Expose area::State's Rect in Memory (#3161)

crates/egui/src/containers/area.rs

@@ -55,6 +55,8 @@ impl State {
 ///     });
 /// # });
 /// ```
+///
+/// The previous rectangle used by this area can be obtained through [`crate::Memory::area_rect()`].
 #[must_use = "You should call .show()"]
 #[derive(Clone, Copy, Debug)]
 pub struct Area {

crates/egui/src/containers/window.rs

@@ -21,6 +21,9 @@ use super::*;
 ///    ui.label("Hello World!");
 /// });
 /// # });
+/// ```
+///
+/// The previous rectangle used by this window can be obtained through [`crate::Memory::area_rect()`].
 #[must_use = "You should call .show()"]
 pub struct Window<'open> {
     title: WidgetText,

crates/egui/src/memory.rs

@@ -487,6 +487,11 @@ impl Memory {
     pub fn reset_areas(&mut self) {
         self.areas = Default::default();
     }
+
+    /// Obtain the previous rectangle of an area.
+    pub fn area_rect(&self, id: impl Into<Id>) -> Option<Rect> {
+        self.areas.get(id.into()).map(|state| state.rect())
+    }
 }
 
 /// ## Popups