implement fixed Split

crates/tek_core/src/space.rs

@@ -92,6 +92,15 @@ pub trait Area<N: Number>: Copy {
     #[inline] fn clip (&self, wh: impl Size<N>) -> [N;4] {
         [self.x(), self.y(), wh.w(), wh.h()]
     }
+    #[inline] fn split_fixed (&self, direction: Direction, a: N) -> ([N;4],[N;4]) {
+        match direction {
+            Direction::Down => (
+                [self.x(), self.y(), self.w(), a],
+                [self.x(), self.y() + a, self.w(), self.h() - a],
+            ),
+            _ => todo!(),
+        }
+    }
 }
 
 impl<N: Number> Area<N> for (N, N, N, N) {
@@ -829,3 +838,33 @@ where
 #[macro_export] macro_rules! row {
     ($($expr:expr),* $(,)?) => { Stack::right(move|add|{ $(add(&$expr)?;)* Ok(()) }) }
 }
+
+/// A binary split with fixed proportion
+pub struct Split<E: Engine, A: Widget<Engine = E>, B: Widget<Engine = E>>(
+    pub Direction, pub E::Unit, A, B, PhantomData<E>
+);
+
+impl<E: Engine, A: Widget<Engine = E>, B: Widget<Engine = E>> Split<E, A, B> {
+    pub fn new (direction: Direction, proportion: E::Unit, a: A, b: B) -> Self {
+        Self(direction, proportion, a, b, Default::default())
+    }
+}
+
+impl<E: Engine, A: Widget<Engine = E>, B: Widget<Engine = E>> Widget for Split<E, A, B> {
+    type Engine = E;
+    fn layout (&self, to: E::Size) -> Perhaps<E::Size> {
+        Ok(Some(to))
+    }
+    fn render (&self, to: &mut E::Output) -> Usually<()> {
+        let (a, b) = to.area().split_fixed(self.0, self.1);
+        to.render_in(a.into(), &self.2)?;
+        to.render_in(b.into(), &self.3)?;
+        Ok(())
+    }
+}
+
+/// A scrollable area.
+pub struct Scroll<
+    E: Engine,
+    F: Send + Sync + Fn(&mut dyn FnMut(&dyn Widget<Engine = E>)->Usually<()>)->Usually<()>
+>(pub F, pub Direction, pub u64, PhantomData<E>);