Implement pure version of PaneGrid widget

Cargo.toml

@@ -89,6 +89,7 @@ members = [
     "examples/pure/component",
     "examples/pure/counter",
     "examples/pure/game_of_life",
+    "examples/pure/pane_grid",
     "examples/pure/pick_list",
     "examples/pure/todos",
     "examples/pure/tour",

examples/pure/pane_grid/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "pure_pane_grid"
+version = "0.1.0"
+authors = ["Héctor Ramón Jiménez <hector0193@gmail.com>"]
+edition = "2021"
+publish = false
+
+[dependencies]
+iced = { path = "../../..", features = ["pure", "debug"] }
+iced_native = { path = "../../../native" }
+iced_lazy = { path = "../../../lazy", features = ["pure"] }

examples/pure/pane_grid/src/main.rs

@@ -0,0 +1,437 @@
+use iced::alignment::{self, Alignment};
+use iced::executor;
+use iced::keyboard;
+use iced::pure::pane_grid::{self, PaneGrid};
+use iced::pure::{button, column, container, row, scrollable, text};
+use iced::pure::{Application, Element};
+use iced::{Color, Command, Length, Settings, Size, Subscription};
+use iced_lazy::pure::responsive;
+use iced_native::{event, subscription, Event};
+
+pub fn main() -> iced::Result {
+    Example::run(Settings::default())
+}
+
+struct Example {
+    panes: pane_grid::Map<Pane>,
+    panes_created: usize,
+    focus: Option<pane_grid::Pane>,
+}
+
+#[derive(Debug, Clone, Copy)]
+enum Message {
+    Split(pane_grid::Axis, pane_grid::Pane),
+    SplitFocused(pane_grid::Axis),
+    FocusAdjacent(pane_grid::Direction),
+    Clicked(pane_grid::Pane),
+    Dragged(pane_grid::DragEvent),
+    Resized(pane_grid::ResizeEvent),
+    TogglePin(pane_grid::Pane),
+    Close(pane_grid::Pane),
+    CloseFocused,
+}
+
+impl Application for Example {
+    type Message = Message;
+    type Executor = executor::Default;
+    type Flags = ();
+
+    fn new(_flags: ()) -> (Self, Command<Message>) {
+        let (panes, _) = pane_grid::Map::new(Pane::new(0));
+
+        (
+            Example {
+                panes,
+                panes_created: 1,
+                focus: None,
+            },
+            Command::none(),
+        )
+    }
+
+    fn title(&self) -> String {
+        String::from("Pane grid - Iced")
+    }
+
+    fn update(&mut self, message: Message) -> Command<Message> {
+        match message {
+            Message::Split(axis, pane) => {
+                let result = self.panes.split(
+                    axis,
+                    &pane,
+                    Pane::new(self.panes_created),
+                );
+
+                if let Some((pane, _)) = result {
+                    self.focus = Some(pane);
+                }
+
+                self.panes_created += 1;
+            }
+            Message::SplitFocused(axis) => {
+                if let Some(pane) = self.focus {
+                    let result = self.panes.split(
+                        axis,
+                        &pane,
+                        Pane::new(self.panes_created),
+                    );
+
+                    if let Some((pane, _)) = result {
+                        self.focus = Some(pane);
+                    }
+
+                    self.panes_created += 1;
+                }
+            }
+            Message::FocusAdjacent(direction) => {
+                if let Some(pane) = self.focus {
+                    if let Some(adjacent) =
+                        self.panes.adjacent(&pane, direction)
+                    {
+                        self.focus = Some(adjacent);
+                    }
+                }
+            }
+            Message::Clicked(pane) => {
+                self.focus = Some(pane);
+            }
+            Message::Resized(pane_grid::ResizeEvent { split, ratio }) => {
+                self.panes.resize(&split, ratio);
+            }
+            Message::Dragged(pane_grid::DragEvent::Dropped {
+                pane,
+                target,
+            }) => {
+                self.panes.swap(&pane, &target);
+            }
+            Message::Dragged(_) => {}
+            Message::TogglePin(pane) => {
+                if let Some(Pane { is_pinned, .. }) = self.panes.get_mut(&pane)
+                {
+                    *is_pinned = !*is_pinned;
+                }
+            }
+            Message::Close(pane) => {
+                if let Some((_, sibling)) = self.panes.close(&pane) {
+                    self.focus = Some(sibling);
+                }
+            }
+            Message::CloseFocused => {
+                if let Some(pane) = self.focus {
+                    if let Some(Pane { is_pinned, .. }) = self.panes.get(&pane)
+                    {
+                        if !is_pinned {
+                            if let Some((_, sibling)) = self.panes.close(&pane)
+                            {
+                                self.focus = Some(sibling);
+                            }
+                        }
+                    }
+                }
+            }
+        }
+
+        Command::none()
+    }
+
+    fn subscription(&self) -> Subscription<Message> {
+        subscription::events_with(|event, status| {
+            if let event::Status::Captured = status {
+                return None;
+            }
+
+            match event {
+                Event::Keyboard(keyboard::Event::KeyPressed {
+                    modifiers,
+                    key_code,
+                }) if modifiers.command() => handle_hotkey(key_code),
+                _ => None,
+            }
+        })
+    }
+
+    fn view(&self) -> Element<Message> {
+        let focus = self.focus;
+        let total_panes = self.panes.len();
+
+        let pane_grid = PaneGrid::new(&mut self.panes, |id, pane| {
+            let is_focused = focus == Some(id);
+
+            let Pane { id, is_pinned } = pane;
+
+            let pin_button =
+                button(text(if *is_pinned { "Unpin" } else { "Pin" }).size(14))
+                    .on_press(Message::TogglePin(id))
+                    .style(style::Button::Pin)
+                    .padding(3);
+
+            let title = row()
+                .push(pin_button)
+                .push("Pane")
+                .push(text(id.to_string()).color(if is_focused {
+                    PANE_ID_COLOR_FOCUSED
+                } else {
+                    PANE_ID_COLOR_UNFOCUSED
+                }))
+                .spacing(5);
+
+            let title_bar = pane_grid::TitleBar::new(title)
+                .controls(view_controls(id, total_panes, *is_pinned))
+                .padding(10)
+                .style(if is_focused {
+                    style::TitleBar::Focused
+                } else {
+                    style::TitleBar::Active
+                });
+
+            pane_grid::Content::new(responsive(move |size| {
+                view_content(id, total_panes, *is_pinned, size)
+            }))
+            .title_bar(title_bar)
+            .style(if is_focused {
+                style::Pane::Focused
+            } else {
+                style::Pane::Active
+            })
+        })
+        .width(Length::Fill)
+        .height(Length::Fill)
+        .spacing(10)
+        .on_click(Message::Clicked)
+        .on_drag(Message::Dragged)
+        .on_resize(10, Message::Resized);
+
+        container(pane_grid)
+            .width(Length::Fill)
+            .height(Length::Fill)
+            .padding(10)
+            .into()
+    }
+}
+
+const PANE_ID_COLOR_UNFOCUSED: Color = Color::from_rgb(
+    0xFF as f32 / 255.0,
+    0xC7 as f32 / 255.0,
+    0xC7 as f32 / 255.0,
+);
+const PANE_ID_COLOR_FOCUSED: Color = Color::from_rgb(
+    0xFF as f32 / 255.0,
+    0x47 as f32 / 255.0,
+    0x47 as f32 / 255.0,
+);
+
+fn handle_hotkey(key_code: keyboard::KeyCode) -> Option<Message> {
+    use keyboard::KeyCode;
+    use pane_grid::{Axis, Direction};
+
+    let direction = match key_code {
+        KeyCode::Up => Some(Direction::Up),
+        KeyCode::Down => Some(Direction::Down),
+        KeyCode::Left => Some(Direction::Left),
+        KeyCode::Right => Some(Direction::Right),
+        _ => None,
+    };
+
+    match key_code {
+        KeyCode::V => Some(Message::SplitFocused(Axis::Vertical)),
+        KeyCode::H => Some(Message::SplitFocused(Axis::Horizontal)),
+        KeyCode::W => Some(Message::CloseFocused),
+        _ => direction.map(Message::FocusAdjacent),
+    }
+}
+
+struct Pane {
+    id: usize,
+    pub is_pinned: bool,
+}
+
+impl Pane {
+    fn new(id: usize) -> Self {
+        Self {
+            id,
+            is_pinned: false,
+        }
+    }
+}
+
+fn view_content<'a>(
+    pane: pane_grid::Pane,
+    total_panes: usize,
+    is_pinned: bool,
+    size: Size,
+) -> Element<'a, Message> {
+    let button = |label, message, style| {
+        button(
+            text(label)
+                .width(Length::Fill)
+                .horizontal_alignment(alignment::Horizontal::Center)
+                .size(16),
+        )
+        .width(Length::Fill)
+        .padding(8)
+        .on_press(message)
+        .style(style)
+    };
+
+    let mut controls = column()
+        .spacing(5)
+        .max_width(150)
+        .push(button(
+            "Split horizontally",
+            Message::Split(pane_grid::Axis::Horizontal, pane),
+            style::Button::Primary,
+        ))
+        .push(button(
+            "Split vertically",
+            Message::Split(pane_grid::Axis::Vertical, pane),
+            style::Button::Primary,
+        ));
+
+    if total_panes > 1 && !is_pinned {
+        controls = controls.push(button(
+            "Close",
+            Message::Close(pane),
+            style::Button::Destructive,
+        ));
+    }
+
+    let content = column()
+        .width(Length::Fill)
+        .spacing(10)
+        .align_items(Alignment::Center)
+        .push(text(format!("{}x{}", size.width, size.height)).size(24))
+        .push(controls);
+
+    container(scrollable(content))
+        .width(Length::Fill)
+        .height(Length::Fill)
+        .padding(5)
+        .center_y()
+        .into()
+}
+
+fn view_controls<'a>(
+    pane: pane_grid::Pane,
+    total_panes: usize,
+    is_pinned: bool,
+) -> Element<'a, Message> {
+    let mut button = button(text("Close").size(14))
+        .style(style::Button::Control)
+        .padding(3);
+
+    if total_panes > 1 && !is_pinned {
+        button = button.on_press(Message::Close(pane));
+    }
+
+    button.into()
+}
+
+mod style {
+    use crate::PANE_ID_COLOR_FOCUSED;
+    use iced::{button, container, Background, Color, Vector};
+
+    const SURFACE: Color = Color::from_rgb(
+        0xF2 as f32 / 255.0,
+        0xF3 as f32 / 255.0,
+        0xF5 as f32 / 255.0,
+    );
+
+    const ACTIVE: Color = Color::from_rgb(
+        0x72 as f32 / 255.0,
+        0x89 as f32 / 255.0,
+        0xDA as f32 / 255.0,
+    );
+
+    const HOVERED: Color = Color::from_rgb(
+        0x67 as f32 / 255.0,
+        0x7B as f32 / 255.0,
+        0xC4 as f32 / 255.0,
+    );
+
+    pub enum TitleBar {
+        Active,
+        Focused,
+    }
+
+    impl container::StyleSheet for TitleBar {
+        fn style(&self) -> container::Style {
+            let pane = match self {
+                Self::Active => Pane::Active,
+                Self::Focused => Pane::Focused,
+            }
+            .style();
+
+            container::Style {
+                text_color: Some(Color::WHITE),
+                background: Some(pane.border_color.into()),
+                ..Default::default()
+            }
+        }
+    }
+
+    pub enum Pane {
+        Active,
+        Focused,
+    }
+
+    impl container::StyleSheet for Pane {
+        fn style(&self) -> container::Style {
+            container::Style {
+                background: Some(Background::Color(SURFACE)),
+                border_width: 2.0,
+                border_color: match self {
+                    Self::Active => Color::from_rgb(0.7, 0.7, 0.7),
+                    Self::Focused => Color::BLACK,
+                },
+                ..Default::default()
+            }
+        }
+    }
+
+    pub enum Button {
+        Primary,
+        Destructive,
+        Control,
+        Pin,
+    }
+
+    impl button::StyleSheet for Button {
+        fn active(&self) -> button::Style {
+            let (background, text_color) = match self {
+                Button::Primary => (Some(ACTIVE), Color::WHITE),
+                Button::Destructive => {
+                    (None, Color::from_rgb8(0xFF, 0x47, 0x47))
+                }
+                Button::Control => (Some(PANE_ID_COLOR_FOCUSED), Color::WHITE),
+                Button::Pin => (Some(ACTIVE), Color::WHITE),
+            };
+
+            button::Style {
+                text_color,
+                background: background.map(Background::Color),
+                border_radius: 5.0,
+                shadow_offset: Vector::new(0.0, 0.0),
+                ..button::Style::default()
+            }
+        }
+
+        fn hovered(&self) -> button::Style {
+            let active = self.active();
+
+            let background = match self {
+                Button::Primary => Some(HOVERED),
+                Button::Destructive => Some(Color {
+                    a: 0.2,
+                    ..active.text_color
+                }),
+                Button::Control => Some(PANE_ID_COLOR_FOCUSED),
+                Button::Pin => Some(HOVERED),
+            };
+
+            button::Style {
+                background: background.map(Background::Color),
+                ..active
+            }
+        }
+    }
+}

native/src/widget/pane_grid.rs

@@ -11,16 +11,19 @@ mod axis;
 mod configuration;
 mod content;
 mod direction;
+mod draggable;
 mod node;
 mod pane;
 mod split;
-mod state;
 mod title_bar;
 
+pub mod state;
+
 pub use axis::Axis;
 pub use configuration::Configuration;
 pub use content::Content;
 pub use direction::Direction;
+pub use draggable::Draggable;
 pub use node::Node;
 pub use pane::Pane;
 pub use split::Split;
@@ -92,6 +95,7 @@ pub use iced_style::pane_grid::{Line, StyleSheet};
 #[allow(missing_debug_implementations)]
 pub struct PaneGrid<'a, Message, Renderer> {
     state: &'a mut state::Internal,
+    action: &'a mut state::Action,
     elements: Vec<(Pane, Content<'a, Message, Renderer>)>,
     width: Length,
     height: Length,
@@ -124,6 +128,7 @@ where
 
         Self {
             state: &mut state.internal,
+            action: &mut state.action,
             elements,
             width: Length::Fill,
             height: Length::Fill,
@@ -197,80 +202,407 @@ where
     }
 }
 
-impl<'a, Message, Renderer> PaneGrid<'a, Message, Renderer>
+/// Calculates the [`Layout`] of a [`PaneGrid`].
-where
+pub fn layout<Renderer, T>(
-    Renderer: crate::Renderer,
+    renderer: &Renderer,
-{
+    limits: &layout::Limits,
-    fn click_pane(
+    state: &state::Internal,
-        &mut self,
+    width: Length,
-        layout: Layout<'_>,
+    height: Length,
-        cursor_position: Point,
+    spacing: u16,
-        shell: &mut Shell<'_, Message>,
+    elements: impl Iterator<Item = (Pane, T)>,
-    ) {
+    layout_element: impl Fn(T, &Renderer, &layout::Limits) -> layout::Node,
-        let mut clicked_region =
+) -> layout::Node {
-            self.elements.iter().zip(layout.children()).filter(
+    let limits = limits.width(width).height(height);
-                |(_, layout)| layout.bounds().contains(cursor_position),
+    let size = limits.resolve(Size::ZERO);
+
+    let regions = state.pane_regions(f32::from(spacing), size);
+    let children = elements
+        .filter_map(|(pane, element)| {
+            let region = regions.get(&pane)?;
+            let size = Size::new(region.width, region.height);
+
+            let mut node = layout_element(
+                element,
+                renderer,
+                &layout::Limits::new(size, size),
             );
 
-        if let Some(((pane, content), layout)) = clicked_region.next() {
+            node.move_to(Point::new(region.x, region.y));
-            if let Some(on_click) = &self.on_click {
-                shell.publish(on_click(*pane));
-            }
 
-            if let Some(on_drag) = &self.on_drag {
+            Some(node)
-                if content.can_be_picked_at(layout, cursor_position) {
+        })
-                    let pane_position = layout.position();
+        .collect();
 
-                    let origin = cursor_position
+    layout::Node::with_children(size, children)
-                        - Vector::new(pane_position.x, pane_position.y);
+}
 
-                    self.state.pick_pane(pane, origin);
+/// Processes an [`Event`] and updates the [`state`] of a [`PaneGrid`]
+/// accordingly.
+pub fn update<'a, Message, T: Draggable>(
+    action: &mut state::Action,
+    state: &state::Internal,
+    event: &Event,
+    layout: Layout<'_>,
+    cursor_position: Point,
+    shell: &mut Shell<'_, Message>,
+    spacing: u16,
+    elements: impl Iterator<Item = (Pane, T)>,
+    on_click: &Option<Box<dyn Fn(Pane) -> Message + 'a>>,
+    on_drag: &Option<Box<dyn Fn(DragEvent) -> Message + 'a>>,
+    on_resize: &Option<(u16, Box<dyn Fn(ResizeEvent) -> Message + 'a>)>,
+) -> event::Status {
+    let mut event_status = event::Status::Ignored;
 
-                    shell.publish(on_drag(DragEvent::Picked { pane: *pane }));
+    match event {
+        Event::Mouse(mouse::Event::ButtonPressed(mouse::Button::Left))
+        | Event::Touch(touch::Event::FingerPressed { .. }) => {
+            let bounds = layout.bounds();
+
+            if bounds.contains(cursor_position) {
+                event_status = event::Status::Captured;
+
+                match on_resize {
+                    Some((leeway, _)) => {
+                        let relative_cursor = Point::new(
+                            cursor_position.x - bounds.x,
+                            cursor_position.y - bounds.y,
+                        );
+
+                        let splits = state.split_regions(
+                            f32::from(spacing),
+                            Size::new(bounds.width, bounds.height),
+                        );
+
+                        let clicked_split = hovered_split(
+                            splits.iter(),
+                            f32::from(spacing + leeway),
+                            relative_cursor,
+                        );
+
+                        if let Some((split, axis, _)) = clicked_split {
+                            if action.picked_pane().is_none() {
+                                *action =
+                                    state::Action::Resizing { split, axis };
+                            }
+                        } else {
+                            click_pane(
+                                action,
+                                layout,
+                                cursor_position,
+                                shell,
+                                elements,
+                                on_click,
+                                on_drag,
+                            );
+                        }
+                    }
+                    None => {
+                        click_pane(
+                            action,
+                            layout,
+                            cursor_position,
+                            shell,
+                            elements,
+                            on_click,
+                            on_drag,
+                        );
+                    }
                 }
             }
         }
+        Event::Mouse(mouse::Event::ButtonReleased(mouse::Button::Left))
+        | Event::Touch(touch::Event::FingerLifted { .. })
+        | Event::Touch(touch::Event::FingerLost { .. }) => {
+            if let Some((pane, _)) = action.picked_pane() {
+                if let Some(on_drag) = on_drag {
+                    let mut dropped_region = elements
+                        .zip(layout.children())
+                        .filter(|(_, layout)| {
+                            layout.bounds().contains(cursor_position)
+                        });
+
+                    let event = match dropped_region.next() {
+                        Some(((target, _), _)) if pane != target => {
+                            DragEvent::Dropped { pane, target }
+                        }
+                        _ => DragEvent::Canceled { pane },
+                    };
+
+                    shell.publish(on_drag(event));
+                }
+
+                *action = state::Action::Idle;
+
+                event_status = event::Status::Captured;
+            } else if action.picked_split().is_some() {
+                *action = state::Action::Idle;
+
+                event_status = event::Status::Captured;
+            }
+        }
+        Event::Mouse(mouse::Event::CursorMoved { .. })
+        | Event::Touch(touch::Event::FingerMoved { .. }) => {
+            if let Some((_, on_resize)) = on_resize {
+                if let Some((split, _)) = action.picked_split() {
+                    let bounds = layout.bounds();
+
+                    let splits = state.split_regions(
+                        f32::from(spacing),
+                        Size::new(bounds.width, bounds.height),
+                    );
+
+                    if let Some((axis, rectangle, _)) = splits.get(&split) {
+                        let ratio = match axis {
+                            Axis::Horizontal => {
+                                let position =
+                                    cursor_position.y - bounds.y - rectangle.y;
+
+                                (position / rectangle.height).max(0.1).min(0.9)
+                            }
+                            Axis::Vertical => {
+                                let position =
+                                    cursor_position.x - bounds.x - rectangle.x;
+
+                                (position / rectangle.width).max(0.1).min(0.9)
+                            }
+                        };
+
+                        shell.publish(on_resize(ResizeEvent { split, ratio }));
+
+                        event_status = event::Status::Captured;
+                    }
+                }
+            }
+        }
+        _ => {}
+    }
+
+    event_status
+}
+
+fn click_pane<'a, Message, T>(
+    action: &mut state::Action,
+    layout: Layout<'_>,
+    cursor_position: Point,
+    shell: &mut Shell<'_, Message>,
+    elements: impl Iterator<Item = (Pane, T)>,
+    on_click: &Option<Box<dyn Fn(Pane) -> Message + 'a>>,
+    on_drag: &Option<Box<dyn Fn(DragEvent) -> Message + 'a>>,
+) where
+    T: Draggable,
+{
+    let mut clicked_region = elements
+        .zip(layout.children())
+        .filter(|(_, layout)| layout.bounds().contains(cursor_position));
+
+    if let Some(((pane, content), layout)) = clicked_region.next() {
+        if let Some(on_click) = &on_click {
+            shell.publish(on_click(pane));
+        }
+
+        if let Some(on_drag) = &on_drag {
+            if content.can_be_dragged_at(layout, cursor_position) {
+                let pane_position = layout.position();
+
+                let origin = cursor_position
+                    - Vector::new(pane_position.x, pane_position.y);
+
+                *action = state::Action::Dragging { pane, origin };
+
+                shell.publish(on_drag(DragEvent::Picked { pane }));
+            }
+        }
+    }
+}
+
+/// Returns the current [`mouse::Interaction`] of a [`PaneGrid`].
+pub fn mouse_interaction(
+    action: &state::Action,
+    state: &state::Internal,
+    layout: Layout<'_>,
+    cursor_position: Point,
+    spacing: u16,
+    resize_leeway: Option<u16>,
+) -> Option<mouse::Interaction> {
+    if action.picked_pane().is_some() {
+        return Some(mouse::Interaction::Grab);
+    }
+
+    let resize_axis =
+        action.picked_split().map(|(_, axis)| axis).or_else(|| {
+            resize_leeway.and_then(|leeway| {
+                let bounds = layout.bounds();
+
+                let splits =
+                    state.split_regions(f32::from(spacing), bounds.size());
+
+                let relative_cursor = Point::new(
+                    cursor_position.x - bounds.x,
+                    cursor_position.y - bounds.y,
+                );
+
+                hovered_split(
+                    splits.iter(),
+                    f32::from(spacing + leeway),
+                    relative_cursor,
+                )
+                .map(|(_, axis, _)| axis)
+            })
+        });
+
+    if let Some(resize_axis) = resize_axis {
+        return Some(match resize_axis {
+            Axis::Horizontal => mouse::Interaction::ResizingVertically,
+            Axis::Vertical => mouse::Interaction::ResizingHorizontally,
+        });
+    }
+
+    None
+}
+
+/// Draws a [`PaneGrid`].
+pub fn draw<Renderer, T>(
+    action: &state::Action,
+    state: &state::Internal,
+    layout: Layout<'_>,
+    cursor_position: Point,
+    renderer: &mut Renderer,
+    style: &renderer::Style,
+    viewport: &Rectangle,
+    spacing: u16,
+    resize_leeway: Option<u16>,
+    style_sheet: &dyn StyleSheet,
+    elements: impl Iterator<Item = (Pane, T)>,
+    draw_pane: impl Fn(
+        T,
+        &mut Renderer,
+        &renderer::Style,
+        Layout<'_>,
+        Point,
+        &Rectangle,
+    ),
+) where
+    Renderer: crate::Renderer,
+{
+    let picked_pane = action.picked_pane();
+
+    let picked_split = action
+        .picked_split()
+        .and_then(|(split, axis)| {
+            let bounds = layout.bounds();
+
+            let splits = state.split_regions(f32::from(spacing), bounds.size());
+
+            let (_axis, region, ratio) = splits.get(&split)?;
+
+            let region =
+                axis.split_line_bounds(*region, *ratio, f32::from(spacing));
+
+            Some((axis, region + Vector::new(bounds.x, bounds.y), true))
+        })
+        .or_else(|| match resize_leeway {
+            Some(leeway) => {
+                let bounds = layout.bounds();
+
+                let relative_cursor = Point::new(
+                    cursor_position.x - bounds.x,
+                    cursor_position.y - bounds.y,
+                );
+
+                let splits =
+                    state.split_regions(f32::from(spacing), bounds.size());
+
+                let (_split, axis, region) = hovered_split(
+                    splits.iter(),
+                    f32::from(spacing + leeway),
+                    relative_cursor,
+                )?;
+
+                Some((axis, region + Vector::new(bounds.x, bounds.y), false))
+            }
+            None => None,
+        });
+
+    let pane_cursor_position = if picked_pane.is_some() {
+        // TODO: Remove once cursor availability is encoded in the type
+        // system
+        Point::new(-1.0, -1.0)
+    } else {
+        cursor_position
+    };
+
+    for ((id, pane), layout) in elements.zip(layout.children()) {
+        match picked_pane {
+            Some((dragging, origin)) if id == dragging => {
+                let bounds = layout.bounds();
+
+                renderer.with_translation(
+                    cursor_position
+                        - Point::new(bounds.x + origin.x, bounds.y + origin.y),
+                    |renderer| {
+                        renderer.with_layer(bounds, |renderer| {
+                            draw_pane(
+                                pane,
+                                renderer,
+                                style,
+                                layout,
+                                pane_cursor_position,
+                                viewport,
+                            );
+                        });
+                    },
+                );
+            }
+            _ => {
+                draw_pane(
+                    pane,
+                    renderer,
+                    style,
+                    layout,
+                    pane_cursor_position,
+                    viewport,
+                );
+            }
+        }
     }
 
-    fn trigger_resize(
+    if let Some((axis, split_region, is_picked)) = picked_split {
-        &mut self,
+        let highlight = if is_picked {
-        layout: Layout<'_>,
+            style_sheet.picked_split()
-        cursor_position: Point,
+        } else {
-        shell: &mut Shell<'_, Message>,
+            style_sheet.hovered_split()
-    ) -> event::Status {
+        };
-        if let Some((_, on_resize)) = &self.on_resize {
-            if let Some((split, _)) = self.state.picked_split() {
-                let bounds = layout.bounds();
 
-                let splits = self.state.split_regions(
+        if let Some(highlight) = highlight {
-                    f32::from(self.spacing),
+            renderer.fill_quad(
-                    Size::new(bounds.width, bounds.height),
+                renderer::Quad {
-                );
+                    bounds: match axis {
-
+                        Axis::Horizontal => Rectangle {
-                if let Some((axis, rectangle, _)) = splits.get(&split) {
+                            x: split_region.x,
-                    let ratio = match axis {
+                            y: (split_region.y
-                        Axis::Horizontal => {
+                                + (split_region.height - highlight.width)
-                            let position =
+                                    / 2.0)
-                                cursor_position.y - bounds.y - rectangle.y;
+                                .round(),
-
+                            width: split_region.width,
-                            (position / rectangle.height).max(0.1).min(0.9)
+                            height: highlight.width,
-                        }
+                        },
-                        Axis::Vertical => {
+                        Axis::Vertical => Rectangle {
-                            let position =
+                            x: (split_region.x
-                                cursor_position.x - bounds.x - rectangle.x;
+                                + (split_region.width - highlight.width) / 2.0)
-
+                                .round(),
-                            (position / rectangle.width).max(0.1).min(0.9)
+                            y: split_region.y,
-                        }
+                            width: highlight.width,
-                    };
+                            height: split_region.height,
-
+                        },
-                    shell.publish(on_resize(ResizeEvent { split, ratio }));
+                    },
-
+                    border_radius: 0.0,
-                    return event::Status::Captured;
+                    border_width: 0.0,
-                }
+                    border_color: Color::TRANSPARENT,
-            }
+                },
+                highlight.color,
+            );
         }
-
-        event::Status::Ignored
     }
 }
 
@@ -331,28 +663,16 @@ where
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {
-        let limits = limits.width(self.width).height(self.height);
+        layout(
-        let size = limits.resolve(Size::ZERO);
+            renderer,
-
+            limits,
-        let regions = self.state.pane_regions(f32::from(self.spacing), size);
+            self.state,
-
+            self.width,
-        let children = self
+            self.height,
-            .elements
+            self.spacing,
-            .iter()
+            self.elements.iter().map(|(pane, content)| (*pane, content)),
-            .filter_map(|(pane, element)| {
+            |element, renderer, limits| element.layout(renderer, limits),
-                let region = regions.get(pane)?;
+        )
-                let size = Size::new(region.width, region.height);
-
-                let mut node =
-                    element.layout(renderer, &layout::Limits::new(size, size));
-
-                node.move_to(Point::new(region.x, region.y));
-
-                Some(node)
-            })
-            .collect();
-
-        layout::Node::with_children(size, children)
     }
 
     fn on_event(
@@ -364,89 +684,21 @@ where
         clipboard: &mut dyn Clipboard,
         shell: &mut Shell<'_, Message>,
     ) -> event::Status {
-        let mut event_status = event::Status::Ignored;
+        let event_status = update(
+            self.action,
+            self.state,
+            &event,
+            layout,
+            cursor_position,
+            shell,
+            self.spacing,
+            self.elements.iter().map(|(pane, content)| (*pane, content)),
+            &self.on_click,
+            &self.on_drag,
+            &self.on_resize,
+        );
 
-        match event {
+        let picked_pane = self.action.picked_pane().map(|(pane, _)| pane);
-            Event::Mouse(mouse::Event::ButtonPressed(mouse::Button::Left))
-            | Event::Touch(touch::Event::FingerPressed { .. }) => {
-                let bounds = layout.bounds();
-
-                if bounds.contains(cursor_position) {
-                    event_status = event::Status::Captured;
-
-                    match self.on_resize {
-                        Some((leeway, _)) => {
-                            let relative_cursor = Point::new(
-                                cursor_position.x - bounds.x,
-                                cursor_position.y - bounds.y,
-                            );
-
-                            let splits = self.state.split_regions(
-                                f32::from(self.spacing),
-                                Size::new(bounds.width, bounds.height),
-                            );
-
-                            let clicked_split = hovered_split(
-                                splits.iter(),
-                                f32::from(self.spacing + leeway),
-                                relative_cursor,
-                            );
-
-                            if let Some((split, axis, _)) = clicked_split {
-                                self.state.pick_split(&split, axis);
-                            } else {
-                                self.click_pane(layout, cursor_position, shell);
-                            }
-                        }
-                        None => {
-                            self.click_pane(layout, cursor_position, shell);
-                        }
-                    }
-                }
-            }
-            Event::Mouse(mouse::Event::ButtonReleased(mouse::Button::Left))
-            | Event::Touch(touch::Event::FingerLifted { .. })
-            | Event::Touch(touch::Event::FingerLost { .. }) => {
-                if let Some((pane, _)) = self.state.picked_pane() {
-                    if let Some(on_drag) = &self.on_drag {
-                        let mut dropped_region =
-                            self.elements.iter().zip(layout.children()).filter(
-                                |(_, layout)| {
-                                    layout.bounds().contains(cursor_position)
-                                },
-                            );
-
-                        let event = match dropped_region.next() {
-                            Some(((target, _), _)) if pane != *target => {
-                                DragEvent::Dropped {
-                                    pane,
-                                    target: *target,
-                                }
-                            }
-                            _ => DragEvent::Canceled { pane },
-                        };
-
-                        shell.publish(on_drag(event));
-                    }
-
-                    self.state.idle();
-
-                    event_status = event::Status::Captured;
-                } else if self.state.picked_split().is_some() {
-                    self.state.idle();
-
-                    event_status = event::Status::Captured;
-                }
-            }
-            Event::Mouse(mouse::Event::CursorMoved { .. })
-            | Event::Touch(touch::Event::FingerMoved { .. }) => {
-                event_status =
-                    self.trigger_resize(layout, cursor_position, shell);
-            }
-            _ => {}
-        }
-
-        let picked_pane = self.state.picked_pane().map(|(pane, _)| pane);
 
         self.elements
             .iter_mut()
@@ -474,53 +726,29 @@ where
         viewport: &Rectangle,
         renderer: &Renderer,
     ) -> mouse::Interaction {
-        if self.state.picked_pane().is_some() {
+        mouse_interaction(
-            return mouse::Interaction::Grab;
+            self.action,
-        }
+            self.state,
-
+            layout,
-        let resize_axis =
+            cursor_position,
-            self.state.picked_split().map(|(_, axis)| axis).or_else(|| {
+            self.spacing,
-                self.on_resize.as_ref().and_then(|(leeway, _)| {
+            self.on_resize.as_ref().map(|(leeway, _)| *leeway),
-                    let bounds = layout.bounds();
+        )
-
+        .unwrap_or_else(|| {
-                    let splits = self
+            self.elements
-                        .state
+                .iter()
-                        .split_regions(f32::from(self.spacing), bounds.size());
+                .zip(layout.children())
-
+                .map(|((_pane, content), layout)| {
-                    let relative_cursor = Point::new(
+                    content.mouse_interaction(
-                        cursor_position.x - bounds.x,
+                        layout,
-                        cursor_position.y - bounds.y,
+                        cursor_position,
-                    );
+                        viewport,
-
+                        renderer,
-                    hovered_split(
-                        splits.iter(),
-                        f32::from(self.spacing + leeway),
-                        relative_cursor,
                     )
-                    .map(|(_, axis, _)| axis)
                 })
-            });
+                .max()
-
+                .unwrap_or_default()
-        if let Some(resize_axis) = resize_axis {
+        })
-            return match resize_axis {
-                Axis::Horizontal => mouse::Interaction::ResizingVertically,
-                Axis::Vertical => mouse::Interaction::ResizingHorizontally,
-            };
-        }
-
-        self.elements
-            .iter()
-            .zip(layout.children())
-            .map(|((_pane, content), layout)| {
-                content.mouse_interaction(
-                    layout,
-                    cursor_position,
-                    viewport,
-                    renderer,
-                )
-            })
-            .max()
-            .unwrap_or_default()
     }
 
     fn draw(
@@ -531,139 +759,22 @@ where
         cursor_position: Point,
         viewport: &Rectangle,
     ) {
-        let picked_pane = self.state.picked_pane();
+        draw(
-
+            self.action,
-        let picked_split = self
+            self.state,
-            .state
+            layout,
-            .picked_split()
+            cursor_position,
-            .and_then(|(split, axis)| {
+            renderer,
-                let bounds = layout.bounds();
+            style,
-
+            viewport,
-                let splits = self
+            self.spacing,
-                    .state
+            self.on_resize.as_ref().map(|(leeway, _)| *leeway),
-                    .split_regions(f32::from(self.spacing), bounds.size());
+            self.style_sheet.as_ref(),
-
+            self.elements.iter().map(|(pane, content)| (*pane, content)),
-                let (_axis, region, ratio) = splits.get(&split)?;
+            |pane, renderer, style, layout, cursor_position, rectangle| {
-
+                pane.draw(renderer, style, layout, cursor_position, rectangle);
-                let region = axis.split_line_bounds(
+            },
-                    *region,
+        )
-                    *ratio,
-                    f32::from(self.spacing),
-                );
-
-                Some((axis, region + Vector::new(bounds.x, bounds.y), true))
-            })
-            .or_else(|| match self.on_resize {
-                Some((leeway, _)) => {
-                    let bounds = layout.bounds();
-
-                    let relative_cursor = Point::new(
-                        cursor_position.x - bounds.x,
-                        cursor_position.y - bounds.y,
-                    );
-
-                    let splits = self
-                        .state
-                        .split_regions(f32::from(self.spacing), bounds.size());
-
-                    let (_split, axis, region) = hovered_split(
-                        splits.iter(),
-                        f32::from(self.spacing + leeway),
-                        relative_cursor,
-                    )?;
-
-                    Some((
-                        axis,
-                        region + Vector::new(bounds.x, bounds.y),
-                        false,
-                    ))
-                }
-                None => None,
-            });
-
-        let pane_cursor_position = if picked_pane.is_some() {
-            // TODO: Remove once cursor availability is encoded in the type
-            // system
-            Point::new(-1.0, -1.0)
-        } else {
-            cursor_position
-        };
-
-        for ((id, pane), layout) in self.elements.iter().zip(layout.children())
-        {
-            match picked_pane {
-                Some((dragging, origin)) if *id == dragging => {
-                    let bounds = layout.bounds();
-
-                    renderer.with_translation(
-                        cursor_position
-                            - Point::new(
-                                bounds.x + origin.x,
-                                bounds.y + origin.y,
-                            ),
-                        |renderer| {
-                            renderer.with_layer(bounds, |renderer| {
-                                pane.draw(
-                                    renderer,
-                                    style,
-                                    layout,
-                                    pane_cursor_position,
-                                    viewport,
-                                );
-                            });
-                        },
-                    );
-                }
-                _ => {
-                    pane.draw(
-                        renderer,
-                        style,
-                        layout,
-                        pane_cursor_position,
-                        viewport,
-                    );
-                }
-            }
-        }
-
-        if let Some((axis, split_region, is_picked)) = picked_split {
-            let highlight = if is_picked {
-                self.style_sheet.picked_split()
-            } else {
-                self.style_sheet.hovered_split()
-            };
-
-            if let Some(highlight) = highlight {
-                renderer.fill_quad(
-                    renderer::Quad {
-                        bounds: match axis {
-                            Axis::Horizontal => Rectangle {
-                                x: split_region.x,
-                                y: (split_region.y
-                                    + (split_region.height - highlight.width)
-                                        / 2.0)
-                                    .round(),
-                                width: split_region.width,
-                                height: highlight.width,
-                            },
-                            Axis::Vertical => Rectangle {
-                                x: (split_region.x
-                                    + (split_region.width - highlight.width)
-                                        / 2.0)
-                                    .round(),
-                                y: split_region.y,
-                                width: highlight.width,
-                                height: split_region.height,
-                            },
-                        },
-                        border_radius: 0.0,
-                        border_width: 0.0,
-                        border_color: Color::TRANSPARENT,
-                    },
-                    highlight.color,
-                );
-            }
-        }
     }
 
     fn overlay(

native/src/widget/pane_grid/axis.rs

@@ -10,7 +10,9 @@ pub enum Axis {
 }
 
 impl Axis {
-    pub(super) fn split(
+    /// Splits the provided [`Rectangle`] on the current [`Axis`] with the
+    /// given `ratio` and `spacing`.
+    pub fn split(
         &self,
         rectangle: &Rectangle,
         ratio: f32,
@@ -54,7 +56,8 @@ impl Axis {
         }
     }
 
-    pub(super) fn split_line_bounds(
+    /// Calculates the bounds of the split line in a [`Rectangle`] region.
+    pub fn split_line_bounds(
         &self,
         rectangle: Rectangle,
         ratio: f32,

native/src/widget/pane_grid/content.rs

@@ -4,7 +4,7 @@ use crate::mouse;
 use crate::overlay;
 use crate::renderer;
 use crate::widget::container;
-use crate::widget::pane_grid::TitleBar;
+use crate::widget::pane_grid::{Draggable, TitleBar};
 use crate::{Clipboard, Element, Layout, Point, Rectangle, Shell, Size};
 
 /// The content of a [`Pane`].
@@ -101,23 +101,6 @@ where
         }
     }
 
-    /// Returns whether the [`Content`] with the given [`Layout`] can be picked
-    /// at the provided cursor position.
-    pub fn can_be_picked_at(
-        &self,
-        layout: Layout<'_>,
-        cursor_position: Point,
-    ) -> bool {
-        if let Some(title_bar) = &self.title_bar {
-            let mut children = layout.children();
-            let title_bar_layout = children.next().unwrap();
-
-            title_bar.is_over_pick_area(title_bar_layout, cursor_position)
-        } else {
-            false
-        }
-    }
-
     pub(crate) fn layout(
         &self,
         renderer: &Renderer,
@@ -253,6 +236,26 @@ where
     }
 }
 
+impl<'a, Message, Renderer> Draggable for &Content<'a, Message, Renderer>
+where
+    Renderer: crate::Renderer,
+{
+    fn can_be_dragged_at(
+        &self,
+        layout: Layout<'_>,
+        cursor_position: Point,
+    ) -> bool {
+        if let Some(title_bar) = &self.title_bar {
+            let mut children = layout.children();
+            let title_bar_layout = children.next().unwrap();
+
+            title_bar.is_over_pick_area(title_bar_layout, cursor_position)
+        } else {
+            false
+        }
+    }
+}
+
 impl<'a, T, Message, Renderer> From<T> for Content<'a, Message, Renderer>
 where
     T: Into<Element<'a, Message, Renderer>>,

native/src/widget/pane_grid/draggable.rs

@@ -0,0 +1,12 @@
+use crate::{Layout, Point};
+
+/// A pane that can be dragged.
+pub trait Draggable {
+    /// Returns whether the [`Draggable`] with the given [`Layout`] can be picked
+    /// at the provided cursor position.
+    fn can_be_dragged_at(
+        &self,
+        layout: Layout<'_>,
+        cursor_position: Point,
+    ) -> bool;
+}

native/src/widget/pane_grid/state.rs

@@ -1,3 +1,4 @@
+//! The state of a [`PaneGrid`].
 use crate::widget::pane_grid::{
     Axis, Configuration, Direction, Node, Pane, Split,
 };
@@ -19,8 +20,13 @@ use std::collections::{BTreeMap, HashMap};
 /// [`PaneGrid::new`]: crate::widget::PaneGrid::new
 #[derive(Debug, Clone)]
 pub struct State<T> {
-    pub(super) panes: HashMap<Pane, T>,
+    /// The panes of the [`PaneGrid`].
-    pub(super) internal: Internal,
+    pub panes: HashMap<Pane, T>,
+
+    /// The internal state of the [`PaneGrid`].
+    pub internal: Internal,
+
+    pub(super) action: Action,
 }
 
 impl<T> State<T> {
@@ -39,16 +45,13 @@ impl<T> State<T> {
     pub fn with_configuration(config: impl Into<Configuration<T>>) -> Self {
         let mut panes = HashMap::new();
 
-        let (layout, last_id) =
+        let internal =
-            Self::distribute_content(&mut panes, config.into(), 0);
+            Internal::from_configuration(&mut panes, config.into(), 0);
 
         State {
             panes,
-            internal: Internal {
+            internal,
-                layout,
+            action: Action::Idle,
-                last_id,
-                action: Action::Idle,
-            },
         }
     }
 
@@ -192,16 +195,34 @@ impl<T> State<T> {
             None
         }
     }
+}
 
-    fn distribute_content(
+/// The internal state of a [`PaneGrid`].
+#[derive(Debug, Clone)]
+pub struct Internal {
+    layout: Node,
+    last_id: usize,
+}
+
+impl Internal {
+    /// Initializes the [`Internal`] state of a [`PaneGrid`] from a
+    /// [`Configuration`].
+    pub fn from_configuration<T>(
         panes: &mut HashMap<Pane, T>,
         content: Configuration<T>,
         next_id: usize,
-    ) -> (Node, usize) {
+    ) -> Self {
-        match content {
+        let (layout, last_id) = match content {
             Configuration::Split { axis, ratio, a, b } => {
-                let (a, next_id) = Self::distribute_content(panes, *a, next_id);
+                let Internal {
-                let (b, next_id) = Self::distribute_content(panes, *b, next_id);
+                    layout: a,
+                    last_id: next_id,
+                } = Self::from_configuration(panes, *a, next_id);
+
+                let Internal {
+                    layout: b,
+                    last_id: next_id,
+                } = Self::from_configuration(panes, *b, next_id);
 
                 (
                     Node::Split {
@@ -220,39 +241,53 @@ impl<T> State<T> {
 
                 (Node::Pane(id), next_id + 1)
             }
-        }
+        };
+
+        Self { layout, last_id }
     }
 }
 
-#[derive(Debug, Clone)]
+/// The current action of a [`PaneGrid`].
-pub struct Internal {
-    layout: Node,
-    last_id: usize,
-    action: Action,
-}
-
 #[derive(Debug, Clone, Copy, PartialEq)]
 pub enum Action {
+    /// The [`PaneGrid`] is idle.
     Idle,
-    Dragging { pane: Pane, origin: Point },
+    /// A [`Pane`] in the [`PaneGrid`] is being dragged.
-    Resizing { split: Split, axis: Axis },
+    Dragging {
+        /// The [`Pane`] being dragged.
+        pane: Pane,
+        /// The starting [`Point`] of the drag interaction.
+        origin: Point,
+    },
+    /// A [`Split`] in the [`PaneGrid`] is being dragged.
+    Resizing {
+        /// The [`Split`] being dragged.
+        split: Split,
+        /// The [`Axis`] of the [`Split`].
+        axis: Axis,
+    },
 }
 
-impl Internal {
+impl Action {
+    /// Returns the current [`Pane`] that is being dragged, if any.
     pub fn picked_pane(&self) -> Option<(Pane, Point)> {
-        match self.action {
+        match *self {
             Action::Dragging { pane, origin, .. } => Some((pane, origin)),
             _ => None,
         }
     }
 
+    /// Returns the current [`Split`] that is being dragged, if any.
     pub fn picked_split(&self) -> Option<(Split, Axis)> {
-        match self.action {
+        match *self {
             Action::Resizing { split, axis, .. } => Some((split, axis)),
             _ => None,
         }
     }
+}
 
+impl Internal {
+    /// Calculates the current [`Pane`] regions from the [`PaneGrid`] layout.
     pub fn pane_regions(
         &self,
         spacing: f32,
@@ -261,6 +296,7 @@ impl Internal {
         self.layout.pane_regions(spacing, size)
     }
 
+    /// Calculates the current [`Split`] regions from the [`PaneGrid`] layout.
     pub fn split_regions(
         &self,
         spacing: f32,
@@ -268,28 +304,4 @@ impl Internal {
     ) -> BTreeMap<Split, (Axis, Rectangle, f32)> {
         self.layout.split_regions(spacing, size)
     }
-
-    pub fn pick_pane(&mut self, pane: &Pane, origin: Point) {
-        self.action = Action::Dragging {
-            pane: *pane,
-            origin,
-        };
-    }
-
-    pub fn pick_split(&mut self, split: &Split, axis: Axis) {
-        // TODO: Obtain `axis` from layout itself. Maybe we should implement
-        // `Node::find_split`
-        if self.picked_pane().is_some() {
-            return;
-        }
-
-        self.action = Action::Resizing {
-            split: *split,
-            axis,
-        };
-    }
-
-    pub fn idle(&mut self) {
-        self.action = Action::Idle;
-    }
 }

pure/src/widget.rs

@@ -1,4 +1,5 @@
 pub mod image;
+pub mod pane_grid;
 pub mod progress_bar;
 pub mod rule;
 pub mod tree;
@@ -24,6 +25,7 @@ pub use column::Column;
 pub use container::Container;
 pub use element::Element;
 pub use image::Image;
+pub use pane_grid::PaneGrid;
 pub use pick_list::PickList;
 pub use progress_bar::ProgressBar;
 pub use radio::Radio;

pure/src/widget/pane_grid.rs

@@ -0,0 +1,399 @@
+//! Let your users split regions of your application and organize layout dynamically.
+//!
+//! [![Pane grid - Iced](https://thumbs.gfycat.com/MixedFlatJellyfish-small.gif)](https://gfycat.com/mixedflatjellyfish)
+//!
+//! # Example
+//! The [`pane_grid` example] showcases how to use a [`PaneGrid`] with resizing,
+//! drag and drop, and hotkey support.
+//!
+//! [`pane_grid` example]: https://github.com/iced-rs/iced/tree/0.3/examples/pane_grid
+mod content;
+mod title_bar;
+
+pub use content::Content;
+pub use title_bar::TitleBar;
+
+pub use iced_native::widget::pane_grid::{
+    Axis, Configuration, Direction, DragEvent, Node, Pane, ResizeEvent, Split,
+    State,
+};
+
+use crate::overlay;
+use crate::widget::tree::{self, Tree};
+use crate::{Element, Widget};
+
+use iced_native::event::{self, Event};
+use iced_native::layout;
+use iced_native::mouse;
+use iced_native::renderer;
+use iced_native::widget::pane_grid;
+use iced_native::widget::pane_grid::state;
+use iced_native::{Clipboard, Layout, Length, Point, Rectangle, Shell};
+
+pub use iced_style::pane_grid::{Line, StyleSheet};
+
+/// A collection of panes distributed using either vertical or horizontal splits
+/// to completely fill the space available.
+///
+/// [![Pane grid - Iced](https://thumbs.gfycat.com/FrailFreshAiredaleterrier-small.gif)](https://gfycat.com/frailfreshairedaleterrier)
+///
+/// This distribution of space is common in tiling window managers (like
+/// [`awesome`](https://awesomewm.org/), [`i3`](https://i3wm.org/), or even
+/// [`tmux`](https://github.com/tmux/tmux)).
+///
+/// A [`PaneGrid`] supports:
+///
+/// * Vertical and horizontal splits
+/// * Tracking of the last active pane
+/// * Mouse-based resizing
+/// * Drag and drop to reorganize panes
+/// * Hotkey support
+/// * Configurable modifier keys
+/// * [`State`] API to perform actions programmatically (`split`, `swap`, `resize`, etc.)
+///
+/// ## Example
+///
+/// ```
+/// # use iced_pure::widget::{pane_grid, text};
+/// #
+/// # type PaneGrid<'a, Message> =
+/// #     iced_pure::widget::PaneGrid<'a, Message, iced_native::renderer::Null>;
+/// #
+/// enum PaneState {
+///     SomePane,
+///     AnotherKindOfPane,
+/// }
+///
+/// enum Message {
+///     PaneDragged(pane_grid::DragEvent),
+///     PaneResized(pane_grid::ResizeEvent),
+/// }
+///
+/// let (mut state, _) = pane_grid::State::new(PaneState::SomePane);
+///
+/// let pane_grid =
+///     PaneGrid::new(&state, |pane, state| {
+///         pane_grid::Content::new(match state {
+///             PaneState::SomePane => text("This is some pane"),
+///             PaneState::AnotherKindOfPane => text("This is another kind of pane"),
+///         })
+///     })
+///     .on_drag(Message::PaneDragged)
+///     .on_resize(10, Message::PaneResized);
+/// ```
+#[allow(missing_debug_implementations)]
+pub struct PaneGrid<'a, Message, Renderer> {
+    state: &'a state::Internal,
+    elements: Vec<(Pane, Content<'a, Message, Renderer>)>,
+    width: Length,
+    height: Length,
+    spacing: u16,
+    on_click: Option<Box<dyn Fn(Pane) -> Message + 'a>>,
+    on_drag: Option<Box<dyn Fn(DragEvent) -> Message + 'a>>,
+    on_resize: Option<(u16, Box<dyn Fn(ResizeEvent) -> Message + 'a>)>,
+    style_sheet: Box<dyn StyleSheet + 'a>,
+}
+
+impl<'a, Message, Renderer> PaneGrid<'a, Message, Renderer>
+where
+    Renderer: iced_native::Renderer,
+{
+    /// Creates a [`PaneGrid`] with the given [`State`] and view function.
+    ///
+    /// The view function will be called to display each [`Pane`] present in the
+    /// [`State`].
+    pub fn new<T>(
+        state: &'a State<T>,
+        view: impl Fn(Pane, &'a T) -> Content<'a, Message, Renderer>,
+    ) -> Self {
+        let elements = {
+            state
+                .panes
+                .iter()
+                .map(|(pane, pane_state)| (*pane, view(*pane, pane_state)))
+                .collect()
+        };
+
+        Self {
+            elements,
+            state: &state.internal,
+            width: Length::Fill,
+            height: Length::Fill,
+            spacing: 0,
+            on_click: None,
+            on_drag: None,
+            on_resize: None,
+            style_sheet: Default::default(),
+        }
+    }
+
+    /// Sets the width of the [`PaneGrid`].
+    pub fn width(mut self, width: Length) -> Self {
+        self.width = width;
+        self
+    }
+
+    /// Sets the height of the [`PaneGrid`].
+    pub fn height(mut self, height: Length) -> Self {
+        self.height = height;
+        self
+    }
+
+    /// Sets the spacing _between_ the panes of the [`PaneGrid`].
+    pub fn spacing(mut self, units: u16) -> Self {
+        self.spacing = units;
+        self
+    }
+
+    /// Sets the message that will be produced when a [`Pane`] of the
+    /// [`PaneGrid`] is clicked.
+    pub fn on_click<F>(mut self, f: F) -> Self
+    where
+        F: 'a + Fn(Pane) -> Message,
+    {
+        self.on_click = Some(Box::new(f));
+        self
+    }
+
+    /// Enables the drag and drop interactions of the [`PaneGrid`], which will
+    /// use the provided function to produce messages.
+    pub fn on_drag<F>(mut self, f: F) -> Self
+    where
+        F: 'a + Fn(DragEvent) -> Message,
+    {
+        self.on_drag = Some(Box::new(f));
+        self
+    }
+
+    /// Enables the resize interactions of the [`PaneGrid`], which will
+    /// use the provided function to produce messages.
+    ///
+    /// The `leeway` describes the amount of space around a split that can be
+    /// used to grab it.
+    ///
+    /// The grabbable area of a split will have a length of `spacing + leeway`,
+    /// properly centered. In other words, a length of
+    /// `(spacing + leeway) / 2.0` on either side of the split line.
+    pub fn on_resize<F>(mut self, leeway: u16, f: F) -> Self
+    where
+        F: 'a + Fn(ResizeEvent) -> Message,
+    {
+        self.on_resize = Some((leeway, Box::new(f)));
+        self
+    }
+
+    /// Sets the style of the [`PaneGrid`].
+    pub fn style(mut self, style: impl Into<Box<dyn StyleSheet + 'a>>) -> Self {
+        self.style_sheet = style.into();
+        self
+    }
+}
+
+impl<'a, Message, Renderer> Widget<Message, Renderer>
+    for PaneGrid<'a, Message, Renderer>
+where
+    Renderer: iced_native::Renderer,
+{
+    fn tag(&self) -> tree::Tag {
+        tree::Tag::of::<state::Action>()
+    }
+
+    fn state(&self) -> tree::State {
+        tree::State::new(state::Action::Idle)
+    }
+
+    fn children(&self) -> Vec<Tree> {
+        self.elements
+            .iter()
+            .map(|(_, content)| content.state())
+            .collect()
+    }
+
+    fn diff(&self, tree: &mut Tree) {
+        tree.diff_children_custom(
+            &self.elements,
+            |(_, content), state| content.diff(state),
+            |(_, content)| content.state(),
+        )
+    }
+
+    fn width(&self) -> Length {
+        self.width
+    }
+
+    fn height(&self) -> Length {
+        self.height
+    }
+
+    fn layout(
+        &self,
+        renderer: &Renderer,
+        limits: &layout::Limits,
+    ) -> layout::Node {
+        pane_grid::layout(
+            renderer,
+            limits,
+            self.state,
+            self.width,
+            self.height,
+            self.spacing,
+            self.elements.iter().map(|(pane, content)| (*pane, content)),
+            |element, renderer, limits| element.layout(renderer, limits),
+        )
+    }
+
+    fn on_event(
+        &mut self,
+        tree: &mut Tree,
+        event: Event,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        renderer: &Renderer,
+        clipboard: &mut dyn Clipboard,
+        shell: &mut Shell<'_, Message>,
+    ) -> event::Status {
+        let action = tree.state.downcast_mut::<state::Action>();
+
+        let event_status = pane_grid::update(
+            action,
+            self.state,
+            &event,
+            layout,
+            cursor_position,
+            shell,
+            self.spacing,
+            self.elements.iter().map(|(pane, content)| (*pane, content)),
+            &self.on_click,
+            &self.on_drag,
+            &self.on_resize,
+        );
+
+        let picked_pane = action.picked_pane().map(|(pane, _)| pane);
+
+        self.elements
+            .iter_mut()
+            .zip(&mut tree.children)
+            .zip(layout.children())
+            .map(|(((pane, content), tree), layout)| {
+                let is_picked = picked_pane == Some(*pane);
+
+                content.on_event(
+                    tree,
+                    event.clone(),
+                    layout,
+                    cursor_position,
+                    renderer,
+                    clipboard,
+                    shell,
+                    is_picked,
+                )
+            })
+            .fold(event_status, event::Status::merge)
+    }
+
+    fn mouse_interaction(
+        &self,
+        tree: &Tree,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        viewport: &Rectangle,
+        renderer: &Renderer,
+    ) -> mouse::Interaction {
+        pane_grid::mouse_interaction(
+            tree.state.downcast_ref(),
+            self.state,
+            layout,
+            cursor_position,
+            self.spacing,
+            self.on_resize.as_ref().map(|(leeway, _)| *leeway),
+        )
+        .unwrap_or_else(|| {
+            self.elements
+                .iter()
+                .zip(&tree.children)
+                .zip(layout.children())
+                .map(|(((_pane, content), tree), layout)| {
+                    content.mouse_interaction(
+                        tree,
+                        layout,
+                        cursor_position,
+                        viewport,
+                        renderer,
+                    )
+                })
+                .max()
+                .unwrap_or_default()
+        })
+    }
+
+    fn draw(
+        &self,
+        tree: &Tree,
+        renderer: &mut Renderer,
+        style: &renderer::Style,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        viewport: &Rectangle,
+    ) {
+        pane_grid::draw(
+            tree.state.downcast_ref(),
+            self.state,
+            layout,
+            cursor_position,
+            renderer,
+            style,
+            viewport,
+            self.spacing,
+            self.on_resize.as_ref().map(|(leeway, _)| *leeway),
+            self.style_sheet.as_ref(),
+            self.elements
+                .iter()
+                .zip(&tree.children)
+                .map(|((pane, content), tree)| (*pane, (content, tree))),
+            |(content, tree),
+             renderer,
+             style,
+             layout,
+             cursor_position,
+             rectangle| {
+                content.draw(
+                    tree,
+                    renderer,
+                    style,
+                    layout,
+                    cursor_position,
+                    rectangle,
+                );
+            },
+        )
+    }
+
+    fn overlay<'b>(
+        &'b self,
+        tree: &'b mut Tree,
+        layout: Layout<'_>,
+        renderer: &Renderer,
+    ) -> Option<overlay::Element<'_, Message, Renderer>> {
+        self.elements
+            .iter()
+            .zip(&mut tree.children)
+            .zip(layout.children())
+            .filter_map(|(((_, pane), tree), layout)| {
+                pane.overlay(tree, layout, renderer)
+            })
+            .next()
+    }
+}
+
+impl<'a, Message, Renderer> From<PaneGrid<'a, Message, Renderer>>
+    for Element<'a, Message, Renderer>
+where
+    Renderer: 'a + iced_native::Renderer,
+    Message: 'a,
+{
+    fn from(
+        pane_grid: PaneGrid<'a, Message, Renderer>,
+    ) -> Element<'a, Message, Renderer> {
+        Element::new(pane_grid)
+    }
+}

pure/src/widget/pane_grid/content.rs

@@ -0,0 +1,331 @@
+use crate::widget::pane_grid::TitleBar;
+use crate::widget::tree::Tree;
+use crate::Element;
+
+use iced_native::event::{self, Event};
+use iced_native::layout;
+use iced_native::mouse;
+use iced_native::overlay;
+use iced_native::renderer;
+use iced_native::widget::container;
+use iced_native::widget::pane_grid::Draggable;
+use iced_native::{Clipboard, Layout, Point, Rectangle, Shell, Size};
+
+/// The content of a [`Pane`].
+///
+/// [`Pane`]: crate::widget::pane_grid::Pane
+#[allow(missing_debug_implementations)]
+pub struct Content<'a, Message, Renderer> {
+    title_bar: Option<TitleBar<'a, Message, Renderer>>,
+    body: Element<'a, Message, Renderer>,
+    style_sheet: Box<dyn container::StyleSheet + 'a>,
+}
+
+impl<'a, Message, Renderer> Content<'a, Message, Renderer>
+where
+    Renderer: iced_native::Renderer,
+{
+    /// Creates a new [`Content`] with the provided body.
+    pub fn new(body: impl Into<Element<'a, Message, Renderer>>) -> Self {
+        Self {
+            title_bar: None,
+            body: body.into(),
+            style_sheet: Default::default(),
+        }
+    }
+
+    /// Sets the [`TitleBar`] of this [`Content`].
+    pub fn title_bar(
+        mut self,
+        title_bar: TitleBar<'a, Message, Renderer>,
+    ) -> Self {
+        self.title_bar = Some(title_bar);
+        self
+    }
+
+    /// Sets the style of the [`Content`].
+    pub fn style(
+        mut self,
+        style_sheet: impl Into<Box<dyn container::StyleSheet + 'a>>,
+    ) -> Self {
+        self.style_sheet = style_sheet.into();
+        self
+    }
+}
+
+impl<'a, Message, Renderer> Content<'a, Message, Renderer>
+where
+    Renderer: iced_native::Renderer,
+{
+    pub fn state(&self) -> Tree {
+        let children = if let Some(title_bar) = self.title_bar.as_ref() {
+            vec![Tree::new(&self.body), title_bar.state()]
+        } else {
+            vec![Tree::new(&self.body), Tree::empty()]
+        };
+
+        Tree {
+            children,
+            ..Tree::empty()
+        }
+    }
+
+    pub fn diff(&self, tree: &mut Tree) {
+        if tree.children.len() == 2 {
+            if let Some(title_bar) = self.title_bar.as_ref() {
+                title_bar.diff(&mut tree.children[1]);
+            }
+
+            tree.children[0].diff(&self.body);
+        } else {
+            *tree = self.state();
+        }
+    }
+
+    /// Draws the [`Content`] with the provided [`Renderer`] and [`Layout`].
+    ///
+    /// [`Renderer`]: crate::widget::pane_grid::Renderer
+    pub fn draw(
+        &self,
+        tree: &Tree,
+        renderer: &mut Renderer,
+        style: &renderer::Style,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        viewport: &Rectangle,
+    ) {
+        let bounds = layout.bounds();
+
+        {
+            let style = self.style_sheet.style();
+
+            container::draw_background(renderer, &style, bounds);
+        }
+
+        if let Some(title_bar) = &self.title_bar {
+            let mut children = layout.children();
+            let title_bar_layout = children.next().unwrap();
+            let body_layout = children.next().unwrap();
+
+            let show_controls = bounds.contains(cursor_position);
+
+            title_bar.draw(
+                &tree.children[1],
+                renderer,
+                style,
+                title_bar_layout,
+                cursor_position,
+                viewport,
+                show_controls,
+            );
+
+            self.body.as_widget().draw(
+                &tree.children[0],
+                renderer,
+                style,
+                body_layout,
+                cursor_position,
+                viewport,
+            );
+        } else {
+            self.body.as_widget().draw(
+                &tree.children[0],
+                renderer,
+                style,
+                layout,
+                cursor_position,
+                viewport,
+            );
+        }
+    }
+
+    pub(crate) fn layout(
+        &self,
+        renderer: &Renderer,
+        limits: &layout::Limits,
+    ) -> layout::Node {
+        if let Some(title_bar) = &self.title_bar {
+            let max_size = limits.max();
+
+            let title_bar_layout = title_bar
+                .layout(renderer, &layout::Limits::new(Size::ZERO, max_size));
+
+            let title_bar_size = title_bar_layout.size();
+
+            let mut body_layout = self.body.as_widget().layout(
+                renderer,
+                &layout::Limits::new(
+                    Size::ZERO,
+                    Size::new(
+                        max_size.width,
+                        max_size.height - title_bar_size.height,
+                    ),
+                ),
+            );
+
+            body_layout.move_to(Point::new(0.0, title_bar_size.height));
+
+            layout::Node::with_children(
+                max_size,
+                vec![title_bar_layout, body_layout],
+            )
+        } else {
+            self.body.as_widget().layout(renderer, limits)
+        }
+    }
+
+    pub(crate) fn on_event(
+        &mut self,
+        tree: &mut Tree,
+        event: Event,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        renderer: &Renderer,
+        clipboard: &mut dyn Clipboard,
+        shell: &mut Shell<'_, Message>,
+        is_picked: bool,
+    ) -> event::Status {
+        let mut event_status = event::Status::Ignored;
+
+        let body_layout = if let Some(title_bar) = &mut self.title_bar {
+            let mut children = layout.children();
+
+            event_status = title_bar.on_event(
+                &mut tree.children[1],
+                event.clone(),
+                children.next().unwrap(),
+                cursor_position,
+                renderer,
+                clipboard,
+                shell,
+            );
+
+            children.next().unwrap()
+        } else {
+            layout
+        };
+
+        let body_status = if is_picked {
+            event::Status::Ignored
+        } else {
+            self.body.as_widget_mut().on_event(
+                &mut tree.children[0],
+                event,
+                body_layout,
+                cursor_position,
+                renderer,
+                clipboard,
+                shell,
+            )
+        };
+
+        event_status.merge(body_status)
+    }
+
+    pub(crate) fn mouse_interaction(
+        &self,
+        tree: &Tree,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        viewport: &Rectangle,
+        renderer: &Renderer,
+    ) -> mouse::Interaction {
+        let (body_layout, title_bar_interaction) =
+            if let Some(title_bar) = &self.title_bar {
+                let mut children = layout.children();
+                let title_bar_layout = children.next().unwrap();
+
+                let is_over_pick_area = title_bar
+                    .is_over_pick_area(title_bar_layout, cursor_position);
+
+                if is_over_pick_area {
+                    return mouse::Interaction::Grab;
+                }
+
+                let mouse_interaction = title_bar.mouse_interaction(
+                    &tree.children[1],
+                    title_bar_layout,
+                    cursor_position,
+                    viewport,
+                    renderer,
+                );
+
+                (children.next().unwrap(), mouse_interaction)
+            } else {
+                (layout, mouse::Interaction::default())
+            };
+
+        self.body
+            .as_widget()
+            .mouse_interaction(
+                &tree.children[0],
+                body_layout,
+                cursor_position,
+                viewport,
+                renderer,
+            )
+            .max(title_bar_interaction)
+    }
+
+    pub(crate) fn overlay<'b>(
+        &'b self,
+        tree: &'b mut Tree,
+        layout: Layout<'_>,
+        renderer: &Renderer,
+    ) -> Option<overlay::Element<'b, Message, Renderer>> {
+        if let Some(title_bar) = self.title_bar.as_ref() {
+            let mut children = layout.children();
+            let title_bar_layout = children.next()?;
+
+            let mut states = tree.children.iter_mut();
+            let body_state = states.next().unwrap();
+            let title_bar_state = states.next().unwrap();
+
+            match title_bar.overlay(title_bar_state, title_bar_layout, renderer)
+            {
+                Some(overlay) => Some(overlay),
+                None => self.body.as_widget().overlay(
+                    body_state,
+                    children.next()?,
+                    renderer,
+                ),
+            }
+        } else {
+            self.body.as_widget().overlay(
+                &mut tree.children[0],
+                layout,
+                renderer,
+            )
+        }
+    }
+}
+
+impl<'a, Message, Renderer> Draggable for &Content<'a, Message, Renderer>
+where
+    Renderer: iced_native::Renderer,
+{
+    fn can_be_dragged_at(
+        &self,
+        layout: Layout<'_>,
+        cursor_position: Point,
+    ) -> bool {
+        if let Some(title_bar) = &self.title_bar {
+            let mut children = layout.children();
+            let title_bar_layout = children.next().unwrap();
+
+            title_bar.is_over_pick_area(title_bar_layout, cursor_position)
+        } else {
+            false
+        }
+    }
+}
+
+impl<'a, T, Message, Renderer> From<T> for Content<'a, Message, Renderer>
+where
+    T: Into<Element<'a, Message, Renderer>>,
+    Renderer: iced_native::Renderer,
+{
+    fn from(element: T) -> Self {
+        Self::new(element)
+    }
+}

pure/src/widget/pane_grid/title_bar.rs

@@ -0,0 +1,355 @@
+use crate::widget::Tree;
+use crate::Element;
+
+use iced_native::event::{self, Event};
+use iced_native::layout;
+use iced_native::mouse;
+use iced_native::overlay;
+use iced_native::renderer;
+use iced_native::widget::container;
+use iced_native::{Clipboard, Layout, Padding, Point, Rectangle, Shell, Size};
+
+/// The title bar of a [`Pane`].
+///
+/// [`Pane`]: crate::widget::pane_grid::Pane
+#[allow(missing_debug_implementations)]
+pub struct TitleBar<'a, Message, Renderer> {
+    content: Element<'a, Message, Renderer>,
+    controls: Option<Element<'a, Message, Renderer>>,
+    padding: Padding,
+    always_show_controls: bool,
+    style_sheet: Box<dyn container::StyleSheet + 'a>,
+}
+
+impl<'a, Message, Renderer> TitleBar<'a, Message, Renderer>
+where
+    Renderer: iced_native::Renderer,
+{
+    /// Creates a new [`TitleBar`] with the given content.
+    pub fn new<E>(content: E) -> Self
+    where
+        E: Into<Element<'a, Message, Renderer>>,
+    {
+        Self {
+            content: content.into(),
+            controls: None,
+            padding: Padding::ZERO,
+            always_show_controls: false,
+            style_sheet: Default::default(),
+        }
+    }
+
+    /// Sets the controls of the [`TitleBar`].
+    pub fn controls(
+        mut self,
+        controls: impl Into<Element<'a, Message, Renderer>>,
+    ) -> Self {
+        self.controls = Some(controls.into());
+        self
+    }
+
+    /// Sets the [`Padding`] of the [`TitleBar`].
+    pub fn padding<P: Into<Padding>>(mut self, padding: P) -> Self {
+        self.padding = padding.into();
+        self
+    }
+
+    /// Sets the style of the [`TitleBar`].
+    pub fn style(
+        mut self,
+        style: impl Into<Box<dyn container::StyleSheet + 'a>>,
+    ) -> Self {
+        self.style_sheet = style.into();
+        self
+    }
+
+    /// Sets whether or not the [`controls`] attached to this [`TitleBar`] are
+    /// always visible.
+    ///
+    /// By default, the controls are only visible when the [`Pane`] of this
+    /// [`TitleBar`] is hovered.
+    ///
+    /// [`controls`]: Self::controls
+    /// [`Pane`]: crate::widget::pane_grid::Pane
+    pub fn always_show_controls(mut self) -> Self {
+        self.always_show_controls = true;
+        self
+    }
+}
+
+impl<'a, Message, Renderer> TitleBar<'a, Message, Renderer>
+where
+    Renderer: iced_native::Renderer,
+{
+    pub fn state(&self) -> Tree {
+        let children = if let Some(controls) = self.controls.as_ref() {
+            vec![Tree::new(&self.content), Tree::new(controls)]
+        } else {
+            vec![Tree::new(&self.content), Tree::empty()]
+        };
+
+        Tree {
+            children,
+            ..Tree::empty()
+        }
+    }
+
+    pub fn diff(&self, tree: &mut Tree) {
+        if tree.children.len() == 2 {
+            if let Some(controls) = self.controls.as_ref() {
+                tree.children[1].diff(controls);
+            }
+
+            tree.children[0].diff(&self.content);
+        } else {
+            *tree = self.state();
+        }
+    }
+
+    /// Draws the [`TitleBar`] with the provided [`Renderer`] and [`Layout`].
+    ///
+    /// [`Renderer`]: crate::widget::pane_grid::Renderer
+    pub fn draw(
+        &self,
+        tree: &Tree,
+        renderer: &mut Renderer,
+        inherited_style: &renderer::Style,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        viewport: &Rectangle,
+        show_controls: bool,
+    ) {
+        let bounds = layout.bounds();
+        let style = self.style_sheet.style();
+        let inherited_style = renderer::Style {
+            text_color: style.text_color.unwrap_or(inherited_style.text_color),
+        };
+
+        container::draw_background(renderer, &style, bounds);
+
+        let mut children = layout.children();
+        let padded = children.next().unwrap();
+
+        let mut children = padded.children();
+        let title_layout = children.next().unwrap();
+
+        self.content.as_widget().draw(
+            &tree.children[0],
+            renderer,
+            &inherited_style,
+            title_layout,
+            cursor_position,
+            viewport,
+        );
+
+        if let Some(controls) = &self.controls {
+            let controls_layout = children.next().unwrap();
+
+            if show_controls || self.always_show_controls {
+                controls.as_widget().draw(
+                    &tree.children[1],
+                    renderer,
+                    &inherited_style,
+                    controls_layout,
+                    cursor_position,
+                    viewport,
+                );
+            }
+        }
+    }
+
+    /// Returns whether the mouse cursor is over the pick area of the
+    /// [`TitleBar`] or not.
+    ///
+    /// The whole [`TitleBar`] is a pick area, except its controls.
+    pub fn is_over_pick_area(
+        &self,
+        layout: Layout<'_>,
+        cursor_position: Point,
+    ) -> bool {
+        if layout.bounds().contains(cursor_position) {
+            let mut children = layout.children();
+            let padded = children.next().unwrap();
+            let mut children = padded.children();
+            let title_layout = children.next().unwrap();
+
+            if self.controls.is_some() {
+                let controls_layout = children.next().unwrap();
+
+                !controls_layout.bounds().contains(cursor_position)
+                    && !title_layout.bounds().contains(cursor_position)
+            } else {
+                !title_layout.bounds().contains(cursor_position)
+            }
+        } else {
+            false
+        }
+    }
+
+    pub(crate) fn layout(
+        &self,
+        renderer: &Renderer,
+        limits: &layout::Limits,
+    ) -> layout::Node {
+        let limits = limits.pad(self.padding);
+        let max_size = limits.max();
+
+        let title_layout = self
+            .content
+            .as_widget()
+            .layout(renderer, &layout::Limits::new(Size::ZERO, max_size));
+
+        let title_size = title_layout.size();
+
+        let mut node = if let Some(controls) = &self.controls {
+            let mut controls_layout = controls
+                .as_widget()
+                .layout(renderer, &layout::Limits::new(Size::ZERO, max_size));
+
+            let controls_size = controls_layout.size();
+            let space_before_controls = max_size.width - controls_size.width;
+
+            let height = title_size.height.max(controls_size.height);
+
+            controls_layout.move_to(Point::new(space_before_controls, 0.0));
+
+            layout::Node::with_children(
+                Size::new(max_size.width, height),
+                vec![title_layout, controls_layout],
+            )
+        } else {
+            layout::Node::with_children(
+                Size::new(max_size.width, title_size.height),
+                vec![title_layout],
+            )
+        };
+
+        node.move_to(Point::new(
+            self.padding.left.into(),
+            self.padding.top.into(),
+        ));
+
+        layout::Node::with_children(node.size().pad(self.padding), vec![node])
+    }
+
+    pub(crate) fn on_event(
+        &mut self,
+        tree: &mut Tree,
+        event: Event,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        renderer: &Renderer,
+        clipboard: &mut dyn Clipboard,
+        shell: &mut Shell<'_, Message>,
+    ) -> event::Status {
+        let mut children = layout.children();
+        let padded = children.next().unwrap();
+
+        let mut children = padded.children();
+        let title_layout = children.next().unwrap();
+
+        let control_status = if let Some(controls) = &mut self.controls {
+            let controls_layout = children.next().unwrap();
+
+            controls.as_widget_mut().on_event(
+                &mut tree.children[1],
+                event.clone(),
+                controls_layout,
+                cursor_position,
+                renderer,
+                clipboard,
+                shell,
+            )
+        } else {
+            event::Status::Ignored
+        };
+
+        let title_status = self.content.as_widget_mut().on_event(
+            &mut tree.children[0],
+            event,
+            title_layout,
+            cursor_position,
+            renderer,
+            clipboard,
+            shell,
+        );
+
+        control_status.merge(title_status)
+    }
+
+    pub(crate) fn mouse_interaction(
+        &self,
+        tree: &Tree,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        viewport: &Rectangle,
+        renderer: &Renderer,
+    ) -> mouse::Interaction {
+        let mut children = layout.children();
+        let padded = children.next().unwrap();
+
+        let mut children = padded.children();
+        let title_layout = children.next().unwrap();
+
+        let title_interaction = self.content.as_widget().mouse_interaction(
+            &tree.children[0],
+            title_layout,
+            cursor_position,
+            viewport,
+            renderer,
+        );
+
+        if let Some(controls) = &self.controls {
+            let controls_layout = children.next().unwrap();
+
+            controls
+                .as_widget()
+                .mouse_interaction(
+                    &tree.children[1],
+                    controls_layout,
+                    cursor_position,
+                    viewport,
+                    renderer,
+                )
+                .max(title_interaction)
+        } else {
+            title_interaction
+        }
+    }
+
+    pub(crate) fn overlay<'b>(
+        &'b self,
+        tree: &'b mut Tree,
+        layout: Layout<'_>,
+        renderer: &Renderer,
+    ) -> Option<overlay::Element<'b, Message, Renderer>> {
+        let mut children = layout.children();
+        let padded = children.next()?;
+
+        let mut children = padded.children();
+        let title_layout = children.next()?;
+
+        let Self {
+            content, controls, ..
+        } = self;
+
+        let mut states = tree.children.iter_mut();
+        let title_state = states.next().unwrap();
+        let controls_state = states.next().unwrap();
+
+        content
+            .as_widget()
+            .overlay(title_state, title_layout, renderer)
+            .or_else(move || {
+                controls.as_ref().and_then(|controls| {
+                    let controls_layout = children.next()?;
+
+                    controls.as_widget().overlay(
+                        controls_state,
+                        controls_layout,
+                        renderer,
+                    )
+                })
+            })
+    }
+}

pure/src/widget/tree.rs

@@ -41,6 +41,19 @@ impl Tree {
     pub fn diff_children<Message, Renderer>(
         &mut self,
         new_children: &[Element<'_, Message, Renderer>],
+    ) {
+        self.diff_children_custom(
+            new_children,
+            |new, child_state| child_state.diff(new),
+            Self::new,
+        )
+    }
+
+    pub fn diff_children_custom<T>(
+        &mut self,
+        new_children: &[T],
+        diff: impl Fn(&T, &mut Tree),
+        new_state: impl Fn(&T) -> Self,
     ) {
         if self.children.len() > new_children.len() {
             self.children.truncate(new_children.len());
@@ -49,12 +62,12 @@ impl Tree {
         for (child_state, new) in
             self.children.iter_mut().zip(new_children.iter())
         {
-            child_state.diff(new);
+            diff(new, child_state);
         }
 
         if self.children.len() < new_children.len() {
             self.children.extend(
-                new_children[self.children.len()..].iter().map(Self::new),
+                new_children[self.children.len()..].iter().map(new_state),
             );
         }
     }