wip: generic layout!

crates/tek_core/src/engine.rs

@@ -1,22 +1,36 @@
 use crate::*;
+use std::ops::{Add, Sub};
+use std::cmp::{Ord, Eq, PartialEq};
 
 /// Entry point for main loop
 pub trait App<T: Engine> {
     fn run (self, context: T) -> Usually<T>;
 }
 
+pub trait Number: Send + Sync + Copy
+    + Add<Self, Output=Self>
+    + Sub<Self, Output=Self>
+    + Ord + PartialEq + Eq {}
+
+impl<T> Number for T where
+    T: Send + Sync + Copy
+        + Add<Self, Output=Self>
+        + Sub<Self, Output=Self>
+        + Ord + PartialEq + Eq
+{}
+
 /// Platform backend.
 pub trait Engine: Sized {
     fn setup (&mut self) -> Usually<()> { Ok(()) }
     fn exited (&self) -> bool;
     fn teardown (&mut self) -> Usually<()> { Ok(()) }
 
-    type HandleInput;
-    fn handle (&self, _: &mut impl Handle<Self>) -> Usually<()> where Self: Sized;
-    type Handled;
+    /// Unit of distance.
+    type Unit: Number;
 
+    type HandleInput;
+    type Handled;
     type RenderInput;
-    fn render (&mut self, _: &impl Render<Self>) -> Usually<()> where Self: Sized;
     type Rendered;
 }
 
@@ -25,9 +39,14 @@ pub trait HandleContext {}
 pub trait RenderContext {}
 
 submod! {
+    collect
+    component
     exit
     focus
     handle
     keymap
+    layered
+    layout
     render
+    split
 }