Add Layer widget

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(())
+    }
+}