Remove Layer trait and simplify Canvas

wgpu/src/widget/canvas/cache.rs

@@ -1,10 +1,10 @@
 use crate::{
-    canvas::{Drawable, Frame, Layer},
+    canvas::{Drawable, Frame, Geometry},
     Primitive,
 };
 
 use iced_native::Size;
-use std::{borrow::Borrow, cell::RefCell, marker::PhantomData, sync::Arc};
+use std::{cell::RefCell, sync::Arc};
 
 enum State {
     Empty,
@@ -48,61 +48,51 @@ impl Cache {
         *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, T>(
-        &'a self,
-        input: impl Borrow<T> + std::fmt::Debug + 'a,
-    ) -> impl Layer + 'a
+    pub fn draw<T>(&self, new_bounds: Size, input: T) -> Geometry
     where
-        T: Drawable + std::fmt::Debug + 'a,
+        T: Drawable + std::fmt::Debug,
     {
-        Bind {
-            cache: self,
-            input: input,
-            drawable: PhantomData,
-        }
-    }
-}
-
-#[derive(Debug)]
-struct Bind<'a, T: Drawable, I: Borrow<T> + 'a> {
-    cache: &'a Cache,
-    input: I,
-    drawable: PhantomData<T>,
-}
-
-impl<'a, T, I> Layer for Bind<'a, T, I>
-where
-    T: Drawable + std::fmt::Debug,
-    I: Borrow<T> + std::fmt::Debug + 'a,
-{
-    fn draw(&self, current_bounds: Size) -> Arc<Primitive> {
         use std::ops::Deref;
 
-        if let State::Filled { bounds, primitive } =
-            self.cache.state.borrow().deref()
+        if let State::Filled { bounds, primitive } = self.state.borrow().deref()
         {
-            if *bounds == current_bounds {
-                return primitive.clone();
+            if *bounds == new_bounds {
+                return Geometry::from_primitive(primitive.clone());
             }
         }
 
-        let mut frame = Frame::new(current_bounds.width, current_bounds.height);
-        self.input.borrow().draw(&mut frame);
+        let mut frame = Frame::new(new_bounds.width, new_bounds.height);
+        input.draw(&mut frame);
 
         let primitive = Arc::new(frame.into_primitive());
 
-        *self.cache.state.borrow_mut() = State::Filled {
-            bounds: current_bounds,
+        *self.state.borrow_mut() = State::Filled {
+            bounds: new_bounds,
             primitive: primitive.clone(),
         };
 
-        primitive
+        Geometry::from_primitive(primitive)
+    }
+
+    pub fn with<'a, T>(&'a self, input: T) -> impl crate::canvas::State + 'a
+    where
+        T: Drawable + std::fmt::Debug + 'a,
+    {
+        Bind { cache: self, input }
+    }
+}
+
+struct Bind<'a, T> {
+    cache: &'a Cache,
+    input: T,
+}
+
+impl<'a, T> crate::canvas::State 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)]
     }
 }
 

wgpu/src/widget/canvas/drawable.rs

@@ -16,3 +16,12 @@ impl<'a> Drawable for dyn Fn(&mut Frame) + 'a {
         self(frame)
     }
 }
+
+impl<T> Drawable for &T
+where
+    T: Drawable,
+{
+    fn draw(&self, frame: &mut Frame) {
+        T::draw(self, frame)
+    }
+}

wgpu/src/widget/canvas/geometry.rs

@@ -0,0 +1,15 @@
+use crate::Primitive;
+use std::sync::Arc;
+
+#[derive(Debug)]
+pub struct Geometry(Arc<Primitive>);
+
+impl Geometry {
+    pub(crate) fn from_primitive(primitive: Arc<Primitive>) -> Self {
+        Self(primitive)
+    }
+
+    pub(crate) fn into_primitive(self) -> Arc<Primitive> {
+        self.0
+    }
+}

wgpu/src/widget/canvas/layer.rs

@@ -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>;
-}

wgpu/src/widget/canvas/program.rs

@@ -1,16 +0,0 @@
-use crate::canvas::{Event, Layer, Size};
-
-pub trait Program {
-    type Input;
-
-    fn layers<'a>(&'a self, input: &'a Self::Input)
-        -> Vec<Box<dyn Layer + 'a>>;
-
-    fn update<'a>(
-        &'a mut self,
-        _event: Event,
-        _bounds: Size,
-        _input: &'a Self::Input,
-    ) {
-    }
-}

wgpu/src/widget/canvas/state.rs

@@ -0,0 +1,20 @@
+use crate::canvas::{Event, Geometry, Size};
+
+pub trait State {
+    fn update(&mut self, _event: Event, _bounds: Size) {}
+
+    fn draw(&self, bounds: Size) -> Vec<Geometry>;
+}
+
+impl<T> State for &mut T
+where
+    T: State,
+{
+    fn update(&mut self, event: Event, bounds: Size) {
+        T::update(self, event, bounds);
+    }
+
+    fn draw(&self, bounds: Size) -> Vec<Geometry> {
+        T::draw(self, bounds)
+    }
+}