fix(macos): forward back/forward mouse buttons in capture and emulation (#392)

* fix(macos): forward back/forward mouse buttons in capture and emulation

OtherMouseDown/Up events on macOS carry a button number field that
distinguishes middle (2), back (3), and forward (4) buttons. The
capture backend was unconditionally mapping all OtherMouse events to
BTN_MIDDLE, silently dropping back/forward. The emulation backend had
no match arms for BTN_BACK/BTN_FORWARD, causing them to be dropped
with a warning.

Fix capture by reading MOUSE_EVENT_BUTTON_NUMBER and mapping 3->BTN_BACK,
4->BTN_FORWARD. Fix emulation by adding match arms for BTN_BACK/BTN_FORWARD
and setting MOUSE_EVENT_BUTTON_NUMBER on the emitted CGEvent so macOS
apps receive the correct button identity.

* fix(macos): track button state and double-clicks by evdev code instead of CGMouseButton

Back, forward, and middle buttons all map to CGMouseButton::Center on
macOS, which caused them to share a single pressed-state boolean and
alias in double-click detection. Replace the ButtonState struct with a
HashSet<u32> keyed by evdev button code so each button is tracked
independently.

---------

Co-authored-by: Ferdinand Schober <ferdinandschober20@gmail.com>

input-capture/src/macos.rs

@@ -18,7 +18,9 @@ use core_graphics::{
     event_source::{CGEventSource, CGEventSourceStateID},
 };
 use futures_core::Stream;
-use input_event::{BTN_LEFT, BTN_MIDDLE, BTN_RIGHT, Event, KeyboardEvent, PointerEvent};
+use input_event::{
+    BTN_BACK, BTN_FORWARD, BTN_LEFT, BTN_MIDDLE, BTN_RIGHT, Event, KeyboardEvent, PointerEvent,
+};
 use keycode::{KeyMap, KeyMapping};
 use libc::c_void;
 use once_cell::unsync::Lazy;
@@ -304,16 +306,28 @@ fn get_events(
             })))
         }
         CGEventType::OtherMouseDown => {
+            let btn_num = ev.get_integer_value_field(EventField::MOUSE_EVENT_BUTTON_NUMBER);
+            let button = match btn_num {
+                3 => BTN_BACK,
+                4 => BTN_FORWARD,
+                _ => BTN_MIDDLE,
+            };
             result.push(CaptureEvent::Input(Event::Pointer(PointerEvent::Button {
                 time: 0,
-                button: BTN_MIDDLE,
+                button,
                 state: 1,
             })))
         }
         CGEventType::OtherMouseUp => {
+            let btn_num = ev.get_integer_value_field(EventField::MOUSE_EVENT_BUTTON_NUMBER);
+            let button = match btn_num {
+                3 => BTN_BACK,
+                4 => BTN_FORWARD,
+                _ => BTN_MIDDLE,
+            };
             result.push(CaptureEvent::Input(Event::Pointer(PointerEvent::Button {
                 time: 0,
-                button: BTN_MIDDLE,
+                button,
                 state: 0,
             })))
         }

input-emulation/src/macos.rs

@@ -10,10 +10,13 @@ use core_graphics::event::{
     ScrollEventUnit,
 };
 use core_graphics::event_source::{CGEventSource, CGEventSourceStateID};
-use input_event::{BTN_LEFT, BTN_MIDDLE, BTN_RIGHT, Event, KeyboardEvent, PointerEvent, scancode};
+use input_event::{
+    BTN_BACK, BTN_FORWARD, BTN_LEFT, BTN_MIDDLE, BTN_RIGHT, Event, KeyboardEvent, PointerEvent,
+    scancode,
+};
 use keycode::{KeyMap, KeyMapping};
 use std::cell::Cell;
-use std::ops::{Index, IndexMut};
+use std::collections::HashSet;
 use std::rc::Rc;
 use std::sync::Arc;
 use std::time::{Duration, Instant};
@@ -30,10 +33,10 @@ pub(crate) struct MacOSEmulation {
     event_source: CGEventSource,
     /// task handle for key repeats
     repeat_task: Option<JoinHandle<()>>,
-    /// current state of the mouse buttons
+    /// current state of the mouse buttons (tracked by evdev button code)
-    button_state: ButtonState,
+    pressed_buttons: HashSet<u32>,
-    /// button previously pressed
+    /// button previously pressed (evdev button code)
-    previous_button: Option<CGMouseButton>,
+    previous_button: Option<u32>,
     /// timestamp of previous click (button down)
     previous_button_click: Option<Instant>,
     /// click state, i.e. number of clicks in quick succession
@@ -44,31 +47,13 @@ pub(crate) struct MacOSEmulation {
     notify_repeat_task: Arc<Notify>,
 }
 
-struct ButtonState {
+/// Maps an evdev button code to the CGEventType used for drag events.
-    left: bool,
+fn drag_event_type(button: u32) -> CGEventType {
-    right: bool,
+    match button {
-    center: bool,
+        BTN_LEFT => CGEventType::LeftMouseDragged,
-}
+        BTN_RIGHT => CGEventType::RightMouseDragged,
-
+        // middle, back, forward, and any other button all use OtherMouseDragged
-impl Index<CGMouseButton> for ButtonState {
+        _ => CGEventType::OtherMouseDragged,
-    type Output = bool;
-
-    fn index(&self, index: CGMouseButton) -> &Self::Output {
-        match index {
-            CGMouseButton::Left => &self.left,
-            CGMouseButton::Right => &self.right,
-            CGMouseButton::Center => &self.center,
-        }
-    }
-}
-
-impl IndexMut<CGMouseButton> for ButtonState {
-    fn index_mut(&mut self, index: CGMouseButton) -> &mut Self::Output {
-        match index {
-            CGMouseButton::Left => &mut self.left,
-            CGMouseButton::Right => &mut self.right,
-            CGMouseButton::Center => &mut self.center,
-        }
     }
 }
 
@@ -78,14 +63,9 @@ impl MacOSEmulation {
     pub(crate) fn new() -> Result<Self, MacOSEmulationCreationError> {
         let event_source = CGEventSource::new(CGEventSourceStateID::CombinedSessionState)
             .map_err(|_| MacOSEmulationCreationError::EventSourceCreation)?;
-        let button_state = ButtonState {
-            left: false,
-            right: false,
-            center: false,
-        };
         Ok(Self {
             event_source,
-            button_state,
+            pressed_buttons: HashSet::new(),
             previous_button: None,
             previous_button_click: None,
             button_click_state: 0,
@@ -261,14 +241,14 @@ impl Emulation for MacOSEmulation {
                         mouse_location.x = new_mouse_x;
                         mouse_location.y = new_mouse_y;
 
-                        let mut event_type = CGEventType::MouseMoved;
+                        // If any button is held, emit a drag event for it;
-                        if self.button_state.left {
+                        // otherwise emit a normal mouse-moved event.
-                            event_type = CGEventType::LeftMouseDragged
+                        let event_type = self
-                        } else if self.button_state.right {
+                            .pressed_buttons
-                            event_type = CGEventType::RightMouseDragged
+                            .iter()
-                        } else if self.button_state.center {
+                            .next()
-                            event_type = CGEventType::OtherMouseDragged
+                            .map(|&btn| drag_event_type(btn))
-                        };
+                            .unwrap_or(CGEventType::MouseMoved);
                         let event = match CGEvent::new_mouse_event(
                             self.event_source.clone(),
                             event_type,
@@ -290,6 +270,12 @@ impl Emulation for MacOSEmulation {
                         button,
                         state,
                     } => {
+                        // button number for OtherMouse events (3 = back, 4 = forward, etc.)
+                        let cg_button_number: Option<i64> = match button {
+                            BTN_BACK => Some(3),
+                            BTN_FORWARD => Some(4),
+                            _ => None,
+                        };
                         let (event_type, mouse_button) = match (button, state) {
                             (BTN_LEFT, 1) => (CGEventType::LeftMouseDown, CGMouseButton::Left),
                             (BTN_LEFT, 0) => (CGEventType::LeftMouseUp, CGMouseButton::Left),
@@ -297,17 +283,29 @@ impl Emulation for MacOSEmulation {
                             (BTN_RIGHT, 0) => (CGEventType::RightMouseUp, CGMouseButton::Right),
                             (BTN_MIDDLE, 1) => (CGEventType::OtherMouseDown, CGMouseButton::Center),
                             (BTN_MIDDLE, 0) => (CGEventType::OtherMouseUp, CGMouseButton::Center),
+                            (BTN_BACK, 1) | (BTN_FORWARD, 1) => {
+                                (CGEventType::OtherMouseDown, CGMouseButton::Center)
+                            }
+                            (BTN_BACK, 0) | (BTN_FORWARD, 0) => {
+                                (CGEventType::OtherMouseUp, CGMouseButton::Center)
+                            }
                             _ => {
                                 log::warn!("invalid button event: {button},{state}");
                                 return Ok(());
                             }
                         };
-                        // store button state
+                        // store button state using the evdev button code so
-                        self.button_state[mouse_button] = state == 1;
+                        // back, forward, and middle are tracked independently
-
-                        // update previous button state
                         if state == 1 {
-                            if self.previous_button.is_some_and(|b| b.eq(&mouse_button))
+                            self.pressed_buttons.insert(button);
+                        } else {
+                            self.pressed_buttons.remove(&button);
+                        }
+
+                        // update double-click tracking using the evdev button
+                        // code so that back/forward don't alias with middle
+                        if state == 1 {
+                            if self.previous_button == Some(button)
                                 && self
                                     .previous_button_click
                                     .is_some_and(|i| i.elapsed() < DOUBLE_CLICK_INTERVAL)
@@ -316,7 +314,7 @@ impl Emulation for MacOSEmulation {
                             } else {
                                 self.button_click_state = 1;
                             }
-                            self.previous_button = Some(mouse_button);
+                            self.previous_button = Some(button);
                             self.previous_button_click = Some(Instant::now());
                         }
 
@@ -338,6 +336,13 @@ impl Emulation for MacOSEmulation {
                             EventField::MOUSE_EVENT_CLICK_STATE,
                             self.button_click_state,
                         );
+                        // Set the button number for extra buttons (back=3, forward=4)
+                        if let Some(btn_num) = cg_button_number {
+                            event.set_integer_value_field(
+                                EventField::MOUSE_EVENT_BUTTON_NUMBER,
+                                btn_num,
+                            );
+                        }
                         event.post(CGEventTapLocation::HID);
                     }
                     PointerEvent::Axis {
@@ -448,21 +453,6 @@ impl Emulation for MacOSEmulation {
     async fn terminate(&mut self) {}
 }
 
-trait ButtonEq {
-    fn eq(&self, other: &Self) -> bool;
-}
-
-impl ButtonEq for CGMouseButton {
-    fn eq(&self, other: &Self) -> bool {
-        matches!(
-            (self, other),
-            (CGMouseButton::Left, CGMouseButton::Left)
-                | (CGMouseButton::Right, CGMouseButton::Right)
-                | (CGMouseButton::Center, CGMouseButton::Center)
-        )
-    }
-}
-
 fn update_modifiers(modifiers: &Cell<XMods>, key: u32, state: u8) -> bool {
     if let Ok(key) = scancode::Linux::try_from(key) {
         let mask = match key {