Expose winit always_on_top

Cargo.toml

@@ -1503,6 +1503,17 @@ category = "UI (User Interface)"
 wasm = true
 
 # Window
+[[example]]
+name = "always_on_top"
+path = "examples/window/always_on_top.rs"
+
+[package.metadata.example.always_on_top]
+name = "Always On Top"
+description = "A Window which is always over other windows."
+category = "Window"
+wasm = false
+
+
 [[example]]
 name = "clear_color"
 path = "examples/window/clear_color.rs"

crates/bevy_window/src/window.rs

@@ -972,6 +972,12 @@ pub struct WindowDescriptor {
     pub fit_canvas_to_parent: bool,
     /// Specifies how the alpha channel of the textures should be handled during compositing.
     pub alpha_mode: CompositeAlphaMode,
+    /// Sets the window to always be on top of other windows.
+    ///
+    /// ## Platform-specific
+    /// - iOS / Android / Web: Unsupported.
+    /// - Linux (Wayland): Unsupported.
+    pub always_on_top: bool,
 }
 
 impl Default for WindowDescriptor {
@@ -994,6 +1000,7 @@ impl Default for WindowDescriptor {
             canvas: None,
             fit_canvas_to_parent: false,
             alpha_mode: CompositeAlphaMode::Auto,
+            always_on_top: false,
         }
     }
 }

crates/bevy_winit/src/winit_windows.rs

@@ -72,7 +72,8 @@ impl WinitWindows {
             }
             .with_resizable(window_descriptor.resizable)
             .with_decorations(window_descriptor.decorations)
-            .with_transparent(window_descriptor.transparent),
+            .with_transparent(window_descriptor.transparent)
+            .with_always_on_top(window_descriptor.always_on_top),
         };
 
         let constraints = window_descriptor.resize_constraints.check_constraints();

examples/window/always_on_top.rs

@@ -0,0 +1,29 @@
+//! Shows how to display a window in transparent mode.
+//!
+//! This feature works as expected depending on the platform. Please check the
+//! [documentation](https://docs.rs/bevy/latest/bevy/prelude/struct.WindowDescriptor.html#structfield.transparent)
+//! for more details.
+
+use bevy::prelude::*;
+
+fn main() {
+    App::new()
+        .add_startup_system(setup)
+        .add_plugins(DefaultPlugins.set(WindowPlugin {
+            window: WindowDescriptor {
+                // Set always_on_top to force the window to stay on top of other windows.
+                always_on_top: true,
+                ..default()
+            },
+            ..default()
+        }))
+        .run();
+}
+
+fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
+    commands.spawn(Camera2dBundle::default());
+    commands.spawn(SpriteBundle {
+        texture: asset_server.load("branding/icon.png"),
+        ..default()
+    });
+}