Remove `Drawable` and rename `State` to `Program`

11 files changed, 197 insertions, 299 deletions

diff --git a/core/src/rectangle.rs b/core/src/rectangle.rs
index 87046df4..e8d0538a 100644
--- a/core/src/rectangle.rs
+++ b/core/src/rectangle.rs
@@ -135,8 +135,8 @@ impl From<Rectangle<f32>> for Rectangle<u32> {
         Rectangle {
             x: rectangle.x as u32,
             y: rectangle.y as u32,
-            width: rectangle.width.ceil() as u32,
-            height: rectangle.height.ceil() as u32,
+            width: (rectangle.width + 0.5).round() as u32,
+            height: (rectangle.height + 0.5).round() as u32,
         }
     }
 }
diff --git a/examples/bezier_tool/src/main.rs b/examples/bezier_tool/src/main.rs
index 5473bc07..2112f662 100644
--- a/examples/bezier_tool/src/main.rs
+++ b/examples/bezier_tool/src/main.rs
@@ -69,10 +69,8 @@ impl Sandbox for Example {
 
 mod bezier {
     use iced::{
-        canvas::{
-            self, Canvas, Drawable, Event, Frame, Geometry, Path, Stroke,
-        },
-        mouse, ButtonState, Element, Length, Point, Size,
+        canvas::{self, Canvas, Event, Frame, Geometry, Path, Stroke},
+        mouse, ButtonState, Element, Length, Point, Rectangle, Size,
     };
 
     #[derive(Default)]
@@ -106,8 +104,10 @@ mod bezier {
         curves: &'a [Curve],
     }
 
-    impl<'a> canvas::State<Curve> for Bezier<'a> {
-        fn update(&mut self, event: Event, _bounds: Size) -> Option<Curve> {
+    impl<'a> canvas::Program<Curve> for Bezier<'a> {
+        fn update(&mut self, event: Event, bounds: Size) -> Option<Curve> {
+            let bounds = Rectangle::new(Point::ORIGIN, bounds);
+
             match event {
                 Event::Mouse(mouse_event) => match mouse_event {
                     mouse::Event::CursorMoved { x, y } => {
@@ -118,46 +118,55 @@ mod bezier {
                     mouse::Event::Input {
                         button: mouse::Button::Left,
                         state: ButtonState::Pressed,
-                    } => match self.state.pending {
-                        None => {
-                            self.state.pending = Some(Pending::One {
-                                from: self.state.cursor_position,
-                            });
-                            None
-                        }
-                        Some(Pending::One { from }) => {
-                            self.state.pending = Some(Pending::Two {
-                                from,
-                                to: self.state.cursor_position,
-                            });
-
-                            None
-                        }
-                        Some(Pending::Two { from, to }) => {
-                            self.state.pending = None;
-
-                            Some(Curve {
-                                from,
-                                to,
-                                control: self.state.cursor_position,
-                            })
+                    } if bounds.contains(self.state.cursor_position) => {
+                        match self.state.pending {
+                            None => {
+                                self.state.pending = Some(Pending::One {
+                                    from: self.state.cursor_position,
+                                });
+                                None
+                            }
+                            Some(Pending::One { from }) => {
+                                self.state.pending = Some(Pending::Two {
+                                    from,
+                                    to: self.state.cursor_position,
+                                });
+
+                                None
+                            }
+                            Some(Pending::Two { from, to }) => {
+                                self.state.pending = None;
+
+                                Some(Curve {
+                                    from,
+                                    to,
+                                    control: self.state.cursor_position,
+                                })
+                            }
                         }
-                    },
+                    }
                     _ => None,
                 },
             }
         }
 
         fn draw(&self, bounds: Size) -> Vec<Geometry> {
-            let curves = self.state.cache.draw(bounds, &self.curves);
+            let content = self.state.cache.draw(bounds, |frame: &mut Frame| {
+                Curve::draw_all(self.curves, frame);
+
+                frame.stroke(
+                    &Path::rectangle(Point::ORIGIN, frame.size()),
+                    Stroke::default(),
+                );
+            });
 
             if let Some(pending) = &self.state.pending {
                 let pending_curve =
                     pending.draw(bounds, self.state.cursor_position);
 
-                vec![curves, pending_curve]
+                vec![content, pending_curve]
             } else {
-                vec![curves]
+                vec![content]
             }
         }
     }
@@ -169,14 +178,16 @@ mod bezier {
         control: Point,
     }
 
-    impl Drawable for Curve {
-        fn draw(&self, frame: &mut Frame) {
-            let curve = Path::new(|p| {
-                p.move_to(self.from);
-                p.quadratic_curve_to(self.control, self.to);
+    impl Curve {
+        fn draw_all(curves: &[Curve], frame: &mut Frame) {
+            let curves = Path::new(|p| {
+                for curve in curves {
+                    p.move_to(curve.from);
+                    p.quadratic_curve_to(curve.control, curve.to);
+                }
             });
 
-            frame.stroke(&curve, Stroke::default().with_width(2.0));
+            frame.stroke(&curves, Stroke::default().with_width(2.0));
         }
     }
 
@@ -202,7 +213,7 @@ mod bezier {
                         control: cursor_position,
                     };
 
-                    curve.draw(&mut frame);
+                    Curve::draw_all(&[curve], &mut frame);
                 }
             };
 
diff --git a/examples/clock/Cargo.toml b/examples/clock/Cargo.toml
index 308cbfbb..ab771405 100644
--- a/examples/clock/Cargo.toml
+++ b/examples/clock/Cargo.toml
@@ -5,9 +5,6 @@ authors = ["Héctor Ramón Jiménez <hector0193@gmail.com>"]
 edition = "2018"
 publish = false
 
-[features]
-canvas = []
-
 [dependencies]
 iced = { path = "../..", features = ["canvas", "async-std", "debug"] }
 iced_native = { path = "../../native" }
diff --git a/examples/clock/src/main.rs b/examples/clock/src/main.rs
index 8b3a92c7..c2beddef 100644
--- a/examples/clock/src/main.rs
+++ b/examples/clock/src/main.rs
@@ -1,6 +1,7 @@
 use iced::{
-    canvas, executor, Application, Canvas, Color, Command, Container, Element,
-    Length, Point, Settings, Subscription, Vector,
+    canvas::{self, Cache, Canvas, Geometry, LineCap, Path, Stroke},
+    executor, Application, Color, Command, Container, Element, Length, Point,
+    Settings, Size, Subscription, Vector,
 };
 
 pub fn main() {
@@ -11,8 +12,8 @@ pub fn main() {
 }
 
 struct Clock {
-    now: LocalTime,
-    clock: canvas::Cache,
+    now: chrono::DateTime<chrono::Local>,
+    clock: Cache,
 }
 
 #[derive(Debug, Clone, Copy)]
@@ -28,7 +29,7 @@ impl Application for Clock {
     fn new(_flags: ()) -> (Self, Command<Message>) {
         (
             Clock {
-                now: chrono::Local::now().into(),
+                now: chrono::Local::now(),
                 clock: Default::default(),
             },
             Command::none(),
@@ -59,7 +60,7 @@ impl Application for Clock {
     }
 
     fn view(&mut self) -> Element<Message> {
-        let canvas = Canvas::new(self.clock.with(&self.now))
+        let canvas = Canvas::new(self)
             .width(Length::Units(400))
             .height(Length::Units(400));
 
@@ -73,69 +74,54 @@ impl Application for Clock {
     }
 }
 
-#[derive(Debug, PartialEq, Eq)]
-struct LocalTime {
-    hour: u32,
-    minute: u32,
-    second: u32,
-}
-
-impl From<chrono::DateTime<chrono::Local>> for LocalTime {
-    fn from(date_time: chrono::DateTime<chrono::Local>) -> LocalTime {
+impl canvas::Program<Message> for Clock {
+    fn draw(&self, bounds: Size) -> Vec<Geometry> {
         use chrono::Timelike;
 
-        LocalTime {
-            hour: date_time.hour(),
-            minute: date_time.minute(),
-            second: date_time.second(),
-        }
-    }
-}
-
-impl canvas::Drawable for LocalTime {
-    fn draw(&self, frame: &mut canvas::Frame) {
-        use canvas::Path;
+        let clock = self.clock.draw(bounds, |frame| {
+            let center = frame.center();
+            let radius = frame.width().min(frame.height()) / 2.0;
 
-        let center = frame.center();
-        let radius = frame.width().min(frame.height()) / 2.0;
+            let background = Path::circle(center, radius);
+            frame.fill(&background, Color::from_rgb8(0x12, 0x93, 0xD8));
 
-        let clock = Path::circle(center, radius);
-        frame.fill(&clock, Color::from_rgb8(0x12, 0x93, 0xD8));
+            let short_hand =
+                Path::line(Point::ORIGIN, Point::new(0.0, -0.5 * radius));
 
-        let short_hand =
-            Path::line(Point::ORIGIN, Point::new(0.0, -0.5 * radius));
+            let long_hand =
+                Path::line(Point::ORIGIN, Point::new(0.0, -0.8 * radius));
 
-        let long_hand =
-            Path::line(Point::ORIGIN, Point::new(0.0, -0.8 * radius));
+            let thin_stroke = Stroke {
+                width: radius / 100.0,
+                color: Color::WHITE,
+                line_cap: LineCap::Round,
+                ..Stroke::default()
+            };
 
-        let thin_stroke = canvas::Stroke {
-            width: radius / 100.0,
-            color: Color::WHITE,
-            line_cap: canvas::LineCap::Round,
-            ..canvas::Stroke::default()
-        };
+            let wide_stroke = Stroke {
+                width: thin_stroke.width * 3.0,
+                ..thin_stroke
+            };
 
-        let wide_stroke = canvas::Stroke {
-            width: thin_stroke.width * 3.0,
-            ..thin_stroke
-        };
+            frame.translate(Vector::new(center.x, center.y));
 
-        frame.translate(Vector::new(center.x, center.y));
+            frame.with_save(|frame| {
+                frame.rotate(hand_rotation(self.now.hour(), 12));
+                frame.stroke(&short_hand, wide_stroke);
+            });
 
-        frame.with_save(|frame| {
-            frame.rotate(hand_rotation(self.hour, 12));
-            frame.stroke(&short_hand, wide_stroke);
-        });
+            frame.with_save(|frame| {
+                frame.rotate(hand_rotation(self.now.minute(), 60));
+                frame.stroke(&long_hand, wide_stroke);
+            });
 
-        frame.with_save(|frame| {
-            frame.rotate(hand_rotation(self.minute, 60));
-            frame.stroke(&long_hand, wide_stroke);
+            frame.with_save(|frame| {
+                frame.rotate(hand_rotation(self.now.second(), 60));
+                frame.stroke(&long_hand, thin_stroke);
+            })
         });
 
-        frame.with_save(|frame| {
-            frame.rotate(hand_rotation(self.second, 60));
-            frame.stroke(&long_hand, thin_stroke);
-        });
+        vec![clock]
     }
 }
 
diff --git a/examples/solar_system/Cargo.toml b/examples/solar_system/Cargo.toml
index c88cda50..0555aa96 100644
--- a/examples/solar_system/Cargo.toml
+++ b/examples/solar_system/Cargo.toml
@@ -5,9 +5,6 @@ authors = ["Héctor Ramón Jiménez <hector0193@gmail.com>"]
 edition = "2018"
 publish = false
 
-[features]
-canvas = []
-
 [dependencies]
 iced = { path = "../..", features = ["canvas", "async-std", "debug"] }
 iced_native = { path = "../../native" }
diff --git a/examples/solar_system/src/main.rs b/examples/solar_system/src/main.rs
index 9337c7b5..e2f107bd 100644
--- a/examples/solar_system/src/main.rs
+++ b/examples/solar_system/src/main.rs
@@ -81,6 +81,12 @@ struct State {
 }
 
 impl State {
+    const SUN_RADIUS: f32 = 70.0;
+    const ORBIT_RADIUS: f32 = 150.0;
+    const EARTH_RADIUS: f32 = 12.0;
+    const MOON_RADIUS: f32 = 4.0;
+    const MOON_DISTANCE: f32 = 28.0;
+
     pub fn new() -> State {
         let now = Instant::now();
         let (width, height) = window::Settings::default().size;
@@ -95,17 +101,6 @@ impl State {
         }
     }
 
-    pub fn space(&self) -> Space<'_> {
-        Space { stars: &self.stars }
-    }
-
-    pub fn system(&self) -> System {
-        System {
-            start: self.start,
-            now: self.now,
-        }
-    }
-
     pub fn update(&mut self, now: Instant) {
         self.now = now;
         self.system_cache.clear();
@@ -136,106 +131,81 @@ impl State {
     }
 }
 
-impl<Message> canvas::State<Message> for State {
+impl<Message> canvas::Program<Message> for State {
     fn draw(&self, bounds: Size) -> Vec<canvas::Geometry> {
-        vec![
-            self.space_cache.draw(bounds, self.space()),
-            self.system_cache.draw(bounds, self.system()),
-        ]
-    }
-}
+        use canvas::{Path, Stroke};
+        use std::f32::consts::PI;
 
-#[derive(Debug)]
-struct Space<'a> {
-    stars: &'a [(Point, f32)],
-}
+        let background = self.space_cache.draw(bounds, |frame| {
+            let space = Path::rectangle(Point::new(0.0, 0.0), frame.size());
 
-impl canvas::Drawable for Space<'_> {
-    fn draw(&self, frame: &mut canvas::Frame) {
-        use canvas::Path;
+            let stars = Path::new(|path| {
+                for (p, size) in &self.stars {
+                    path.rectangle(*p, Size::new(*size, *size));
+                }
+            });
 
-        let space = Path::rectangle(Point::new(0.0, 0.0), frame.size());
+            frame.fill(&space, Color::BLACK);
 
-        let stars = Path::new(|path| {
-            for (p, size) in self.stars {
-                path.rectangle(*p, Size::new(*size, *size));
-            }
+            frame.translate(frame.center() - Point::ORIGIN);
+            frame.fill(&stars, Color::WHITE);
         });
 
-        frame.fill(&space, Color::BLACK);
+        let system = self.system_cache.draw(bounds, |frame| {
+            let center = frame.center();
 
-        frame.translate(frame.center() - Point::ORIGIN);
-        frame.fill(&stars, Color::WHITE);
-    }
-}
+            let sun = Path::circle(center, Self::SUN_RADIUS);
+            let orbit = Path::circle(center, Self::ORBIT_RADIUS);
 
-#[derive(Debug)]
-struct System {
-    start: Instant,
-    now: Instant,
-}
-
-impl System {
-    const SUN_RADIUS: f32 = 70.0;
-    const ORBIT_RADIUS: f32 = 150.0;
-    const EARTH_RADIUS: f32 = 12.0;
-    const MOON_RADIUS: f32 = 4.0;
-    const MOON_DISTANCE: f32 = 28.0;
-}
-
-impl canvas::Drawable for System {
-    fn draw(&self, frame: &mut canvas::Frame) {
-        use canvas::{Path, Stroke};
-        use std::f32::consts::PI;
-
-        let center = frame.center();
-
-        let sun = Path::circle(center, Self::SUN_RADIUS);
-        let orbit = Path::circle(center, Self::ORBIT_RADIUS);
-
-        frame.fill(&sun, Color::from_rgb8(0xF9, 0xD7, 0x1C));
-        frame.stroke(
-            &orbit,
-            Stroke {
-                width: 1.0,
-                color: Color::from_rgba8(0, 153, 255, 0.1),
-                ..Stroke::default()
-            },
-        );
+            frame.fill(&sun, Color::from_rgb8(0xF9, 0xD7, 0x1C));
+            frame.stroke(
+                &orbit,
+                Stroke {
+                    width: 1.0,
+                    color: Color::from_rgba8(0, 153, 255, 0.1),
+                    ..Stroke::default()
+                },
+            );
 
-        let elapsed = self.now - self.start;
-        let rotation = (2.0 * PI / 60.0) * elapsed.as_secs() as f32
-            + (2.0 * PI / 60_000.0) * elapsed.subsec_millis() as f32;
+            let elapsed = self.now - self.start;
+            let rotation = (2.0 * PI / 60.0) * elapsed.as_secs() as f32
+                + (2.0 * PI / 60_000.0) * elapsed.subsec_millis() as f32;
 
-        frame.with_save(|frame| {
-            frame.translate(Vector::new(center.x, center.y));
-            frame.rotate(rotation);
-            frame.translate(Vector::new(Self::ORBIT_RADIUS, 0.0));
+            frame.with_save(|frame| {
+                frame.translate(Vector::new(center.x, center.y));
+                frame.rotate(rotation);
+                frame.translate(Vector::new(Self::ORBIT_RADIUS, 0.0));
+
+                let earth = Path::circle(Point::ORIGIN, Self::EARTH_RADIUS);
+                let shadow = Path::rectangle(
+                    Point::new(0.0, -Self::EARTH_RADIUS),
+                    Size::new(
+                        Self::EARTH_RADIUS * 4.0,
+                        Self::EARTH_RADIUS * 2.0,
+                    ),
+                );
 
-            let earth = Path::circle(Point::ORIGIN, Self::EARTH_RADIUS);
-            let shadow = Path::rectangle(
-                Point::new(0.0, -Self::EARTH_RADIUS),
-                Size::new(Self::EARTH_RADIUS * 4.0, Self::EARTH_RADIUS * 2.0),
-            );
+                frame.fill(&earth, Color::from_rgb8(0x6B, 0x93, 0xD6));
 
-            frame.fill(&earth, Color::from_rgb8(0x6B, 0x93, 0xD6));
+                frame.with_save(|frame| {
+                    frame.rotate(rotation * 10.0);
+                    frame.translate(Vector::new(0.0, Self::MOON_DISTANCE));
 
-            frame.with_save(|frame| {
-                frame.rotate(rotation * 10.0);
-                frame.translate(Vector::new(0.0, Self::MOON_DISTANCE));
+                    let moon = Path::circle(Point::ORIGIN, Self::MOON_RADIUS);
+                    frame.fill(&moon, Color::WHITE);
+                });
 
-                let moon = Path::circle(Point::ORIGIN, Self::MOON_RADIUS);
-                frame.fill(&moon, Color::WHITE);
+                frame.fill(
+                    &shadow,
+                    Color {
+                        a: 0.7,
+                        ..Color::BLACK
+                    },
+                );
             });
-
-            frame.fill(
-                &shadow,
-                Color {
-                    a: 0.7,
-                    ..Color::BLACK
-                },
-            );
         });
+
+        vec![background, system]
     }
 }
 
diff --git a/src/lib.rs b/src/lib.rs
index 77044984..eee7a6ee 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -207,7 +207,7 @@ use iced_web as runtime;
 
 pub use runtime::{
     futures, Align, Background, Color, Command, Font, HorizontalAlignment,
-    Length, Point, Size, Subscription, Vector, VerticalAlignment,
+    Length, Point, Rectangle, Size, Subscription, Vector, VerticalAlignment,
 };
 
 #[cfg(not(target_arch = "wasm32"))]
diff --git a/wgpu/src/widget/canvas.rs b/wgpu/src/widget/canvas.rs
index 044bc3ec..c0506cf7 100644
--- a/wgpu/src/widget/canvas.rs
+++ b/wgpu/src/widget/canvas.rs
@@ -18,34 +18,27 @@ use std::marker::PhantomData;
 pub mod path;
 
 mod cache;
-mod drawable;
 mod event;
 mod fill;
 mod frame;
 mod geometry;
-mod state;
+mod program;
 mod stroke;
 mod text;
 
 pub use cache::Cache;
-pub use drawable::Drawable;
 pub use event::Event;
 pub use fill::Fill;
 pub use frame::Frame;
 pub use geometry::Geometry;
 pub use path::Path;
-pub use state::State;
+pub use program::Program;
 pub use stroke::{LineCap, LineJoin, Stroke};
 pub use text::Text;
 
 /// A widget capable of drawing 2D graphics.
 ///
-/// A [`Canvas`] may contain multiple layers. A [`Layer`] is drawn using the
-/// painter's algorithm. In other words, layers will be drawn on top of each
-/// other in the same order they are pushed into the [`Canvas`].
-///
 /// [`Canvas`]: struct.Canvas.html
-/// [`Layer`]: layer/trait.Layer.html
 ///
 /// # Examples
 /// The repository has a couple of [examples] showcasing how to use a
@@ -66,10 +59,10 @@ pub use text::Text;
 /// ```no_run
 /// # mod iced {
 /// #     pub use iced_wgpu::canvas;
-/// #     pub use iced_native::Color;
+/// #     pub use iced_native::{Color, Size};
 /// # }
-/// use iced::canvas::{self, Cache, Canvas, Drawable, Fill, Frame, Path};
-/// use iced::Color;
+/// use iced::canvas::{self, Cache, Canvas, Fill, Frame, Geometry, Path, Program};
+/// use iced::{Color, Size};
 ///
 /// // First, we define the data we need for drawing
 /// #[derive(Debug)]
@@ -77,42 +70,45 @@ pub use text::Text;
 ///     radius: f32,
 /// }
 ///
-/// // Then, we implement the `Drawable` trait
-/// impl Drawable for Circle {
-///     fn draw(&self, frame: &mut Frame) {
+/// // Then, we implement the `Program` trait
+/// impl Program<()> for Circle {
+///     fn draw(&self, bounds: Size) -> Vec<Geometry>{
+///         // We prepare a new `Frame`
+///         let mut frame = Frame::new(bounds);
+///
 ///         // We create a `Path` representing a simple circle
 ///         let circle = Path::circle(frame.center(), self.radius);
 ///
 ///         // And fill it with some color
 ///         frame.fill(&circle, Fill::Color(Color::BLACK));
+///
+///         // Finally, we produce the geometry
+///         vec![frame.into_geometry()]
 ///     }
 /// }
 ///
-/// // We can use a `Cache` to avoid unnecessary re-tessellation
-/// let cache = Cache::new();
-///
 /// // Finally, we simply use our `Cache` to create the `Canvas`!
-/// let canvas: Canvas<_, ()> = Canvas::new(cache.with(Circle { radius: 50.0 }));
+/// let canvas = Canvas::new(Circle { radius: 50.0 });
 /// ```
 #[derive(Debug)]
-pub struct Canvas<S: State<Message>, Message> {
+pub struct Canvas<Message, P: Program<Message>> {
     width: Length,
     height: Length,
-    state: S,
+    program: P,
     phantom: PhantomData<Message>,
 }
 
-impl<Message, S: State<Message>> Canvas<S, Message> {
+impl<Message, P: Program<Message>> Canvas<Message, P> {
     const DEFAULT_SIZE: u16 = 100;
 
-    /// Creates a new [`Canvas`] with no layers.
+    /// Creates a new [`Canvas`].
     ///
     /// [`Canvas`]: struct.Canvas.html
-    pub fn new(state: S) -> Self {
+    pub fn new(program: P) -> Self {
         Canvas {
             width: Length::Units(Self::DEFAULT_SIZE),
             height: Length::Units(Self::DEFAULT_SIZE),
-            state,
+            program,
             phantom: PhantomData,
         }
     }
@@ -134,8 +130,8 @@ impl<Message, S: State<Message>> Canvas<S, Message> {
     }
 }
 
-impl<Message, S: State<Message>> Widget<Message, Renderer>
-    for Canvas<S, Message>
+impl<Message, P: Program<Message>> Widget<Message, Renderer>
+    for Canvas<Message, P>
 {
     fn width(&self) -> Length {
         self.width
@@ -184,7 +180,7 @@ impl<Message, S: State<Message>> Widget<Message, Renderer>
 
         if let Some(canvas_event) = canvas_event {
             if let Some(message) =
-                self.state.update(canvas_event, bounds.size())
+                self.program.update(canvas_event, bounds.size())
             {
                 messages.push(message);
             }
@@ -207,7 +203,7 @@ impl<Message, S: State<Message>> Widget<Message, Renderer>
                 translation,
                 content: Box::new(Primitive::Group {
                     primitives: self
-                        .state
+                        .program
                         .draw(size)
                         .into_iter()
                         .map(Geometry::into_primitive)
@@ -227,12 +223,12 @@ impl<Message, S: State<Message>> Widget<Message, Renderer>
     }
 }
 
-impl<'a, Message, S: State<Message> + 'a> From<Canvas<S, Message>>
+impl<'a, Message, P: Program<Message> + 'a> From<Canvas<Message, P>>
     for Element<'a, Message, Renderer>
 where
     Message: 'static,
 {
-    fn from(canvas: Canvas<S, Message>) -> Element<'a, Message, Renderer> {
+    fn from(canvas: Canvas<Message, P>) -> Element<'a, Message, Renderer> {
         Element::new(canvas)
     }
 }
diff --git a/wgpu/src/widget/canvas/cache.rs b/wgpu/src/widget/canvas/cache.rs
index 2beed0f7..03643f74 100644
--- a/wgpu/src/widget/canvas/cache.rs
+++ b/wgpu/src/widget/canvas/cache.rs
@@ -1,5 +1,5 @@
 use crate::{
-    canvas::{Drawable, Frame, Geometry},
+    canvas::{Frame, Geometry},
     Primitive,
 };
 
@@ -48,10 +48,11 @@ impl Cache {
         *self.state.borrow_mut() = State::Empty;
     }
 
-    pub fn draw<T>(&self, new_bounds: Size, input: T) -> Geometry
-    where
-        T: Drawable + std::fmt::Debug,
-    {
+    pub fn draw(
+        &self,
+        new_bounds: Size,
+        draw_fn: impl Fn(&mut Frame),
+    ) -> Geometry {
         use std::ops::Deref;
 
         if let State::Filled { bounds, primitive } = self.state.borrow().deref()
@@ -64,7 +65,7 @@ impl Cache {
         }
 
         let mut frame = Frame::new(new_bounds);
-        input.draw(&mut frame);
+        draw_fn(&mut frame);
 
         let primitive = {
             let geometry = frame.into_geometry();
@@ -79,30 +80,6 @@ impl Cache {
 
         Geometry::from_primitive(Primitive::Cached { cache: primitive })
     }
-
-    pub fn with<'a, T, Message>(
-        &'a self,
-        input: T,
-    ) -> impl crate::canvas::State<Message> + 'a
-    where
-        T: Drawable + std::fmt::Debug + 'a,
-    {
-        Bind { cache: self, input }
-    }
-}
-
-struct Bind<'a, T> {
-    cache: &'a Cache,
-    input: T,
-}
-
-impl<'a, T, Message> crate::canvas::State<Message> for Bind<'a, T>
-where
-    T: Drawable + std::fmt::Debug + 'a,
-{
-    fn draw(&self, bounds: Size) -> Vec<Geometry> {
-        vec![self.cache.draw(bounds, &self.input)]
-    }
 }
 
 impl std::fmt::Debug for State {
diff --git a/wgpu/src/widget/canvas/drawable.rs b/wgpu/src/widget/canvas/drawable.rs
deleted file mode 100644
index 5209fa6f..00000000
--- a/wgpu/src/widget/canvas/drawable.rs
+++ /dev/null
@@ -1,36 +0,0 @@
-use crate::canvas::Frame;
-
-/// A type that can be drawn on a [`Frame`].
-///
-/// [`Frame`]: struct.Frame.html
-pub trait Drawable {
-    /// Draws the [`Drawable`] on the given [`Frame`].
-    ///
-    /// [`Drawable`]: trait.Drawable.html
-    /// [`Frame`]: struct.Frame.html
-    fn draw(&self, frame: &mut Frame);
-}
-
-impl<'a> Drawable for dyn Fn(&mut Frame) + 'a {
-    fn draw(&self, frame: &mut Frame) {
-        self(frame)
-    }
-}
-
-impl<T> Drawable for &T
-where
-    T: Drawable,
-{
-    fn draw(&self, frame: &mut Frame) {
-        T::draw(self, frame)
-    }
-}
-
-impl<T> Drawable for &[T]
-where
-    T: Drawable,
-{
-    fn draw(&self, frame: &mut Frame) {
-        self.iter().for_each(|drawable| drawable.draw(frame));
-    }
-}
diff --git a/wgpu/src/widget/canvas/state.rs b/wgpu/src/widget/canvas/program.rs
index ab433dd1..8e35fdfb 100644
--- a/wgpu/src/widget/canvas/state.rs
+++ b/wgpu/src/widget/canvas/program.rs
@@ -1,6 +1,6 @@
 use crate::canvas::{Event, Geometry, Size};
 
-pub trait State<Message> {
+pub trait Program<Message> {
     fn update(&mut self, _event: Event, _bounds: Size) -> Option<Message> {
         None
     }
@@ -8,9 +8,9 @@ pub trait State<Message> {
     fn draw(&self, bounds: Size) -> Vec<Geometry>;
 }
 
-impl<T, Message> State<Message> for &mut T
+impl<T, Message> Program<Message> for &mut T
 where
-    T: State<Message>,
+    T: Program<Message>,
 {
     fn update(&mut self, event: Event, bounds: Size) -> Option<Message> {
         T::update(self, event, bounds)