x11: don't forward key events to IME when it's disabled

Fixes #3815.

src/changelog/unreleased.md

@@ -187,3 +187,4 @@ changelog entry.
 - On macOS, fix `WindowEvent::Moved` sometimes being triggered unnecessarily on resize.
 - On MacOS, package manifest definitions of `LSUIElement` will no longer be overridden with the
   default activation policy, unless explicitly provided during initialization.
+- On X11, key events forward to IME anyway, even when it's disabled.

src/platform_impl/linux/x11/event_processor.rs

@@ -142,8 +142,18 @@ impl EventProcessor {
     {
         let event_type = xev.get_type();
 
-        if self.filter_event(xev) {
-            if event_type == xlib::KeyPress || event_type == xlib::KeyRelease {
+        // If we have IME disabled, don't try to `filter_event`, since only IME can consume them
+        // and forward back. This is not desired for e.g. games since some IMEs may delay the input
+        // and game can toggle IME back when e.g. typing into some field where latency won't really
+        // matter.
+        if event_type == xlib::KeyPress || event_type == xlib::KeyRelease {
+            let ime = self.target.ime.as_ref();
+            let window = self.active_window.map(|window| window as XWindow);
+            let forward_to_ime = ime
+                .and_then(|ime| window.map(|window| ime.borrow().is_ime_allowed(window)))
+                .unwrap_or(false);
+
+            if forward_to_ime && self.filter_event(xev) {
                 let xev: &XKeyEvent = xev.as_ref();
                 if self.xmodmap.is_modifier(xev.keycode as u8) {
                     // Don't grow the buffer past the `MAX_MOD_REPLAY_LEN`. This could happen
@@ -156,7 +166,8 @@ impl EventProcessor {
                     self.xfiltered_modifiers.push_front(xev.serial);
                 }
             }
-            return;
+        } else {
+            self.filter_event(xev);
         }
 
         match event_type {

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

@@ -225,6 +225,16 @@ impl Ime {
         // Create new context supporting IME input.
         let _ = self.create_context(window, allowed);
     }
+
+    pub fn is_ime_allowed(&self, window: ffi::Window) -> bool {
+        if self.is_destroyed() {
+            false
+        } else if let Some(Some(context)) = self.inner.contexts.get(&window) {
+            context.is_allowed()
+        } else {
+            false
+        }
+    }
 }
 
 impl Drop for Ime {