refactor engine and layout into input and output

output/src/render.rs

@@ -0,0 +1,66 @@
+use crate::*;
+use std::ops::Deref;
+
+/// Custom layout and rendering.
+pub trait Render<E: Output>: Send + Sync {
+    fn layout (&self, area: E::Area) -> E::Area;
+    fn render (&self, output: &mut E);
+    fn boxed <'a> (self) -> RenderBox<'a, E> where Self: Sized + 'a {
+        Box::new(self) as RenderBox<'a, E>
+    }
+}
+
+pub type RenderDyn<'a, Output> = dyn Render<Output> + 'a;
+impl<'a, E: Output> Content<E> for &RenderDyn<'a, E> where Self: Sized {
+    fn content (&self) -> impl Render<E> { self.deref() }
+    fn layout (&self, area: E::Area) -> E::Area { Render::layout(self.deref(), area) }
+    fn render (&self, output: &mut E) { Render::render(self.deref(), output) }
+}
+
+pub type RenderBox<'a, E: Output> = Box<RenderDyn<'a, E>>;
+impl<'a, E: Output> Content<E> for RenderBox<'a, E> {
+    fn content (&self) -> impl Render<E> { self.deref() }
+    //fn boxed <'b> (self) -> RenderBox<'b, E> where Self: Sized + 'b { self }
+}
+
+impl<E: Output, C: Content<E>> Render<E> for C {
+    fn layout (&self, area: E::Area) -> E::Area { Content::layout(self, area) }
+    fn render (&self, output: &mut E) { Content::render(self, output) }
+}
+
+#[macro_export] macro_rules! render {
+    (($self:ident:$Struct:ty) => $content:expr) => {
+        impl <E: Output> Content<E> for $Struct {
+            fn content (&$self) -> impl Render<E> { Some($content) }
+        }
+    };
+    (|$self:ident:$Struct:ident $(<
+        $($L:lifetime),* $($T:ident $(:$Trait:path)?),*
+    >)?, $to:ident | $render:expr) => {
+        impl <$($($L),*)? E: Output, $($T$(:$Trait)?),*> Content<E>
+        for $Struct $(<$($L),* $($T),*>>)? {
+            fn render (&$self, $to: &mut E) { $render }
+        }
+    };
+    ($Output:ty:
+        ($self:ident:$Struct:ident $(<$(
+            $($L:lifetime)? $($T:ident)? $(:$Trait:path)?
+        ),+>)?) => $content:expr
+    ) => {
+        impl $(<$($($L)? $($T)? $(:$Trait)?),+>)? Content<$Output>
+        for $Struct $(<$($($L)? $($T)?),+>)? {
+            fn content (&$self) -> impl Render<$Output> { $content }
+        }
+    };
+
+    ($Output:ty:
+        |$self:ident : $Struct:ident $(<$(
+            $($L:lifetime)? $($T:ident)? $(:$Trait:path)?
+        ),+>)?, $to:ident| $render:expr
+    ) => {
+        impl $(<$($($L)? $($T)? $(:$Trait)?),+>)? Content<$Output>
+        for $Struct $(<$($($L)? $($T)?),+>)? {
+            fn render (&$self, $to: &mut $Output) { $render }
+        }
+    };
+}