Allow `canvas::State` to produce messages

1 files changed, 8 insertions, 6 deletions

diff --git a/wgpu/src/widget/canvas/state.rs b/wgpu/src/widget/canvas/state.rs
index 8388f94d..ab433dd1 100644
--- a/wgpu/src/widget/canvas/state.rs
+++ b/wgpu/src/widget/canvas/state.rs
@@ -1,17 +1,19 @@
 use crate::canvas::{Event, Geometry, Size};
 
-pub trait State {
-    fn update(&mut self, _event: Event, _bounds: Size) {}
+pub trait State<Message> {
+    fn update(&mut self, _event: Event, _bounds: Size) -> Option<Message> {
+        None
+    }
 
     fn draw(&self, bounds: Size) -> Vec<Geometry>;
 }
 
-impl<T> State for &mut T
+impl<T, Message> State<Message> for &mut T
 where
-    T: State,
+    T: State<Message>,
 {
-    fn update(&mut self, event: Event, bounds: Size) {
-        T::update(self, event, bounds);
+    fn update(&mut self, event: Event, bounds: Size) -> Option<Message> {
+        T::update(self, event, bounds)
     }
 
     fn draw(&self, bounds: Size) -> Vec<Geometry> {