Draft custom layout engine based on `druid`

21 files changed, 813 insertions, 146 deletions

diff --git a/native/src/element.rs b/native/src/element.rs
index acae1135..361d7567 100644
--- a/native/src/element.rs
+++ b/native/src/element.rs
@@ -1,4 +1,6 @@
-use crate::{layout, renderer, Color, Event, Hasher, Layout, Point, Widget};
+use crate::{
+    layout, renderer, Color, Event, Hasher, Layout, Length, Point, Widget,
+};
 
 /// A generic [`Widget`].
 ///
@@ -39,18 +41,26 @@ where
         }
     }
 
+    pub fn width(&self) -> Length {
+        self.widget.width()
+    }
+
+    pub fn height(&self) -> Length {
+        self.widget.height()
+    }
+
     pub fn layout(
         &self,
         renderer: &Renderer,
         limits: &layout::Limits,
-    ) -> Layout {
+    ) -> layout::Node {
         self.widget.layout(renderer, limits)
     }
 
     pub fn draw(
         &self,
         renderer: &mut Renderer,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
     ) -> Renderer::Output {
         self.widget.draw(renderer, layout, cursor_position)
@@ -285,14 +295,18 @@ where
     A: Clone,
     Renderer: crate::Renderer,
 {
-    fn layout(&self, renderer: &Renderer, limits: &layout::Limits) -> Layout {
+    fn layout(
+        &self,
+        renderer: &Renderer,
+        limits: &layout::Limits,
+    ) -> layout::Node {
         self.widget.layout(renderer, limits)
     }
 
     fn on_event(
         &mut self,
         event: Event,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
         messages: &mut Vec<B>,
         renderer: &Renderer,
@@ -316,7 +330,7 @@ where
     fn draw(
         &self,
         renderer: &mut Renderer,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
     ) -> Renderer::Output {
         self.widget.draw(renderer, layout, cursor_position)
@@ -357,14 +371,18 @@ impl<'a, Message, Renderer> Widget<Message, Renderer>
 where
     Renderer: crate::Renderer + renderer::Debugger,
 {
-    fn layout(&self, renderer: &Renderer, limits: &layout::Limits) -> Layout {
+    fn layout(
+        &self,
+        renderer: &Renderer,
+        limits: &layout::Limits,
+    ) -> layout::Node {
         self.element.widget.layout(renderer, limits)
     }
 
     fn on_event(
         &mut self,
         event: Event,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
         messages: &mut Vec<Message>,
         renderer: &Renderer,
@@ -381,7 +399,7 @@ where
     fn draw(
         &self,
         renderer: &mut Renderer,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
     ) -> Renderer::Output {
         renderer.explain(
diff --git a/native/src/layout.rs b/native/src/layout.rs
index 520bcd88..0a744346 100644
--- a/native/src/layout.rs
+++ b/native/src/layout.rs
@@ -1,57 +1,50 @@
-use crate::Rectangle;
-
 mod limits;
+mod node;
+
+pub mod flex;
 
 pub use limits::Limits;
+pub use node::Node;
 
-/// The computed bounds of a [`Node`] and its children.
-///
-/// This type is provided by the GUI runtime to [`Widget::on_event`] and
-/// [`Widget::draw`], describing the layout of the [`Node`] produced by
-/// [`Widget::node`].
-///
-/// [`Node`]: struct.Node.html
-/// [`Widget::on_event`]: widget/trait.Widget.html#method.on_event
-/// [`Widget::draw`]: widget/trait.Widget.html#tymethod.draw
-/// [`Widget::node`]: widget/trait.Widget.html#tymethod.node
-#[derive(Debug, Clone)]
-pub struct Layout {
-    bounds: Rectangle,
-    children: Vec<Layout>,
+use crate::{Point, Rectangle, Vector};
+
+#[derive(Debug, Clone, Copy)]
+pub struct Layout<'a> {
+    position: Point,
+    node: &'a Node,
 }
 
-impl Layout {
-    pub fn new(bounds: Rectangle) -> Self {
-        Layout {
-            bounds,
-            children: Vec::new(),
-        }
+impl<'a> Layout<'a> {
+    pub(crate) fn new(node: &'a Node) -> Self {
+        Self::with_offset(Vector::new(0.0, 0.0), node)
     }
 
-    pub fn push(&mut self, mut child: Layout) {
-        child.bounds.x += self.bounds.x;
-        child.bounds.y += self.bounds.y;
+    pub(crate) fn with_offset(offset: Vector, node: &'a Node) -> Self {
+        let bounds = node.bounds();
 
-        self.children.push(child);
+        Self {
+            position: Point::new(bounds.x, bounds.y) + offset,
+            node,
+        }
     }
 
-    /// Gets the bounds of the [`Layout`].
-    ///
-    /// The returned [`Rectangle`] describes the position and size of a
-    /// [`Node`].
-    ///
-    /// [`Layout`]: struct.Layout.html
-    /// [`Rectangle`]: struct.Rectangle.html
-    /// [`Node`]: struct.Node.html
     pub fn bounds(&self) -> Rectangle {
-        self.bounds
+        let bounds = self.node.bounds();
+
+        Rectangle {
+            x: self.position.x,
+            y: self.position.y,
+            width: bounds.width,
+            height: bounds.height,
+        }
     }
 
-    /// Returns an iterator over the [`Layout`] of the children of a [`Node`].
-    ///
-    /// [`Layout`]: struct.Layout.html
-    /// [`Node`]: struct.Node.html
-    pub fn children(&self) -> impl Iterator<Item = &Layout> {
-        self.children.iter()
+    pub fn children(&'a self) -> impl Iterator<Item = Layout<'a>> {
+        self.node.children().iter().map(move |node| {
+            Layout::with_offset(
+                Vector::new(self.position.x, self.position.y),
+                node,
+            )
+        })
     }
 }
diff --git a/native/src/layout/DRUID_LICENSE b/native/src/layout/DRUID_LICENSE
new file mode 100644
index 00000000..d6456956
--- /dev/null
+++ b/native/src/layout/DRUID_LICENSE
@@ -0,0 +1,202 @@
+
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diff --git a/native/src/layout/flex.rs b/native/src/layout/flex.rs
new file mode 100644
index 00000000..98cc344e
--- /dev/null
+++ b/native/src/layout/flex.rs
@@ -0,0 +1,155 @@
+// This code is heavily inspired by the [`druid`] codebase.
+//
+// [`druid`]: https://github.com/xi-editor/druid
+//
+// Copyright 2018 The xi-editor Authors, Héctor Ramón
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+use crate::{
+    layout::{Limits, Node},
+    Element, Size,
+};
+
+#[derive(Debug)]
+pub enum Axis {
+    Horizontal,
+    Vertical,
+}
+
+impl Axis {
+    fn main(&self, size: Size) -> f32 {
+        match self {
+            Axis::Horizontal => size.width,
+            Axis::Vertical => size.height,
+        }
+    }
+
+    fn cross(&self, size: Size) -> f32 {
+        match self {
+            Axis::Horizontal => size.height,
+            Axis::Vertical => size.width,
+        }
+    }
+
+    fn pack(&self, main: f32, cross: f32) -> (f32, f32) {
+        match self {
+            Axis::Horizontal => (main, cross),
+            Axis::Vertical => (cross, main),
+        }
+    }
+}
+
+// TODO: Remove `Message` type parameter
+pub fn resolve<Message, Renderer>(
+    axis: Axis,
+    renderer: &Renderer,
+    limits: &Limits,
+    padding: f32,
+    spacing: f32,
+    children: &[Element<'_, Message, Renderer>],
+) -> Node
+where
+    Renderer: crate::Renderer,
+{
+    let limits = limits.pad(padding);
+
+    let mut total_non_fill = spacing as f32 * (children.len() - 1) as f32;
+    let mut fill_sum = 0;
+
+    let mut nodes: Vec<Node> = Vec::with_capacity(children.len());
+    nodes.resize(children.len(), Node::default());
+
+    for (i, child) in children.iter().enumerate() {
+        let fill_factor = match axis {
+            Axis::Horizontal => child.width(),
+            Axis::Vertical => child.height(),
+        }
+        .fill_factor();
+
+        if fill_factor == 0 {
+            let child_limits = Limits::new(Size::ZERO, limits.max());
+
+            let layout = child.layout(renderer, &child_limits);
+
+            total_non_fill += axis.main(layout.size());
+
+            nodes[i] = layout;
+        } else {
+            fill_sum += fill_factor;
+        }
+    }
+
+    let available = axis.main(limits.max());
+    let remaining = (available - total_non_fill).max(0.0);
+
+    for (i, child) in children.iter().enumerate() {
+        let fill_factor = match axis {
+            Axis::Horizontal => child.width(),
+            Axis::Vertical => child.height(),
+        }
+        .fill_factor();
+
+        if fill_factor != 0 {
+            let max_main = remaining * fill_factor as f32 / fill_sum as f32;
+            let min_main = if max_main.is_infinite() {
+                0.0
+            } else {
+                max_main
+            };
+
+            let (min_main, min_cross) =
+                axis.pack(min_main, axis.cross(limits.min()));
+
+            let (max_main, max_cross) =
+                axis.pack(max_main, axis.cross(limits.max()));
+
+            let child_limits = Limits::new(
+                Size::new(min_main, min_cross),
+                Size::new(max_main, max_cross),
+            );
+
+            let layout = child.layout(renderer, &child_limits);
+
+            nodes[i] = layout;
+        }
+    }
+
+    let mut main = padding;
+    let mut cross = axis.cross(limits.min());
+
+    for (i, node) in nodes.iter_mut().enumerate() {
+        if i > 0 {
+            main += spacing;
+        }
+
+        let (x, y) = axis.pack(main, padding);
+
+        node.bounds.x = x;
+        node.bounds.y = y;
+
+        let size = node.size();
+
+        main += axis.main(size);
+        cross = cross.max(axis.cross(size));
+    }
+
+    let (width, height) = axis.pack(main, cross);
+    let size = limits.resolve(Size::new(width, height));
+
+    let (padding_x, padding_y) = axis.pack(padding, padding * 2.0);
+
+    Node::with_children(
+        Size::new(size.width + padding_x, size.height + padding_y),
+        nodes,
+    )
+}
diff --git a/native/src/layout/limits.rs b/native/src/layout/limits.rs
index ad105119..e5cee5df 100644
--- a/native/src/layout/limits.rs
+++ b/native/src/layout/limits.rs
@@ -1,6 +1,131 @@
-#[derive(Debug)]
-pub struct Limits {}
+use crate::{Length, Size};
+
+#[derive(Debug, Clone, Copy)]
+pub struct Limits {
+    min: Size,
+    max: Size,
+    fill: Size,
+}
 
 impl Limits {
-    pub const NONE: Limits = Limits {};
+    pub const NONE: Limits = Limits {
+        min: Size::ZERO,
+        max: Size::INFINITY,
+        fill: Size::INFINITY,
+    };
+
+    pub fn new(min: Size, max: Size) -> Limits {
+        Limits {
+            min,
+            max,
+            fill: Size::INFINITY,
+        }
+    }
+
+    pub fn width(mut self, width: Length) -> Limits {
+        match width {
+            Length::Shrink => {
+                self.fill.width = self.min.width;
+            }
+            Length::Fill => {
+                self.fill.width = self.fill.width.min(self.max.width);
+            }
+            Length::Units(units) => {
+                let new_width =
+                    (units as f32).min(self.max.width).max(self.min.width);
+
+                self.min.width = new_width;
+                self.max.width = new_width;
+                self.fill.width = new_width;
+            }
+        }
+
+        self
+    }
+
+    pub fn height(mut self, height: Length) -> Limits {
+        match height {
+            Length::Shrink => {
+                self.fill.height = self.min.height;
+            }
+            Length::Fill => {
+                self.fill.height = self.fill.height.min(self.max.height);
+            }
+            Length::Units(units) => {
+                let new_height =
+                    (units as f32).min(self.max.height).max(self.min.height);
+
+                self.min.height = new_height;
+                self.max.height = new_height;
+                self.fill.height = new_height;
+            }
+        }
+
+        self
+    }
+
+    pub fn min_width(mut self, min_width: u32) -> Limits {
+        self.min.width =
+            self.min.width.max(min_width as f32).min(self.max.width);
+
+        self
+    }
+
+    pub fn max_width(mut self, max_width: u32) -> Limits {
+        self.max.width =
+            self.max.width.min(max_width as f32).max(self.min.width);
+
+        self
+    }
+
+    pub fn max_height(mut self, max_height: u32) -> Limits {
+        self.max.height =
+            self.max.height.min(max_height as f32).max(self.min.height);
+
+        self
+    }
+
+    pub fn resolve(&self, intrinsic_size: Size) -> Size {
+        Size::new(
+            intrinsic_size
+                .width
+                .min(self.max.width)
+                .max(self.fill.width),
+            intrinsic_size
+                .height
+                .min(self.max.height)
+                .max(self.fill.height),
+        )
+    }
+
+    pub fn min(&self) -> Size {
+        self.min
+    }
+
+    pub fn max(&self) -> Size {
+        self.max
+    }
+
+    pub fn pad(&self, padding: f32) -> Limits {
+        self.shrink(Size::new(padding * 2.0, padding * 2.0))
+    }
+
+    pub fn shrink(&self, size: Size) -> Limits {
+        let min = Size::new(
+            (self.min().width - size.width).max(0.0),
+            (self.min().height - size.height).max(0.0),
+        );
+
+        let max = Size::new(
+            (self.max().width - size.width).max(0.0),
+            (self.max().height - size.height).max(0.0),
+        );
+
+        let fill = Size::new(
+            (self.fill.width - size.width).max(0.0),
+            (self.fill.height - size.height).max(0.0),
+        );
+
+        Limits { min, max, fill }
+    }
 }
diff --git a/native/src/layout/node.rs b/native/src/layout/node.rs
new file mode 100644
index 00000000..7537ad3b
--- /dev/null
+++ b/native/src/layout/node.rs
@@ -0,0 +1,37 @@
+use crate::{Rectangle, Size};
+
+#[derive(Debug, Clone, Default)]
+pub struct Node {
+    pub bounds: Rectangle,
+    children: Vec<Node>,
+}
+
+impl Node {
+    pub fn new(size: Size) -> Self {
+        Self::with_children(size, Vec::new())
+    }
+
+    pub fn with_children(size: Size, children: Vec<Node>) -> Self {
+        Node {
+            bounds: Rectangle {
+                x: 0.0,
+                y: 0.0,
+                width: size.width,
+                height: size.height,
+            },
+            children,
+        }
+    }
+
+    pub fn size(&self) -> Size {
+        Size::new(self.bounds.width, self.bounds.height)
+    }
+
+    pub fn bounds(&self) -> Rectangle {
+        self.bounds
+    }
+
+    pub fn children(&self) -> &[Node] {
+        &self.children
+    }
+}
diff --git a/native/src/lib.rs b/native/src/lib.rs
index d2388ee2..453a3ad5 100644
--- a/native/src/lib.rs
+++ b/native/src/lib.rs
@@ -207,6 +207,7 @@ mod element;
 mod event;
 mod hasher;
 mod mouse_cursor;
+mod size;
 mod user_interface;
 
 pub use iced_core::{
@@ -219,5 +220,6 @@ pub use hasher::Hasher;
 pub use layout::Layout;
 pub use mouse_cursor::MouseCursor;
 pub use renderer::Renderer;
+pub use size::Size;
 pub use user_interface::{Cache, UserInterface};
 pub use widget::*;
diff --git a/native/src/renderer/debugger.rs b/native/src/renderer/debugger.rs
index 4184860e..4cc50661 100644
--- a/native/src/renderer/debugger.rs
+++ b/native/src/renderer/debugger.rs
@@ -18,7 +18,7 @@ pub trait Debugger: super::Renderer {
     fn explain<Message>(
         &mut self,
         widget: &dyn Widget<Message, Self>,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
         color: Color,
     ) -> Self::Output;
diff --git a/native/src/size.rs b/native/src/size.rs
new file mode 100644
index 00000000..bd909292
--- /dev/null
+++ b/native/src/size.rs
@@ -0,0 +1,25 @@
+use std::f32;
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub struct Size {
+    /// The width.
+    pub width: f32,
+    /// The height.
+    pub height: f32,
+}
+
+impl Size {
+    pub const ZERO: Size = Size::new(0., 0.);
+    pub const INFINITY: Size = Size::new(f32::INFINITY, f32::INFINITY);
+
+    pub const fn new(width: f32, height: f32) -> Self {
+        Size { width, height }
+    }
+
+    pub fn pad(&self, padding: f32) -> Self {
+        Size {
+            width: self.width + padding * 2.0,
+            height: self.height + padding * 2.0,
+        }
+    }
+}
diff --git a/native/src/user_interface.rs b/native/src/user_interface.rs
index 7c166094..4343086b 100644
--- a/native/src/user_interface.rs
+++ b/native/src/user_interface.rs
@@ -1,4 +1,4 @@
-use crate::{input::mouse, layout, Element, Event, Layout, Point, Rectangle};
+use crate::{input::mouse, layout, Element, Event, Layout, Point, Size};
 
 use std::hash::Hasher;
 
@@ -14,7 +14,7 @@ use std::hash::Hasher;
 pub struct UserInterface<'a, Message, Renderer> {
     hash: u64,
     root: Element<'a, Message, Renderer>,
-    layout: Layout,
+    layout: layout::Node,
     cursor_position: Point,
 }
 
@@ -109,7 +109,11 @@ where
         let layout = if hash == cache.hash {
             cache.layout
         } else {
-            root.layout(renderer, &layout::Limits::NONE)
+            let layout_start = std::time::Instant::now();
+            let layout = root.layout(renderer, &layout::Limits::NONE);
+            dbg!(std::time::Instant::now() - layout_start);
+
+            layout
         };
 
         UserInterface {
@@ -209,7 +213,7 @@ where
 
             self.root.widget.on_event(
                 event,
-                &self.layout,
+                Layout::new(&self.layout),
                 self.cursor_position,
                 &mut messages,
                 renderer,
@@ -298,9 +302,11 @@ where
     /// }
     /// ```
     pub fn draw(&self, renderer: &mut Renderer) -> Renderer::Output {
-        self.root
-            .widget
-            .draw(renderer, &self.layout, self.cursor_position)
+        self.root.widget.draw(
+            renderer,
+            Layout::new(&self.layout),
+            self.cursor_position,
+        )
     }
 
     /// Extract the [`Cache`] of the [`UserInterface`], consuming it in the
@@ -323,7 +329,7 @@ where
 #[derive(Debug, Clone)]
 pub struct Cache {
     hash: u64,
-    layout: Layout,
+    layout: layout::Node,
     cursor_position: Point,
 }
 
@@ -338,12 +344,7 @@ impl Cache {
     pub fn new() -> Cache {
         Cache {
             hash: 0,
-            layout: Layout::new(Rectangle {
-                x: 0.0,
-                y: 0.0,
-                width: 0.0,
-                height: 0.0,
-            }),
+            layout: layout::Node::new(Size::new(0.0, 0.0)),
             cursor_position: Point::new(-1.0, -1.0),
         }
     }
diff --git a/native/src/widget.rs b/native/src/widget.rs
index 0dfd5fd7..2d6d347f 100644
--- a/native/src/widget.rs
+++ b/native/src/widget.rs
@@ -52,7 +52,7 @@ pub use text::Text;
 #[doc(no_inline)]
 pub use text_input::TextInput;
 
-use crate::{layout, Event, Hasher, Layout, Point};
+use crate::{layout, Event, Hasher, Layout, Length, Point};
 
 /// A component that displays information and allows interaction.
 ///
@@ -73,7 +73,19 @@ where
     /// [`Node`]: ../struct.Node.html
     /// [`Widget`]: trait.Widget.html
     /// [`Layout`]: ../struct.Layout.html
-    fn layout(&self, renderer: &Renderer, limits: &layout::Limits) -> Layout;
+    fn layout(
+        &self,
+        renderer: &Renderer,
+        limits: &layout::Limits,
+    ) -> layout::Node;
+
+    fn width(&self) -> Length {
+        Length::Shrink
+    }
+
+    fn height(&self) -> Length {
+        Length::Shrink
+    }
 
     /// Draws the [`Widget`] using the associated `Renderer`.
     ///
@@ -81,7 +93,7 @@ where
     fn draw(
         &self,
         renderer: &mut Renderer,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
     ) -> Renderer::Output;
 
@@ -117,7 +129,7 @@ where
     fn on_event(
         &mut self,
         _event: Event,
-        _layout: &Layout,
+        _layout: Layout<'_>,
         _cursor_position: Point,
         _messages: &mut Vec<Message>,
         _renderer: &Renderer,
diff --git a/native/src/widget/button.rs b/native/src/widget/button.rs
index 882d4a6c..980c2aae 100644
--- a/native/src/widget/button.rs
+++ b/native/src/widget/button.rs
@@ -7,7 +7,7 @@
 //! [`Class`]: enum.Class.html
 
 use crate::input::{mouse, ButtonState};
-use crate::{layout, Element, Event, Hasher, Layout, Point, Widget};
+use crate::{layout, Element, Event, Hasher, Layout, Length, Point, Widget};
 use std::hash::Hash;
 
 pub use iced_core::button::State;
@@ -21,14 +21,18 @@ where
     Renderer: self::Renderer,
     Message: Clone + std::fmt::Debug,
 {
-    fn layout(&self, renderer: &Renderer, limits: &layout::Limits) -> Layout {
+    fn layout(
+        &self,
+        renderer: &Renderer,
+        limits: &layout::Limits,
+    ) -> layout::Node {
         renderer.layout(&self, limits)
     }
 
     fn on_event(
         &mut self,
         event: Event,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
         messages: &mut Vec<Message>,
         _renderer: &Renderer,
@@ -66,7 +70,7 @@ where
     fn draw(
         &self,
         renderer: &mut Renderer,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
     ) -> Renderer::Output {
         renderer.draw(&self, layout, cursor_position)
@@ -95,7 +99,7 @@ pub trait Renderer: crate::Renderer + Sized {
         &self,
         button: &Button<'_, Message, Self>,
         limits: &layout::Limits,
-    ) -> Layout;
+    ) -> layout::Node;
 
     /// Draws a [`Button`].
     ///
@@ -103,7 +107,7 @@ pub trait Renderer: crate::Renderer + Sized {
     fn draw<Message>(
         &mut self,
         button: &Button<'_, Message, Self>,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
     ) -> Self::Output;
 }
diff --git a/native/src/widget/checkbox.rs b/native/src/widget/checkbox.rs
index 12a6a728..a7040e02 100644
--- a/native/src/widget/checkbox.rs
+++ b/native/src/widget/checkbox.rs
@@ -10,14 +10,18 @@ impl<Message, Renderer> Widget<Message, Renderer> for Checkbox<Message>
 where
     Renderer: self::Renderer,
 {
-    fn layout(&self, renderer: &Renderer, limits: &layout::Limits) -> Layout {
+    fn layout(
+        &self,
+        renderer: &Renderer,
+        limits: &layout::Limits,
+    ) -> layout::Node {
         renderer.layout(&self, limits)
     }
 
     fn on_event(
         &mut self,
         event: Event,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
         messages: &mut Vec<Message>,
         _renderer: &Renderer,
@@ -40,7 +44,7 @@ where
     fn draw(
         &self,
         renderer: &mut Renderer,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
     ) -> Renderer::Output {
         renderer.draw(&self, layout, cursor_position)
@@ -67,7 +71,7 @@ pub trait Renderer: crate::Renderer {
         &self,
         checkbox: &Checkbox<Message>,
         limits: &layout::Limits,
-    ) -> Layout;
+    ) -> layout::Node;
 
     /// Draws a [`Checkbox`].
     ///
@@ -81,7 +85,7 @@ pub trait Renderer: crate::Renderer {
     fn draw<Message>(
         &mut self,
         checkbox: &Checkbox<Message>,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
     ) -> Self::Output;
 }
diff --git a/native/src/widget/column.rs b/native/src/widget/column.rs
index d0446ec9..ed8a2b89 100644
--- a/native/src/widget/column.rs
+++ b/native/src/widget/column.rs
@@ -1,6 +1,8 @@
 use std::hash::Hash;
 
-use crate::{layout, Element, Event, Hasher, Layout, Point, Rectangle, Widget};
+use crate::{
+    layout, Element, Event, Hasher, Layout, Length, Point, Size, Widget,
+};
 
 /// A container that distributes its contents vertically.
 pub type Column<'a, Message, Renderer> =
@@ -11,20 +13,35 @@ impl<'a, Message, Renderer> Widget<Message, Renderer>
 where
     Renderer: self::Renderer,
 {
-    fn layout(&self, renderer: &Renderer, limits: &layout::Limits) -> Layout {
-        // TODO
-        Layout::new(Rectangle {
-            x: 0.0,
-            y: 0.0,
-            width: 0.0,
-            height: 0.0,
-        })
+    fn width(&self) -> Length {
+        self.width
+    }
+
+    fn layout(
+        &self,
+        renderer: &Renderer,
+        limits: &layout::Limits,
+    ) -> layout::Node {
+        let limits = limits
+            .max_width(self.max_width)
+            .max_height(self.max_height)
+            .width(self.width)
+            .height(self.height);
+
+        layout::flex::resolve(
+            layout::flex::Axis::Vertical,
+            renderer,
+            &limits,
+            self.padding as f32,
+            self.spacing as f32,
+            &self.children,
+        )
     }
 
     fn on_event(
         &mut self,
         event: Event,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
         messages: &mut Vec<Message>,
         renderer: &Renderer,
@@ -45,7 +62,7 @@ where
     fn draw(
         &self,
         renderer: &mut Renderer,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
     ) -> Renderer::Output {
         renderer.draw(&self, layout, cursor_position)
@@ -72,7 +89,7 @@ pub trait Renderer: crate::Renderer + Sized {
     fn draw<Message>(
         &mut self,
         row: &Column<'_, Message, Self>,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
     ) -> Self::Output;
 }
diff --git a/native/src/widget/image.rs b/native/src/widget/image.rs
index b503f95c..abc45d6a 100644
--- a/native/src/widget/image.rs
+++ b/native/src/widget/image.rs
@@ -10,14 +10,18 @@ impl<Message, Renderer> Widget<Message, Renderer> for Image
 where
     Renderer: self::Renderer,
 {
-    fn layout(&self, renderer: &Renderer, limits: &layout::Limits) -> Layout {
+    fn layout(
+        &self,
+        renderer: &Renderer,
+        limits: &layout::Limits,
+    ) -> layout::Node {
         renderer.layout(&self, limits)
     }
 
     fn draw(
         &self,
         renderer: &mut Renderer,
-        layout: &Layout,
+        layout: Layout<'_>,
         _cursor_position: Point,
     ) -> Renderer::Output {
         renderer.draw(&self, layout)
@@ -44,12 +48,12 @@ pub trait Renderer: crate::Renderer {
     ///
     /// [`Node`]: ../../struct.Node.html
     /// [`Image`]: struct.Image.html
-    fn layout(&self, image: &Image, limits: &layout::Limits) -> Layout;
+    fn layout(&self, image: &Image, limits: &layout::Limits) -> layout::Node;
 
     /// Draws an [`Image`].
     ///
     /// [`Image`]: struct.Image.html
-    fn draw(&mut self, image: &Image, layout: &Layout) -> Self::Output;
+    fn draw(&mut self, image: &Image, layout: Layout<'_>) -> Self::Output;
 }
 
 impl<'a, Message, Renderer> From<Image> for Element<'a, Message, Renderer>
diff --git a/native/src/widget/radio.rs b/native/src/widget/radio.rs
index 86d507da..b68919e5 100644
--- a/native/src/widget/radio.rs
+++ b/native/src/widget/radio.rs
@@ -1,6 +1,6 @@
 //! Create choices using radio buttons.
 use crate::input::{mouse, ButtonState};
-use crate::{layout, Element, Event, Hasher, Layout, Point, Widget};
+use crate::{layout, Element, Event, Hasher, Layout, Length, Point, Widget};
 
 use std::hash::Hash;
 
@@ -11,14 +11,22 @@ where
     Renderer: self::Renderer,
     Message: Clone + std::fmt::Debug,
 {
-    fn layout(&self, renderer: &Renderer, limits: &layout::Limits) -> Layout {
+    fn width(&self) -> Length {
+        Length::Fill
+    }
+
+    fn layout(
+        &self,
+        renderer: &Renderer,
+        limits: &layout::Limits,
+    ) -> layout::Node {
         renderer.layout(&self, limits)
     }
 
     fn on_event(
         &mut self,
         event: Event,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
         messages: &mut Vec<Message>,
         _renderer: &Renderer,
@@ -39,7 +47,7 @@ where
     fn draw(
         &self,
         renderer: &mut Renderer,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
     ) -> Renderer::Output {
         renderer.draw(&self, layout, cursor_position)
@@ -66,7 +74,7 @@ pub trait Renderer: crate::Renderer {
         &self,
         radio: &Radio<Message>,
         limits: &layout::Limits,
-    ) -> Layout;
+    ) -> layout::Node;
 
     /// Draws a [`Radio`] button.
     ///
@@ -80,7 +88,7 @@ pub trait Renderer: crate::Renderer {
     fn draw<Message>(
         &mut self,
         radio: &Radio<Message>,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
     ) -> Self::Output;
 }
diff --git a/native/src/widget/row.rs b/native/src/widget/row.rs
index ca1cda23..7ea54a71 100644
--- a/native/src/widget/row.rs
+++ b/native/src/widget/row.rs
@@ -1,6 +1,6 @@
 use std::hash::Hash;
 
-use crate::{layout, Element, Event, Hasher, Layout, Point, Rectangle, Widget};
+use crate::{layout, Element, Event, Hasher, Layout, Length, Point, Widget};
 
 /// A container that distributes its contents horizontally.
 pub type Row<'a, Message, Renderer> =
@@ -11,20 +11,35 @@ impl<'a, Message, Renderer> Widget<Message, Renderer>
 where
     Renderer: self::Renderer,
 {
-    fn layout(&self, renderer: &Renderer, limits: &layout::Limits) -> Layout {
-        // TODO
-        Layout::new(Rectangle {
-            x: 0.0,
-            y: 0.0,
-            width: 0.0,
-            height: 0.0,
-        })
+    fn width(&self) -> Length {
+        self.width
+    }
+
+    fn layout(
+        &self,
+        renderer: &Renderer,
+        limits: &layout::Limits,
+    ) -> layout::Node {
+        let limits = limits
+            .max_width(self.max_width)
+            .max_height(self.max_height)
+            .width(self.width)
+            .height(self.height);
+
+        layout::flex::resolve(
+            layout::flex::Axis::Horizontal,
+            renderer,
+            &limits,
+            self.padding as f32,
+            self.spacing as f32,
+            &self.children,
+        )
     }
 
     fn on_event(
         &mut self,
         event: Event,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
         messages: &mut Vec<Message>,
         renderer: &Renderer,
@@ -45,7 +60,7 @@ where
     fn draw(
         &self,
         renderer: &mut Renderer,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
     ) -> Renderer::Output {
         renderer.draw(&self, layout, cursor_position)
@@ -73,7 +88,7 @@ pub trait Renderer: crate::Renderer + Sized {
     fn draw<Message>(
         &mut self,
         row: &Row<'_, Message, Self>,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
     ) -> Self::Output;
 }
diff --git a/native/src/widget/scrollable.rs b/native/src/widget/scrollable.rs
index a5eb2f01..775c59db 100644
--- a/native/src/widget/scrollable.rs
+++ b/native/src/widget/scrollable.rs
@@ -1,11 +1,13 @@
 use crate::{
     column,
     input::{mouse, ButtonState},
-    layout, Element, Event, Hasher, Layout, Point, Rectangle, Widget,
+    layout, Element, Event, Hasher, Layout, Length, Point, Rectangle, Size,
+    Widget,
 };
 
 pub use iced_core::scrollable::State;
 
+use std::f32;
 use std::hash::Hash;
 
 /// A scrollable [`Column`].
@@ -19,15 +21,31 @@ impl<'a, Message, Renderer> Widget<Message, Renderer>
 where
     Renderer: self::Renderer + column::Renderer,
 {
-    fn layout(&self, renderer: &Renderer, limits: &layout::Limits) -> Layout {
-        // TODO
-        self.content.layout(renderer, limits)
+    fn layout(
+        &self,
+        renderer: &Renderer,
+        limits: &layout::Limits,
+    ) -> layout::Node {
+        let limits = limits
+            .max_height(self.max_height)
+            .width(Length::Fill)
+            .height(self.height);
+
+        let child_limits = layout::Limits::new(
+            Size::new(limits.min().width, 0.0),
+            Size::new(limits.max().width, f32::INFINITY),
+        );
+
+        let content = self.content.layout(renderer, &child_limits);
+        let size = limits.resolve(content.size());
+
+        layout::Node::with_children(size, vec![content])
     }
 
     fn on_event(
         &mut self,
         event: Event,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
         messages: &mut Vec<Message>,
         renderer: &Renderer,
@@ -130,7 +148,7 @@ where
     fn draw(
         &self,
         renderer: &mut Renderer,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
     ) -> Renderer::Output {
         let bounds = layout.bounds();
@@ -168,7 +186,7 @@ pub trait Renderer: crate::Renderer + Sized {
         &mut self,
         scrollable: &Scrollable<'_, Message, Self>,
         bounds: Rectangle,
-        content_layout: &Layout,
+        content_layout: Layout<'_>,
         cursor_position: Point,
     ) -> Self::Output;
 }
diff --git a/native/src/widget/slider.rs b/native/src/widget/slider.rs
index be4ed564..3a998c40 100644
--- a/native/src/widget/slider.rs
+++ b/native/src/widget/slider.rs
@@ -7,7 +7,7 @@
 use std::hash::Hash;
 
 use crate::input::{mouse, ButtonState};
-use crate::{layout, Element, Event, Hasher, Layout, Point, Widget};
+use crate::{layout, Element, Event, Hasher, Layout, Length, Point, Widget};
 
 pub use iced_core::slider::*;
 
@@ -15,14 +15,22 @@ impl<'a, Message, Renderer> Widget<Message, Renderer> for Slider<'a, Message>
 where
     Renderer: self::Renderer,
 {
-    fn layout(&self, renderer: &Renderer, limits: &layout::Limits) -> Layout {
+    fn width(&self) -> Length {
+        self.width
+    }
+
+    fn layout(
+        &self,
+        renderer: &Renderer,
+        limits: &layout::Limits,
+    ) -> layout::Node {
         renderer.layout(&self, limits)
     }
 
     fn on_event(
         &mut self,
         event: Event,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
         messages: &mut Vec<Message>,
         _renderer: &Renderer,
@@ -70,7 +78,7 @@ where
     fn draw(
         &self,
         renderer: &mut Renderer,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
     ) -> Renderer::Output {
         renderer.draw(&self, layout, cursor_position)
@@ -97,7 +105,7 @@ pub trait Renderer: crate::Renderer {
         &self,
         slider: &Slider<'_, Message>,
         limits: &layout::Limits,
-    ) -> Layout;
+    ) -> layout::Node;
 
     /// Draws a [`Slider`].
     ///
@@ -114,7 +122,7 @@ pub trait Renderer: crate::Renderer {
     fn draw<Message>(
         &mut self,
         slider: &Slider<'_, Message>,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
     ) -> Self::Output;
 }
diff --git a/native/src/widget/text.rs b/native/src/widget/text.rs
index da8563a4..10d892a3 100644
--- a/native/src/widget/text.rs
+++ b/native/src/widget/text.rs
@@ -1,5 +1,5 @@
 //! Write some text for your users to read.
-use crate::{layout, Element, Hasher, Layout, Point, Widget};
+use crate::{layout, Element, Hasher, Layout, Length, Point, Widget};
 
 use std::hash::Hash;
 
@@ -9,14 +9,22 @@ impl<Message, Renderer> Widget<Message, Renderer> for Text
 where
     Renderer: self::Renderer,
 {
-    fn layout(&self, renderer: &Renderer, limits: &layout::Limits) -> Layout {
+    fn width(&self) -> Length {
+        self.width
+    }
+
+    fn layout(
+        &self,
+        renderer: &Renderer,
+        limits: &layout::Limits,
+    ) -> layout::Node {
         renderer.layout(&self, limits)
     }
 
     fn draw(
         &self,
         renderer: &mut Renderer,
-        layout: &Layout,
+        layout: Layout<'_>,
         _cursor_position: Point,
     ) -> Renderer::Output {
         renderer.draw(&self, layout)
@@ -49,7 +57,7 @@ pub trait Renderer: crate::Renderer {
     /// [`Style`]: ../../struct.Style.html
     /// [`Text`]: struct.Text.html
     /// [`Node::with_measure`]: ../../struct.Node.html#method.with_measure
-    fn layout(&self, text: &Text, limits: &layout::Limits) -> Layout;
+    fn layout(&self, text: &Text, limits: &layout::Limits) -> layout::Node;
 
     /// Draws a [`Text`] fragment.
     ///
@@ -64,7 +72,7 @@ pub trait Renderer: crate::Renderer {
     /// [`Text`]: struct.Text.html
     /// [`HorizontalAlignment`]: enum.HorizontalAlignment.html
     /// [`VerticalAlignment`]: enum.VerticalAlignment.html
-    fn draw(&mut self, text: &Text, layout: &Layout) -> Self::Output;
+    fn draw(&mut self, text: &Text, layout: Layout<'_>) -> Self::Output;
 }
 
 impl<'a, Message, Renderer> From<Text> for Element<'a, Message, Renderer>
diff --git a/native/src/widget/text_input.rs b/native/src/widget/text_input.rs
index ca72801d..7e81e257 100644
--- a/native/src/widget/text_input.rs
+++ b/native/src/widget/text_input.rs
@@ -1,6 +1,7 @@
 use crate::{
     input::{keyboard, mouse, ButtonState},
-    layout, Element, Event, Hasher, Layout, Point, Rectangle, Widget,
+    layout, Element, Event, Hasher, Layout, Length, Point, Rectangle, Size,
+    Widget,
 };
 
 pub use iced_core::{text_input::State, TextInput};
@@ -10,20 +11,30 @@ where
     Renderer: self::Renderer,
     Message: Clone + std::fmt::Debug,
 {
-    fn layout(&self, renderer: &Renderer, limits: &layout::Limits) -> Layout {
-        // TODO
-        Layout::new(Rectangle {
-            x: 0.0,
-            y: 0.0,
-            width: 0.0,
-            height: 0.0,
-        })
+    fn layout(
+        &self,
+        renderer: &Renderer,
+        limits: &layout::Limits,
+    ) -> layout::Node {
+        let padding = self.padding as f32;
+        let text_size = self.size.unwrap_or(renderer.default_size());
+
+        let limits = limits
+            .pad(padding)
+            .width(self.width)
+            .height(Length::Units(text_size));
+
+        let mut text = layout::Node::new(limits.resolve(Size::ZERO));
+        text.bounds.x = padding;
+        text.bounds.y = padding;
+
+        layout::Node::with_children(text.size().pad(padding), vec![text])
     }
 
     fn on_event(
         &mut self,
         event: Event,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
         messages: &mut Vec<Message>,
         _renderer: &Renderer,
@@ -95,7 +106,7 @@ where
     fn draw(
         &self,
         renderer: &mut Renderer,
-        layout: &Layout,
+        layout: Layout<'_>,
         cursor_position: Point,
     ) -> Renderer::Output {
         let bounds = layout.bounds();