Fix Overlay composition

Translations were not easily composable.

core/src/overlay.rs

@@ -11,7 +11,7 @@ use crate::mouse;
 use crate::renderer;
 use crate::widget;
 use crate::widget::Tree;
-use crate::{Clipboard, Layout, Point, Rectangle, Shell, Size};
+use crate::{Clipboard, Layout, Point, Rectangle, Shell, Size, Vector};
 
 /// An interactive component that can be displayed on top of other widgets.
 pub trait Overlay<Message, Renderer>
@@ -29,6 +29,7 @@ where
         renderer: &Renderer,
         bounds: Size,
         position: Point,
+        translation: Vector,
     ) -> layout::Node;
 
     /// Draws the [`Overlay`] using the associated `Renderer`.

core/src/overlay/element.rs

@@ -13,6 +13,7 @@ use std::any::Any;
 #[allow(missing_debug_implementations)]
 pub struct Element<'a, Message, Renderer> {
     position: Point,
+    translation: Vector,
     overlay: Box<dyn Overlay<Message, Renderer> + 'a>,
 }
 
@@ -25,7 +26,11 @@ where
         position: Point,
         overlay: Box<dyn Overlay<Message, Renderer> + 'a>,
     ) -> Self {
-        Self { position, overlay }
+        Self {
+            position,
+            overlay,
+            translation: Vector::ZERO,
+        }
     }
 
     /// Returns the position of the [`Element`].
@@ -36,6 +41,7 @@ where
     /// Translates the [`Element`].
     pub fn translate(mut self, translation: Vector) -> Self {
         self.position = self.position + translation;
+        self.translation = self.translation + translation;
         self
     }
 
@@ -48,6 +54,7 @@ where
     {
         Element {
             position: self.position,
+            translation: self.translation,
             overlay: Box::new(Map::new(self.overlay, f)),
         }
     }
@@ -59,8 +66,12 @@ where
         bounds: Size,
         translation: Vector,
     ) -> layout::Node {
-        self.overlay
-            .layout(renderer, bounds, self.position + translation)
+        self.overlay.layout(
+            renderer,
+            bounds,
+            self.position + translation,
+            self.translation + translation,
+        )
     }
 
     /// Processes a runtime [`Event`].
@@ -154,8 +165,9 @@ where
         renderer: &Renderer,
         bounds: Size,
         position: Point,
+        translation: Vector,
     ) -> layout::Node {
-        self.content.layout(renderer, bounds, position)
+        self.content.layout(renderer, bounds, position, translation)
     }
 
     fn operate(

core/src/overlay/group.rs

@@ -4,7 +4,9 @@ use crate::mouse;
 use crate::overlay;
 use crate::renderer;
 use crate::widget;
-use crate::{Clipboard, Event, Layout, Overlay, Point, Rectangle, Shell, Size};
+use crate::{
+    Clipboard, Event, Layout, Overlay, Point, Rectangle, Shell, Size, Vector,
+};
 
 /// An [`Overlay`] container that displays multiple overlay [`overlay::Element`]
 /// children.
@@ -64,10 +66,9 @@ where
         &mut self,
         renderer: &Renderer,
         bounds: Size,
-        position: Point,
+        _position: Point,
+        translation: Vector,
     ) -> layout::Node {
-        let translation = position - Point::ORIGIN;
-
         layout::Node::with_children(
             bounds,
             self.children