output: refactor Content and Render traits

output/src/output_content.rs

@@ -1,88 +1,67 @@
 use crate::*;
 
 /// Composable renderable with static dispatch.
-pub trait Content<E: Output> {
-    /// Return a [Render]able of a specific type.
-    fn content (&self) -> impl Render<E> + '_ {
-        ()
-    }
-    /// Perform layout. By default, delegates to [Self::content].
-    fn layout (&self, area: E::Area) -> E::Area {
-        self.content().layout(area)
-    }
-    /// Draw to output. By default, delegates to [Self::content].
-    fn render (&self, output: &mut E) {
-        self.content().render(output) 
-    }
-}
-
-/// Every pointer to [Content] is a [Content].
-impl<E: Output, C: Content<E>> Content<E> for &C {
-    fn content (&self) -> impl Render<E> + '_ { (*self).content() }
-    fn layout (&self, area: E::Area) -> E::Area { (*self).layout(area) }
-    fn render (&self, output: &mut E) { (*self).render(output) }
+pub trait Content<E: Output>: Sized {
+    /// Return opaque [Render]able.
+    fn content (&self) -> Option<impl Render<E> + '_> { Option::<()>::None }
 }
 
 /// The platonic ideal unit of [Content]: total emptiness at dead center (e=1vg^sqrt(-1))
-impl<E: Output> Content<E> for () {
-    fn layout (&self, area: E::Area) -> E::Area { area.center().to_area_pos().into() }
-    fn render (&self, _: &mut E) {}
+impl<E: Output> Content<E> for () {}
+
+impl<E: Output> Content<E> for fn(&mut E) {
+    fn content (&self) -> Option<impl Render<E> + '_> {
+        Some(self)
+    }
+}
+
+impl<E: Output, T: Render<E>> Content<E> for fn()->T {
+    fn content (&self) -> Option<impl Render<E> + '_> {
+        Some(self())
+    }
 }
 
 impl<E: Output, T: Content<E>> Content<E> for Option<T> {
-    fn content (&self) -> impl Render<E> + '_ {
-        self.as_ref()
-    }
-    fn layout (&self, area: E::Area) -> E::Area {
-        self.as_ref()
-            .map(|content|content.layout(area))
-            .unwrap_or([0.into(), 0.into(), 0.into(), 0.into(),].into())
-    }
-    fn render (&self, output: &mut E) {
-        self.as_ref()
-            .map(|content|content.render(output));
+    fn content (&self) -> Option<impl Render<E> + '_> {
+        if let Some(content) = self {
+            content.content()
+        } else {
+            None
+        }
     }
 }
 
 /// You can render from a box.
 impl<E: Output> Content<E> for RenderBox<E> {
-    fn content (&self) -> impl Render<E> + '_ { self.deref() }
-    //fn boxed <'b> (self) -> RenderBox<'b, E> where Self: Sized + 'b { self }
+    fn content (&self) -> Option<impl Render<E> + '_> {
+        Some(self.deref())
+    }
 }
 
 /// You can render from an opaque pointer.
 impl<E: Output> Content<E> for &dyn Render<E> where Self: Sized {
-    fn content (&self) -> impl Render<E> + '_ {
+    fn content (&self) -> Option<impl Render<E> + '_> {
         #[allow(suspicious_double_ref_op)]
-        self.deref()
-    }
-    fn layout (&self, area: E::Area) -> E::Area {
-        #[allow(suspicious_double_ref_op)]
-        Render::layout(self.deref(), area)
-    }
-    fn render (&self, output: &mut E) {
-        #[allow(suspicious_double_ref_op)]
-        Render::render(self.deref(), output)
+        Some(self.deref())
     }
 }
 
-/// Implement [Content] with custom rendering for a struct.
-#[macro_export] macro_rules! render {
-    (|$self:ident:$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) { $render }
+/// Implement composable content for a struct.
+#[macro_export] macro_rules! content {
+    // Implement for all [Output]s.
+    (|$self:ident:$Struct:ty| $content:expr) => {
+        impl<E: Output> Content<E> for $Struct {
+            fn content (&$self) -> impl Render<E> + '_ { Some($content) }
         }
     };
+    // Implement for specific [Output].
     ($Output:ty:|
         $self:ident:
-        $Struct:ident $(<$($($L:lifetime)? $($T:ident)? $(:$Trait:path)?),+>)?, $to:ident
-    |$render:expr) => {
+        $Struct:ident$(<$($($L:lifetime)? $($T:ident)? $(:$Trait:path)?),+>)?
+    |$content:expr) => {
         impl $(<$($($L)? $($T)? $(:$Trait)?),+>)? Content<$Output>
         for $Struct $(<$($($L)? $($T)?),+>)? {
-            fn render (&$self, $to: &mut $Output) { $render }
+            fn content (&$self) -> impl Render<$Output> + '_ { $content }
         }
     };
 }