10 files changed, 245 insertions, 180 deletions

diff --git a/wgpu/src/widget/canvas/cache.rs b/wgpu/src/widget/canvas/cache.rs
new file mode 100644
index 00000000..03643f74
--- /dev/null
+++ b/wgpu/src/widget/canvas/cache.rs
@@ -0,0 +1,96 @@
+use crate::{
+    canvas::{Frame, Geometry},
+    Primitive,
+};
+
+use iced_native::Size;
+use std::{cell::RefCell, sync::Arc};
+
+enum State {
+    Empty,
+    Filled {
+        bounds: Size,
+        primitive: Arc<Primitive>,
+    },
+}
+
+impl Default for State {
+    fn default() -> Self {
+        State::Empty
+    }
+}
+/// A simple cache that stores generated geometry to avoid recomputation.
+///
+/// A [`Cache`] will not redraw its geometry unless the dimensions of its layer
+/// change or it is explicitly cleared.
+///
+/// [`Layer`]: ../trait.Layer.html
+/// [`Cache`]: struct.Cache.html
+#[derive(Debug, Default)]
+pub struct Cache {
+    state: RefCell<State>,
+}
+
+impl Cache {
+    /// Creates a new empty [`Cache`].
+    ///
+    /// [`Cache`]: struct.Cache.html
+    pub fn new() -> Self {
+        Cache {
+            state: Default::default(),
+        }
+    }
+
+    /// Clears the cache, forcing a redraw the next time it is used.
+    ///
+    /// [`Cached`]: struct.Cached.html
+    pub fn clear(&mut self) {
+        *self.state.borrow_mut() = State::Empty;
+    }
+
+    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()
+        {
+            if *bounds == new_bounds {
+                return Geometry::from_primitive(Primitive::Cached {
+                    cache: primitive.clone(),
+                });
+            }
+        }
+
+        let mut frame = Frame::new(new_bounds);
+        draw_fn(&mut frame);
+
+        let primitive = {
+            let geometry = frame.into_geometry();
+
+            Arc::new(geometry.into_primitive())
+        };
+
+        *self.state.borrow_mut() = State::Filled {
+            bounds: new_bounds,
+            primitive: primitive.clone(),
+        };
+
+        Geometry::from_primitive(Primitive::Cached { cache: primitive })
+    }
+}
+
+impl std::fmt::Debug for State {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            State::Empty => write!(f, "Empty"),
+            State::Filled { primitive, bounds } => f
+                .debug_struct("Filled")
+                .field("primitive", primitive)
+                .field("bounds", bounds)
+                .finish(),
+        }
+    }
+}
diff --git a/wgpu/src/widget/canvas/cursor.rs b/wgpu/src/widget/canvas/cursor.rs
new file mode 100644
index 00000000..a559782a
--- /dev/null
+++ b/wgpu/src/widget/canvas/cursor.rs
@@ -0,0 +1,50 @@
+use iced_native::{Point, Rectangle};
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub enum Cursor {
+    Available(Point),
+    Unavailable,
+}
+
+impl Cursor {
+    // TODO: Remove this once this type is used in `iced_native` to encode
+    // proper cursor availability
+    pub(crate) fn from_window_position(position: Point) -> Self {
+        if position.x < 0.0 || position.y < 0.0 {
+            Cursor::Unavailable
+        } else {
+            Cursor::Available(position)
+        }
+    }
+
+    pub fn position(&self) -> Option<Point> {
+        match self {
+            Cursor::Available(position) => Some(*position),
+            Cursor::Unavailable => None,
+        }
+    }
+
+    pub fn relative_position(&self, bounds: &Rectangle) -> Option<Point> {
+        match self {
+            Cursor::Available(position) => {
+                Some(Point::new(position.x - bounds.x, position.y - bounds.y))
+            }
+            _ => None,
+        }
+    }
+
+    pub fn internal_position(&self, bounds: &Rectangle) -> Option<Point> {
+        if self.is_over(bounds) {
+            self.relative_position(bounds)
+        } else {
+            None
+        }
+    }
+
+    pub fn is_over(&self, bounds: &Rectangle) -> bool {
+        match self {
+            Cursor::Available(position) => bounds.contains(*position),
+            Cursor::Unavailable => false,
+        }
+    }
+}
diff --git a/wgpu/src/widget/canvas/drawable.rs b/wgpu/src/widget/canvas/drawable.rs
deleted file mode 100644
index 6c74071c..00000000
--- a/wgpu/src/widget/canvas/drawable.rs
+++ /dev/null
@@ -1,12 +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);
-}
diff --git a/wgpu/src/widget/canvas/event.rs b/wgpu/src/widget/canvas/event.rs
new file mode 100644
index 00000000..7a8b0829
--- /dev/null
+++ b/wgpu/src/widget/canvas/event.rs
@@ -0,0 +1,6 @@
+use iced_native::input::mouse;
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub enum Event {
+    Mouse(mouse::Event),
+}
diff --git a/wgpu/src/widget/canvas/frame.rs b/wgpu/src/widget/canvas/frame.rs
index de4717f1..1c4a038a 100644
--- a/wgpu/src/widget/canvas/frame.rs
+++ b/wgpu/src/widget/canvas/frame.rs
@@ -1,7 +1,7 @@
 use iced_native::{Point, Rectangle, Size, Vector};
 
 use crate::{
-    canvas::{Fill, Path, Stroke, Text},
+    canvas::{Fill, Geometry, Path, Stroke, Text},
     triangle, Primitive,
 };
 
@@ -10,8 +10,7 @@ use crate::{
 /// [`Canvas`]: struct.Canvas.html
 #[derive(Debug)]
 pub struct Frame {
-    width: f32,
-    height: f32,
+    size: Size,
     buffers: lyon::tessellation::VertexBuffers<triangle::Vertex2D, u32>,
     primitives: Vec<Primitive>,
     transforms: Transforms,
@@ -36,10 +35,9 @@ impl Frame {
     /// top-left corner of its bounds.
     ///
     /// [`Frame`]: struct.Frame.html
-    pub fn new(width: f32, height: f32) -> Frame {
+    pub fn new(size: Size) -> Frame {
         Frame {
-            width,
-            height,
+            size,
             buffers: lyon::tessellation::VertexBuffers::new(),
             primitives: Vec::new(),
             transforms: Transforms {
@@ -57,7 +55,7 @@ impl Frame {
     /// [`Frame`]: struct.Frame.html
     #[inline]
     pub fn width(&self) -> f32 {
-        self.width
+        self.size.width
     }
 
     /// Returns the width of the [`Frame`].
@@ -65,7 +63,7 @@ impl Frame {
     /// [`Frame`]: struct.Frame.html
     #[inline]
     pub fn height(&self) -> f32 {
-        self.height
+        self.size.height
     }
 
     /// Returns the dimensions of the [`Frame`].
@@ -73,7 +71,7 @@ impl Frame {
     /// [`Frame`]: struct.Frame.html
     #[inline]
     pub fn size(&self) -> Size {
-        Size::new(self.width, self.height)
+        self.size
     }
 
     /// Returns the coordinate of the center of the [`Frame`].
@@ -81,7 +79,7 @@ impl Frame {
     /// [`Frame`]: struct.Frame.html
     #[inline]
     pub fn center(&self) -> Point {
-        Point::new(self.width / 2.0, self.height / 2.0)
+        Point::new(self.size.width / 2.0, self.size.height / 2.0)
     }
 
     /// Draws the given [`Path`] on the [`Frame`] by filling it with the
@@ -262,13 +260,14 @@ impl Frame {
         self.transforms.current.is_identity = false;
     }
 
-    /// Produces the primitive representing everything drawn on the [`Frame`].
+    /// Produces the [`Geometry`] representing everything drawn on the [`Frame`].
     ///
     /// [`Frame`]: struct.Frame.html
-    pub fn into_primitive(mut self) -> Primitive {
+    /// [`Geometry`]: struct.Geometry.html
+    pub fn into_geometry(mut self) -> Geometry {
         if !self.buffers.indices.is_empty() {
             self.primitives.push(Primitive::Mesh2D {
-                origin: Point::ORIGIN,
+                size: self.size,
                 buffers: triangle::Mesh2D {
                     vertices: self.buffers.vertices,
                     indices: self.buffers.indices,
@@ -276,9 +275,9 @@ impl Frame {
             });
         }
 
-        Primitive::Group {
+        Geometry::from_primitive(Primitive::Group {
             primitives: self.primitives,
-        }
+        })
     }
 }
 
diff --git a/wgpu/src/widget/canvas/geometry.rs b/wgpu/src/widget/canvas/geometry.rs
new file mode 100644
index 00000000..12ef828f
--- /dev/null
+++ b/wgpu/src/widget/canvas/geometry.rs
@@ -0,0 +1,20 @@
+use crate::Primitive;
+
+#[derive(Debug, Clone)]
+pub struct Geometry(Primitive);
+
+impl Geometry {
+    pub(crate) fn from_primitive(primitive: Primitive) -> Self {
+        Self(primitive)
+    }
+
+    pub fn into_primitive(self) -> Primitive {
+        self.0
+    }
+}
+
+impl From<Geometry> for Primitive {
+    fn from(geometry: Geometry) -> Primitive {
+        geometry.0
+    }
+}
diff --git a/wgpu/src/widget/canvas/layer.rs b/wgpu/src/widget/canvas/layer.rs
deleted file mode 100644
index a46b7fb1..00000000
--- a/wgpu/src/widget/canvas/layer.rs
+++ /dev/null
@@ -1,25 +0,0 @@
-//! Produce, store, and reuse geometry.
-mod cache;
-
-pub use cache::Cache;
-
-use crate::Primitive;
-use iced_native::Size;
-
-use std::sync::Arc;
-
-/// A layer that can be presented at a [`Canvas`].
-///
-/// [`Canvas`]: ../struct.Canvas.html
-pub trait Layer: std::fmt::Debug {
-    /// Draws the [`Layer`] in the given bounds and produces a [`Primitive`] as
-    /// a result.
-    ///
-    /// The [`Layer`] may choose to store the produced [`Primitive`] locally and
-    /// only recompute it when the bounds change, its contents change, or is
-    /// otherwise explicitly cleared by other means.
-    ///
-    /// [`Layer`]: trait.Layer.html
-    /// [`Primitive`]: ../../../enum.Primitive.html
-    fn draw(&self, bounds: Size) -> Arc<Primitive>;
-}
diff --git a/wgpu/src/widget/canvas/layer/cache.rs b/wgpu/src/widget/canvas/layer/cache.rs
deleted file mode 100644
index 4f8c2bec..00000000
--- a/wgpu/src/widget/canvas/layer/cache.rs
+++ /dev/null
@@ -1,128 +0,0 @@
-use crate::{
-    canvas::{Drawable, Frame, Layer},
-    Primitive,
-};
-
-use iced_native::Size;
-use std::{cell::RefCell, marker::PhantomData, sync::Arc};
-
-enum State {
-    Empty,
-    Filled {
-        bounds: Size,
-        primitive: Arc<Primitive>,
-    },
-}
-
-impl Default for State {
-    fn default() -> Self {
-        State::Empty
-    }
-}
-/// A simple cache that stores generated geometry to avoid recomputation.
-///
-/// A [`Cache`] will not redraw its geometry unless the dimensions of its layer
-/// change or it is explicitly cleared.
-///
-/// [`Layer`]: ../trait.Layer.html
-/// [`Cache`]: struct.Cache.html
-#[derive(Debug)]
-pub struct Cache<T: Drawable> {
-    input: PhantomData<T>,
-    state: RefCell<State>,
-}
-
-impl<T> Default for Cache<T>
-where
-    T: Drawable,
-{
-    fn default() -> Self {
-        Self {
-            input: PhantomData,
-            state: Default::default(),
-        }
-    }
-}
-
-impl<T> Cache<T>
-where
-    T: Drawable + std::fmt::Debug,
-{
-    /// Creates a new empty [`Cache`].
-    ///
-    /// [`Cache`]: struct.Cache.html
-    pub fn new() -> Self {
-        Cache {
-            input: PhantomData,
-            state: Default::default(),
-        }
-    }
-
-    /// Clears the cache, forcing a redraw the next time it is used.
-    ///
-    /// [`Cached`]: struct.Cached.html
-    pub fn clear(&mut self) {
-        *self.state.borrow_mut() = State::Empty;
-    }
-
-    /// Binds the [`Cache`] with some data, producing a [`Layer`] that can be
-    /// added to a [`Canvas`].
-    ///
-    /// [`Cache`]: struct.Cache.html
-    /// [`Layer`]: ../trait.Layer.html
-    /// [`Canvas`]: ../../struct.Canvas.html
-    pub fn with<'a>(&'a self, input: &'a T) -> impl Layer + 'a {
-        Bind {
-            cache: self,
-            input: input,
-        }
-    }
-}
-
-#[derive(Debug)]
-struct Bind<'a, T: Drawable> {
-    cache: &'a Cache<T>,
-    input: &'a T,
-}
-
-impl<'a, T> Layer for Bind<'a, T>
-where
-    T: Drawable + std::fmt::Debug,
-{
-    fn draw(&self, current_bounds: Size) -> Arc<Primitive> {
-        use std::ops::Deref;
-
-        if let State::Filled { bounds, primitive } =
-            self.cache.state.borrow().deref()
-        {
-            if *bounds == current_bounds {
-                return primitive.clone();
-            }
-        }
-
-        let mut frame = Frame::new(current_bounds.width, current_bounds.height);
-        self.input.draw(&mut frame);
-
-        let primitive = Arc::new(frame.into_primitive());
-
-        *self.cache.state.borrow_mut() = State::Filled {
-            bounds: current_bounds,
-            primitive: primitive.clone(),
-        };
-
-        primitive
-    }
-}
-
-impl std::fmt::Debug for State {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        match self {
-            State::Empty => write!(f, "Empty"),
-            State::Filled { primitive, bounds } => f
-                .debug_struct("Filled")
-                .field("primitive", primitive)
-                .field("bounds", bounds)
-                .finish(),
-        }
-    }
-}
diff --git a/wgpu/src/widget/canvas/program.rs b/wgpu/src/widget/canvas/program.rs
new file mode 100644
index 00000000..f8e54514
--- /dev/null
+++ b/wgpu/src/widget/canvas/program.rs
@@ -0,0 +1,41 @@
+use crate::canvas::{Cursor, Event, Geometry};
+use iced_native::{MouseCursor, Rectangle};
+
+pub trait Program<Message> {
+    fn update(
+        &mut self,
+        _event: Event,
+        _bounds: Rectangle,
+        _cursor: Cursor,
+    ) -> Option<Message> {
+        None
+    }
+
+    fn draw(&self, bounds: Rectangle, cursor: Cursor) -> Vec<Geometry>;
+
+    fn mouse_cursor(&self, _bounds: Rectangle, _cursor: Cursor) -> MouseCursor {
+        MouseCursor::default()
+    }
+}
+
+impl<T, Message> Program<Message> for &mut T
+where
+    T: Program<Message>,
+{
+    fn update(
+        &mut self,
+        event: Event,
+        bounds: Rectangle,
+        cursor: Cursor,
+    ) -> Option<Message> {
+        T::update(self, event, bounds, cursor)
+    }
+
+    fn draw(&self, bounds: Rectangle, cursor: Cursor) -> Vec<Geometry> {
+        T::draw(self, bounds, cursor)
+    }
+
+    fn mouse_cursor(&self, bounds: Rectangle, cursor: Cursor) -> MouseCursor {
+        T::mouse_cursor(self, bounds, cursor)
+    }
+}
diff --git a/wgpu/src/widget/canvas/stroke.rs b/wgpu/src/widget/canvas/stroke.rs
index 46d669c4..e20379cd 100644
--- a/wgpu/src/widget/canvas/stroke.rs
+++ b/wgpu/src/widget/canvas/stroke.rs
@@ -14,6 +14,24 @@ pub struct Stroke {
     pub line_join: LineJoin,
 }
 
+impl Stroke {
+    pub fn with_color(self, color: Color) -> Stroke {
+        Stroke { color, ..self }
+    }
+
+    pub fn with_width(self, width: f32) -> Stroke {
+        Stroke { width, ..self }
+    }
+
+    pub fn with_line_cap(self, line_cap: LineCap) -> Stroke {
+        Stroke { line_cap, ..self }
+    }
+
+    pub fn with_line_join(self, line_join: LineJoin) -> Stroke {
+        Stroke { line_join, ..self }
+    }
+}
+
 impl Default for Stroke {
     fn default() -> Stroke {
         Stroke {