Add retained paints and shared text selection

core/src/widget/mod.rs

@@ -15,6 +15,16 @@ pub use tag::*;
 pub use view::*;
 pub use widgets::*;
 
+#[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
+pub enum ChildOrder {
+    /// The order in which the parent drew its children.
+    #[default]
+    Draw,
+    /// Ascending visual position on one screen axis. Equal positions keep
+    /// draw order; the resolved coordinates are sorted only when queried.
+    Axis(Axis),
+}
+
 pub trait Widget: Any {
     fn draw(&mut self, painter: &mut Painter);
 
@@ -34,6 +44,10 @@ pub trait Widget: Any {
         accesskit::Role::Unknown
     }
 
+    fn child_order(&self) -> ChildOrder {
+        ChildOrder::Draw
+    }
+
     #[allow(unused_variables)]
     fn tick(&mut self, now: std::time::Instant) -> bool {
         false