Implement WindowEvent ModifiersChanged for X11 and Wayland (#1132)

* Implement WindowEvent ModifiersChanged for X11 and Wayland

* Fix modifier key state desync on X11

* Run cargo fmt

src/event.rs

@@ -133,6 +133,9 @@ pub enum WindowEvent {
         input: KeyboardInput,
     },
 
+    /// Keyboard modifiers have changed
+    ModifiersChanged { modifiers: ModifiersState },
+
     /// The cursor has moved on the window.
     CursorMoved {
         device_id: DeviceId,

src/platform_impl/linux/wayland/keyboard.rs

@@ -83,7 +83,17 @@ pub fn init_keyboard(
                 KbEvent::RepeatInfo { .. } => { /* Handled by smithay client toolkit */ }
                 KbEvent::Modifiers {
                     modifiers: event_modifiers,
-                } => *modifiers_tracker.lock().unwrap() = event_modifiers.into(),
+                } => {
+                    let modifiers = event_modifiers.into();
+
+                    *modifiers_tracker.lock().unwrap() = modifiers;
+
+                    if let Some(wid) = *target.lock().unwrap() {
+                        my_sink
+                            .send((WindowEvent::ModifiersChanged { modifiers }, wid))
+                            .unwrap();
+                    }
+                }
             }
         },
         move |repeat_event: KeyRepeatEvent, _| {

src/platform_impl/linux/x11/event_processor.rs

@@ -8,6 +8,8 @@ use super::{
     XExtension,
 };
 
+use util::modifiers::{ModifierKeyState, ModifierKeymap};
+
 use crate::{
     dpi::{LogicalPosition, LogicalSize},
     event::{DeviceEvent, Event, KeyboardInput, ModifiersState, WindowEvent},
@@ -21,6 +23,9 @@ pub(super) struct EventProcessor<T: 'static> {
     pub(super) devices: RefCell<HashMap<DeviceId, Device>>,
     pub(super) xi2ext: XExtension,
     pub(super) target: Rc<RootELW<T>>,
+    pub(super) mod_keymap: ModifierKeymap,
+    pub(super) device_mod_state: ModifierKeyState,
+    pub(super) window_mod_state: ModifierKeyState,
 }
 
 impl<T: 'static> EventProcessor<T> {
@@ -112,12 +117,22 @@ impl<T: 'static> EventProcessor<T> {
         let event_type = xev.get_type();
         match event_type {
             ffi::MappingNotify => {
-                unsafe {
-                    (wt.xconn.xlib.XRefreshKeyboardMapping)(xev.as_mut());
+                let mapping: &ffi::XMappingEvent = xev.as_ref();
+
+                if mapping.request == ffi::MappingModifier
+                    || mapping.request == ffi::MappingKeyboard
+                {
+                    unsafe {
+                        (wt.xconn.xlib.XRefreshKeyboardMapping)(xev.as_mut());
+                    }
+                    wt.xconn
+                        .check_errors()
+                        .expect("Failed to call XRefreshKeyboardMapping");
+
+                    self.mod_keymap.reset_from_x_connection(&wt.xconn);
+                    self.device_mod_state.update(&self.mod_keymap);
+                    self.window_mod_state.update(&self.mod_keymap);
                 }
-                wt.xconn
-                    .check_errors()
-                    .expect("Failed to call XRefreshKeyboardMapping");
             }
 
             ffi::ClientMessage => {
@@ -514,13 +529,6 @@ impl<T: 'static> EventProcessor<T> {
                 // When a compose sequence or IME pre-edit is finished, it ends in a KeyPress with
                 // a keycode of 0.
                 if xkev.keycode != 0 {
-                    let modifiers = ModifiersState {
-                        alt: xkev.state & ffi::Mod1Mask != 0,
-                        shift: xkev.state & ffi::ShiftMask != 0,
-                        ctrl: xkev.state & ffi::ControlMask != 0,
-                        logo: xkev.state & ffi::Mod4Mask != 0,
-                    };
-
                     let keysym = unsafe {
                         let mut keysym = 0;
                         (wt.xconn.xlib.XLookupString)(
@@ -535,6 +543,8 @@ impl<T: 'static> EventProcessor<T> {
                     };
                     let virtual_keycode = events::keysym_to_element(keysym as c_uint);
 
+                    let modifiers = self.window_mod_state.modifiers();
+
                     callback(Event::WindowEvent {
                         window_id,
                         event: WindowEvent::KeyboardInput {
@@ -547,6 +557,27 @@ impl<T: 'static> EventProcessor<T> {
                             },
                         },
                     });
+
+                    if let Some(modifier) =
+                        self.mod_keymap.get_modifier(xkev.keycode as ffi::KeyCode)
+                    {
+                        self.window_mod_state.key_event(
+                            state,
+                            xkev.keycode as ffi::KeyCode,
+                            modifier,
+                        );
+
+                        let new_modifiers = self.window_mod_state.modifiers();
+
+                        if modifiers != new_modifiers {
+                            callback(Event::WindowEvent {
+                                window_id,
+                                event: WindowEvent::ModifiersChanged {
+                                    modifiers: new_modifiers,
+                                },
+                            });
+                        }
+                    }
                 }
 
                 if state == Pressed {
@@ -859,6 +890,21 @@ impl<T: 'static> EventProcessor<T> {
                             event: Focused(true),
                         });
 
+                        // When focus is gained, send any existing modifiers
+                        // to the window in a ModifiersChanged event. This is
+                        // done to compensate for modifier keys that may be
+                        // changed while a window is out of focus.
+                        if !self.device_mod_state.is_empty() {
+                            self.window_mod_state = self.device_mod_state.clone();
+
+                            let modifiers = self.window_mod_state.modifiers();
+
+                            callback(Event::WindowEvent {
+                                window_id,
+                                event: WindowEvent::ModifiersChanged { modifiers },
+                            });
+                        }
+
                         // The deviceid for this event is for a keyboard instead of a pointer,
                         // so we have to do a little extra work.
                         let pointer_id = self
@@ -890,6 +936,22 @@ impl<T: 'static> EventProcessor<T> {
                             .borrow_mut()
                             .unfocus(xev.event)
                             .expect("Failed to unfocus input context");
+
+                        // When focus is lost, send a ModifiersChanged event
+                        // containing no modifiers set. This is done to compensate
+                        // for modifier keys that may be changed while a window
+                        // is out of focus.
+                        if !self.window_mod_state.is_empty() {
+                            self.window_mod_state.clear();
+
+                            callback(Event::WindowEvent {
+                                window_id: mkwid(xev.event),
+                                event: WindowEvent::ModifiersChanged {
+                                    modifiers: ModifiersState::default(),
+                                },
+                            });
+                        }
+
                         callback(Event::WindowEvent {
                             window_id: mkwid(xev.event),
                             event: Focused(false),
@@ -1022,18 +1084,25 @@ impl<T: 'static> EventProcessor<T> {
 
                         let virtual_keycode = events::keysym_to_element(keysym as c_uint);
 
+                        if let Some(modifier) =
+                            self.mod_keymap.get_modifier(keycode as ffi::KeyCode)
+                        {
+                            self.device_mod_state.key_event(
+                                state,
+                                keycode as ffi::KeyCode,
+                                modifier,
+                            );
+                        }
+
+                        let modifiers = self.device_mod_state.modifiers();
+
                         callback(Event::DeviceEvent {
                             device_id: mkdid(device_id),
                             event: DeviceEvent::Key(KeyboardInput {
                                 scancode,
                                 virtual_keycode,
                                 state,
-                                // So, in an ideal world we can use libxkbcommon to get modifiers.
-                                // However, libxkbcommon-x11 isn't as commonly installed as one
-                                // would hope. We can still use the Xkb extension to get
-                                // comprehensive keyboard state updates, but interpreting that
-                                // info manually is going to be involved.
-                                modifiers: ModifiersState::default(),
+                                modifiers,
                             }),
                         });
                     }

src/platform_impl/linux/x11/mod.rs

@@ -34,6 +34,7 @@ use self::{
     dnd::{Dnd, DndState},
     event_processor::EventProcessor,
     ime::{Ime, ImeCreationError, ImeReceiver, ImeSender},
+    util::modifiers::ModifierKeymap,
 };
 use crate::{
     error::OsError as RootOsError,
@@ -143,6 +144,9 @@ impl<T: 'static> EventLoop<T> {
 
         xconn.update_cached_wm_info(root);
 
+        let mut mod_keymap = ModifierKeymap::new();
+        mod_keymap.reset_from_x_connection(&xconn);
+
         let target = Rc::new(RootELW {
             p: super::EventLoopWindowTarget::X(EventLoopWindowTarget {
                 ime,
@@ -186,6 +190,9 @@ impl<T: 'static> EventLoop<T> {
             randr_event_offset,
             ime_receiver,
             xi2ext,
+            mod_keymap,
+            device_mod_state: Default::default(),
+            window_mod_state: Default::default(),
         };
 
         // Register for device hotplug events

src/platform_impl/linux/x11/util/mod.rs

@@ -10,6 +10,7 @@ mod hint;
 mod icon;
 mod input;
 mod memory;
+pub mod modifiers;
 mod randr;
 mod window_property;
 mod wm;

src/platform_impl/linux/x11/util/modifiers.rs

@@ -0,0 +1,149 @@
+use std::{collections::HashMap, slice};
+
+use super::*;
+
+use crate::event::{ElementState, ModifiersState};
+
+// Offsets within XModifierKeymap to each set of keycodes.
+// We are only interested in Shift, Control, Alt, and Logo.
+//
+// There are 8 sets total. The order of keycode sets is:
+//     Shift, Lock, Control, Mod1 (Alt), Mod2, Mod3, Mod4 (Logo), Mod5
+//
+// https://tronche.com/gui/x/xlib/input/XSetModifierMapping.html
+const SHIFT_OFFSET: usize = 0;
+const CONTROL_OFFSET: usize = 2;
+const ALT_OFFSET: usize = 3;
+const LOGO_OFFSET: usize = 6;
+const NUM_MODS: usize = 8;
+
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+pub enum Modifier {
+    Alt,
+    Ctrl,
+    Shift,
+    Logo,
+}
+
+#[derive(Debug, Default)]
+pub struct ModifierKeymap {
+    // Maps keycodes to modifiers
+    keys: HashMap<ffi::KeyCode, Modifier>,
+}
+
+#[derive(Clone, Debug, Default)]
+pub struct ModifierKeyState {
+    // Contains currently pressed modifier keys and their corresponding modifiers
+    keys: HashMap<ffi::KeyCode, Modifier>,
+}
+
+impl ModifierKeymap {
+    pub fn new() -> ModifierKeymap {
+        ModifierKeymap::default()
+    }
+
+    pub fn get_modifier(&self, keycode: ffi::KeyCode) -> Option<Modifier> {
+        self.keys.get(&keycode).cloned()
+    }
+
+    pub fn reset_from_x_connection(&mut self, xconn: &XConnection) {
+        unsafe {
+            let keymap = (xconn.xlib.XGetModifierMapping)(xconn.display);
+
+            if keymap.is_null() {
+                panic!("failed to allocate XModifierKeymap");
+            }
+
+            self.reset_from_x_keymap(&*keymap);
+
+            (xconn.xlib.XFreeModifiermap)(keymap);
+        }
+    }
+
+    pub fn reset_from_x_keymap(&mut self, keymap: &ffi::XModifierKeymap) {
+        let keys_per_mod = keymap.max_keypermod as usize;
+
+        let keys = unsafe {
+            slice::from_raw_parts(keymap.modifiermap as *const _, keys_per_mod * NUM_MODS)
+        };
+
+        self.keys.clear();
+
+        self.read_x_keys(keys, SHIFT_OFFSET, keys_per_mod, Modifier::Shift);
+        self.read_x_keys(keys, CONTROL_OFFSET, keys_per_mod, Modifier::Ctrl);
+        self.read_x_keys(keys, ALT_OFFSET, keys_per_mod, Modifier::Alt);
+        self.read_x_keys(keys, LOGO_OFFSET, keys_per_mod, Modifier::Logo);
+    }
+
+    fn read_x_keys(
+        &mut self,
+        keys: &[ffi::KeyCode],
+        offset: usize,
+        keys_per_mod: usize,
+        modifier: Modifier,
+    ) {
+        let start = offset * keys_per_mod;
+        let end = start + keys_per_mod;
+
+        for &keycode in &keys[start..end] {
+            if keycode != 0 {
+                self.keys.insert(keycode, modifier);
+            }
+        }
+    }
+}
+
+impl ModifierKeyState {
+    pub fn clear(&mut self) {
+        self.keys.clear();
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.keys.is_empty()
+    }
+
+    pub fn update(&mut self, mods: &ModifierKeymap) {
+        self.keys.retain(|k, v| {
+            if let Some(m) = mods.get_modifier(*k) {
+                *v = m;
+                true
+            } else {
+                false
+            }
+        });
+    }
+
+    pub fn modifiers(&self) -> ModifiersState {
+        let mut state = ModifiersState::default();
+
+        for &m in self.keys.values() {
+            set_modifier(&mut state, m);
+        }
+
+        state
+    }
+
+    pub fn key_event(&mut self, state: ElementState, keycode: ffi::KeyCode, modifier: Modifier) {
+        match state {
+            ElementState::Pressed => self.key_press(keycode, modifier),
+            ElementState::Released => self.key_release(keycode),
+        }
+    }
+
+    pub fn key_press(&mut self, keycode: ffi::KeyCode, modifier: Modifier) {
+        self.keys.insert(keycode, modifier);
+    }
+
+    pub fn key_release(&mut self, keycode: ffi::KeyCode) {
+        self.keys.remove(&keycode);
+    }
+}
+
+fn set_modifier(state: &mut ModifiersState, modifier: Modifier) {
+    match modifier {
+        Modifier::Alt => state.alt = true,
+        Modifier::Ctrl => state.ctrl = true,
+        Modifier::Shift => state.shift = true,
+        Modifier::Logo => state.logo = true,
+    }
+}