genericize layout rendering

crates/tek_core/src/engine.rs

@@ -7,6 +7,28 @@ pub trait App<T: Engine> {
     fn run (self, context: T) -> Usually<T>;
 }
 
+/// Platform backend.
+pub trait Engine: Sized {
+    fn setup (&mut self) -> Usually<()> { Ok(()) }
+    fn exited (&self) -> bool;
+    fn teardown (&mut self) -> Usually<()> { Ok(()) }
+
+    /// Unit of distance.
+    type Unit: Number;
+    type Area: Rectangle<Self::Unit>;
+
+    type HandleInput;
+    type Handled;
+    type RenderInput;
+    type Rendered;
+
+    // FIXME
+    fn area (&self) -> Self::Area;
+    // FIXME
+    fn with_area (&mut self, x: Self::Unit, y: Self::Unit, w: Self::Unit, h: Self::Unit)
+        -> &mut Self;
+}
+
 pub trait Number: Send + Sync + Copy
     + Add<Self, Output=Self>
     + Sub<Self, Output=Self>
@@ -19,25 +41,6 @@ impl<T> Number for T where
         + 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(()) }
-
-    /// Unit of distance.
-    type Unit: Number;
-
-    type HandleInput;
-    type Handled;
-    type RenderInput;
-    type Rendered;
-}
-
-pub trait HandleContext {}
-
-pub trait RenderContext {}
-
 submod! {
     collect
     component