.layout(renderer, self.bounds, Point::ORIGIN)
+                overlay.layout(
+                    renderer,
+                    self.bounds,
+                    Point::ORIGIN,
+                    Vector::ZERO,
+                )
             });
 
             let cursor = if cursor
@@ -566,8 +578,12 @@ where
             .map(overlay::Nested::new)
         {
             if self.overlay.is_none() {
-                self.overlay =
-                    Some(overlay.layout(renderer, self.bounds, Point::ORIGIN));
+                self.overlay = Some(overlay.layout(
+                    renderer,
+                    self.bounds,
+                    Point::ORIGIN,
+                    Vector::ZERO,
+                ));
             }
 
             overlay.operate(
diff --git a/runtime/src/window.rs b/runtime/src/window.rs
index 41816967..2136d64d 100644
--- a/runtime/src/window.rs
+++ b/runtime/src/window.rs
@@ -8,95 +8,135 @@ pub use screenshot::Screenshot;
 
 use crate::command::{self, Command};
 use crate::core::time::Instant;
-use crate::core::window::{Event, Icon, Level, Mode, UserAttention};
-use crate::core::Size;
+use crate::core::window::{
+    Event, Icon, Id, Level, Mode, Settings, UserAttention,
+};
+use crate::core::{Point, Size};
 use crate::futures::event;
 use crate::futures::Subscription;
 
 /// Subscribes to the frames of the window of the running application.
 ///
 /// The resulting [`Subscription`] will produce items at a rate equal to the
-/// refresh rate of the window. Note that this rate may be variable, as it is
+/// refresh rate of the first application window. Note that this rate may be variable, as it is
 /// normally managed by the graphics driver and/or the OS.
 ///
 /// In any case, this [`Subscription`] is useful to smoothly draw application-driven
 /// animations without missing any frames.
 pub fn frames() -> Subscription<Instant> {
     event::listen_raw(|event, _status| match event {
-        iced_core::Event::Window(Event::RedrawRequested(at)) => Some(at),
+        crate::core::Event::Window(_, Event::RedrawRequested(at)) => Some(at),
         _ => None,
     })
 }
 
-/// Closes the current window and exits the application.
-pub fn close<Message>() -> Command<Message> {
-    Command::single(command::Action::Window(Action::Close))
+/// Spawns a new window with the given `settings`.
+///
+/// Returns the new window [`Id`] alongside the [`Command`].
+pub fn spawn<Message>(settings: Settings) -> (Id, Command<Message>) {
+    let id = Id::unique();
+
+    (
+        id,
+        Command::single(command::Action::Window(Action::Spawn(id, settings))),
+    )
+}
+
+/// Closes the window with `id`.
+pub fn close<Message>(id: Id) -> Command<Message> {
+    Command::single(command::Action::Window(Action::Close(id)))
 }
 
 /// Begins dragging the window while the left mouse button is held.
-pub fn drag<Message>() -> Command<Message> {
-    Command::single(command::Action::Window(Action::Drag))
+pub fn drag<Message>(id: Id) -> Command<Message> {
+    Command::single(command::Action::Window(Action::Drag(id)))
 }
 
 /// Resizes the window to the given logical dimensions.
-pub fn resize<Message>(new_size: Size<u32>) -> Command<Message> {
-    Command::single(command::Action::Window(Action::Resize(new_size)))
+pub fn resize<Message>(id: Id, new_size: Size) -> Command<Message> {
+    Command::single(command::Action::Window(Action::Resize(id, new_size)))
 }
 
-/// Fetches the current window size in logical dimensions.
+/// Fetches the window's size in logical dimensions.
 pub fn fetch_size<Message>(
-    f: impl FnOnce(Size<u32>) -> Message + 'static,
+    id: Id,
+    f: impl FnOnce(Size) -> Message + 'static,
 ) -> Command<Message> {
-    Command::single(command::Action::Window(Action::FetchSize(Box::new(f))))
+    Command::single(command::Action::Window(Action::FetchSize(id, Box::new(f))))
+}
+
+/// Fetches if the window is maximized.
+pub fn fetch_maximized<Message>(
+    id: Id,
+    f: impl FnOnce(bool) -> Message + 'static,
+) -> Command<Message> {
+    Command::single(command::Action::Window(Action::FetchMaximized(
+        id,
+        Box::new(f),
+    )))
 }
 
 /// Maximizes the window.
-pub fn maximize<Message>(maximized: bool) -> Command<Message> {
-    Command::single(command::Action::Window(Action::Maximize(maximized)))
+pub fn maximize<Message>(id: Id, maximized: bool) -> Command<Message> {
+    Command::single(command::Action::Window(Action::Maximize(id, maximized)))
+}
+
+/// Fetches if the window is minimized.
+pub fn fetch_minimized<Message>(
+    id: Id,
+    f: impl FnOnce(Option<bool>) -> Message + 'static,
+) -> Command<Message> {
+    Command::single(command::Action::Window(Action::FetchMinimized(
+        id,
+        Box::new(f),
+    )))
 }
 
-/// Minimes the window.
-pub fn minimize<Message>(minimized: bool) -> Command<Message> {
-    Command::single(command::Action::Window(Action::Minimize(minimized)))
+/// Minimizes the window.
+pub fn minimize<Message>(id: Id, minimized: bool) -> Command<Message> {
+    Command::single(command::Action::Window(Action::Minimize(id, minimized)))
 }
 
-/// Moves a window to the given logical coordinates.
-pub fn move_to<Message>(x: i32, y: i32) -> Command<Message> {
-    Command::single(command::Action::Window(Action::Move { x, y }))
+/// Moves the window to the given logical coordinates.
+pub fn move_to<Message>(id: Id, position: Point) -> Command<Message> {
+    Command::single(command::Action::Window(Action::Move(id, position)))
 }
 
 /// Changes the [`Mode`] of the window.
-pub fn change_mode<Message>(mode: Mode) -> Command<Message> {
-    Command::single(command::Action::Window(Action::ChangeMode(mode)))
+pub fn change_mode<Message>(id: Id, mode: Mode) -> Command<Message> {
+    Command::single(command::Action::Window(Action::ChangeMode(id, mode)))
 }
 
 /// Fetches the current [`Mode`] of the window.
 pub fn fetch_mode<Message>(
+    id: Id,
     f: impl FnOnce(Mode) -> Message + 'static,
 ) -> Command<Message> {
-    Command::single(command::Action::Window(Action::FetchMode(Box::new(f))))
+    Command::single(command::Action::Window(Action::FetchMode(id, Box::new(f))))
 }
 
 /// Toggles the window to maximized or back.
-pub fn toggle_maximize<Message>() -> Command<Message> {
-    Command::single(command::Action::Window(Action::ToggleMaximize))
+pub fn toggle_maximize<Message>(id: Id) -> Command<Message> {
+    Command::single(command::Action::Window(Action::ToggleMaximize(id)))
 }
 
 /// Toggles the window decorations.
-pub fn toggle_decorations<Message>() -> Command<Message> {
-    Command::single(command::Action::Window(Action::ToggleDecorations))
+pub fn toggle_decorations<Message>(id: Id) -> Command<Message> {
+    Command::single(command::Action::Window(Action::ToggleDecorations(id)))
 }
 
-/// Request user attention to the window, this has no effect if the application
+/// Request user attention to the window. This has no effect if the application
 /// is already focused. How requesting for user attention manifests is platform dependent,
 /// see [`UserAttention`] for details.
 ///
 /// Providing `None` will unset the request for user attention. Unsetting the request for
 /// user attention might not be done automatically by the WM when the window receives input.
 pub fn request_user_attention<Message>(
+    id: Id,
     user_attention: Option<UserAttention>,
 ) -> Command<Message> {
     Command::single(command::Action::Window(Action::RequestUserAttention(
+        id,
         user_attention,
     )))
 }
@@ -107,30 +147,36 @@ pub fn request_user_attention<Message>(
 /// This [`Command`] steals input focus from other applications. Do not use this method unless
 /// you are certain that's what the user wants. Focus stealing can cause an extremely disruptive
 /// user experience.
-pub fn gain_focus<Message>() -> Command<Message> {
-    Command::single(command::Action::Window(Action::GainFocus))
+pub fn gain_focus<Message>(id: Id) -> Command<Message> {
+    Command::single(command::Action::Window(Action::GainFocus(id)))
 }
 
 /// Changes the window [`Level`].
-pub fn change_level<Message>(level: Level) -> Command<Message> {
-    Command::single(command::Action::Window(Action::ChangeLevel(level)))
+pub fn change_level<Message>(id: Id, level: Level) -> Command<Message> {
+    Command::single(command::Action::Window(Action::ChangeLevel(id, level)))
 }
 
-/// Fetches an identifier unique to the window.
+/// Fetches an identifier unique to the window, provided by the underlying windowing system. This is
+/// not to be confused with [`Id`].
 pub fn fetch_id<Message>(
+    id: Id,
     f: impl FnOnce(u64) -> Message + 'static,
 ) -> Command<Message> {
-    Command::single(command::Action::Window(Action::FetchId(Box::new(f))))
+    Command::single(command::Action::Window(Action::FetchId(id, Box::new(f))))
 }
 
 /// Changes the [`Icon`] of the window.
-pub fn change_icon<Message>(icon: Icon) -> Command<Message> {
-    Command::single(command::Action::Window(Action::ChangeIcon(icon)))
+pub fn change_icon<Message>(id: Id, icon: Icon) -> Command<Message> {
+    Command::single(command::Action::Window(Action::ChangeIcon(id, icon)))
 }
 
 /// Captures a [`Screenshot`] from the window.
 pub fn screenshot<Message>(
+    id: Id,
     f: impl FnOnce(Screenshot) -> Message + Send + 'static,
 ) -> Command<Message> {
-    Command::single(command::Action::Window(Action::Screenshot(Box::new(f))))
+    Command::single(command::Action::Window(Action::Screenshot(
+        id,
+        Box::new(f),
+    )))
 }
diff --git a/runtime/src/window/action.rs b/runtime/src/window/action.rs
index b6964e36..8b532569 100644
--- a/runtime/src/window/action.rs
+++ b/runtime/src/window/action.rs
@@ -1,5 +1,5 @@
-use crate::core::window::{Icon, Level, Mode, UserAttention};
-use crate::core::Size;
+use crate::core::window::{Icon, Id, Level, Mode, Settings, UserAttention};
+use crate::core::{Point, Size};
 use crate::futures::MaybeSend;
 use crate::window::Screenshot;
 
@@ -7,43 +7,51 @@ use std::fmt;
 
 /// An operation to be performed on some window.
 pub enum Action<T> {
-    /// Close the current window and exits the application.
-    Close,
+    /// Spawns a new window with some [`Settings`].
+    Spawn(Id, Settings),
+    /// Close the window and exits the application.
+    Close(Id),
     /// Move the window with the left mouse button until the button is
     /// released.
     ///
     /// There’s no guarantee that this will work unless the left mouse
     /// button was pressed immediately before this function is called.
-    Drag,
-    /// Resize the window.
-    Resize(Size<u32>),
-    /// Fetch the current size of the window.
-    FetchSize(Box<dyn FnOnce(Size<u32>) -> T + 'static>),
+    Drag(Id),
+    /// Resize the window to the given logical dimensions.
+    Resize(Id, Size),
+    /// Fetch the current logical dimensions of the window.
+    FetchSize(Id, Box<dyn FnOnce(Size) -> T + 'static>),
+    /// Fetch if the current window is maximized or not.
+    ///
+    /// ## Platform-specific
+    /// - **iOS / Android / Web:** Unsupported.
+    FetchMaximized(Id, Box<dyn FnOnce(bool) -> T + 'static>),
     /// Set the window to maximized or back
-    Maximize(bool),
+    Maximize(Id, bool),
+    /// Fetch if the current window is minimized or not.
+    ///
+    /// ## Platform-specific
+    /// - **Wayland:** Always `None`.
+    /// - **iOS / Android / Web:** Unsupported.
+    FetchMinimized(Id, Box<dyn FnOnce(Option<bool>) -> T + 'static>),
     /// Set the window to minimized or back
-    Minimize(bool),
-    /// Move the window.
+    Minimize(Id, bool),
+    /// Move the window to the given logical coordinates.
     ///
     /// Unsupported on Wayland.
-    Move {
-        /// The new logical x location of the window
-        x: i32,
-        /// The new logical y location of the window
-        y: i32,
-    },
+    Move(Id, Point),
     /// Change the [`Mode`] of the window.
-    ChangeMode(Mode),
+    ChangeMode(Id, Mode),
     /// Fetch the current [`Mode`] of the window.
-    FetchMode(Box<dyn FnOnce(Mode) -> T + 'static>),
+    FetchMode(Id, Box<dyn FnOnce(Mode) -> T + 'static>),
     /// Toggle the window to maximized or back
-    ToggleMaximize,
+    ToggleMaximize(Id),
     /// Toggle whether window has decorations.
     ///
     /// ## Platform-specific
     /// - **X11:** Not implemented.
     /// - **Web:** Unsupported.
-    ToggleDecorations,
+    ToggleDecorations(Id),
     /// Request user attention to the window, this has no effect if the application
     /// is already focused. How requesting for user attention manifests is platform dependent,
     /// see [`UserAttention`] for details.
@@ -57,7 +65,7 @@ pub enum Action<T> {
     /// - **macOS:** `None` has no effect.
     /// - **X11:** Requests for user attention must be manually cleared.
     /// - **Wayland:** Requires `xdg_activation_v1` protocol, `None` has no effect.
-    RequestUserAttention(Option<UserAttention>),
+    RequestUserAttention(Id, Option<UserAttention>),
     /// Bring the window to the front and sets input focus. Has no effect if the window is
     /// already in focus, minimized, or not visible.
     ///
@@ -68,11 +76,11 @@ pub enum Action<T> {
     /// ## Platform-specific
     ///
     /// - **Web / Wayland:** Unsupported.
-    GainFocus,
+    GainFocus(Id),
     /// Change the window [`Level`].
-    ChangeLevel(Level),
-    /// Fetch an identifier unique to the window.
-    FetchId(Box<dyn FnOnce(u64) -> T + 'static>),
+    ChangeLevel(Id, Level),
+    /// Fetch the raw identifier unique to the window.
+    FetchId(Id, Box<dyn FnOnce(u64) -> T + 'static>),
     /// Change the window [`Icon`].
     ///
     /// On Windows and X11, this is typically the small icon in the top-left
@@ -87,9 +95,9 @@ pub enum Action<T> {
     ///
     /// - **X11:** Has no universal guidelines for icon sizes, so you're at the whims of the WM. That
     ///   said, it's usually in the same ballpark as on Windows.
-    ChangeIcon(Icon),
+    ChangeIcon(Id, Icon),
     /// Screenshot the viewport of the window.
-    Screenshot(Box<dyn FnOnce(Screenshot) -> T + 'static>),
+    Screenshot(Id, Box<dyn FnOnce(Screenshot) -> T + 'static>),
 }
 
 impl<T> Action<T> {
@@ -102,29 +110,41 @@ impl<T> Action<T> {
         T: 'static,
     {
         match self {
-            Self::Close => Action::Close,
-            Self::Drag => Action::Drag,
-            Self::Resize(size) => Action::Resize(size),
-            Self::FetchSize(o) => Action::FetchSize(Box::new(move |s| f(o(s)))),
-            Self::Maximize(maximized) => Action::Maximize(maximized),
-            Self::Minimize(minimized) => Action::Minimize(minimized),
-            Self::Move { x, y } => Action::Move { x, y },
-            Self::ChangeMode(mode) => Action::ChangeMode(mode),
-            Self::FetchMode(o) => Action::FetchMode(Box::new(move |s| f(o(s)))),
-            Self::ToggleMaximize => Action::ToggleMaximize,
-            Self::ToggleDecorations => Action::ToggleDecorations,
-            Self::RequestUserAttention(attention_type) => {
-                Action::RequestUserAttention(attention_type)
-            }
-            Self::GainFocus => Action::GainFocus,
-            Self::ChangeLevel(level) => Action::ChangeLevel(level),
-            Self::FetchId(o) => Action::FetchId(Box::new(move |s| f(o(s)))),
-            Self::ChangeIcon(icon) => Action::ChangeIcon(icon),
-            Self::Screenshot(tag) => {
-                Action::Screenshot(Box::new(move |screenshot| {
-                    f(tag(screenshot))
-                }))
+            Self::Spawn(id, settings) => Action::Spawn(id, settings),
+            Self::Close(id) => Action::Close(id),
+            Self::Drag(id) => Action::Drag(id),
+            Self::Resize(id, size) => Action::Resize(id, size),
+            Self::FetchSize(id, o) => {
+                Action::FetchSize(id, Box::new(move |s| f(o(s))))
             }
+            Self::FetchMaximized(id, o) => {
+                Action::FetchMaximized(id, Box::new(move |s| f(o(s))))
+            }
+            Self::Maximize(id, maximized) => Action::Maximize(id, maximized),
+            Self::FetchMinimized(id, o) => {
+                Action::FetchMinimized(id, Box::new(move |s| f(o(s))))
+            }
+            Self::Minimize(id, minimized) => Action::Minimize(id, minimized),
+            Self::Move(id, position) => Action::Move(id, position),
+            Self::ChangeMode(id, mode) => Action::ChangeMode(id, mode),
+            Self::FetchMode(id, o) => {
+                Action::FetchMode(id, Box::new(move |s| f(o(s))))
+            }
+            Self::ToggleMaximize(id) => Action::ToggleMaximize(id),
+            Self::ToggleDecorations(id) => Action::ToggleDecorations(id),
+            Self::RequestUserAttention(id, attention_type) => {
+                Action::RequestUserAttention(id, attention_type)
+            }
+            Self::GainFocus(id) => Action::GainFocus(id),
+            Self::ChangeLevel(id, level) => Action::ChangeLevel(id, level),
+            Self::FetchId(id, o) => {
+                Action::FetchId(id, Box::new(move |s| f(o(s))))
+            }
+            Self::ChangeIcon(id, icon) => Action::ChangeIcon(id, icon),
+            Self::Screenshot(id, tag) => Action::Screenshot(
+                id,
+                Box::new(move |screenshot| f(tag(screenshot))),
+            ),
         }
     }
 }
@@ -132,35 +152,52 @@ impl<T> Action<T> {
 impl<T> fmt::Debug for Action<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
-            Self::Close => write!(f, "Action::Close"),
-            Self::Drag => write!(f, "Action::Drag"),
-            Self::Resize(size) => write!(f, "Action::Resize({size:?})"),
-            Self::FetchSize(_) => write!(f, "Action::FetchSize"),
-            Self::Maximize(maximized) => {
-                write!(f, "Action::Maximize({maximized})")
-            }
-            Self::Minimize(minimized) => {
-                write!(f, "Action::Minimize({minimized}")
-            }
-            Self::Move { x, y } => {
-                write!(f, "Action::Move {{ x: {x}, y: {y} }}")
-            }
-            Self::ChangeMode(mode) => write!(f, "Action::SetMode({mode:?})"),
-            Self::FetchMode(_) => write!(f, "Action::FetchMode"),
-            Self::ToggleMaximize => write!(f, "Action::ToggleMaximize"),
-            Self::ToggleDecorations => write!(f, "Action::ToggleDecorations"),
-            Self::RequestUserAttention(_) => {
-                write!(f, "Action::RequestUserAttention")
-            }
-            Self::GainFocus => write!(f, "Action::GainFocus"),
-            Self::ChangeLevel(level) => {
-                write!(f, "Action::ChangeLevel({level:?})")
-            }
-            Self::FetchId(_) => write!(f, "Action::FetchId"),
-            Self::ChangeIcon(_icon) => {
-                write!(f, "Action::ChangeIcon(icon)")
-            }
-            Self::Screenshot(_) => write!(f, "Action::Screenshot"),
+            Self::Spawn(id, settings) => {
+                write!(f, "Action::Spawn({id:?}, {settings:?})")
+            }
+            Self::Close(id) => write!(f, "Action::Close({id:?})"),
+            Self::Drag(id) => write!(f, "Action::Drag({id:?})"),
+            Self::Resize(id, size) => {
+                write!(f, "Action::Resize({id:?}, {size:?})")
+            }
+            Self::FetchSize(id, _) => write!(f, "Action::FetchSize({id:?})"),
+            Self::FetchMaximized(id, _) => {
+                write!(f, "Action::FetchMaximized({id:?})")
+            }
+            Self::Maximize(id, maximized) => {
+                write!(f, "Action::Maximize({id:?}, {maximized})")
+            }
+            Self::FetchMinimized(id, _) => {
+                write!(f, "Action::FetchMinimized({id:?})")
+            }
+            Self::Minimize(id, minimized) => {
+                write!(f, "Action::Minimize({id:?}, {minimized}")
+            }
+            Self::Move(id, position) => {
+                write!(f, "Action::Move({id:?}, {position})")
+            }
+            Self::ChangeMode(id, mode) => {
+                write!(f, "Action::SetMode({id:?}, {mode:?})")
+            }
+            Self::FetchMode(id, _) => write!(f, "Action::FetchMode({id:?})"),
+            Self::ToggleMaximize(id) => {
+                write!(f, "Action::ToggleMaximize({id:?})")
+            }
+            Self::ToggleDecorations(id) => {
+                write!(f, "Action::ToggleDecorations({id:?})")
+            }
+            Self::RequestUserAttention(id, _) => {
+                write!(f, "Action::RequestUserAttention({id:?})")
+            }
+            Self::GainFocus(id) => write!(f, "Action::GainFocus({id:?})"),
+            Self::ChangeLevel(id, level) => {
+                write!(f, "Action::ChangeLevel({id:?}, {level:?})")
+            }
+            Self::FetchId(id, _) => write!(f, "Action::FetchId({id:?})"),
+            Self::ChangeIcon(id, _icon) => {
+                write!(f, "Action::ChangeIcon({id:?})")
+            }
+            Self::Screenshot(id, _) => write!(f, "Action::Screenshot({id:?})"),
         }
     }
 }