Merge pull request #444 from hecrj/feature/overlay

Overlay support and `PickList` widget

18 files changed, 1358 insertions, 64 deletions

diff --git a/native/src/element.rs b/native/src/element.rs
index 73e39012..514a135b 100644
--- a/native/src/element.rs
+++ b/native/src/element.rs
@@ -1,5 +1,6 @@
 use crate::{
-    layout, Clipboard, Color, Event, Hasher, Layout, Length, Point, Widget,
+    layout, overlay, Clipboard, Color, Event, Hasher, Layout, Length, Point,
+    Widget,
 };
 
 /// A generic [`Widget`].
@@ -22,7 +23,7 @@ impl<'a, Message, Renderer> Element<'a, Message, Renderer>
 where
     Renderer: crate::Renderer,
 {
-    /// Create a new [`Element`] containing the given [`Widget`].
+    /// Creates a new [`Element`] containing the given [`Widget`].
     ///
     /// [`Element`]: struct.Element.html
     /// [`Widget`]: widget/trait.Widget.html
@@ -270,6 +271,16 @@ where
     pub fn hash_layout(&self, state: &mut Hasher) {
         self.widget.hash_layout(state);
     }
+
+    /// Returns the overlay of the [`Element`], if there is any.
+    ///
+    /// [`Element`]: struct.Element.html
+    pub fn overlay<'b>(
+        &'b mut self,
+        layout: Layout<'_>,
+    ) -> Option<overlay::Element<'b, Message, Renderer>> {
+        self.widget.overlay(layout)
+    }
 }
 
 struct Map<'a, A, B, Renderer> {
@@ -294,7 +305,9 @@ impl<'a, A, B, Renderer> Map<'a, A, B, Renderer> {
 
 impl<'a, A, B, Renderer> Widget<B, Renderer> for Map<'a, A, B, Renderer>
 where
-    Renderer: crate::Renderer,
+    Renderer: crate::Renderer + 'a,
+    A: 'static,
+    B: 'static,
 {
     fn width(&self) -> Length {
         self.widget.width()
@@ -351,6 +364,17 @@ where
     fn hash_layout(&self, state: &mut Hasher) {
         self.widget.hash_layout(state);
     }
+
+    fn overlay(
+        &mut self,
+        layout: Layout<'_>,
+    ) -> Option<overlay::Element<'_, B, Renderer>> {
+        let mapper = &self.mapper;
+
+        self.widget
+            .overlay(layout)
+            .map(move |overlay| overlay.map(mapper))
+    }
 }
 
 struct Explain<'a, Message, Renderer: crate::Renderer> {
@@ -426,4 +450,11 @@ where
     fn hash_layout(&self, state: &mut Hasher) {
         self.element.widget.hash_layout(state);
     }
+
+    fn overlay(
+        &mut self,
+        layout: Layout<'_>,
+    ) -> Option<overlay::Element<'_, Message, Renderer>> {
+        self.element.overlay(layout)
+    }
 }
diff --git a/native/src/lib.rs b/native/src/lib.rs
index b67ff2a1..067e3c0a 100644
--- a/native/src/lib.rs
+++ b/native/src/lib.rs
@@ -38,6 +38,7 @@
 pub mod keyboard;
 pub mod layout;
 pub mod mouse;
+pub mod overlay;
 pub mod program;
 pub mod renderer;
 pub mod subscription;
@@ -75,6 +76,7 @@ pub use element::Element;
 pub use event::Event;
 pub use hasher::Hasher;
 pub use layout::Layout;
+pub use overlay::Overlay;
 pub use program::Program;
 pub use renderer::Renderer;
 pub use runtime::Runtime;
diff --git a/native/src/overlay.rs b/native/src/overlay.rs
new file mode 100644
index 00000000..7c3bec32
--- /dev/null
+++ b/native/src/overlay.rs
@@ -0,0 +1,84 @@
+//! Display interactive elements on top of other widgets.
+mod element;
+
+pub mod menu;
+
+pub use element::Element;
+pub use menu::Menu;
+
+use crate::{layout, Clipboard, Event, Hasher, Layout, Point, Size};
+
+/// An interactive component that can be displayed on top of other widgets.
+pub trait Overlay<Message, Renderer>
+where
+    Renderer: crate::Renderer,
+{
+    /// Returns the layout [`Node`] of the [`Overlay`].
+    ///
+    /// This [`Node`] is used by the runtime to compute the [`Layout`] of the
+    /// user interface.
+    ///
+    /// [`Node`]: ../layout/struct.Node.html
+    /// [`Widget`]: trait.Overlay.html
+    /// [`Layout`]: ../layout/struct.Layout.html
+    fn layout(
+        &self,
+        renderer: &Renderer,
+        bounds: Size,
+        position: Point,
+    ) -> layout::Node;
+
+    /// Draws the [`Overlay`] using the associated `Renderer`.
+    ///
+    /// [`Overlay`]: trait.Overlay.html
+    fn draw(
+        &self,
+        renderer: &mut Renderer,
+        defaults: &Renderer::Defaults,
+        layout: Layout<'_>,
+        cursor_position: Point,
+    ) -> Renderer::Output;
+
+    /// Computes the _layout_ hash of the [`Overlay`].
+    ///
+    /// The produced hash is used by the runtime to decide if the [`Layout`]
+    /// needs to be recomputed between frames. Therefore, to ensure maximum
+    /// efficiency, the hash should only be affected by the properties of the
+    /// [`Overlay`] that can affect layouting.
+    ///
+    /// For example, the [`Text`] widget does not hash its color property, as
+    /// its value cannot affect the overall [`Layout`] of the user interface.
+    ///
+    /// [`Overlay`]: trait.Overlay.html
+    /// [`Layout`]: ../layout/struct.Layout.html
+    /// [`Text`]: text/struct.Text.html
+    fn hash_layout(&self, state: &mut Hasher, position: Point);
+
+    /// Processes a runtime [`Event`].
+    ///
+    /// It receives:
+    ///   * an [`Event`] describing user interaction
+    ///   * the computed [`Layout`] of the [`Overlay`]
+    ///   * the current cursor position
+    ///   * a mutable `Message` list, allowing the [`Overlay`] to produce
+    ///   new messages based on user interaction.
+    ///   * the `Renderer`
+    ///   * a [`Clipboard`], if available
+    ///
+    /// By default, it does nothing.
+    ///
+    /// [`Event`]: ../enum.Event.html
+    /// [`Overlay`]: trait.Widget.html
+    /// [`Layout`]: ../layout/struct.Layout.html
+    /// [`Clipboard`]: ../trait.Clipboard.html
+    fn on_event(
+        &mut self,
+        _event: Event,
+        _layout: Layout<'_>,
+        _cursor_position: Point,
+        _messages: &mut Vec<Message>,
+        _renderer: &Renderer,
+        _clipboard: Option<&dyn Clipboard>,
+    ) {
+    }
+}
diff --git a/native/src/overlay/element.rs b/native/src/overlay/element.rs
new file mode 100644
index 00000000..e1fd9b88
--- /dev/null
+++ b/native/src/overlay/element.rs
@@ -0,0 +1,170 @@
+pub use crate::Overlay;
+
+use crate::{layout, Clipboard, Event, Hasher, Layout, Point, Size, Vector};
+
+/// A generic [`Overlay`].
+///
+/// [`Overlay`]: trait.Overlay.html
+#[allow(missing_debug_implementations)]
+pub struct Element<'a, Message, Renderer> {
+    position: Point,
+    overlay: Box<dyn Overlay<Message, Renderer> + 'a>,
+}
+
+impl<'a, Message, Renderer> Element<'a, Message, Renderer>
+where
+    Renderer: crate::Renderer,
+{
+    /// Creates a new [`Element`] containing the given [`Overlay`].
+    ///
+    /// [`Element`]: struct.Element.html
+    /// [`Overlay`]: trait.Overlay.html
+    pub fn new(
+        position: Point,
+        overlay: Box<dyn Overlay<Message, Renderer> + 'a>,
+    ) -> Self {
+        Self { position, overlay }
+    }
+
+    /// Translates the [`Element`].
+    ///
+    /// [`Element`]: struct.Element.html
+    pub fn translate(mut self, translation: Vector) -> Self {
+        self.position = self.position + translation;
+        self
+    }
+
+    /// Applies a transformation to the produced message of the [`Element`].
+    ///
+    /// [`Element`]: struct.Element.html
+    pub fn map<B>(self, f: &'a dyn Fn(Message) -> B) -> Element<'a, B, Renderer>
+    where
+        Message: 'a,
+        Renderer: 'a,
+        B: 'static,
+    {
+        Element {
+            position: self.position,
+            overlay: Box::new(Map::new(self.overlay, f)),
+        }
+    }
+
+    /// Computes the layout of the [`Element`] in the given bounds.
+    ///
+    /// [`Element`]: struct.Element.html
+    pub fn layout(&self, renderer: &Renderer, bounds: Size) -> layout::Node {
+        self.overlay.layout(renderer, bounds, self.position)
+    }
+
+    /// Processes a runtime [`Event`].
+    ///
+    /// [`Event`]: enum.Event.html
+    pub fn on_event(
+        &mut self,
+        event: Event,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        messages: &mut Vec<Message>,
+        renderer: &Renderer,
+        clipboard: Option<&dyn Clipboard>,
+    ) {
+        self.overlay.on_event(
+            event,
+            layout,
+            cursor_position,
+            messages,
+            renderer,
+            clipboard,
+        )
+    }
+
+    /// Draws the [`Element`] and its children using the given [`Layout`].
+    ///
+    /// [`Element`]: struct.Element.html
+    /// [`Layout`]: layout/struct.Layout.html
+    pub fn draw(
+        &self,
+        renderer: &mut Renderer,
+        defaults: &Renderer::Defaults,
+        layout: Layout<'_>,
+        cursor_position: Point,
+    ) -> Renderer::Output {
+        self.overlay
+            .draw(renderer, defaults, layout, cursor_position)
+    }
+
+    /// Computes the _layout_ hash of the [`Element`].
+    ///
+    /// [`Element`]: struct.Element.html
+    pub fn hash_layout(&self, state: &mut Hasher) {
+        self.overlay.hash_layout(state, self.position);
+    }
+}
+
+struct Map<'a, A, B, Renderer> {
+    content: Box<dyn Overlay<A, Renderer> + 'a>,
+    mapper: &'a dyn Fn(A) -> B,
+}
+
+impl<'a, A, B, Renderer> Map<'a, A, B, Renderer> {
+    pub fn new(
+        content: Box<dyn Overlay<A, Renderer> + 'a>,
+        mapper: &'a dyn Fn(A) -> B,
+    ) -> Map<'a, A, B, Renderer> {
+        Map { content, mapper }
+    }
+}
+
+impl<'a, A, B, Renderer> Overlay<B, Renderer> for Map<'a, A, B, Renderer>
+where
+    Renderer: crate::Renderer,
+{
+    fn layout(
+        &self,
+        renderer: &Renderer,
+        bounds: Size,
+        position: Point,
+    ) -> layout::Node {
+        self.content.layout(renderer, bounds, position)
+    }
+
+    fn on_event(
+        &mut self,
+        event: Event,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        messages: &mut Vec<B>,
+        renderer: &Renderer,
+        clipboard: Option<&dyn Clipboard>,
+    ) {
+        let mut original_messages = Vec::new();
+
+        self.content.on_event(
+            event,
+            layout,
+            cursor_position,
+            &mut original_messages,
+            renderer,
+            clipboard,
+        );
+
+        original_messages
+            .drain(..)
+            .for_each(|message| messages.push((self.mapper)(message)));
+    }
+
+    fn draw(
+        &self,
+        renderer: &mut Renderer,
+        defaults: &Renderer::Defaults,
+        layout: Layout<'_>,
+        cursor_position: Point,
+    ) -> Renderer::Output {
+        self.content
+            .draw(renderer, defaults, layout, cursor_position)
+    }
+
+    fn hash_layout(&self, state: &mut Hasher, position: Point) {
+        self.content.hash_layout(state, position);
+    }
+}
diff --git a/native/src/overlay/menu.rs b/native/src/overlay/menu.rs
new file mode 100644
index 00000000..0d4bc63c
--- /dev/null
+++ b/native/src/overlay/menu.rs
@@ -0,0 +1,464 @@
+//! Build and show dropdown menus.
+use crate::{
+    container, layout, mouse, overlay, scrollable, text, Clipboard, Container,
+    Element, Event, Hasher, Layout, Length, Point, Rectangle, Scrollable, Size,
+    Vector, Widget,
+};
+
+/// A list of selectable options.
+#[allow(missing_debug_implementations)]
+pub struct Menu<'a, T, Message, Renderer: self::Renderer> {
+    state: &'a mut State,
+    options: &'a [T],
+    on_selected: &'a dyn Fn(T) -> Message,
+    width: u16,
+    padding: u16,
+    text_size: Option<u16>,
+    font: Renderer::Font,
+    style: <Renderer as self::Renderer>::Style,
+}
+
+impl<'a, T, Message, Renderer> Menu<'a, T, Message, Renderer>
+where
+    T: ToString + Clone,
+    Message: 'a,
+    Renderer: self::Renderer + 'a,
+{
+    /// Creates a new [`Menu`] with the given [`State`], a list of options, and
+    /// the message to produced when an option is selected.
+    ///
+    /// [`Menu`]: struct.Menu.html
+    /// [`State`]: struct.State.html
+    pub fn new(
+        state: &'a mut State,
+        options: &'a [T],
+        on_selected: &'a dyn Fn(T) -> Message,
+    ) -> Self {
+        Menu {
+            state,
+            options,
+            on_selected,
+            width: 0,
+            padding: 0,
+            text_size: None,
+            font: Default::default(),
+            style: Default::default(),
+        }
+    }
+
+    /// Sets the width of the [`Menu`].
+    ///
+    /// [`Menu`]: struct.Menu.html
+    pub fn width(mut self, width: u16) -> Self {
+        self.width = width;
+        self
+    }
+
+    /// Sets the padding of the [`Menu`].
+    ///
+    /// [`Menu`]: struct.Menu.html
+    pub fn padding(mut self, padding: u16) -> Self {
+        self.padding = padding;
+        self
+    }
+
+    /// Sets the text size of the [`Menu`].
+    ///
+    /// [`Menu`]: struct.Menu.html
+    pub fn text_size(mut self, text_size: u16) -> Self {
+        self.text_size = Some(text_size);
+        self
+    }
+
+    /// Sets the font of the [`Menu`].
+    ///
+    /// [`Menu`]: struct.Menu.html
+    pub fn font(mut self, font: Renderer::Font) -> Self {
+        self.font = font;
+        self
+    }
+
+    /// Sets the style of the [`Menu`].
+    ///
+    /// [`Menu`]: struct.Menu.html
+    pub fn style(
+        mut self,
+        style: impl Into<<Renderer as self::Renderer>::Style>,
+    ) -> Self {
+        self.style = style.into();
+        self
+    }
+
+    /// Turns the [`Menu`] into an overlay [`Element`] at the given target
+    /// position.
+    ///
+    /// The `target_height` will be used to display the menu either on top
+    /// of the target or under it, depending on the screen position and the
+    /// dimensions of the [`Menu`].
+    ///
+    /// [`Menu`]: struct.Menu.html
+    pub fn overlay(
+        self,
+        position: Point,
+        target_height: f32,
+    ) -> overlay::Element<'a, Message, Renderer> {
+        overlay::Element::new(
+            position,
+            Box::new(Overlay::new(self, target_height)),
+        )
+    }
+}
+
+/// The local state of a [`Menu`].
+///
+/// [`Menu`]: struct.Menu.html
+#[derive(Debug, Clone, Default)]
+pub struct State {
+    scrollable: scrollable::State,
+    hovered_option: Option<usize>,
+    is_open: bool,
+}
+
+impl State {
+    /// Returns whether the [`Menu`] is currently open or not.
+    ///
+    /// [`Menu`]: struct.Menu.html
+    pub fn is_open(&self) -> bool {
+        self.is_open
+    }
+
+    /// Opens the [`Menu`] with the given option hovered by default.
+    ///
+    /// [`Menu`]: struct.Menu.html
+    pub fn open(&mut self, hovered_option: Option<usize>) {
+        self.is_open = true;
+        self.hovered_option = hovered_option;
+    }
+}
+
+struct Overlay<'a, Message, Renderer: self::Renderer> {
+    container: Container<'a, Message, Renderer>,
+    is_open: &'a mut bool,
+    width: u16,
+    target_height: f32,
+    style: <Renderer as self::Renderer>::Style,
+}
+
+impl<'a, Message, Renderer: self::Renderer> Overlay<'a, Message, Renderer>
+where
+    Message: 'a,
+    Renderer: 'a,
+{
+    pub fn new<T>(
+        menu: Menu<'a, T, Message, Renderer>,
+        target_height: f32,
+    ) -> Self
+    where
+        T: Clone + ToString,
+    {
+        let Menu {
+            state,
+            options,
+            on_selected,
+            width,
+            padding,
+            font,
+            text_size,
+            style,
+        } = menu;
+
+        let container =
+            Container::new(Scrollable::new(&mut state.scrollable).push(List {
+                options,
+                hovered_option: &mut state.hovered_option,
+                on_selected,
+                font,
+                text_size,
+                padding,
+                style: style.clone(),
+            }))
+            .padding(1);
+
+        Self {
+            container,
+            is_open: &mut state.is_open,
+            width: width,
+            target_height,
+            style: style,
+        }
+    }
+}
+
+impl<'a, Message, Renderer> crate::Overlay<Message, Renderer>
+    for Overlay<'a, Message, Renderer>
+where
+    Renderer: self::Renderer,
+{
+    fn layout(
+        &self,
+        renderer: &Renderer,
+        bounds: Size,
+        position: Point,
+    ) -> layout::Node {
+        let space_below = bounds.height - (position.y + self.target_height);
+        let space_above = position.y;
+
+        let limits = layout::Limits::new(
+            Size::ZERO,
+            Size::new(
+                bounds.width - position.x,
+                if space_below > space_above {
+                    space_below
+                } else {
+                    space_above
+                },
+            ),
+        )
+        .width(Length::Units(self.width));
+
+        let mut node = self.container.layout(renderer, &limits);
+
+        node.move_to(if space_below > space_above {
+            position + Vector::new(0.0, self.target_height)
+        } else {
+            position - Vector::new(0.0, node.size().height)
+        });
+
+        node
+    }
+
+    fn hash_layout(&self, state: &mut Hasher, position: Point) {
+        use std::hash::Hash;
+
+        struct Marker;
+        std::any::TypeId::of::<Marker>().hash(state);
+
+        (position.x as u32).hash(state);
+        (position.y as u32).hash(state);
+    }
+
+    fn on_event(
+        &mut self,
+        event: Event,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        messages: &mut Vec<Message>,
+        renderer: &Renderer,
+        clipboard: Option<&dyn Clipboard>,
+    ) {
+        let bounds = layout.bounds();
+        let current_messages = messages.len();
+
+        self.container.on_event(
+            event.clone(),
+            layout,
+            cursor_position,
+            messages,
+            renderer,
+            clipboard,
+        );
+
+        let option_was_selected = current_messages < messages.len();
+
+        match event {
+            Event::Mouse(mouse::Event::ButtonPressed(mouse::Button::Left))
+                if !bounds.contains(cursor_position) || option_was_selected =>
+            {
+                *self.is_open = false;
+            }
+            _ => {}
+        }
+    }
+
+    fn draw(
+        &self,
+        renderer: &mut Renderer,
+        defaults: &Renderer::Defaults,
+        layout: Layout<'_>,
+        cursor_position: Point,
+    ) -> Renderer::Output {
+        let primitives =
+            self.container
+                .draw(renderer, defaults, layout, cursor_position);
+
+        renderer.decorate(
+            layout.bounds(),
+            cursor_position,
+            &self.style,
+            primitives,
+        )
+    }
+}
+
+struct List<'a, T, Message, Renderer: self::Renderer> {
+    options: &'a [T],
+    hovered_option: &'a mut Option<usize>,
+    on_selected: &'a dyn Fn(T) -> Message,
+    padding: u16,
+    text_size: Option<u16>,
+    font: Renderer::Font,
+    style: <Renderer as self::Renderer>::Style,
+}
+
+impl<'a, T, Message, Renderer: self::Renderer> Widget<Message, Renderer>
+    for List<'a, T, Message, Renderer>
+where
+    T: Clone + ToString,
+    Renderer: self::Renderer,
+{
+    fn width(&self) -> Length {
+        Length::Fill
+    }
+
+    fn height(&self) -> Length {
+        Length::Shrink
+    }
+
+    fn layout(
+        &self,
+        renderer: &Renderer,
+        limits: &layout::Limits,
+    ) -> layout::Node {
+        use std::f32;
+
+        let limits = limits.width(Length::Fill).height(Length::Shrink);
+        let text_size = self.text_size.unwrap_or(renderer.default_size());
+
+        let size = {
+            let intrinsic = Size::new(
+                0.0,
+                f32::from(text_size + self.padding * 2)
+                    * self.options.len() as f32,
+            );
+
+            limits.resolve(intrinsic)
+        };
+
+        layout::Node::new(size)
+    }
+
+    fn hash_layout(&self, state: &mut Hasher) {
+        use std::hash::Hash as _;
+
+        struct Marker;
+        std::any::TypeId::of::<Marker>().hash(state);
+
+        self.options.len().hash(state);
+        self.text_size.hash(state);
+        self.padding.hash(state);
+    }
+
+    fn on_event(
+        &mut self,
+        event: Event,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        messages: &mut Vec<Message>,
+        renderer: &Renderer,
+        _clipboard: Option<&dyn Clipboard>,
+    ) {
+        match event {
+            Event::Mouse(mouse::Event::ButtonPressed(mouse::Button::Left)) => {
+                let bounds = layout.bounds();
+
+                if bounds.contains(cursor_position) {
+                    if let Some(index) = *self.hovered_option {
+                        if let Some(option) = self.options.get(index) {
+                            messages.push((self.on_selected)(option.clone()));
+                        }
+                    }
+                }
+            }
+            Event::Mouse(mouse::Event::CursorMoved { .. }) => {
+                let bounds = layout.bounds();
+                let text_size =
+                    self.text_size.unwrap_or(renderer.default_size());
+
+                if bounds.contains(cursor_position) {
+                    *self.hovered_option = Some(
+                        ((cursor_position.y - bounds.y)
+                            / f32::from(text_size + self.padding * 2))
+                            as usize,
+                    );
+                }
+            }
+            _ => {}
+        }
+    }
+
+    fn draw(
+        &self,
+        renderer: &mut Renderer,
+        _defaults: &Renderer::Defaults,
+        layout: Layout<'_>,
+        cursor_position: Point,
+    ) -> Renderer::Output {
+        self::Renderer::draw(
+            renderer,
+            layout.bounds(),
+            cursor_position,
+            self.options,
+            *self.hovered_option,
+            self.padding,
+            self.text_size.unwrap_or(renderer.default_size()),
+            self.font,
+            &self.style,
+        )
+    }
+}
+
+/// The renderer of a [`Menu`].
+///
+/// Your [renderer] will need to implement this trait before being
+/// able to use a [`Menu`] in your user interface.
+///
+/// [`Menu`]: struct.Menu.html
+/// [renderer]: ../../renderer/index.html
+pub trait Renderer:
+    scrollable::Renderer + container::Renderer + text::Renderer
+{
+    /// The [`Menu`] style supported by this renderer.
+    ///
+    /// [`Menu`]: struct.Menu.html
+    type Style: Default + Clone;
+
+    /// Decorates a the list of options of a [`Menu`].
+    ///
+    /// This method can be used to draw a background for the [`Menu`].
+    ///
+    /// [`Menu`]: struct.Menu.html
+    fn decorate(
+        &mut self,
+        bounds: Rectangle,
+        cursor_position: Point,
+        style: &<Self as Renderer>::Style,
+        primitive: Self::Output,
+    ) -> Self::Output;
+
+    /// Draws the list of options of a [`Menu`].
+    ///
+    /// [`Menu`]: struct.Menu.html
+    fn draw<T: ToString>(
+        &mut self,
+        bounds: Rectangle,
+        cursor_position: Point,
+        options: &[T],
+        hovered_option: Option<usize>,
+        padding: u16,
+        text_size: u16,
+        font: Self::Font,
+        style: &<Self as Renderer>::Style,
+    ) -> Self::Output;
+}
+
+impl<'a, T, Message, Renderer> Into<Element<'a, Message, Renderer>>
+    for List<'a, T, Message, Renderer>
+where
+    T: ToString + Clone,
+    Message: 'a,
+    Renderer: 'a + self::Renderer,
+{
+    fn into(self) -> Element<'a, Message, Renderer> {
+        Element::new(self)
+    }
+}
diff --git a/native/src/program/state.rs b/native/src/program/state.rs
index fdc42e8b..95e6b60c 100644
--- a/native/src/program/state.rs
+++ b/native/src/program/state.rs
@@ -35,7 +35,7 @@ where
         renderer: &mut P::Renderer,
         debug: &mut Debug,
     ) -> Self {
-        let user_interface = build_user_interface(
+        let mut user_interface = build_user_interface(
             &mut program,
             Cache::default(),
             renderer,
@@ -121,12 +121,14 @@ where
 
         debug.event_processing_started();
         let mut messages = user_interface.update(
-            self.queued_events.drain(..),
+            &self.queued_events,
             cursor_position,
             clipboard,
             renderer,
         );
         messages.extend(self.queued_messages.drain(..));
+
+        self.queued_events.clear();
         debug.event_processing_finished();
 
         if messages.is_empty() {
@@ -153,7 +155,7 @@ where
                     command
                 }));
 
-            let user_interface = build_user_interface(
+            let mut user_interface = build_user_interface(
                 &mut self.program,
                 temp_cache,
                 renderer,
diff --git a/native/src/renderer.rs b/native/src/renderer.rs
index a16df72b..d986141f 100644
--- a/native/src/renderer.rs
+++ b/native/src/renderer.rs
@@ -25,7 +25,7 @@ mod null;
 #[cfg(debug_assertions)]
 pub use null::Null;
 
-use crate::{layout, Element};
+use crate::{layout, Element, Rectangle};
 
 /// A component that can take the state of a user interface and produce an
 /// output for its users.
@@ -56,4 +56,13 @@ pub trait Renderer: Sized {
     ) -> layout::Node {
         element.layout(self, limits)
     }
+
+    /// Overlays the `overlay` output with the given bounds on top of the `base`
+    /// output.
+    fn overlay(
+        &mut self,
+        base: Self::Output,
+        overlay: Self::Output,
+        overlay_bounds: Rectangle,
+    ) -> Self::Output;
 }
diff --git a/native/src/renderer/null.rs b/native/src/renderer/null.rs
index 580f58f8..07f79319 100644
--- a/native/src/renderer/null.rs
+++ b/native/src/renderer/null.rs
@@ -23,6 +23,9 @@ impl Null {
 impl Renderer for Null {
     type Output = ();
     type Defaults = ();
+
+    fn overlay(&mut self, _base: (), _overlay: (), _overlay_bounds: Rectangle) {
+    }
 }
 
 impl column::Renderer for Null {
diff --git a/native/src/user_interface.rs b/native/src/user_interface.rs
index b9646043..00a290f1 100644
--- a/native/src/user_interface.rs
+++ b/native/src/user_interface.rs
@@ -1,4 +1,4 @@
-use crate::{layout, Clipboard, Element, Event, Layout, Point, Size};
+use crate::{layout, overlay, Clipboard, Element, Event, Layout, Point, Size};
 
 use std::hash::Hasher;
 
@@ -19,9 +19,9 @@ use std::hash::Hasher;
 /// [`UserInterface`]: struct.UserInterface.html
 #[allow(missing_debug_implementations)]
 pub struct UserInterface<'a, Message, Renderer> {
-    hash: u64,
     root: Element<'a, Message, Renderer>,
-    layout: layout::Node,
+    base: Layer,
+    overlay: Option<Layer>,
     bounds: Size,
 }
 
@@ -94,25 +94,36 @@ where
     ) -> Self {
         let root = root.into();
 
-        let hash = {
-            let hasher = &mut crate::Hasher::default();
-            root.hash_layout(hasher);
+        let (base, overlay) = {
+            let hash = {
+                let hasher = &mut crate::Hasher::default();
+                root.hash_layout(hasher);
 
-            hasher.finish()
-        };
+                hasher.finish()
+            };
 
-        let layout_is_cached = hash == cache.hash && bounds == cache.bounds;
+            let layout_is_cached =
+                hash == cache.base.hash && bounds == cache.bounds;
 
-        let layout = if layout_is_cached {
-            cache.layout
-        } else {
-            renderer.layout(&root, &layout::Limits::new(Size::ZERO, bounds))
+            let (layout, overlay) = if layout_is_cached {
+                (cache.base.layout, cache.overlay)
+            } else {
+                (
+                    renderer.layout(
+                        &root,
+                        &layout::Limits::new(Size::ZERO, bounds),
+                    ),
+                    None,
+                )
+            };
+
+            (Layer { layout, hash }, overlay)
         };
 
         UserInterface {
-            hash,
             root,
-            layout,
+            base,
+            overlay,
             bounds,
         }
     }
@@ -169,7 +180,7 @@ where
     ///
     ///     // Update the user interface
     ///     let messages = user_interface.update(
-    ///         events.drain(..),
+    ///         &events,
     ///         cursor_position,
     ///         None,
     ///         &renderer,
@@ -185,18 +196,54 @@ where
     /// ```
     pub fn update(
         &mut self,
-        events: impl IntoIterator<Item = Event>,
+        events: &[Event],
         cursor_position: Point,
         clipboard: Option<&dyn Clipboard>,
         renderer: &Renderer,
     ) -> Vec<Message> {
         let mut messages = Vec::new();
 
+        let base_cursor = if let Some(mut overlay) =
+            self.root.overlay(Layout::new(&self.base.layout))
+        {
+            let layer = Self::overlay_layer(
+                self.overlay.take(),
+                self.bounds,
+                &mut overlay,
+                renderer,
+            );
+
+            for event in events {
+                overlay.on_event(
+                    event.clone(),
+                    Layout::new(&layer.layout),
+                    cursor_position,
+                    &mut messages,
+                    renderer,
+                    clipboard,
+                );
+            }
+
+            let base_cursor = if layer.layout.bounds().contains(cursor_position)
+            {
+                // TODO: Type-safe cursor availability
+                Point::new(-1.0, -1.0)
+            } else {
+                cursor_position
+            };
+
+            self.overlay = Some(layer);
+
+            base_cursor
+        } else {
+            cursor_position
+        };
+
         for event in events {
             self.root.widget.on_event(
-                event,
-                Layout::new(&self.layout),
-                cursor_position,
+                event.clone(),
+                Layout::new(&self.base.layout),
+                base_cursor,
                 &mut messages,
                 renderer,
                 clipboard,
@@ -256,7 +303,7 @@ where
     ///     );
     ///
     ///     let messages = user_interface.update(
-    ///         events.drain(..),
+    ///         &events,
     ///         cursor_position,
     ///         None,
     ///         &renderer,
@@ -276,16 +323,63 @@ where
     /// }
     /// ```
     pub fn draw(
-        &self,
+        &mut self,
         renderer: &mut Renderer,
         cursor_position: Point,
     ) -> Renderer::Output {
-        self.root.widget.draw(
-            renderer,
-            &Renderer::Defaults::default(),
-            Layout::new(&self.layout),
-            cursor_position,
-        )
+        let overlay = if let Some(mut overlay) =
+            self.root.overlay(Layout::new(&self.base.layout))
+        {
+            let layer = Self::overlay_layer(
+                self.overlay.take(),
+                self.bounds,
+                &mut overlay,
+                renderer,
+            );
+
+            let overlay_bounds = layer.layout.bounds();
+
+            let overlay_primitives = overlay.draw(
+                renderer,
+                &Renderer::Defaults::default(),
+                Layout::new(&layer.layout),
+                cursor_position,
+            );
+
+            self.overlay = Some(layer);
+
+            Some((overlay_primitives, overlay_bounds))
+        } else {
+            None
+        };
+
+        if let Some((overlay_primitives, overlay_bounds)) = overlay {
+            let base_cursor = if overlay_bounds.contains(cursor_position) {
+                Point::new(-1.0, -1.0)
+            } else {
+                cursor_position
+            };
+
+            let base_primitives = self.root.widget.draw(
+                renderer,
+                &Renderer::Defaults::default(),
+                Layout::new(&self.base.layout),
+                base_cursor,
+            );
+
+            renderer.overlay(
+                base_primitives,
+                overlay_primitives,
+                overlay_bounds,
+            )
+        } else {
+            self.root.widget.draw(
+                renderer,
+                &Renderer::Defaults::default(),
+                Layout::new(&self.base.layout),
+                cursor_position,
+            )
+        }
     }
 
     /// Extract the [`Cache`] of the [`UserInterface`], consuming it in the
@@ -295,11 +389,41 @@ where
     /// [`UserInterface`]: struct.UserInterface.html
     pub fn into_cache(self) -> Cache {
         Cache {
-            hash: self.hash,
-            layout: self.layout,
+            base: self.base,
+            overlay: self.overlay,
             bounds: self.bounds,
         }
     }
+
+    fn overlay_layer(
+        cache: Option<Layer>,
+        bounds: Size,
+        overlay: &mut overlay::Element<'_, Message, Renderer>,
+        renderer: &Renderer,
+    ) -> Layer {
+        let new_hash = {
+            let hasher = &mut crate::Hasher::default();
+            overlay.hash_layout(hasher);
+
+            hasher.finish()
+        };
+
+        let layout = match cache {
+            Some(Layer { hash, layout }) if new_hash == hash => layout,
+            _ => overlay.layout(renderer, bounds),
+        };
+
+        Layer {
+            layout,
+            hash: new_hash,
+        }
+    }
+}
+
+#[derive(Debug, Clone)]
+struct Layer {
+    layout: layout::Node,
+    hash: u64,
 }
 
 /// Reusable data of a specific [`UserInterface`].
@@ -307,8 +431,8 @@ where
 /// [`UserInterface`]: struct.UserInterface.html
 #[derive(Debug, Clone)]
 pub struct Cache {
-    hash: u64,
-    layout: layout::Node,
+    base: Layer,
+    overlay: Option<Layer>,
     bounds: Size,
 }
 
@@ -322,8 +446,11 @@ impl Cache {
     /// [`UserInterface`]: struct.UserInterface.html
     pub fn new() -> Cache {
         Cache {
-            hash: 0,
-            layout: layout::Node::new(Size::new(0.0, 0.0)),
+            base: Layer {
+                layout: layout::Node::new(Size::new(0.0, 0.0)),
+                hash: 0,
+            },
+            overlay: None,
             bounds: Size::ZERO,
         }
     }
@@ -334,11 +461,3 @@ impl Default for Cache {
         Cache::new()
     }
 }
-
-impl PartialEq for Cache {
-    fn eq(&self, other: &Cache) -> bool {
-        self.hash == other.hash
-    }
-}
-
-impl Eq for Cache {}
diff --git a/native/src/widget.rs b/native/src/widget.rs
index 4453145b..8539e519 100644
--- a/native/src/widget.rs
+++ b/native/src/widget.rs
@@ -26,6 +26,7 @@ pub mod column;
 pub mod container;
 pub mod image;
 pub mod pane_grid;
+pub mod pick_list;
 pub mod progress_bar;
 pub mod radio;
 pub mod row;
@@ -49,6 +50,8 @@ pub use image::Image;
 #[doc(no_inline)]
 pub use pane_grid::PaneGrid;
 #[doc(no_inline)]
+pub use pick_list::PickList;
+#[doc(no_inline)]
 pub use progress_bar::ProgressBar;
 #[doc(no_inline)]
 pub use radio::Radio;
@@ -67,7 +70,7 @@ pub use text::Text;
 #[doc(no_inline)]
 pub use text_input::TextInput;
 
-use crate::{layout, Clipboard, Event, Hasher, Layout, Length, Point};
+use crate::{layout, overlay, Clipboard, Event, Hasher, Layout, Length, Point};
 
 /// A component that displays information and allows interaction.
 ///
@@ -175,4 +178,14 @@ where
         _clipboard: Option<&dyn Clipboard>,
     ) {
     }
+
+    /// Returns the overlay of the [`Element`], if there is any.
+    ///
+    /// [`Element`]: struct.Element.html
+    fn overlay(
+        &mut self,
+        _layout: Layout<'_>,
+    ) -> Option<overlay::Element<'_, Message, Renderer>> {
+        None
+    }
 }
diff --git a/native/src/widget/column.rs b/native/src/widget/column.rs
index 259a7e6e..42cfe9b9 100644
--- a/native/src/widget/column.rs
+++ b/native/src/widget/column.rs
@@ -2,8 +2,8 @@
 use std::hash::Hash;
 
 use crate::{
-    layout, Align, Clipboard, Element, Event, Hasher, Layout, Length, Point,
-    Widget,
+    layout, overlay, Align, Clipboard, Element, Event, Hasher, Layout, Length,
+    Point, Widget,
 };
 
 use std::u32;
@@ -204,6 +204,17 @@ where
             child.widget.hash_layout(state);
         }
     }
+
+    fn overlay(
+        &mut self,
+        layout: Layout<'_>,
+    ) -> Option<overlay::Element<'_, Message, Renderer>> {
+        self.children
+            .iter_mut()
+            .zip(layout.children())
+            .filter_map(|(child, layout)| child.widget.overlay(layout))
+            .next()
+    }
 }
 
 /// The renderer of a [`Column`].
diff --git a/native/src/widget/container.rs b/native/src/widget/container.rs
index 2590fe3b..b8316e62 100644
--- a/native/src/widget/container.rs
+++ b/native/src/widget/container.rs
@@ -2,8 +2,8 @@
 use std::hash::Hash;
 
 use crate::{
-    layout, Align, Clipboard, Element, Event, Hasher, Layout, Length, Point,
-    Rectangle, Widget,
+    layout, overlay, Align, Clipboard, Element, Event, Hasher, Layout, Length,
+    Point, Rectangle, Widget,
 };
 
 use std::u32;
@@ -214,6 +214,13 @@ where
 
         self.content.hash_layout(state);
     }
+
+    fn overlay(
+        &mut self,
+        layout: Layout<'_>,
+    ) -> Option<overlay::Element<'_, Message, Renderer>> {
+        self.content.overlay(layout.children().next().unwrap())
+    }
 }
 
 /// The renderer of a [`Container`].
diff --git a/native/src/widget/pane_grid.rs b/native/src/widget/pane_grid.rs
index c472d043..0b237b9e 100644
--- a/native/src/widget/pane_grid.rs
+++ b/native/src/widget/pane_grid.rs
@@ -29,8 +29,8 @@ pub use state::{Focus, State};
 pub use title_bar::TitleBar;
 
 use crate::{
-    container, keyboard, layout, mouse, row, text, Clipboard, Element, Event,
-    Hasher, Layout, Length, Point, Rectangle, Size, Vector, Widget,
+    container, keyboard, layout, mouse, overlay, row, text, Clipboard, Element,
+    Event, Hasher, Layout, Length, Point, Rectangle, Size, Vector, Widget,
 };
 
 /// A collection of panes distributed using either vertical or horizontal splits
@@ -636,6 +636,17 @@ where
             element.hash_layout(state);
         }
     }
+
+    fn overlay(
+        &mut self,
+        layout: Layout<'_>,
+    ) -> Option<overlay::Element<'_, Message, Renderer>> {
+        self.elements
+            .iter_mut()
+            .zip(layout.children())
+            .filter_map(|((_, pane), layout)| pane.overlay(layout))
+            .next()
+    }
 }
 
 /// The renderer of a [`PaneGrid`].
diff --git a/native/src/widget/pane_grid/content.rs b/native/src/widget/pane_grid/content.rs
index 1f5ce640..39a92186 100644
--- a/native/src/widget/pane_grid/content.rs
+++ b/native/src/widget/pane_grid/content.rs
@@ -1,5 +1,6 @@
 use crate::container;
 use crate::layout;
+use crate::overlay;
 use crate::pane_grid::{self, TitleBar};
 use crate::{Clipboard, Element, Event, Hasher, Layout, Point, Size};
 
@@ -184,6 +185,24 @@ where
     pub(crate) fn hash_layout(&self, state: &mut Hasher) {
         self.body.hash_layout(state);
     }
+
+    pub(crate) fn overlay(
+        &mut self,
+        layout: Layout<'_>,
+    ) -> Option<overlay::Element<'_, Message, Renderer>> {
+        let body_layout = if self.title_bar.is_some() {
+            let mut children = layout.children();
+
+            // Overlays only allowed in the pane body, for now at least.
+            let _title_bar_layout = children.next();
+
+            children.next()?
+        } else {
+            layout
+        };
+
+        self.body.overlay(body_layout)
+    }
 }
 
 impl<'a, T, Message, Renderer> From<T> for Content<'a, Message, Renderer>
diff --git a/native/src/widget/pick_list.rs b/native/src/widget/pick_list.rs
new file mode 100644
index 00000000..9f62e550
--- /dev/null
+++ b/native/src/widget/pick_list.rs
@@ -0,0 +1,320 @@
+//! Display a dropdown list of selectable values.
+use crate::{
+    layout, mouse, overlay,
+    overlay::menu::{self, Menu},
+    scrollable, text, Clipboard, Element, Event, Hasher, Layout, Length, Point,
+    Rectangle, Size, Widget,
+};
+use std::borrow::Cow;
+
+/// A widget for selecting a single value from a list of options.
+#[allow(missing_debug_implementations)]
+pub struct PickList<'a, T, Message, Renderer: self::Renderer>
+where
+    [T]: ToOwned<Owned = Vec<T>>,
+{
+    menu: &'a mut menu::State,
+    on_selected: Box<dyn Fn(T) -> Message>,
+    options: Cow<'a, [T]>,
+    selected: Option<T>,
+    width: Length,
+    padding: u16,
+    text_size: Option<u16>,
+    font: Renderer::Font,
+    style: <Renderer as self::Renderer>::Style,
+    is_open: bool,
+}
+
+/// The local state of a [`PickList`].
+///
+/// [`PickList`]: struct.PickList.html
+#[derive(Debug, Clone, Default)]
+pub struct State {
+    menu: menu::State,
+}
+
+impl<'a, T: 'a, Message, Renderer: self::Renderer>
+    PickList<'a, T, Message, Renderer>
+where
+    T: ToString,
+    [T]: ToOwned<Owned = Vec<T>>,
+{
+    /// Creates a new [`PickList`] with the given [`State`], a list of options,
+    /// the current selected value, and the message to produce when an option is
+    /// selected.
+    ///
+    /// [`PickList`]: struct.PickList.html
+    /// [`State`]: struct.State.html
+    pub fn new(
+        state: &'a mut State,
+        options: impl Into<Cow<'a, [T]>>,
+        selected: Option<T>,
+        on_selected: impl Fn(T) -> Message + 'static,
+    ) -> Self {
+        let is_open = state.menu.is_open();
+
+        Self {
+            menu: &mut state.menu,
+            on_selected: Box::new(on_selected),
+            options: options.into(),
+            selected,
+            width: Length::Shrink,
+            text_size: None,
+            padding: Renderer::DEFAULT_PADDING,
+            font: Default::default(),
+            style: Default::default(),
+            is_open,
+        }
+    }
+
+    /// Sets the width of the [`PickList`].
+    ///
+    /// [`PickList`]: struct.PickList.html
+    pub fn width(mut self, width: Length) -> Self {
+        self.width = width;
+        self
+    }
+
+    /// Sets the padding of the [`PickList`].
+    ///
+    /// [`PickList`]: struct.PickList.html
+    pub fn padding(mut self, padding: u16) -> Self {
+        self.padding = padding;
+        self
+    }
+
+    /// Sets the text size of the [`PickList`].
+    ///
+    /// [`PickList`]: struct.PickList.html
+    pub fn text_size(mut self, size: u16) -> Self {
+        self.text_size = Some(size);
+        self
+    }
+
+    /// Sets the font of the [`PickList`].
+    ///
+    /// [`PickList`]: struct.PickList.html
+    pub fn font(mut self, font: Renderer::Font) -> Self {
+        self.font = font;
+        self
+    }
+
+    /// Sets the style of the [`PickList`].
+    ///
+    /// [`PickList`]: struct.PickList.html
+    pub fn style(
+        mut self,
+        style: impl Into<<Renderer as self::Renderer>::Style>,
+    ) -> Self {
+        self.style = style.into();
+        self
+    }
+}
+
+impl<'a, T: 'a, Message, Renderer> Widget<Message, Renderer>
+    for PickList<'a, T, Message, Renderer>
+where
+    T: Clone + ToString + Eq,
+    [T]: ToOwned<Owned = Vec<T>>,
+    Message: 'static,
+    Renderer: self::Renderer + scrollable::Renderer + 'a,
+{
+    fn width(&self) -> Length {
+        Length::Shrink
+    }
+
+    fn height(&self) -> Length {
+        Length::Shrink
+    }
+
+    fn layout(
+        &self,
+        renderer: &Renderer,
+        limits: &layout::Limits,
+    ) -> layout::Node {
+        use std::f32;
+
+        let limits = limits
+            .width(self.width)
+            .height(Length::Shrink)
+            .pad(f32::from(self.padding));
+
+        let text_size = self.text_size.unwrap_or(renderer.default_size());
+
+        let max_width = match self.width {
+            Length::Shrink => {
+                let labels = self.options.iter().map(ToString::to_string);
+
+                labels
+                    .map(|label| {
+                        let (width, _) = renderer.measure(
+                            &label,
+                            text_size,
+                            Renderer::Font::default(),
+                            Size::new(f32::INFINITY, f32::INFINITY),
+                        );
+
+                        width.round() as u32
+                    })
+                    .max()
+                    .unwrap_or(100)
+            }
+            _ => 0,
+        };
+
+        let size = {
+            let intrinsic = Size::new(
+                max_width as f32
+                    + f32::from(text_size)
+                    + f32::from(self.padding),
+                f32::from(text_size),
+            );
+
+            limits.resolve(intrinsic).pad(f32::from(self.padding))
+        };
+
+        layout::Node::new(size)
+    }
+
+    fn hash_layout(&self, state: &mut Hasher) {
+        use std::hash::Hash as _;
+
+        match self.width {
+            Length::Shrink => {
+                self.options
+                    .iter()
+                    .map(ToString::to_string)
+                    .for_each(|label| label.hash(state));
+            }
+            _ => {
+                self.width.hash(state);
+            }
+        }
+    }
+
+    fn on_event(
+        &mut self,
+        event: Event,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        _messages: &mut Vec<Message>,
+        _renderer: &Renderer,
+        _clipboard: Option<&dyn Clipboard>,
+    ) {
+        if !self.is_open {
+            match event {
+                Event::Mouse(mouse::Event::ButtonPressed(
+                    mouse::Button::Left,
+                )) => {
+                    if layout.bounds().contains(cursor_position) {
+                        let selected = self.selected.as_ref();
+
+                        self.menu.open(
+                            self.options
+                                .iter()
+                                .position(|option| Some(option) == selected),
+                        );
+                    }
+                }
+                _ => {}
+            }
+        }
+    }
+
+    fn draw(
+        &self,
+        renderer: &mut Renderer,
+        _defaults: &Renderer::Defaults,
+        layout: Layout<'_>,
+        cursor_position: Point,
+    ) -> Renderer::Output {
+        self::Renderer::draw(
+            renderer,
+            layout.bounds(),
+            cursor_position,
+            self.selected.as_ref().map(ToString::to_string),
+            self.padding,
+            self.text_size.unwrap_or(renderer.default_size()),
+            self.font,
+            &self.style,
+        )
+    }
+
+    fn overlay(
+        &mut self,
+        layout: Layout<'_>,
+    ) -> Option<overlay::Element<'_, Message, Renderer>> {
+        if self.menu.is_open() {
+            let bounds = layout.bounds();
+
+            let mut menu =
+                Menu::new(&mut self.menu, &self.options, &self.on_selected)
+                    .width(bounds.width.round() as u16)
+                    .padding(self.padding)
+                    .font(self.font)
+                    .style(Renderer::menu_style(&self.style));
+
+            if let Some(text_size) = self.text_size {
+                menu = menu.text_size(text_size);
+            }
+
+            Some(menu.overlay(layout.position(), bounds.height))
+        } else {
+            None
+        }
+    }
+}
+
+/// The renderer of a [`PickList`].
+///
+/// Your [renderer] will need to implement this trait before being
+/// able to use a [`PickList`] in your user interface.
+///
+/// [`PickList`]: struct.PickList.html
+/// [renderer]: ../../renderer/index.html
+pub trait Renderer: text::Renderer + menu::Renderer {
+    /// The default padding of a [`PickList`].
+    ///
+    /// [`PickList`]: struct.PickList.html
+    const DEFAULT_PADDING: u16;
+
+    /// The [`PickList`] style supported by this renderer.
+    ///
+    /// [`PickList`]: struct.PickList.html
+    type Style: Default;
+
+    /// Returns the style of the [`Menu`] of the [`PickList`].
+    ///
+    /// [`Menu`]: ../../overlay/menu/struct.Menu.html
+    /// [`PickList`]: struct.PickList.html
+    fn menu_style(
+        style: &<Self as Renderer>::Style,
+    ) -> <Self as menu::Renderer>::Style;
+
+    /// Draws a [`PickList`].
+    ///
+    /// [`PickList`]: struct.PickList.html
+    fn draw(
+        &mut self,
+        bounds: Rectangle,
+        cursor_position: Point,
+        selected: Option<String>,
+        padding: u16,
+        text_size: u16,
+        font: Self::Font,
+        style: &<Self as Renderer>::Style,
+    ) -> Self::Output;
+}
+
+impl<'a, T: 'a, Message, Renderer> Into<Element<'a, Message, Renderer>>
+    for PickList<'a, T, Message, Renderer>
+where
+    T: Clone + ToString + Eq,
+    [T]: ToOwned<Owned = Vec<T>>,
+    Renderer: self::Renderer + 'a,
+    Message: 'static,
+{
+    fn into(self) -> Element<'a, Message, Renderer> {
+        Element::new(self)
+    }
+}
diff --git a/native/src/widget/row.rs b/native/src/widget/row.rs
index 31f7472f..2b6db224 100644
--- a/native/src/widget/row.rs
+++ b/native/src/widget/row.rs
@@ -2,8 +2,8 @@
 use std::hash::Hash;
 
 use crate::{
-    layout, Align, Clipboard, Element, Event, Hasher, Layout, Length, Point,
-    Widget,
+    layout, overlay, Align, Clipboard, Element, Event, Hasher, Layout, Length,
+    Point, Widget,
 };
 
 use std::u32;
@@ -206,6 +206,17 @@ where
             child.widget.hash_layout(state);
         }
     }
+
+    fn overlay(
+        &mut self,
+        layout: Layout<'_>,
+    ) -> Option<overlay::Element<'_, Message, Renderer>> {
+        self.children
+            .iter_mut()
+            .zip(layout.children())
+            .filter_map(|(child, layout)| child.widget.overlay(layout))
+            .next()
+    }
 }
 
 /// The renderer of a [`Row`].
diff --git a/native/src/widget/scrollable.rs b/native/src/widget/scrollable.rs
index 3c8e5e5b..75e97027 100644
--- a/native/src/widget/scrollable.rs
+++ b/native/src/widget/scrollable.rs
@@ -1,7 +1,7 @@
 //! Navigate an endless amount of content with a scrollbar.
 use crate::{
-    column, layout, mouse, Align, Clipboard, Column, Element, Event, Hasher,
-    Layout, Length, Point, Rectangle, Size, Widget,
+    column, layout, mouse, overlay, Align, Clipboard, Column, Element, Event,
+    Hasher, Layout, Length, Point, Rectangle, Size, Vector, Widget,
 };
 
 use std::{f32, hash::Hash, u32};
@@ -113,7 +113,7 @@ impl<'a, Message, Renderer: self::Renderer> Scrollable<'a, Message, Renderer> {
 impl<'a, Message, Renderer> Widget<Message, Renderer>
     for Scrollable<'a, Message, Renderer>
 where
-    Renderer: self::Renderer + column::Renderer,
+    Renderer: self::Renderer,
 {
     fn width(&self) -> Length {
         Widget::<Message, Renderer>::width(&self.content)
@@ -315,6 +315,24 @@ where
 
         self.content.hash_layout(state)
     }
+
+    fn overlay(
+        &mut self,
+        layout: Layout<'_>,
+    ) -> Option<overlay::Element<'_, Message, Renderer>> {
+        let Self { content, state, .. } = self;
+
+        content
+            .overlay(layout.children().next().unwrap())
+            .map(|overlay| {
+                let bounds = layout.bounds();
+                let content_layout = layout.children().next().unwrap();
+                let content_bounds = content_layout.bounds();
+                let offset = state.offset(bounds, content_bounds);
+
+                overlay.translate(Vector::new(0.0, -(offset as f32)))
+            })
+    }
 }
 
 /// The local state of a [`Scrollable`].
@@ -454,7 +472,7 @@ pub struct Scroller {
 ///
 /// [`Scrollable`]: struct.Scrollable.html
 /// [renderer]: ../../renderer/index.html
-pub trait Renderer: crate::Renderer + Sized {
+pub trait Renderer: column::Renderer + Sized {
     /// The style supported by this renderer.
     type Style: Default;
 
@@ -502,7 +520,7 @@ pub trait Renderer: crate::Renderer + Sized {
 impl<'a, Message, Renderer> From<Scrollable<'a, Message, Renderer>>
     for Element<'a, Message, Renderer>
 where
-    Renderer: 'a + self::Renderer + column::Renderer,
+    Renderer: 'a + self::Renderer,
     Message: 'a,
 {
     fn from(
diff --git a/native/src/widget/space.rs b/native/src/widget/space.rs
index e56a8fe1..f1576ffb 100644
--- a/native/src/widget/space.rs
+++ b/native/src/widget/space.rs
@@ -43,7 +43,7 @@ impl Space {
     }
 }
 
-impl<'a, Message, Renderer> Widget<Message, Renderer> for Space
+impl<Message, Renderer> Widget<Message, Renderer> for Space
 where
     Renderer: self::Renderer,
 {