add Input and Output traits to Engine

crates/tek_core/src/engine.rs

@@ -7,21 +7,29 @@ pub trait App<T: Engine> {
 
 /// Platform backend.
 pub trait Engine: Send + Sync + Sized {
-    fn setup (&mut self) -> Usually<()> { Ok(()) }
-    fn exited (&self) -> bool;
-    fn teardown (&mut self) -> Usually<()> { Ok(()) }
+    type Input: Input<Self>;
+    type Handled;
+    type Output: Output<Self>;
 
-    /// Unit of distance.
     type Unit: Number;
     type Area: Area<Self::Unit> + From<[Self::Unit;4]> + Debug;
     type Size: Size<Self::Unit> + From<[Self::Unit;2]> + Debug;
 
-    type Input;
-    type Handled;
-    type Output: RenderTarget<Self>;
+    fn setup (&mut self) -> Usually<()> { Ok(()) }
+    fn exited (&self) -> bool;
+    fn teardown (&mut self) -> Usually<()> { Ok(()) }
 }
 
-pub trait RenderTarget<E: Engine> {
+pub trait Input<E: Engine> {
+    type Event;
+    fn event (&self)
+        -> Self::Event;
+    fn is_done (&self)
+        -> bool;
+    fn done (&self);
+}
+
+pub trait Output<E: Engine> {
     fn area (&self)
         -> E::Area;
     fn area_mut (&mut self)