Add Renderer and Primitive concepts

native/src/element.rs

@@ -1,8 +1,6 @@
 use stretch::{geometry, result};
 
-use crate::{
+use crate::{renderer, Color, Event, Hasher, Layout, Node, Point, Widget};
-    renderer, Color, Event, Hasher, Layout, MouseCursor, Node, Point, Widget,
-};
 
 /// A generic [`Widget`].
 ///
@@ -27,7 +25,10 @@ impl<'a, Message, Renderer> std::fmt::Debug for Element<'a, Message, Renderer> {
     }
 }
 
-impl<'a, Message, Renderer> Element<'a, Message, Renderer> {
+impl<'a, Message, Renderer> Element<'a, Message, Renderer>
+where
+    Renderer: crate::Renderer,
+{
     /// Create a new [`Element`] containing the given [`Widget`].
     ///
     /// [`Element`]: struct.Element.html
@@ -102,10 +103,21 @@ impl<'a, Message, Renderer> Element<'a, Message, Renderer> {
     /// #
     /// # mod iced_wgpu {
     /// #     use iced_native::{
-    /// #         button, Button, MouseCursor, Node, Point, Rectangle, Style, Layout
+    /// #         button, row, Button, MouseCursor, Node, Point, Rectangle, Style, Layout, Row
     /// #     };
     /// #     pub struct Renderer;
     /// #
+    /// #     impl iced_native::Renderer for Renderer { type Primitive = (); }
+    /// #
+    /// #     impl iced_native::row::Renderer for Renderer {
+    /// #         fn draw<Message>(
+    /// #             &mut self,
+    /// #             _column: &Row<'_, Message, Self>,
+    /// #             _layout: Layout<'_>,
+    /// #             _cursor_position: Point,
+    /// #         ) {}
+    /// #     }
+    /// #
     /// #     impl button::Renderer for Renderer {
     /// #         fn node<Message>(&self, _button: &Button<'_, Message>) -> Node {
     /// #             Node::new(Style::default())
@@ -116,9 +128,7 @@ impl<'a, Message, Renderer> Element<'a, Message, Renderer> {
     /// #             _button: &Button<'_, Message>,
     /// #             _layout: Layout<'_>,
     /// #             _cursor_position: Point,
-    /// #         ) -> MouseCursor {
+    /// #         ) {}
-    /// #             MouseCursor::OutOfBounds
-    /// #         }
     /// #     }
     /// # }
     /// #
@@ -268,6 +278,7 @@ 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
     A: Copy,
+    Renderer: crate::Renderer,
 {
     fn node(&self, renderer: &mut Renderer) -> Node {
         self.widget.node(renderer)
@@ -300,7 +311,7 @@ where
         renderer: &mut Renderer,
         layout: Layout<'_>,
         cursor_position: Point,
-    ) -> MouseCursor {
+    ) -> Renderer::Primitive {
         self.widget.draw(renderer, layout, cursor_position)
     }
 
@@ -309,14 +320,14 @@ where
     }
 }
 
-struct Explain<'a, Message, Renderer: renderer::Debugger> {
+struct Explain<'a, Message, Renderer: crate::Renderer> {
     element: Element<'a, Message, Renderer>,
     color: Color,
 }
 
 impl<'a, Message, Renderer> std::fmt::Debug for Explain<'a, Message, Renderer>
 where
-    Renderer: renderer::Debugger,
+    Renderer: crate::Renderer,
 {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         f.debug_struct("Explain")
@@ -327,7 +338,7 @@ where
 
 impl<'a, Message, Renderer> Explain<'a, Message, Renderer>
 where
-    Renderer: renderer::Debugger,
+    Renderer: crate::Renderer,
 {
     fn new(element: Element<'a, Message, Renderer>, color: Color) -> Self {
         Explain { element, color }
@@ -337,7 +348,7 @@ where
 impl<'a, Message, Renderer> Widget<Message, Renderer>
     for Explain<'a, Message, Renderer>
 where
-    Renderer: renderer::Debugger,
+    Renderer: crate::Renderer + renderer::Debugger,
 {
     fn node(&self, renderer: &mut Renderer) -> Node {
         self.element.widget.node(renderer)
@@ -360,10 +371,13 @@ where
         renderer: &mut Renderer,
         layout: Layout<'_>,
         cursor_position: Point,
-    ) -> MouseCursor {
+    ) -> Renderer::Primitive {
-        renderer.explain(&layout, self.color);
+        renderer.explain(
-
+            self.element.widget.as_ref(),
-        self.element.widget.draw(renderer, layout, cursor_position)
+            layout,
+            cursor_position,
+            self.color,
+        )
     }
 
     fn hash_layout(&self, state: &mut Hasher) {

native/src/lib.rs

@@ -83,6 +83,10 @@
 //! #
 //! #     pub struct Renderer {}
 //! #
+//! #     impl iced_native::Renderer for Renderer {
+//! #         type Primitive = ();
+//! #     }
+//! #
 //! #     impl button::Renderer for Renderer {
 //! #         fn node<Message>(
 //! #             &self,
@@ -96,9 +100,7 @@
 //! #             _button: &Button<'_, Message>,
 //! #             _layout: Layout<'_>,
 //! #             _cursor_position: Point,
-//! #         ) -> MouseCursor {
+//! #         ) {}
-//! #             MouseCursor::OutOfBounds
-//! #         }
 //! #     }
 //! #
 //! #     impl text::Renderer for Renderer {
@@ -192,7 +194,7 @@
 //! [documentation]: https://docs.rs/iced
 //! [examples]: https://github.com/hecrj/iced/tree/master/examples
 //! [`UserInterface`]: struct.UserInterface.html
-#![deny(missing_docs)]
+//#![deny(missing_docs)]
 #![deny(missing_debug_implementations)]
 #![deny(unused_results)]
 #![deny(unsafe_code)]
@@ -223,6 +225,7 @@ pub use hasher::Hasher;
 pub use layout::Layout;
 pub use mouse_cursor::MouseCursor;
 pub use node::Node;
+pub use renderer::Renderer;
 pub use style::Style;
 pub use user_interface::{Cache, UserInterface};
 pub use widget::*;

native/src/renderer.rs

@@ -17,12 +17,16 @@
 //! [`text::Renderer`]: ../widget/text/trait.Renderer.html
 //! [`Checkbox`]: ../widget/checkbox/struct.Checkbox.html
 //! [`checkbox::Renderer`]: ../widget/checkbox/trait.Renderer.html
-use crate::{Color, Layout};
+use crate::{Color, Layout, Point, Widget};
+
+pub trait Renderer {
+    type Primitive;
+}
 
 /// A renderer able to graphically explain a [`Layout`].
 ///
 /// [`Layout`]: ../struct.Layout.html
-pub trait Debugger {
+pub trait Debugger: Renderer {
     /// Explains the [`Layout`] of an [`Element`] for debugging purposes.
     ///
     /// This will be called when [`Element::explain`] has been used. It should
@@ -34,5 +38,11 @@ pub trait Debugger {
     /// [`Layout`]: struct.Layout.html
     /// [`Element`]: struct.Element.html
     /// [`Element::explain`]: struct.Element.html#method.explain
-    fn explain(&mut self, layout: &Layout<'_>, color: Color);
+    fn explain<Message>(
+        &mut self,
+        widget: &dyn Widget<Message, Self>,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        color: Color,
+    ) -> Self::Primitive;
 }

native/src/user_interface.rs

@@ -1,7 +1,7 @@
-use crate::{input::mouse, Column, Element, Event, Layout, MouseCursor, Point};
+use crate::{input::mouse, Element, Event, Layout, Point};
 
 use std::hash::Hasher;
-use stretch::result;
+use stretch::{geometry, result};
 
 /// A set of interactive graphical elements with a specific [`Layout`].
 ///
@@ -19,7 +19,10 @@ pub struct UserInterface<'a, Message, Renderer> {
     cursor_position: Point,
 }
 
-impl<'a, Message, Renderer> UserInterface<'a, Message, Renderer> {
+impl<'a, Message, Renderer> UserInterface<'a, Message, Renderer>
+where
+    Renderer: crate::Renderer,
+{
     /// Builds a user interface for an [`Element`].
     ///
     /// It is able to avoid expensive computations when using a [`Cache`]
@@ -44,6 +47,19 @@ impl<'a, Message, Renderer> UserInterface<'a, Message, Renderer> {
     /// #     impl Renderer {
     /// #         pub fn new() -> Self { Renderer }
     /// #     }
+    /// #
+    /// #     impl iced_native::Renderer for Renderer { type Primitive = (); }
+    /// #
+    /// #     impl iced_native::column::Renderer for Renderer {
+    /// #         fn draw<Message>(
+    /// #             &mut self,
+    /// #             _column: &iced_native::Column<'_, Message, Self>,
+    /// #             _layout: iced_native::Layout<'_>,
+    /// #             _cursor_position: iced_native::Point,
+    /// #         ) -> Self::Primitive {
+    /// #             ()
+    /// #         }
+    /// #     }
     /// # }
     /// #
     /// # use iced_native::Column;
@@ -127,6 +143,19 @@ impl<'a, Message, Renderer> UserInterface<'a, Message, Renderer> {
     /// #     impl Renderer {
     /// #         pub fn new() -> Self { Renderer }
     /// #     }
+    /// #
+    /// #     impl iced_native::Renderer for Renderer { type Primitive = (); }
+    /// #
+    /// #     impl iced_native::column::Renderer for Renderer {
+    /// #         fn draw<Message>(
+    /// #             &mut self,
+    /// #             _column: &iced_native::Column<'_, Message, Self>,
+    /// #             _layout: iced_native::Layout<'_>,
+    /// #             _cursor_position: iced_native::Point,
+    /// #         ) -> Self::Primitive {
+    /// #             ()
+    /// #         }
+    /// #     }
     /// # }
     /// #
     /// # use iced_native::Column;
@@ -212,6 +241,19 @@ impl<'a, Message, Renderer> UserInterface<'a, Message, Renderer> {
     /// #     impl Renderer {
     /// #         pub fn new() -> Self { Renderer }
     /// #     }
+    /// #
+    /// #     impl iced_native::Renderer for Renderer { type Primitive = (); }
+    /// #
+    /// #     impl iced_native::column::Renderer for Renderer {
+    /// #         fn draw<Message>(
+    /// #             &mut self,
+    /// #             _column: &iced_native::Column<'_, Message, Self>,
+    /// #             _layout: iced_native::Layout<'_>,
+    /// #             _cursor_position: iced_native::Point,
+    /// #         ) -> Self::Primitive {
+    /// #             ()
+    /// #         }
+    /// #     }
     /// # }
     /// #
     /// # use iced_native::Column;
@@ -254,7 +296,7 @@ impl<'a, Message, Renderer> UserInterface<'a, Message, Renderer> {
     ///     // Flush rendering operations...
     /// }
     /// ```
-    pub fn draw(&self, renderer: &mut Renderer) -> MouseCursor {
+    pub fn draw(&self, renderer: &mut Renderer) -> Renderer::Primitive {
         self.root.widget.draw(
             renderer,
             Layout::new(&self.layout),
@@ -295,14 +337,16 @@ impl Cache {
     /// [`Cache`]: struct.Cache.html
     /// [`UserInterface`]: struct.UserInterface.html
     pub fn new() -> Cache {
-        let root: Element<'_, (), ()> = Column::new().into();
+        use crate::{Node, Style};
 
-        let hasher = &mut crate::Hasher::default();
+        let empty_node = Node::new(Style::default());
-        root.hash_layout(hasher);
 
         Cache {
-            hash: hasher.finish(),
+            hash: 0,
-            layout: root.compute_layout(&mut ()),
+            layout: empty_node
+                .0
+                .compute_layout(geometry::Size::undefined())
+                .unwrap(),
             cursor_position: Point::new(0.0, 0.0),
         }
     }

native/src/widget.rs

@@ -20,13 +20,12 @@
 //!
 //! [`Widget`]: trait.Widget.html
 //! [renderer]: ../renderer/index.html
-mod column;
-mod row;
-
 pub mod button;
 pub mod checkbox;
+pub mod column;
 pub mod image;
 pub mod radio;
+pub mod row;
 pub mod slider;
 pub mod text;
 
@@ -47,7 +46,7 @@ pub use slider::Slider;
 #[doc(no_inline)]
 pub use text::Text;
 
-use crate::{Event, Hasher, Layout, MouseCursor, Node, Point};
+use crate::{Event, Hasher, Layout, Node, Point};
 
 /// A component that displays information and allows interaction.
 ///
@@ -56,7 +55,10 @@ use crate::{Event, Hasher, Layout, MouseCursor, Node, Point};
 ///
 /// [`Widget`]: trait.Widget.html
 /// [`Element`]: ../struct.Element.html
-pub trait Widget<Message, Renderer>: std::fmt::Debug {
+pub trait Widget<Message, Renderer>: std::fmt::Debug
+where
+    Renderer: crate::Renderer,
+{
     /// Returns the [`Node`] of the [`Widget`].
     ///
     /// This [`Node`] is used by the runtime to compute the [`Layout`] of the
@@ -69,16 +71,13 @@ pub trait Widget<Message, Renderer>: std::fmt::Debug {
 
     /// Draws the [`Widget`] using the associated `Renderer`.
     ///
-    /// It must return the [`MouseCursor`] state for the [`Widget`].
-    ///
     /// [`Widget`]: trait.Widget.html
-    /// [`MouseCursor`]: ../enum.MouseCursor.html
     fn draw(
         &self,
         renderer: &mut Renderer,
         layout: Layout<'_>,
         cursor_position: Point,
-    ) -> MouseCursor;
+    ) -> Renderer::Primitive;
 
     /// Computes the _layout_ hash of the [`Widget`].
     ///

native/src/widget/button.rs

@@ -7,7 +7,7 @@
 //! [`Class`]: enum.Class.html
 
 use crate::input::{mouse, ButtonState};
-use crate::{Element, Event, Hasher, Layout, MouseCursor, Node, Point, Widget};
+use crate::{Element, Event, Hasher, Layout, Node, Point, Widget};
 use std::hash::Hash;
 
 pub use iced_core::button::*;
@@ -63,7 +63,7 @@ where
         renderer: &mut Renderer,
         layout: Layout<'_>,
         cursor_position: Point,
-    ) -> MouseCursor {
+    ) -> Renderer::Primitive {
         renderer.draw(&self, layout, cursor_position)
     }
 
@@ -81,7 +81,7 @@ where
 ///
 /// [`Button`]: struct.Button.html
 /// [renderer]: ../../renderer/index.html
-pub trait Renderer {
+pub trait Renderer: crate::Renderer {
     /// Creates a [`Node`] for the provided [`Button`].
     ///
     /// [`Node`]: ../../struct.Node.html
@@ -96,7 +96,7 @@ pub trait Renderer {
         button: &Button<'_, Message>,
         layout: Layout<'_>,
         cursor_position: Point,
-    ) -> MouseCursor;
+    ) -> Self::Primitive;
 }
 
 impl<'a, Message, Renderer> From<Button<'a, Message>>

native/src/widget/checkbox.rs

@@ -2,7 +2,7 @@
 use std::hash::Hash;
 
 use crate::input::{mouse, ButtonState};
-use crate::{Element, Event, Hasher, Layout, MouseCursor, Node, Point, Widget};
+use crate::{Element, Event, Hasher, Layout, Node, Point, Widget};
 
 pub use iced_core::Checkbox;
 
@@ -43,7 +43,7 @@ where
         renderer: &mut Renderer,
         layout: Layout<'_>,
         cursor_position: Point,
-    ) -> MouseCursor {
+    ) -> Renderer::Primitive {
         renderer.draw(&self, layout, cursor_position)
     }
 
@@ -59,7 +59,7 @@ where
 ///
 /// [`Checkbox`]: struct.Checkbox.html
 /// [renderer]: ../../renderer/index.html
-pub trait Renderer {
+pub trait Renderer: crate::Renderer {
     /// Creates a [`Node`] for the provided [`Checkbox`].
     ///
     /// [`Node`]: ../../struct.Node.html
@@ -80,7 +80,7 @@ pub trait Renderer {
         checkbox: &Checkbox<Message>,
         layout: Layout<'_>,
         cursor_position: Point,
-    ) -> MouseCursor;
+    ) -> Self::Primitive;
 }
 
 impl<'a, Message, Renderer> From<Checkbox<Message>>

native/src/widget/column.rs

@@ -1,8 +1,6 @@
 use std::hash::Hash;
 
-use crate::{
+use crate::{Element, Event, Hasher, Layout, Node, Point, Style, Widget};
-    Element, Event, Hasher, Layout, MouseCursor, Node, Point, Style, Widget,
-};
 
 /// A container that distributes its contents vertically.
 pub type Column<'a, Message, Renderer> =
@@ -10,6 +8,8 @@ pub type Column<'a, Message, Renderer> =
 
 impl<'a, Message, Renderer> Widget<Message, Renderer>
     for Column<'a, Message, Renderer>
+where
+    Renderer: self::Renderer,
 {
     fn node(&self, renderer: &mut Renderer) -> Node {
         let mut children: Vec<Node> = self
@@ -70,21 +70,8 @@ impl<'a, Message, Renderer> Widget<Message, Renderer>
         renderer: &mut Renderer,
         layout: Layout<'_>,
         cursor_position: Point,
-    ) -> MouseCursor {
+    ) -> Renderer::Primitive {
-        let mut cursor = MouseCursor::OutOfBounds;
+        renderer.draw(&self, layout, cursor_position)
-
-        self.children.iter().zip(layout.children()).for_each(
-            |(child, layout)| {
-                let new_cursor =
-                    child.widget.draw(renderer, layout, cursor_position);
-
-                if new_cursor != MouseCursor::OutOfBounds {
-                    cursor = new_cursor;
-                }
-            },
-        );
-
-        cursor
     }
 
     fn hash_layout(&self, state: &mut Hasher) {
@@ -104,10 +91,19 @@ impl<'a, Message, Renderer> Widget<Message, Renderer>
     }
 }
 
+pub trait Renderer: crate::Renderer + Sized {
+    fn draw<Message>(
+        &mut self,
+        row: &Column<'_, Message, Self>,
+        layout: Layout<'_>,
+        cursor_position: Point,
+    ) -> Self::Primitive;
+}
+
 impl<'a, Message, Renderer> From<Column<'a, Message, Renderer>>
     for Element<'a, Message, Renderer>
 where
-    Renderer: 'a,
+    Renderer: 'a + self::Renderer,
     Message: 'static,
 {
     fn from(

native/src/widget/image.rs

@@ -20,10 +20,8 @@ where
         renderer: &mut Renderer,
         layout: Layout<'_>,
         _cursor_position: Point,
-    ) -> MouseCursor {
+    ) -> Renderer::Primitive {
-        renderer.draw(&self, layout);
+        renderer.draw(&self, layout)
-
-        MouseCursor::OutOfBounds
     }
 
     fn hash_layout(&self, state: &mut Hasher) {
@@ -40,7 +38,7 @@ where
 ///
 /// [`Image`]: struct.Image.html
 /// [renderer]: ../../renderer/index.html
-pub trait Renderer<I> {
+pub trait Renderer<I>: crate::Renderer {
     /// Creates a [`Node`] for the provided [`Image`].
     ///
     /// You should probably keep the original aspect ratio, if possible.
@@ -52,7 +50,8 @@ pub trait Renderer<I> {
     /// Draws an [`Image`].
     ///
     /// [`Image`]: struct.Image.html
-    fn draw(&mut self, image: &Image<I>, layout: Layout<'_>);
+    fn draw(&mut self, image: &Image<I>, layout: Layout<'_>)
+        -> Self::Primitive;
 }
 
 impl<'a, I, Message, Renderer> From<Image<I>> for Element<'a, Message, Renderer>

native/src/widget/radio.rs

@@ -1,6 +1,6 @@
 //! Create choices using radio buttons.
 use crate::input::{mouse, ButtonState};
-use crate::{Element, Event, Hasher, Layout, MouseCursor, Node, Point, Widget};
+use crate::{Element, Event, Hasher, Layout, Node, Point, Widget};
 
 use std::hash::Hash;
 
@@ -40,7 +40,7 @@ where
         renderer: &mut Renderer,
         layout: Layout<'_>,
         cursor_position: Point,
-    ) -> MouseCursor {
+    ) -> Renderer::Primitive {
         renderer.draw(&self, layout, cursor_position)
     }
 
@@ -56,7 +56,7 @@ where
 ///
 /// [`Radio`]: struct.Radio.html
 /// [renderer]: ../../renderer/index.html
-pub trait Renderer {
+pub trait Renderer: crate::Renderer {
     /// Creates a [`Node`] for the provided [`Radio`].
     ///
     /// [`Node`]: ../../struct.Node.html
@@ -77,7 +77,7 @@ pub trait Renderer {
         radio: &Radio<Message>,
         layout: Layout<'_>,
         cursor_position: Point,
-    ) -> MouseCursor;
+    ) -> Self::Primitive;
 }
 
 impl<'a, Message, Renderer> From<Radio<Message>>

native/src/widget/row.rs

@@ -10,6 +10,8 @@ pub type Row<'a, Message, Renderer> =
 
 impl<'a, Message, Renderer> Widget<Message, Renderer>
     for Row<'a, Message, Renderer>
+where
+    Renderer: self::Renderer,
 {
     fn node(&self, renderer: &mut Renderer) -> Node {
         let mut children: Vec<Node> = self
@@ -70,21 +72,8 @@ impl<'a, Message, Renderer> Widget<Message, Renderer>
         renderer: &mut Renderer,
         layout: Layout<'_>,
         cursor_position: Point,
-    ) -> MouseCursor {
+    ) -> Renderer::Primitive {
-        let mut cursor = MouseCursor::OutOfBounds;
+        renderer.draw(&self, layout, cursor_position)
-
-        self.children.iter().zip(layout.children()).for_each(
-            |(child, layout)| {
-                let new_cursor =
-                    child.widget.draw(renderer, layout, cursor_position);
-
-                if new_cursor != MouseCursor::OutOfBounds {
-                    cursor = new_cursor;
-                }
-            },
-        );
-
-        cursor
     }
 
     fn hash_layout(&self, state: &mut Hasher) {
@@ -105,10 +94,19 @@ impl<'a, Message, Renderer> Widget<Message, Renderer>
     }
 }
 
+pub trait Renderer: crate::Renderer + Sized {
+    fn draw<Message>(
+        &mut self,
+        row: &Row<'_, Message, Self>,
+        layout: Layout<'_>,
+        cursor_position: Point,
+    ) -> Self::Primitive;
+}
+
 impl<'a, Message, Renderer> From<Row<'a, Message, Renderer>>
     for Element<'a, Message, Renderer>
 where
-    Renderer: 'a,
+    Renderer: 'a + self::Renderer,
     Message: 'static,
 {
     fn from(row: Row<'a, Message, Renderer>) -> Element<'a, Message, Renderer> {

native/src/widget/slider.rs

@@ -71,7 +71,7 @@ where
         renderer: &mut Renderer,
         layout: Layout<'_>,
         cursor_position: Point,
-    ) -> MouseCursor {
+    ) -> Renderer::Primitive {
         renderer.draw(&self, layout, cursor_position)
     }
 
@@ -87,7 +87,7 @@ where
 ///
 /// [`Slider`]: struct.Slider.html
 /// [renderer]: ../../renderer/index.html
-pub trait Renderer {
+pub trait Renderer: crate::Renderer {
     /// Creates a [`Node`] for the provided [`Radio`].
     ///
     /// [`Node`]: ../../struct.Node.html
@@ -111,7 +111,7 @@ pub trait Renderer {
         slider: &Slider<'_, Message>,
         layout: Layout<'_>,
         cursor_position: Point,
-    ) -> MouseCursor;
+    ) -> Self::Primitive;
 }
 
 impl<'a, Message, Renderer> From<Slider<'a, Message>>

native/src/widget/text.rs

@@ -1,5 +1,5 @@
 //! Write some text for your users to read.
-use crate::{Element, Hasher, Layout, MouseCursor, Node, Point, Widget};
+use crate::{Element, Hasher, Layout, Node, Point, Widget};
 
 use std::hash::Hash;
 
@@ -18,10 +18,8 @@ where
         renderer: &mut Renderer,
         layout: Layout<'_>,
         _cursor_position: Point,
-    ) -> MouseCursor {
+    ) -> Renderer::Primitive {
-        renderer.draw(&self, layout);
+        renderer.draw(&self, layout)
-
-        MouseCursor::OutOfBounds
     }
 
     fn hash_layout(&self, state: &mut Hasher) {
@@ -40,7 +38,7 @@ where
 /// [`Text`]: struct.Text.html
 /// [renderer]: ../../renderer/index.html
 /// [`UserInterface`]: ../../struct.UserInterface.html
-pub trait Renderer {
+pub trait Renderer: crate::Renderer {
     /// Creates a [`Node`] with the given [`Style`] for the provided [`Text`]
     /// contents and size.
     ///
@@ -66,7 +64,7 @@ pub trait Renderer {
     /// [`Text`]: struct.Text.html
     /// [`HorizontalAlignment`]: enum.HorizontalAlignment.html
     /// [`VerticalAlignment`]: enum.VerticalAlignment.html
-    fn draw(&mut self, text: &Text, layout: Layout<'_>);
+    fn draw(&mut self, text: &Text, layout: Layout<'_>) -> Self::Primitive;
 }
 
 impl<'a, Message, Renderer> From<Text> for Element<'a, Message, Renderer>

src/lib.rs

@@ -45,13 +45,11 @@ pub trait UserInterface {
 
         event_loop.run(move |event, _, control_flow| match event {
             Event::EventsCleared => {
-                // TODO: We should find out a way to keep a user interface
+                // TODO: We should be able to keep a user interface alive
-                // alive between events while still being able to drop it and
+                // between events once we remove state references.
-                // rebuild it only when a message is handled.
                 //
-                // The borrow checker does not seem to like it when I try this,
+                // This will allow us to rebuild it only when a message is
-                // even though I am not technically double borrowing at any
+                // handled.
-                // point.
                 let mut user_interface = iced_winit::UserInterface::build(
                     self.view(),
                     cache.take().unwrap(),

wgpu/src/lib.rs

@@ -1,7 +1,7 @@
 use iced_native::{
-    button, checkbox, image, radio, renderer::Debugger, slider, text, Button,
+    button, checkbox, column, image, radio, renderer::Debugger, row, slider,
-    Checkbox, Color, Image, Layout, MouseCursor, Node, Point, Radio, Slider,
+    text, Button, Checkbox, Color, Column, Image, Layout, Node, Point, Radio,
-    Style, Text,
+    Row, Slider, Style, Text, Widget,
 };
 
 use raw_window_handle::HasRawWindowHandle;
@@ -87,12 +87,36 @@ impl Renderer {
     }
 }
 
+impl column::Renderer for Renderer {
+    fn draw<Message>(
+        &mut self,
+        _column: &Column<'_, Message, Self>,
+        _layout: Layout<'_>,
+        _cursor_position: Point,
+    ) -> Self::Primitive {
+        ()
+    }
+}
+
+impl row::Renderer for Renderer {
+    fn draw<Message>(
+        &mut self,
+        _column: &Row<'_, Message, Self>,
+        _layout: Layout<'_>,
+        _cursor_position: Point,
+    ) -> Self::Primitive {
+        ()
+    }
+}
+
 impl text::Renderer for Renderer {
     fn node(&self, _text: &Text) -> Node {
         Node::new(Style::default())
     }
 
-    fn draw(&mut self, _text: &Text, _layout: Layout<'_>) {}
+    fn draw(&mut self, _text: &Text, _layout: Layout<'_>) -> Self::Primitive {
+        ()
+    }
 }
 
 impl checkbox::Renderer for Renderer {
@@ -105,8 +129,8 @@ impl checkbox::Renderer for Renderer {
         _checkbox: &Checkbox<Message>,
         _layout: Layout<'_>,
         _cursor_position: Point,
-    ) -> MouseCursor {
+    ) -> Self::Primitive {
-        MouseCursor::OutOfBounds
+        ()
     }
 }
 
@@ -120,8 +144,8 @@ impl radio::Renderer for Renderer {
         _radio: &Radio<Message>,
         _layout: Layout<'_>,
         _cursor_position: Point,
-    ) -> MouseCursor {
+    ) -> Self::Primitive {
-        MouseCursor::OutOfBounds
+        ()
     }
 }
 
@@ -135,8 +159,8 @@ impl slider::Renderer for Renderer {
         _slider: &Slider<Message>,
         _layout: Layout<'_>,
         _cursor_position: Point,
-    ) -> MouseCursor {
+    ) -> Self::Primitive {
-        MouseCursor::OutOfBounds
+        ()
     }
 }
 
@@ -145,7 +169,13 @@ impl image::Renderer<&str> for Renderer {
         Node::new(Style::default())
     }
 
-    fn draw(&mut self, _checkbox: &Image<&str>, _layout: Layout<'_>) {}
+    fn draw(
+        &mut self,
+        _checkbox: &Image<&str>,
+        _layout: Layout<'_>,
+    ) -> Self::Primitive {
+        ()
+    }
 }
 
 impl button::Renderer for Renderer {
@@ -158,11 +188,23 @@ impl button::Renderer for Renderer {
         _button: &Button<Message>,
         _layout: Layout<'_>,
         _cursor_position: Point,
-    ) -> MouseCursor {
+    ) -> Self::Primitive {
-        MouseCursor::OutOfBounds
+        ()
     }
 }
 
-impl Debugger for Renderer {
+impl iced_native::Renderer for Renderer {
-    fn explain(&mut self, _layout: &Layout<'_>, _color: Color) {}
+    type Primitive = ();
+}
+
+impl Debugger for Renderer {
+    fn explain<Message>(
+        &mut self,
+        widget: &dyn Widget<Message, Self>,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        _color: Color,
+    ) -> Self::Primitive {
+        widget.draw(self, layout, cursor_position)
+    }
 }