Don't discard high-precision cursor position data (#1375)

* Don't discard high-precision cursor position data

Most platforms (X11, wayland, macos, stdweb, ...) provide physical
positions in f64 units, which can contain meaningful fractional
data. For example, this can be empirically observed on modern X11
using a typical laptop touchpad. This is useful for e.g. content
creation tools, where cursor motion might map to brush strokes on a
canvas with higher-than-screen resolution, or positioning of an object
in a vector space.

* Update CHANGELOG.md

Co-Authored-By: Murarth <murarth@gmail.com>

Co-authored-by: Murarth <murarth@gmail.com>

CHANGELOG.md

@@ -3,6 +3,7 @@
 - On Windows, fix bug where `RedrawRequested` would only get emitted every other iteration of the event loop.
 - On X11, fix deadlock on window state when handling certain window events.
 - `WindowBuilder` now implements `Default`.
+- **Breaking:** `WindowEvent::CursorMoved` changed to `f64` units, preserving high-precision data supplied by most backends
 
 # 0.20.0 (2020-01-05)
 

src/event.rs

@@ -242,7 +242,7 @@ pub enum WindowEvent<'a> {
         /// (x,y) coords in pixels relative to the top-left corner of the window. Because the range of this data is
         /// limited by the display area and it may have been transformed by the OS to implement effects such as cursor
         /// acceleration, it should not be used to implement non-cursor-like interactions such as 3D camera control.
-        position: PhysicalPosition<i32>,
+        position: PhysicalPosition<f64>,
         #[deprecated = "Deprecated in favor of DeviceEvent::ModifiersChanged"]
         modifiers: ModifiersState,
     },

src/platform_impl/linux/x11/event_processor.rs

@@ -723,8 +723,7 @@ impl<T: 'static> EventProcessor<T> {
                             util::maybe_change(&mut shared_state_lock.cursor_pos, new_cursor_pos)
                         });
                         if cursor_moved == Some(true) {
-                            let position =
+                            let position = PhysicalPosition::new(xev.event_x, xev.event_y);
-                                PhysicalPosition::new(xev.event_x as i32, xev.event_y as i32);
 
                             callback(Event::WindowEvent {
                                 window_id,
@@ -830,8 +829,7 @@ impl<T: 'static> EventProcessor<T> {
                                 event: CursorEntered { device_id },
                             });
 
-                            let position =
+                            let position = PhysicalPosition::new(xev.event_x, xev.event_y);
-                                PhysicalPosition::new(xev.event_x as i32, xev.event_y as i32);
 
                             // The mods field on this event isn't actually populated, so query the
                             // pointer device. In the future, we can likely remove this round-trip by
@@ -899,8 +897,7 @@ impl<T: 'static> EventProcessor<T> {
                             .map(|device| device.attachment)
                             .unwrap_or(2);
 
-                        let position =
+                        let position = PhysicalPosition::new(xev.event_x, xev.event_y);
-                            PhysicalPosition::new(xev.event_x as i32, xev.event_y as i32);
 
                         callback(Event::WindowEvent {
                             window_id,

src/platform_impl/web/stdweb/canvas.rs

@@ -207,7 +207,7 @@ impl Canvas {
 
     pub fn on_cursor_move<F>(&mut self, mut handler: F)
     where
-        F: 'static + FnMut(i32, PhysicalPosition<i32>, ModifiersState),
+        F: 'static + FnMut(i32, PhysicalPosition<f64>, ModifiersState),
     {
         // todo
         self.on_cursor_move = Some(self.add_event(move |event: PointerMoveEvent| {

src/platform_impl/web/web_sys/canvas.rs

@@ -216,7 +216,7 @@ impl Canvas {
 
     pub fn on_cursor_move<F>(&mut self, mut handler: F)
     where
-        F: 'static + FnMut(i32, PhysicalPosition<i32>, ModifiersState),
+        F: 'static + FnMut(i32, PhysicalPosition<f64>, ModifiersState),
     {
         self.on_cursor_move = Some(self.add_event("pointermove", move |event: PointerEvent| {
             handler(

src/platform_impl/windows/event_loop.rs

@@ -855,8 +855,8 @@ unsafe extern "system" fn public_window_callback<T: 'static>(
                 });
             }
 
-            let x = windowsx::GET_X_LPARAM(lparam) as i32;
+            let x = windowsx::GET_X_LPARAM(lparam) as f64;
-            let y = windowsx::GET_Y_LPARAM(lparam) as i32;
+            let y = windowsx::GET_Y_LPARAM(lparam) as f64;
             let position = PhysicalPosition::new(x, y);
 
             subclass_input.send_event(Event::WindowEvent {