Fix scale factor for cursor position (#2932)

# Objective

- Fixes #2501 
- Builds up on #2639 taking https://github.com/bevyengine/bevy/pull/2639#issuecomment-898701047 into account

## Solution

- keep the physical cursor position in `Window`, and expose it.
- still convert to logical position in event, and when getting `cursor_position`


Co-authored-by: Ahmed Charles <acharles@outlook.com>

crates/bevy_window/src/window.rs

@@ -1,4 +1,4 @@
-use bevy_math::{IVec2, Vec2};
+use bevy_math::{DVec2, IVec2, Vec2};
 use bevy_utils::{tracing::warn, Uuid};
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
@@ -122,7 +122,7 @@ pub struct Window {
     decorations: bool,
     cursor_visible: bool,
     cursor_locked: bool,
-    cursor_position: Option<Vec2>,
+    physical_cursor_position: Option<DVec2>,
     focused: bool,
     mode: WindowMode,
     #[cfg(target_arch = "wasm32")]
@@ -215,7 +215,7 @@ impl Window {
             decorations: window_descriptor.decorations,
             cursor_visible: window_descriptor.cursor_visible,
             cursor_locked: window_descriptor.cursor_locked,
-            cursor_position: None,
+            physical_cursor_position: None,
             focused: true,
             mode: window_descriptor.mode,
             #[cfg(target_arch = "wasm32")]
@@ -466,10 +466,18 @@ impl Window {
         });
     }
 
+    /// The current mouse position, in physical pixels.
+    #[inline]
+    pub fn physical_cursor_position(&self) -> Option<DVec2> {
+        self.physical_cursor_position
+    }
+
+    /// The current mouse position, in logical pixels, taking into account the screen scale factor.
     #[inline]
     #[doc(alias = "mouse position")]
     pub fn cursor_position(&self) -> Option<Vec2> {
-        self.cursor_position
+        self.physical_cursor_position
+            .map(|p| (p / self.scale_factor()).as_vec2())
     }
 
     pub fn set_cursor_position(&mut self, position: Vec2) {
@@ -485,8 +493,8 @@ impl Window {
 
     #[allow(missing_docs)]
     #[inline]
-    pub fn update_cursor_position_from_backend(&mut self, cursor_position: Option<Vec2>) {
-        self.cursor_position = cursor_position;
+    pub fn update_cursor_physical_position_from_backend(&mut self, cursor_position: Option<DVec2>) {
+        self.physical_cursor_position = cursor_position;
     }
 
     #[inline]

crates/bevy_winit/src/lib.rs

@@ -12,7 +12,7 @@ pub use winit_windows::*;
 
 use bevy_app::{App, AppExit, CoreStage, Events, ManualEventReader, Plugin};
 use bevy_ecs::{system::IntoExclusiveSystem, world::World};
-use bevy_math::{ivec2, Vec2};
+use bevy_math::{ivec2, DVec2, Vec2};
 use bevy_utils::tracing::{error, trace, warn};
 use bevy_window::{
     CreateWindow, CursorEntered, CursorLeft, CursorMoved, FileDragAndDrop, ReceivedCharacter,
@@ -303,20 +303,18 @@ pub fn winit_runner_with(mut app: App, mut event_loop: EventLoop<()>) {
                         let mut cursor_moved_events =
                             world.get_resource_mut::<Events<CursorMoved>>().unwrap();
                         let winit_window = winit_windows.get_window(window_id).unwrap();
-                        let position = position.to_logical(winit_window.scale_factor());
-                        let inner_size = winit_window
-                            .inner_size()
-                            .to_logical::<f32>(winit_window.scale_factor());
+                        let inner_size = winit_window.inner_size();
 
                         // move origin to bottom left
-                        let y_position = inner_size.height - position.y;
+                        let y_position = inner_size.height as f64 - position.y;
 
-                        let position = Vec2::new(position.x, y_position);
-                        window.update_cursor_position_from_backend(Some(position));
+                        let physical_position = DVec2::new(position.x, y_position);
+                        window
+                            .update_cursor_physical_position_from_backend(Some(physical_position));
 
                         cursor_moved_events.send(CursorMoved {
                             id: window_id,
-                            position,
+                            position: (physical_position / window.scale_factor()).as_vec2(),
                         });
                     }
                     WindowEvent::CursorEntered { .. } => {
@@ -327,7 +325,7 @@ pub fn winit_runner_with(mut app: App, mut event_loop: EventLoop<()>) {
                     WindowEvent::CursorLeft { .. } => {
                         let mut cursor_left_events =
                             world.get_resource_mut::<Events<CursorLeft>>().unwrap();
-                        window.update_cursor_position_from_backend(None);
+                        window.update_cursor_physical_position_from_backend(None);
                         cursor_left_events.send(CursorLeft { id: window_id });
                     }
                     WindowEvent::MouseInput { state, button, .. } => {
@@ -363,8 +361,7 @@ pub fn winit_runner_with(mut app: App, mut event_loop: EventLoop<()>) {
                         let mut touch_input_events =
                             world.get_resource_mut::<Events<TouchInput>>().unwrap();
 
-                        let winit_window = winit_windows.get_window(window_id).unwrap();
-                        let mut location = touch.location.to_logical(winit_window.scale_factor());
+                        let mut location = touch.location.to_logical(window.scale_factor());
 
                         // On a mobile window, the start is from the top while on PC/Linux/OSX from
                         // bottom