Draft Program interactivity for Canvas

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,
+    ) {
+    }
+}