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/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,
+    }
+}