Exposed a CursorPosition resource

crates/bevy_window/src/cursor.rs

@@ -1,3 +1,51 @@
+use crate::WindowId;
+use bevy_math::Vec2;
+use std::ops::Deref;
+
+#[derive(Debug, Clone, Default, Deref)]
+/// Resource storing the cursor position on the app window
+///
+/// ## Usage
+///
+/// You can use this resource to retrieve the cursor position:
+///
+/// ```rust
+/// # use bevy_window::*;
+/// # use bevy_ecs::prelude::*;
+/// #
+/// fn my_system(cursor: Res<CursorPosition>) {
+///     if let Some(pos) = cursor.position() {
+///         // Do something
+///     }   
+/// }
+/// ```
+///
+/// If you want both the position and window id you may do:
+///
+/// ```rust
+/// # use bevy_window::*;
+/// # use bevy_ecs::prelude::*;
+/// #
+/// fn my_system(cursor: Res<CursorPosition>) {
+///     if let Some((window_id, pos)) = cursor.0 {
+///         // Do something
+///     }   
+/// }
+/// ```
+pub struct CursorPosition(pub Option<(WindowId, Vec2)>);
+
+impl CursorPosition {
+    /// Retrieves the cursor position from the given [`WindowId`]
+    pub fn position(&self) -> Option<Vec2> {
+        self.0.map(|(_, p)| p)
+    }
+
+    /// Retrieves the cursor position from the *primary* window
+    pub fn window_id(&self) -> Option<WindowId> {
+        self.0.map(|(id, _)| id)
+    }
+}
+
 /// The icon to display for a window's cursor.
 ///
 /// Examples of all of these cursors can be found [here](https://www.w3schools.com/cssref/playit.asp?filename=playcss_cursor).

crates/bevy_window/src/lib.rs

@@ -47,6 +47,8 @@ pub struct WindowPlugin {
     /// If this system (or a replacement) is not running, the close button will have no effect.
     /// This may surprise your users. It is recommended to leave this setting as `true`.
     pub close_when_requested: bool,
+    /// Whether the plugin will update a [`CursorPosition`] resource every frame.
+    pub update_cursor_position: bool,
 }
 
 impl Default for WindowPlugin {
@@ -55,6 +57,7 @@ impl Default for WindowPlugin {
             add_primary_window: true,
             exit_on_all_closed: true,
             close_when_requested: true,
+            update_cursor_position: true,
         }
     }
 }
@@ -91,6 +94,11 @@ impl Plugin for WindowPlugin {
             });
         }
 
+        if self.update_cursor_position {
+            app.init_resource::<CursorPosition>();
+            app.add_system(update_cursor_position);
+        }
+
         if self.exit_on_all_closed {
             app.add_system(exit_on_all_closed);
         }

crates/bevy_window/src/system.rs

@@ -1,9 +1,16 @@
-use crate::{Window, WindowCloseRequested, WindowFocused, WindowId, Windows};
+use crate::{CursorPosition, Window, WindowCloseRequested, WindowFocused, WindowId, Windows};
 
 use bevy_app::AppExit;
 use bevy_ecs::prelude::*;
 use bevy_input::{keyboard::KeyCode, Input};
 
+/// Updates the [`CursorPositions`] resource
+pub fn update_cursor_position(mut positions: ResMut<CursorPosition>, windows: Res<Windows>) {
+    positions.0 = windows
+        .iter()
+        .find_map(|w| w.cursor_position().map(|p| (w.id(), p)));
+}
+
 /// Exit the application when there are no open windows.
 ///
 /// This system is added by the [`WindowPlugin`] in the default configuration.