Add new Ime event for desktop platforms

This commit brings new Ime event to account for preedit state of input
method, also adding `Window::set_ime_allowed` to toggle IME input on
the particular window.

This commit implements API as designed in #1497 for desktop platforms.

Co-authored-by: Artur Kovacs <kovacs.artur.barnabas@gmail.com>
Co-authored-by: Markus Siglreithmaier <m.siglreith@gmail.com>
Co-authored-by: Murarth <murarth@gmail.com>
Co-authored-by: Yusuke Kominami <yukke.konan@gmail.com>
Co-authored-by: moko256 <koutaro.mo@gmail.com>

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

@@ -19,9 +19,29 @@ use self::{
     inner::{close_im, ImeInner},
     input_method::PotentialInputMethods,
 };
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub enum ImeEvent {
+    Enabled,
+    Start,
+    Update(String, usize),
+    End,
+    Disabled,
+}
 
-pub type ImeReceiver = Receiver<(ffi::Window, i16, i16)>;
-pub type ImeSender = Sender<(ffi::Window, i16, i16)>;
+pub type ImeReceiver = Receiver<ImeRequest>;
+pub type ImeSender = Sender<ImeRequest>;
+pub type ImeEventReceiver = Receiver<(ffi::Window, ImeEvent)>;
+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),
+
+    /// Allow IME input for the given `window_id`.
+    Allow(ffi::Window, bool),
+}
 
 #[derive(Debug)]
 pub enum ImeCreationError {
@@ -37,11 +57,14 @@ pub struct Ime {
 }
 
 impl Ime {
-    pub fn new(xconn: Arc<XConnection>) -> Result<Self, ImeCreationError> {
+    pub fn new(
+        xconn: Arc<XConnection>,
+        event_sender: ImeEventSender,
+    ) -> Result<Self, ImeCreationError> {
         let potential_input_methods = PotentialInputMethods::new(&xconn);
 
         let (mut inner, client_data) = {
-            let mut inner = Box::new(ImeInner::new(xconn, potential_input_methods));
+            let mut inner = Box::new(ImeInner::new(xconn, potential_input_methods, event_sender));
             let inner_ptr = Box::into_raw(inner);
             let client_data = inner_ptr as _;
             let destroy_callback = ffi::XIMCallback {
@@ -88,12 +111,37 @@ impl Ime {
     // Ok(_) indicates that nothing went wrong internally
     // Ok(true) indicates that the action was actually performed
     // Ok(false) indicates that the action is not presently applicable
-    pub fn create_context(&mut self, window: ffi::Window) -> Result<bool, ImeContextCreationError> {
+    pub fn create_context(
+        &mut self,
+        window: ffi::Window,
+        with_preedit: bool,
+    ) -> Result<bool, ImeContextCreationError> {
         let context = if self.is_destroyed() {
             // Create empty entry in map, so that when IME is rebuilt, this window has a context.
             None
         } else {
-            Some(unsafe { ImeContext::new(&self.inner.xconn, self.inner.im, window, None) }?)
+            let event = if with_preedit {
+                ImeEvent::Enabled
+            } else {
+                // There's no IME without preedit.
+                ImeEvent::Disabled
+            };
+
+            self.inner
+                .event_sender
+                .send((window, event))
+                .expect("Failed to send enabled event");
+
+            Some(unsafe {
+                ImeContext::new(
+                    &self.inner.xconn,
+                    self.inner.im,
+                    window,
+                    None,
+                    with_preedit,
+                    self.inner.event_sender.clone(),
+                )
+            }?)
         };
         self.inner.contexts.insert(window, context);
         Ok(!self.is_destroyed())
@@ -151,6 +199,24 @@ impl Ime {
             context.set_spot(&self.xconn, x as _, y as _);
         }
     }
+
+    pub fn set_ime_allowed(&mut self, window: ffi::Window, allowed: bool) {
+        if self.is_destroyed() {
+            return;
+        }
+
+        if let Some(&mut Some(ref mut context)) = self.inner.contexts.get_mut(&window) {
+            if allowed == context.is_allowed {
+                return;
+            }
+        }
+
+        // Remove context for that window.
+        let _ = self.remove_context(window);
+
+        // Create new context supporting IME input.
+        let _ = self.create_context(window, allowed);
+    }
 }
 
 impl Drop for Ime {