x11: Implement true cursor area with XNArea attribute

src/changelog/unreleased.md

@@ -130,6 +130,7 @@ changelog entry.
   - `Window::request_inner_size` to `request_surface_size`.
   - `Window::set_min_inner_size` to `set_min_surface_size`.
   - `Window::set_max_inner_size` to `set_max_surface_size`.
+- On X11, set an "area" attribute on XIM input connection to convey the cursor area.
 
   To migrate, you can probably just replace all instances of `inner_size` with `surface_size` in your codebase.
 - Every event carrying a `DeviceId` now uses `Option<DeviceId>` instead. A `None` value signifies that the

src/platform_impl/linux/x11/event_processor.rs

@@ -89,8 +89,8 @@ impl EventProcessor {
 
             let ime = ime.get_mut();
             match request {
-                ImeRequest::Position(window_id, x, y) => {
-                    ime.send_xim_spot(window_id, x, y);
+                ImeRequest::Area(window_id, x, y, w, h) => {
+                    ime.send_xim_area(window_id, x, y, w, h);
                 },
                 ImeRequest::Allow(window_id, allowed) => {
                     ime.set_ime_allowed(window_id, allowed);

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

@@ -116,7 +116,7 @@ unsafe fn replace_im(inner: *mut ImeInner) -> Result<(), ReplaceImError> {
 
     let mut new_contexts = HashMap::new();
     for (window, old_context) in unsafe { (*inner).contexts.iter() } {
-        let spot = old_context.as_ref().map(|old_context| old_context.ic_spot);
+        let area = old_context.as_ref().map(|old_context| old_context.ic_area);
 
         // Check if the IME was allowed on that context.
         let is_allowed =
@@ -128,7 +128,7 @@ unsafe fn replace_im(inner: *mut ImeInner) -> Result<(), ReplaceImError> {
                     xconn,
                     &new_im,
                     *window,
-                    spot,
+                    area,
                     (*inner).event_sender.clone(),
                     is_allowed,
                 )

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

@@ -1,6 +1,5 @@
 use std::error::Error;
 use std::ffi::CStr;
-use std::os::raw::c_short;
 use std::sync::Arc;
 use std::{fmt, mem, ptr};
 
@@ -196,7 +195,7 @@ struct ImeContextClientData {
 // through `ImeInner`.
 pub struct ImeContext {
     pub(crate) ic: ffi::XIC,
-    pub(crate) ic_spot: ffi::XPoint,
+    pub(crate) ic_area: ffi::XRectangle,
     pub(crate) allowed: bool,
     // Since the data is passed shared between X11 XIM callbacks, but couldn't be directly free
     // from there we keep the pointer to automatically deallocate it.
@@ -208,7 +207,7 @@ impl ImeContext {
         xconn: &Arc<XConnection>,
         im: &InputMethod,
         window: ffi::Window,
-        ic_spot: Option<ffi::XPoint>,
+        ic_area: Option<ffi::XRectangle>,
         event_sender: ImeEventSender,
         allowed: bool,
     ) -> Result<Self, ImeContextCreationError> {
@@ -244,14 +243,14 @@ impl ImeContext {
 
         let mut context = ImeContext {
             ic,
-            ic_spot: ffi::XPoint { x: 0, y: 0 },
+            ic_area: ffi::XRectangle { x: 0, y: 0, width: 0, height: 0 },
             allowed,
             _client_data: unsafe { Box::from_raw(client_data) },
         };
 
         // Set the spot location, if it's present.
-        if let Some(ic_spot) = ic_spot {
-            context.set_spot(xconn, ic_spot.x, ic_spot.y)
+        if let Some(ic_area) = ic_area {
+            context.set_area(xconn, ic_area.x, ic_area.y, ic_area.width, ic_area.height);
         }
 
         Ok(context)
@@ -355,25 +354,44 @@ impl ImeContext {
         self.allowed
     }
 
-    // Set the spot for preedit text. Setting spot isn't working with libX11 when preedit callbacks
-    // are being used. Certain IMEs do show selection window, but it's placed in bottom left of the
-    // window and couldn't be changed.
-    //
-    // For me see: https://bugs.freedesktop.org/show_bug.cgi?id=1580.
-    pub(crate) fn set_spot(&mut self, xconn: &Arc<XConnection>, x: c_short, y: c_short) {
-        if !self.is_allowed() || self.ic_spot.x == x && self.ic_spot.y == y {
+    /// Set the spot and area for preedit text.
+    ///
+    /// This functionality depends on the libx11 version.
+    ///  - Until libx11 1.8.2, XNSpotLocation was blocked by libx11 in On-The-Spot mode.
+    ///  - Until libx11 1.8.11, XNArea was blocked by libx11 in On-The-Spot mode.
+    ///
+    /// Use of this information is discretionary by input method servers,
+    /// and some may not use it by default, even if they have support.
+    pub(crate) fn set_area(
+        &mut self,
+        xconn: &Arc<XConnection>,
+        x: i16,
+        y: i16,
+        width: u16,
+        height: u16,
+    ) {
+        if !self.is_allowed()
+            || self.ic_area.x == x
+                && self.ic_area.y == y
+                && self.ic_area.width == width
+                && self.ic_area.height == height
+        {
             return;
         }
 
-        self.ic_spot = ffi::XPoint { x, y };
+        self.ic_area = ffi::XRectangle { x, y, width, height };
+        let ic_spot =
+            ffi::XPoint { x: x.saturating_add(width as i16), y: y.saturating_add(height as i16) };
 
         unsafe {
             let preedit_attr = util::memory::XSmartPointer::new(
                 xconn,
                 (xconn.xlib.XVaCreateNestedList)(
                     0,
                     ffi::XNSpotLocation_0.as_ptr(),
-                    &self.ic_spot,
+                    &ic_spot,
+                    ffi::XNArea_0.as_ptr(),
+                    &self.ic_area,
                     ptr::null_mut::<()>(),
                 ),
             )

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

@@ -36,8 +36,8 @@ pub type ImeEventSender = Sender<(ffi::Window, ImeEvent)>;
 
 /// Request to control XIM handler from the window.
 pub enum ImeRequest {
-    /// Set IME spot position for given `window_id`.
-    Position(ffi::Window, i16, i16),
+    /// Set IME preedit area for given `window_id`.
+    Area(ffi::Window, i16, i16, u16, u16),
 
     /// Allow IME input for the given `window_id`.
     Allow(ffi::Window, bool),
@@ -192,12 +192,12 @@ impl Ime {
         }
     }
 
-    pub fn send_xim_spot(&mut self, window: ffi::Window, x: i16, y: i16) {
+    pub fn send_xim_area(&mut self, window: ffi::Window, x: i16, y: i16, w: u16, h: u16) {
         if self.is_destroyed() {
             return;
         }
         if let Some(&mut Some(ref mut context)) = self.inner.contexts.get_mut(&window) {
-            context.set_spot(&self.xconn, x as _, y as _);
+            context.set_area(&self.xconn, x as _, y as _, w as _, h as _);
         }
     }
 

src/platform_impl/linux/x11/window.rs

@@ -2050,17 +2050,13 @@ impl UnownedWindow {
     #[inline]
     pub fn set_ime_cursor_area(&self, spot: Position, size: Size) {
         let PhysicalPosition { x, y } = spot.to_physical::<i16>(self.scale_factor());
-        let PhysicalSize { width, height } = size.to_physical::<i16>(self.scale_factor());
-        // We only currently support reporting a caret position via XIM.
-        // No IM servers currently process preedit area information from XIM clients
-        // and it is unclear this is even part of the standard protocol.
-        // Fcitx and iBus both assume that the position reported is at the insertion
-        // caret, and by default will place the candidate window under and to the
-        // right of the reported point.
-        let _ = self.ime_sender.lock().unwrap().send(ImeRequest::Position(
+        let PhysicalSize { width, height } = size.to_physical::<u16>(self.scale_factor());
+        let _ = self.ime_sender.lock().unwrap().send(ImeRequest::Area(
             self.xwindow as ffi::Window,
-            x.saturating_add(width),
-            y.saturating_add(height),
+            x,
+            y,
+            width,
+            height,
         ));
     }
 

src/window.rs

@@ -1064,8 +1064,6 @@ pub trait Window: AsAny + Send + Sync + fmt::Debug {
     ///
     /// ## Platform-specific
     ///
-    /// - **X11:** Area is not supported, only position. The bottom-right corner of the provided
-    ///   area is reported as the position.
     /// - **iOS / Android / Web / Orbital:** Unsupported.
     ///
     /// [chinese]: https://support.apple.com/guide/chinese-input-method/use-the-candidate-window-cim12992/104/mac/12.0