Use nested for lazy widgets

7 files changed, 77 insertions, 49 deletions

diff --git a/runtime/src/lib.rs b/runtime/src/lib.rs
index 50abf7b2..4bbf9687 100644
--- a/runtime/src/lib.rs
+++ b/runtime/src/lib.rs
@@ -47,6 +47,7 @@ pub mod clipboard;
 pub mod command;
 pub mod font;
 pub mod keyboard;
+pub mod overlay;
 pub mod program;
 pub mod system;
 pub mod user_interface;
diff --git a/runtime/src/overlay.rs b/runtime/src/overlay.rs
new file mode 100644
index 00000000..03390980
--- /dev/null
+++ b/runtime/src/overlay.rs
@@ -0,0 +1,4 @@
+//! Overlays for user interfaces.
+mod nested;
+
+pub use nested::Nested;
diff --git a/runtime/src/user_interface/overlay.rs b/runtime/src/overlay/nested.rs
index 1211d55b..5c5fafde 100644
--- a/runtime/src/user_interface/overlay.rs
+++ b/runtime/src/overlay/nested.rs
@@ -21,6 +21,12 @@ where
         Self { overlay: element }
     }
 
+    /// Returns the position of the [`Nested`] overlay.
+    pub fn position(&self) -> Point {
+        self.overlay.position()
+    }
+
+    /// Returns the layout [`Node`] of the [`Nested`] overlay.
     pub fn layout(
         &mut self,
         renderer: &Renderer,
@@ -36,7 +42,7 @@ where
         where
             Renderer: renderer::Renderer,
         {
-            let translation = position - Point::ORIGIN;
+            let translation = position - element.position();
 
             let node = element.layout(renderer, bounds, translation);
 
@@ -58,6 +64,7 @@ where
         recurse(&mut self.overlay, renderer, bounds, position)
     }
 
+    /// Draws the [`Nested`] overlay using the associated `Renderer`.
     pub fn draw(
         &mut self,
         renderer: &mut Renderer,
@@ -127,6 +134,7 @@ where
         recurse(&mut self.overlay, layout, renderer, theme, style, cursor);
     }
 
+    /// Applies a [`widget::Operation`] to the [`Nested`] overlay.
     pub fn operate(
         &mut self,
         layout: Layout<'_>,
@@ -157,6 +165,7 @@ where
         recurse(&mut self.overlay, layout, renderer, operation)
     }
 
+    /// Processes a runtime [`Event`].
     pub fn on_event(
         &mut self,
         event: Event,
@@ -247,6 +256,7 @@ where
         status
     }
 
+    /// Returns the current [`mouse::Interaction`] of the [`Nested`] overlay.
     pub fn mouse_interaction(
         &mut self,
         layout: Layout<'_>,
@@ -298,6 +308,7 @@ where
             .unwrap_or_default()
     }
 
+    /// Returns true if the cursor is over the [`Nested`] overlay.
     pub fn is_over(
         &mut self,
         layout: Layout<'_>,
diff --git a/runtime/src/user_interface.rs b/runtime/src/user_interface.rs
index 1d55970e..619423fd 100644
--- a/runtime/src/user_interface.rs
+++ b/runtime/src/user_interface.rs
@@ -1,14 +1,12 @@
 //! Implement your own event loop to drive a user interface.
-mod overlay;
-
 use crate::core::event::{self, Event};
 use crate::core::layout;
 use crate::core::mouse;
 use crate::core::renderer;
 use crate::core::widget;
 use crate::core::window;
-use crate::core::{Clipboard, Point, Rectangle, Size};
-use crate::core::{Element, Layout, Shell};
+use crate::core::{Clipboard, Element, Layout, Point, Rectangle, Shell, Size};
+use crate::overlay;
 
 /// A set of interactive graphical elements with a specific [`Layout`].
 ///
diff --git a/widget/src/lazy.rs b/widget/src/lazy.rs
index 89376136..4903d0ed 100644
--- a/widget/src/lazy.rs
+++ b/widget/src/lazy.rs
@@ -20,6 +20,7 @@ use crate::core::Element;
 use crate::core::{
     self, Clipboard, Hasher, Length, Point, Rectangle, Shell, Size,
 };
+use crate::runtime::overlay::Nested;
 
 use ouroboros::self_referencing;
 use std::cell::RefCell;
@@ -260,14 +261,17 @@ where
                     .unwrap(),
                 tree: &mut tree.children[0],
                 overlay_builder: |element, tree| {
-                    element.as_widget_mut().overlay(tree, layout, renderer)
+                    element
+                        .as_widget_mut()
+                        .overlay(tree, layout, renderer)
+                        .map(|overlay| RefCell::new(Nested::new(overlay)))
                 },
             }
             .build(),
         ));
 
-        let has_overlay = overlay
-            .with_overlay_maybe(|overlay| overlay::Element::position(overlay));
+        let has_overlay =
+            overlay.with_overlay_maybe(|overlay| overlay.position());
 
         has_overlay
             .map(|position| overlay::Element::new(position, Box::new(overlay)))
@@ -285,8 +289,8 @@ where
     tree: &'a mut Tree,
 
     #[borrows(mut element, mut tree)]
-    #[covariant]
-    overlay: Option<overlay::Element<'this, Message, Renderer>>,
+    #[not_covariant]
+    overlay: Option<RefCell<Nested<'this, Message, Renderer>>>,
 }
 
 struct Overlay<'a, Message, Renderer>(Option<Inner<'a, Message, Renderer>>);
@@ -301,19 +305,20 @@ impl<'a, Message, Renderer> Drop for Overlay<'a, Message, Renderer> {
 impl<'a, Message, Renderer> Overlay<'a, Message, Renderer> {
     fn with_overlay_maybe<T>(
         &self,
-        f: impl FnOnce(&overlay::Element<'_, Message, Renderer>) -> T,
+        f: impl FnOnce(&mut Nested<'_, Message, Renderer>) -> T,
     ) -> Option<T> {
-        self.0.as_ref().unwrap().borrow_overlay().as_ref().map(f)
+        self.0.as_ref().unwrap().with_overlay(|overlay| {
+            overlay.as_ref().map(|nested| (f)(&mut nested.borrow_mut()))
+        })
     }
 
     fn with_overlay_mut_maybe<T>(
         &mut self,
-        f: impl FnOnce(&mut overlay::Element<'_, Message, Renderer>) -> T,
+        f: impl FnOnce(&mut Nested<'_, Message, Renderer>) -> T,
     ) -> Option<T> {
-        self.0
-            .as_mut()
-            .unwrap()
-            .with_overlay_mut(|overlay| overlay.as_mut().map(f))
+        self.0.as_mut().unwrap().with_overlay_mut(|overlay| {
+            overlay.as_mut().map(|nested| (f)(nested.get_mut()))
+        })
     }
 }
 
@@ -329,9 +334,7 @@ where
         position: Point,
     ) -> layout::Node {
         self.with_overlay_maybe(|overlay| {
-            let translation = position - overlay.position();
-
-            overlay.layout(renderer, bounds, translation)
+            overlay.layout(renderer, bounds, position)
         })
         .unwrap_or_default()
     }
diff --git a/widget/src/lazy/component.rs b/widget/src/lazy/component.rs
index edd0c2a2..f955d9dd 100644
--- a/widget/src/lazy/component.rs
+++ b/widget/src/lazy/component.rs
@@ -9,6 +9,7 @@ use crate::core::widget::tree::{self, Tree};
 use crate::core::{
     self, Clipboard, Element, Length, Point, Rectangle, Shell, Size, Widget,
 };
+use crate::runtime::overlay::Nested;
 
 use ouroboros::self_referencing;
 use std::cell::RefCell;
@@ -455,11 +456,18 @@ where
                 overlay_builder: |instance, tree| {
                     instance.state.get_mut().as_mut().unwrap().with_element_mut(
                         move |element| {
-                            element.as_mut().unwrap().as_widget_mut().overlay(
-                                &mut tree.children[0],
-                                layout,
-                                renderer,
-                            )
+                            element
+                                .as_mut()
+                                .unwrap()
+                                .as_widget_mut()
+                                .overlay(
+                                    &mut tree.children[0],
+                                    layout,
+                                    renderer,
+                                )
+                                .map(|overlay| {
+                                    RefCell::new(Nested::new(overlay))
+                                })
                         },
                     )
                 },
@@ -468,7 +476,7 @@ where
         ));
 
         let has_overlay = overlay.0.as_ref().unwrap().with_overlay(|overlay| {
-            overlay.as_ref().map(overlay::Element::position)
+            overlay.as_ref().map(|nested| nested.borrow().position())
         });
 
         has_overlay.map(|position| {
@@ -503,8 +511,8 @@ struct Inner<'a, 'b, Message, Renderer, Event, S> {
     types: PhantomData<(Message, Event, S)>,
 
     #[borrows(mut instance, mut tree)]
-    #[covariant]
-    overlay: Option<overlay::Element<'this, Event, Renderer>>,
+    #[not_covariant]
+    overlay: Option<RefCell<Nested<'this, Event, Renderer>>>,
 }
 
 struct OverlayInstance<'a, 'b, Message, Renderer, Event, S> {
@@ -516,7 +524,7 @@ impl<'a, 'b, Message, Renderer, Event, S>
 {
     fn with_overlay_maybe<T>(
         &self,
-        f: impl FnOnce(&overlay::Element<'_, Event, Renderer>) -> T,
+        f: impl FnOnce(&mut Nested<'_, Event, Renderer>) -> T,
     ) -> Option<T> {
         self.overlay
             .as_ref()
@@ -524,14 +532,14 @@ impl<'a, 'b, Message, Renderer, Event, S>
             .0
             .as_ref()
             .unwrap()
-            .borrow_overlay()
-            .as_ref()
-            .map(f)
+            .with_overlay(|overlay| {
+                overlay.as_ref().map(|nested| (f)(&mut nested.borrow_mut()))
+            })
     }
 
     fn with_overlay_mut_maybe<T>(
         &mut self,
-        f: impl FnOnce(&mut overlay::Element<'_, Event, Renderer>) -> T,
+        f: impl FnOnce(&mut Nested<'_, Event, Renderer>) -> T,
     ) -> Option<T> {
         self.overlay
             .as_mut()
@@ -539,7 +547,9 @@ impl<'a, 'b, Message, Renderer, Event, S>
             .0
             .as_mut()
             .unwrap()
-            .with_overlay_mut(|overlay| overlay.as_mut().map(f))
+            .with_overlay_mut(|overlay| {
+                overlay.as_mut().map(|nested| (f)(nested.get_mut()))
+            })
     }
 }
 
@@ -556,9 +566,7 @@ where
         position: Point,
     ) -> layout::Node {
         self.with_overlay_maybe(|overlay| {
-            let translation = position - overlay.position();
-
-            overlay.layout(renderer, bounds, translation)
+            overlay.layout(renderer, bounds, position)
         })
         .unwrap_or_default()
     }
diff --git a/widget/src/lazy/responsive.rs b/widget/src/lazy/responsive.rs
index c00b8618..07300857 100644
--- a/widget/src/lazy/responsive.rs
+++ b/widget/src/lazy/responsive.rs
@@ -9,6 +9,7 @@ use crate::core::{
     self, Clipboard, Element, Length, Point, Rectangle, Shell, Size, Widget,
 };
 use crate::horizontal_space;
+use crate::runtime::overlay::Nested;
 
 use ouroboros::self_referencing;
 use std::cell::{RefCell, RefMut};
@@ -298,13 +299,13 @@ where
                 element
                     .as_widget_mut()
                     .overlay(tree, content_layout, renderer)
+                    .map(|overlay| RefCell::new(Nested::new(overlay)))
             },
         }
         .build();
 
-        let has_overlay = overlay.with_overlay(|overlay| {
-            overlay.as_ref().map(overlay::Element::position)
-        });
+        let has_overlay =
+            overlay.with_overlay_maybe(|overlay| overlay.position());
 
         has_overlay
             .map(|position| overlay::Element::new(position, Box::new(overlay)))
@@ -329,23 +330,27 @@ struct Overlay<'a, 'b, Message, Renderer> {
     types: PhantomData<Message>,
 
     #[borrows(mut content, mut tree)]
-    #[covariant]
-    overlay: Option<overlay::Element<'this, Message, Renderer>>,
+    #[not_covariant]
+    overlay: Option<RefCell<Nested<'this, Message, Renderer>>>,
 }
 
 impl<'a, 'b, Message, Renderer> Overlay<'a, 'b, Message, Renderer> {
     fn with_overlay_maybe<T>(
         &self,
-        f: impl FnOnce(&overlay::Element<'_, Message, Renderer>) -> T,
+        f: impl FnOnce(&mut Nested<'_, Message, Renderer>) -> T,
     ) -> Option<T> {
-        self.borrow_overlay().as_ref().map(f)
+        self.with_overlay(|overlay| {
+            overlay.as_ref().map(|nested| (f)(&mut nested.borrow_mut()))
+        })
     }
 
     fn with_overlay_mut_maybe<T>(
         &mut self,
-        f: impl FnOnce(&mut overlay::Element<'_, Message, Renderer>) -> T,
+        f: impl FnOnce(&mut Nested<'_, Message, Renderer>) -> T,
     ) -> Option<T> {
-        self.with_overlay_mut(|overlay| overlay.as_mut().map(f))
+        self.with_overlay_mut(|overlay| {
+            overlay.as_mut().map(|nested| (f)(nested.get_mut()))
+        })
     }
 }
 
@@ -361,9 +366,7 @@ where
         position: Point,
     ) -> layout::Node {
         self.with_overlay_maybe(|overlay| {
-            let translation = position - overlay.position();
-
-            overlay.layout(renderer, bounds, translation)
+            overlay.layout(renderer, bounds, position)
         })
         .unwrap_or_default()
     }