Add move_to_top and top_most_layer (#1242)

CHANGELOG.md

@@ -24,9 +24,10 @@ NOTE: [`epaint`](epaint/CHANGELOG.md), [`eframe`](eframe/CHANGELOG.md), [`egui_w
 * Added linked axis support for plots via `plot::LinkedAxisGroup` ([#1184](https://github.com/emilk/egui/pull/1184)).
 * Added `Response::on_hover_text_at_pointer` as a convenience akin to `Response::on_hover_text` ([1179](https://github.com/emilk/egui/pull/1179)).
 * Added `ui.weak(text)`.
+* Added `Context::move_to_top` and `Context::top_most_layer` for managing the layer on the top ([#1242](https://github.com/emilk/egui/pull/1242)).
 * Added plot pointer coordinates with `Plot::coordinates_formatter`. ([#1235](https://github.com/emilk/egui/pull/1235)).
 * Added `Slider::step_by` ([1255](https://github.com/emilk/egui/pull/1225)).
-* Added ability to scroll an UI into view without specifying an alignment ([1247](https://github.com/emilk/egui/pull/1247))
+* Added ability to scroll an UI into view without specifying an alignment ([1247](https://github.com/emilk/egui/pull/1247)).
 
 ### Changed 🔧
 * ⚠️ `Context::input` and `Ui::input` now locks a mutex. This can lead to a dead-lock is used in an `if let` binding!

egui/src/context.rs

@@ -889,6 +889,17 @@ impl Context {
         self.memory().layer_id_at(pos, resize_grab_radius_side)
     }
 
+    /// The overall top-most layer. When an area is clicked on or interacted
+    /// with, it is moved above all other areas.
+    pub fn top_most_layer(&self) -> Option<LayerId> {
+        self.memory().top_most_layer()
+    }
+
+    /// Moves the given area to the top.
+    pub fn move_to_top(&self, layer_id: LayerId) {
+        self.memory().areas.move_to_top(layer_id);
+    }
+
     pub(crate) fn rect_contains_pointer(&self, layer_id: LayerId, rect: Rect) -> bool {
         let pointer_pos = self.input().pointer.interact_pos();
         if let Some(pointer_pos) = pointer_pos {

egui/src/memory.rs

@@ -329,6 +329,12 @@ impl Memory {
         self.areas.layer_id_at(pos, resize_interact_radius_side)
     }
 
+    /// The overall top-most layer. When an area is clicked on or interacted
+    /// with, it is moved above all other areas.
+    pub fn top_most_layer(&self) -> Option<LayerId> {
+        self.areas.order().last().copied()
+    }
+
     pub(crate) fn had_focus_last_frame(&self, id: Id) -> bool {
         self.interaction.focus.id_previous_frame == Some(id)
     }