4 files changed, 43 insertions, 1 deletions
diff --git a/wgpu/src/widget/canvas/drawable.rs b/wgpu/src/widget/canvas/drawable.rs
index 6c74071c..48ba6b4c 100644
--- a/wgpu/src/widget/canvas/drawable.rs
+++ b/wgpu/src/widget/canvas/drawable.rs
@@ -10,3 +10,9 @@ pub trait Drawable {
     /// [`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)
+    }
+}
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/layer/cache.rs b/wgpu/src/widget/canvas/layer/cache.rs
index 4f8c2bec..2e87297c 100644
--- a/wgpu/src/widget/canvas/layer/cache.rs
+++ b/wgpu/src/widget/canvas/layer/cache.rs
@@ -1,5 +1,5 @@
 use crate::{
-    canvas::{Drawable, Frame, Layer},
+    canvas::{Drawable, Frame, Layer, Program},
     Primitive,
 };
 
@@ -79,6 +79,20 @@ where
     }
 }
 
+impl<T> Program for Cache<T>
+where
+    T: Drawable + std::fmt::Debug,
+{
+    type Input = T;
+
+    fn layers<'a>(
+        &'a self,
+        input: &'a Self::Input,
+    ) -> Vec<Box<dyn Layer + 'a>> {
+        vec![Box::new(self.with(input))]
+    }
+}
+
 #[derive(Debug)]
 struct Bind<'a, T: Drawable> {
     cache: &'a Cache<T>,
diff --git a/wgpu/src/widget/canvas/program.rs b/wgpu/src/widget/canvas/program.rs
new file mode 100644
index 00000000..c65a078b
--- /dev/null
+++ b/wgpu/src/widget/canvas/program.rs
@@ -0,0 +1,16 @@
+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,
+    ) {
+    }
+}