refactor engine and layout into input and output

output/src/align.rs

@@ -0,0 +1,54 @@
+use crate::*;
+
+#[derive(Debug, Copy, Clone, Default)]
+pub enum Alignment { #[default] Center, X, Y, NW, N, NE, E, SE, S, SW, W }
+
+pub struct Align<T>(Alignment, T);
+
+impl<T> Align<T> {
+    pub fn c  (a: T) -> Self { Self(Alignment::Center, a) }
+    pub fn x  (a: T) -> Self { Self(Alignment::X,      a) }
+    pub fn y  (a: T) -> Self { Self(Alignment::Y,      a) }
+    pub fn n  (a: T) -> Self { Self(Alignment::N,      a) }
+    pub fn s  (a: T) -> Self { Self(Alignment::S,      a) }
+    pub fn e  (a: T) -> Self { Self(Alignment::E,      a) }
+    pub fn w  (a: T) -> Self { Self(Alignment::W,      a) }
+    pub fn nw (a: T) -> Self { Self(Alignment::NW,     a) }
+    pub fn sw (a: T) -> Self { Self(Alignment::SW,     a) }
+    pub fn ne (a: T) -> Self { Self(Alignment::NE,     a) }
+    pub fn se (a: T) -> Self { Self(Alignment::SE,     a) }
+}
+
+impl<E: Output, T: Content<E>> Content<E> for Align<T> {
+    fn content (&self) -> impl Render<E> {
+        &self.1
+    }
+    fn layout (&self, on: E::Area) -> E::Area {
+        use Alignment::*;
+        let it = Render::layout(&self.content(), on).xywh();
+        let centered = on.center_xy(it.wh());
+        let far_x = (on.x() + on.w()).minus(it.w());
+        let far_y = (on.y() + on.h()).minus(it.h());
+        let [x, y] = match self.0 {
+            NW => [on.x(),       on.y()],
+            N  => [centered.x(), on.y()],
+            NE => [far_x,        on.y()],
+            E  => [far_x,  centered.y()],
+            SE => [far_x,        far_y ],
+            S  => [centered.x(), far_y ],
+            SW => [on.x(),       far_y ],
+            W  => [on.x(), centered.y()],
+
+            Center => centered.xy(),
+
+            X  => [centered.x(), it.y()],
+            Y  => [it.x(), centered.y()],
+        };
+        [x, y, centered.w(), centered.h()].into()
+    }
+    fn render (&self, render: &mut E) {
+        let content = &self.content();
+        let it = Render::layout(content, render.area()).xywh();
+        render.place(it.into(), content)
+    }
+}