Add overlay support in iced_pure and port PickList 🎉

pure/src/overlay.rs

@@ -0,0 +1,21 @@
+use crate::Tree;
+
+use iced_native::Layout;
+
+pub use iced_native::overlay::*;
+
+pub fn from_children<'a, Message, Renderer>(
+    children: &'a mut [crate::Element<'_, Message, Renderer>],
+    tree: &'a mut Tree,
+    layout: Layout<'_>,
+    renderer: &Renderer,
+) -> Option<Element<'a, Message, Renderer>> {
+    children
+        .iter_mut()
+        .zip(&mut tree.children)
+        .zip(layout.children())
+        .filter_map(|((child, state), layout)| {
+            child.as_widget_mut().overlay(state, layout, renderer)
+        })
+        .next()
+}