Add Layer widget

src/widget.rs

@@ -1,6 +1,6 @@
 use async_trait::async_trait;
 
-use crate::widgets::{Background, Border, Float, Padding};
+use crate::widgets::{Background, Border, Float, Padding, Layer};
 use crate::{Frame, Size};
 
 // TODO Feature-gate these traits
@@ -41,6 +41,14 @@ pub trait WidgetExt: Sized {
         Float::new(self)
     }
 
+    fn below<W>(self, top: W) -> Layer<Self, W> {
+        Layer::new(self, top)
+    }
+
+    fn above<W>(self, bottom: W) -> Layer<W, Self> {
+        Layer::new(bottom, self)
+    }
+
     fn padding(self) -> Padding<Self> {
         Padding::new(self)
     }

src/widgets.rs

@@ -3,6 +3,7 @@ mod border;
 mod cursor;
 mod empty;
 mod float;
+mod layer;
 mod padding;
 mod text;
 
@@ -11,5 +12,6 @@ pub use border::*;
 pub use cursor::*;
 pub use empty::*;
 pub use float::*;
+pub use layer::*;
 pub use padding::*;
 pub use text::*;

src/widgets/layer.rs

@@ -0,0 +1,65 @@
+use async_trait::async_trait;
+
+use crate::{AsyncWidget, Frame, Size, Widget};
+
+pub struct Layer<I1, I2> {
+    bottom: I1,
+    top: I2,
+}
+
+impl<I1, I2> Layer<I1, I2> {
+    pub fn new(bottom: I1, top: I2) -> Self {
+        Self { bottom, top }
+    }
+
+    fn size(bottom: Size, top: Size) -> Size {
+        Size::new(bottom.width.max(top.width), bottom.height.max(top.height))
+    }
+}
+
+impl<E, I1, I2> Widget<E> for Layer<I1, I2>
+where
+    I1: Widget<E>,
+    I2: Widget<E>,
+{
+    fn size(
+        &self,
+        frame: &mut Frame,
+        max_width: Option<u16>,
+        max_height: Option<u16>,
+    ) -> Result<Size, E> {
+        let bottom = self.bottom.size(frame, max_width, max_height)?;
+        let top = self.top.size(frame, max_width, max_height)?;
+        Ok(Self::size(bottom, top))
+    }
+
+    fn draw(self, frame: &mut Frame) -> Result<(), E> {
+        self.bottom.draw(frame)?;
+        self.top.draw(frame)?;
+        Ok(())
+    }
+}
+
+#[async_trait]
+impl<E, I1, I2> AsyncWidget<E> for Layer<I1, I2>
+where
+    I1: AsyncWidget<E> + Send + Sync,
+    I2: AsyncWidget<E> + Send + Sync,
+{
+    async fn size(
+        &self,
+        frame: &mut Frame,
+        max_width: Option<u16>,
+        max_height: Option<u16>,
+    ) -> Result<Size, E> {
+        let bottom = self.bottom.size(frame, max_width, max_height).await?;
+        let top = self.top.size(frame, max_width, max_height).await?;
+        Ok(Self::size(bottom, top))
+    }
+
+    async fn draw(self, frame: &mut Frame) -> Result<(), E> {
+        self.bottom.draw(frame).await?;
+        self.top.draw(frame).await?;
+        Ok(())
+    }
+}