Add delta to CursorMoved event

crates/bevy_window/src/event.rs

@@ -115,10 +115,13 @@ pub struct WindowDestroyed {
 /// An event reporting that the mouse cursor has moved inside a window.
 ///
 /// The event is sent only if the cursor is over one of the application's windows.
-/// It is the translated version of [`WindowEvent::CursorMoved`] from the `winit` crate.
+/// It is the translated version of [`WindowEvent::CursorMoved`] from the `winit` crate with the addition of `delta`.
 ///
 /// Not to be confused with the [`MouseMotion`] event from `bevy_input`.
 ///
+/// Because the range of data is limited by the window area and it may have been transformed by the OS to implement certain effects like acceleration,
+/// you should not use it for non-cursor-like behaviour such as 3D camera control. Please see [`MouseMotion`] instead.
+///
 /// [`WindowEvent::CursorMoved`]: https://docs.rs/winit/latest/winit/event/enum.WindowEvent.html#variant.CursorMoved
 /// [`MouseMotion`]: bevy_input::mouse::MouseMotion
 #[derive(Event, Debug, Clone, PartialEq, Reflect)]
@@ -133,6 +136,9 @@ pub struct CursorMoved {
     pub window: Entity,
     /// The cursor position in logical pixels.
     pub position: Vec2,
+    /// The change in the position of the cursor since the last event was sent.
+    /// This value is `None` if the cursor was outside the window area during the last frame.
+    pub delta: Option<Vec2>,
 }
 
 /// An event that is sent whenever the user's cursor enters a window.

crates/bevy_winit/src/lib.rs

@@ -444,10 +444,20 @@ fn handle_winit_event(
                 }
                 WindowEvent::CursorMoved { position, .. } => {
                     let physical_position = DVec2::new(position.x, position.y);
+
+                    let last_position = win.physical_cursor_position();
+                    let delta = last_position.map(|last_pos| {
+                        (physical_position.as_vec2() - last_pos) / win.resolution.scale_factor()
+                    });
+
                     win.set_physical_cursor_position(Some(physical_position));
                     let position =
                         (physical_position / win.resolution.scale_factor() as f64).as_vec2();
-                    app.send_event(CursorMoved { window, position });
+                    app.send_event(CursorMoved {
+                        window,
+                        position,
+                        delta,
+                    });
                 }
                 WindowEvent::CursorEntered { .. } => {
                     app.send_event(CursorEntered { window });