Web: fix MouseMotion coordinate space (#3770)

Cargo.toml

@@ -302,6 +302,7 @@ web_sys = { package = "web-sys", version = "0.3.64", features = [
     'MediaQueryList',
     'MessageChannel',
     'MessagePort',
+    'Navigator',
     'Node',
     'PageTransitionEvent',
     'PointerEvent',

src/changelog/unreleased.md

@@ -56,7 +56,6 @@ changelog entry.
   to send specific data to be processed on the main thread.
 - Changed `EventLoopProxy::send_event` to `EventLoopProxy::wake_up`, it now
   only wakes up the loop.
-- On Web, slightly improve accuracy of `DeviceEvent::MouseMotion`.
 - `ApplicationHandler::create|destroy_surfaces()` was split off from
   `ApplicationHandler::resumed/suspended()`.
 
@@ -80,3 +79,4 @@ changelog entry.
 ### Fixed
 
 - On Wayland, avoid crashing when compositor is misbehaving.
+- Account for different browser engine implementations of pointer movement coordinate space.

src/platform_impl/web/event_loop/runner.rs

@@ -234,7 +234,7 @@ impl Shared {
         ));
 
         let runner = self.clone();
-        let mut delta = backend::event::MouseDelta::new();
+        let window = self.window().clone();
         *self.0.on_mouse_move.borrow_mut() = Some(EventListenerHandle::new(
             self.window().clone(),
             "pointermove",
@@ -273,26 +273,23 @@ impl Shared {
                 }
 
                 // pointer move event
+                let mut delta = backend::event::MouseDelta::init(&window, &event);
                 runner.send_events(backend::event::pointer_move_event(event).flat_map(|event| {
-                    let delta = delta.delta(&event);
+                    let delta = delta.delta(&event).to_physical(backend::scale_factor(&window));
 
-                    if delta.x == 0 && delta.y == 0 {
-                        return None.into_iter().chain(None).chain(None);
-                    }
-
-                    let x_motion = (delta.x != 0).then_some(Event::DeviceEvent {
+                    let x_motion = (delta.x != 0.0).then_some(Event::DeviceEvent {
                         device_id,
-                        event: DeviceEvent::Motion { axis: 0, value: delta.x.into() },
+                        event: DeviceEvent::Motion { axis: 0, value: delta.x },
                     });
 
-                    let y_motion = (delta.y != 0).then_some(Event::DeviceEvent {
+                    let y_motion = (delta.y != 0.0).then_some(Event::DeviceEvent {
                         device_id,
-                        event: DeviceEvent::Motion { axis: 1, value: delta.y.into() },
+                        event: DeviceEvent::Motion { axis: 1, value: delta.y },
                     });
 
-                    x_motion.into_iter().chain(y_motion).chain(Some(Event::DeviceEvent {
+                    x_motion.into_iter().chain(y_motion).chain(iter::once(Event::DeviceEvent {
                         device_id,
-                        event: DeviceEvent::MouseMotion { delta: (delta.x.into(), delta.y.into()) },
+                        event: DeviceEvent::MouseMotion { delta: (delta.x, delta.y) },
                     }))
                 }));
             }),

src/platform_impl/web/web_sys/event.rs

@@ -1,13 +1,15 @@
 use crate::event::{MouseButton, MouseScrollDelta};
 use crate::keyboard::{Key, KeyLocation, ModifiersState, NamedKey, PhysicalKey};
 
-use dpi::{LogicalPosition, PhysicalPosition};
+use dpi::{LogicalPosition, PhysicalPosition, Position};
 use smol_str::SmolStr;
 use std::cell::OnceCell;
 use wasm_bindgen::prelude::wasm_bindgen;
 use wasm_bindgen::{JsCast, JsValue};
 use web_sys::{KeyboardEvent, MouseEvent, PointerEvent, WheelEvent};
 
+use super::Engine;
+
 bitflags::bitflags! {
     // https://www.w3.org/TR/pointerevents3/#the-buttons-property
     #[derive(Debug, Clone, Copy, PartialEq, Eq)]
@@ -95,23 +97,48 @@ pub fn mouse_position(event: &MouseEvent) -> LogicalPosition<f64> {
     LogicalPosition { x: event.offset_x(), y: event.offset_y() }
 }
 
-pub struct MouseDelta(Option<PhysicalPosition<i32>>);
+// TODO: Remove this when Firefox supports correct movement values in coalesced events and browsers
+// have agreed on what coordinate space `movementX/Y` is using.
+// See <https://bugzilla.mozilla.org/show_bug.cgi?id=1753724>.
+// See <https://github.com/w3c/pointerlock/issues/42>.
+pub enum MouseDelta {
+    Chromium,
+    Gecko { old_position: LogicalPosition<f64>, old_delta: LogicalPosition<f64> },
+    Other,
+}
 
 impl MouseDelta {
-    pub fn new() -> Self {
-        Self(None)
+    pub fn init(window: &web_sys::Window, event: &PointerEvent) -> Self {
+        match super::engine(window) {
+            Some(Engine::Chromium) => Self::Chromium,
+            // Firefox has wrong movement values in coalesced events.
+            Some(Engine::Gecko) if has_coalesced_events_support(event) => Self::Gecko {
+                old_position: mouse_position(event),
+                old_delta: LogicalPosition::new(
+                    event.movement_x() as f64,
+                    event.movement_y() as f64,
+                ),
+            },
+            _ => Self::Other,
+        }
     }
 
-    pub fn delta(&mut self, event: &MouseEvent) -> PhysicalPosition<i32> {
-        let new = PhysicalPosition::new(event.screen_x(), event.screen_y());
-
-        if let Some(old) = self.0 {
-            let delta = PhysicalPosition::new(new.x - old.x, new.y - old.y);
-            self.0 = Some(new);
-            delta
-        } else {
-            self.0 = Some(new);
-            PhysicalPosition::default()
+    pub fn delta(&mut self, event: &MouseEvent) -> Position {
+        match self {
+            MouseDelta::Chromium => {
+                PhysicalPosition::new(event.movement_x(), event.movement_y()).into()
+            },
+            MouseDelta::Gecko { old_position, old_delta } => {
+                let new_position = mouse_position(event);
+                let x = new_position.x - old_position.x + old_delta.x;
+                let y = new_position.y - old_position.y + old_delta.y;
+                *old_position = new_position;
+                *old_delta = LogicalPosition::new(0., 0.);
+                LogicalPosition::new(x, y).into()
+            },
+            MouseDelta::Other => {
+                LogicalPosition::new(event.movement_x(), event.movement_y()).into()
+            },
         }
     }
 }

src/platform_impl/web/web_sys/mod.rs

@@ -9,6 +9,8 @@ mod pointer;
 mod resize_scaling;
 mod schedule;
 
+use std::sync::OnceLock;
+
 pub use self::canvas::{Canvas, Style};
 pub use self::event::ButtonsState;
 pub use self::event_handle::EventListenerHandle;
@@ -16,8 +18,13 @@ pub use self::resize_scaling::ResizeScaleHandle;
 pub use self::schedule::Schedule;
 
 use crate::dpi::{LogicalPosition, LogicalSize};
+use js_sys::Array;
 use wasm_bindgen::closure::Closure;
-use web_sys::{Document, HtmlCanvasElement, PageTransitionEvent, VisibilityState};
+use wasm_bindgen::prelude::wasm_bindgen;
+use wasm_bindgen::JsCast;
+use web_sys::{
+    Document, HtmlCanvasElement, Navigator, PageTransitionEvent, VisibilityState, Window,
+};
 
 pub fn throw(msg: &str) {
     wasm_bindgen::throw_str(msg);
@@ -158,3 +165,69 @@ pub fn is_visible(document: &Document) -> bool {
 }
 
 pub type RawCanvasType = HtmlCanvasElement;
+
+#[derive(Clone, Copy)]
+pub enum Engine {
+    Chromium,
+    Gecko,
+    WebKit,
+}
+
+pub fn engine(window: &Window) -> Option<Engine> {
+    static ENGINE: OnceLock<Option<Engine>> = OnceLock::new();
+
+    #[wasm_bindgen]
+    extern "C" {
+        #[wasm_bindgen(extends = Navigator)]
+        type NavigatorExt;
+
+        #[wasm_bindgen(method, getter, js_name = userAgentData)]
+        fn user_agent_data(this: &NavigatorExt) -> Option<NavigatorUaData>;
+
+        type NavigatorUaData;
+
+        #[wasm_bindgen(method, getter)]
+        fn brands(this: &NavigatorUaData) -> Array;
+
+        type NavigatorUaBrandVersion;
+
+        #[wasm_bindgen(method, getter)]
+        fn brand(this: &NavigatorUaBrandVersion) -> String;
+    }
+
+    *ENGINE.get_or_init(|| {
+        let navigator: NavigatorExt = window.navigator().unchecked_into();
+
+        if let Some(data) = navigator.user_agent_data() {
+            for brand in data
+                .brands()
+                .iter()
+                .map(NavigatorUaBrandVersion::unchecked_from_js)
+                .map(|brand| brand.brand())
+            {
+                match brand.as_str() {
+                    "Chromium" => return Some(Engine::Chromium),
+                    // TODO: verify when Firefox actually implements it.
+                    "Gecko" => return Some(Engine::Gecko),
+                    // TODO: verify when Safari actually implements it.
+                    "WebKit" => return Some(Engine::WebKit),
+                    _ => (),
+                }
+            }
+
+            None
+        } else {
+            let data = navigator.user_agent().ok()?;
+
+            if data.contains("Chrome/") {
+                Some(Engine::Chromium)
+            } else if data.contains("Gecko/") {
+                Some(Engine::Gecko)
+            } else if data.contains("AppleWebKit/") {
+                Some(Engine::WebKit)
+            } else {
+                None
+            }
+        }
+    })
+}