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 <[email protected]>
Co-authored-by: Markus Siglreithmaier <[email protected]>
Co-authored-by: Murarth <[email protected]>
Co-authored-by: Yusuke Kominami <[email protected]>
Co-authored-by: moko256 <[email protected]>

CHANGELOG.md

@@ -41,6 +41,9 @@ And please only add new entries to the top of this list, right below the `# Unre
 - **Breaking:** Replaced `Window::with_app_id` and `Window::with_class` with `Window::with_name` on `WindowBuilderExtUnix`.
 - On Wayland and X11, fix window not resizing with `Window::set_inner_size` after calling `Window:set_resizable(false)`.
 - On Windows, fix wrong fullscreen monitors being recognized when handling WM_WINDOWPOSCHANGING messages
+- **Breaking:** Added new `WindowEvent::Ime` supported on desktop platforms.
+- Added `Window::set_ime_allowed` supported on desktop platforms.
+- **Breaking:** IME input on desktop platforms won't be received unless it's explicitly allowed via `Window::set_ime_allowed` and new `WindowEvent::Ime` events are handled.
 
 # 0.26.1 (2022-01-05)
 

Cargo.toml

@@ -87,8 +87,8 @@ features = [
 ]
 
 [target.'cfg(any(target_os = "linux", target_os = "dragonfly", target_os = "freebsd", target_os = "openbsd", target_os = "netbsd"))'.dependencies]
-wayland-client = { version = "0.29", default_features = false,  features = ["use_system_lib"], optional = true }
-wayland-protocols = { version = "0.29", features = [ "staging_protocols"], optional = true }
+wayland-client = { version = "0.29.4", default_features = false,  features = ["use_system_lib"], optional = true }
+wayland-protocols = { version = "0.29.4", features = [ "staging_protocols"], optional = true }
 sctk = { package = "smithay-client-toolkit", version = "0.15.4", default_features = false, features = ["calloop"],  optional = true }
 mio = { version = "0.8", features = ["os-ext"], optional = true }
 x11-dl = { version = "2.18.5", optional = true }

examples/ime.rs

@@ -0,0 +1,97 @@
+use log::LevelFilter;
+use simple_logger::SimpleLogger;
+use winit::{
+    dpi::PhysicalPosition,
+    event::{ElementState, Event, Ime, VirtualKeyCode, WindowEvent},
+    event_loop::{ControlFlow, EventLoop},
+    window::WindowBuilder,
+};
+
+fn main() {
+    SimpleLogger::new()
+        .with_level(LevelFilter::Trace)
+        .init()
+        .unwrap();
+
+    println!("IME position will system default");
+    println!("Click to set IME position to cursor's");
+    println!("Press F2 to toggle IME. See the documentation of `set_ime_allowed` for more info");
+
+    let event_loop = EventLoop::new();
+
+    let window = WindowBuilder::new()
+        .with_inner_size(winit::dpi::LogicalSize::new(256f64, 128f64))
+        .build(&event_loop)
+        .unwrap();
+
+    let mut ime_allowed = true;
+    window.set_ime_allowed(ime_allowed);
+
+    let mut may_show_ime = false;
+    let mut cursor_position = PhysicalPosition::new(0.0, 0.0);
+    let mut ime_pos = PhysicalPosition::new(0.0, 0.0);
+
+    event_loop.run(move |event, _, control_flow| {
+        *control_flow = ControlFlow::Wait;
+        match event {
+            Event::WindowEvent {
+                event: WindowEvent::CloseRequested,
+                ..
+            } => *control_flow = ControlFlow::Exit,
+            Event::WindowEvent {
+                event: WindowEvent::CursorMoved { position, .. },
+                ..
+            } => {
+                cursor_position = position;
+            }
+            Event::WindowEvent {
+                event:
+                    WindowEvent::MouseInput {
+                        state: ElementState::Released,
+                        ..
+                    },
+                ..
+            } => {
+                println!(
+                    "Setting ime position to {}, {}",
+                    cursor_position.x, cursor_position.y
+                );
+                ime_pos = cursor_position;
+                if may_show_ime {
+                    window.set_ime_position(ime_pos);
+                }
+            }
+            Event::WindowEvent {
+                event: WindowEvent::Ime(event),
+                ..
+            } => {
+                println!("{:?}", event);
+                may_show_ime = event != Ime::Disabled;
+                if may_show_ime {
+                    window.set_ime_position(ime_pos);
+                }
+            }
+            Event::WindowEvent {
+                event: WindowEvent::ReceivedCharacter(ch),
+                ..
+            } => {
+                println!("ch: {:?}", ch);
+            }
+            Event::WindowEvent {
+                event: WindowEvent::KeyboardInput { input, .. },
+                ..
+            } => {
+                println!("key: {:?}", input);
+
+                if input.state == ElementState::Pressed
+                    && input.virtual_keycode == Some(VirtualKeyCode::F2)
+                {
+                    ime_allowed = !ime_allowed;
+                    window.set_ime_allowed(ime_allowed);
+                    println!("\nIME: {}\n", ime_allowed);
+                }
+            }
+            _ => (),
+        }
+    });
+}

src/event.rs

@@ -36,6 +36,8 @@
 use instant::Instant;
 use std::path::PathBuf;
 
+#[cfg(doc)]
+use crate::window::Window;
 use crate::{
     dpi::{PhysicalPosition, PhysicalSize},
     platform_impl,
@@ -93,8 +95,7 @@ pub enum Event<'a, T: 'static> {
     /// This gets triggered in two scenarios:
     /// - The OS has performed an operation that's invalidated the window's contents (such as
     ///   resizing the window).
-    /// - The application has explicitly requested a redraw via
-    ///   [`Window::request_redraw`](crate::window::Window::request_redraw).
+    /// - The application has explicitly requested a redraw via [`Window::request_redraw`].
     ///
     /// During each iteration of the event loop, Winit will aggregate duplicate redraw requests
     /// into a single event, to help avoid duplicating rendering work.
@@ -206,7 +207,7 @@ pub enum StartCause {
     Init,
 }
 
-/// Describes an event from a `Window`.
+/// Describes an event from a [`Window`].
 #[derive(Debug, PartialEq)]
 pub enum WindowEvent<'a> {
     /// The size of the window has changed. Contains the client area's new dimensions.
@@ -240,6 +241,8 @@ pub enum WindowEvent<'a> {
     HoveredFileCancelled,
 
     /// The window received a unicode character.
+    ///
+    /// See also the [`Ime`](Self::Ime) event for more complex character sequences.
     ReceivedCharacter(char),
 
     /// The window gained or lost focus.
@@ -270,6 +273,14 @@ pub enum WindowEvent<'a> {
     ///   issue, and it should get fixed - but it's the current state of the API.
     ModifiersChanged(ModifiersState),
 
+    /// An event from input method.
+    ///
+    /// **Note :** You have to explicitly enable this event using [`Window::set_ime_allowed`].
+    ///
+    /// Platform-specific behavior:
+    /// - **iOS / Android / Web :** Unsupported.
+    Ime(Ime),
+
     /// The cursor has moved on the window.
     CursorMoved {
         device_id: DeviceId,
@@ -376,7 +387,7 @@ impl Clone for WindowEvent<'static> {
                 input: *input,
                 is_synthetic: *is_synthetic,
             },
-
+            Ime(preedit_state) => Ime(preedit_state.clone()),
             ModifiersChanged(modifiers) => ModifiersChanged(*modifiers),
             #[allow(deprecated)]
             CursorMoved {
@@ -468,6 +479,7 @@ impl<'a> WindowEvent<'a> {
                 is_synthetic,
             }),
             ModifiersChanged(modifiers) => Some(ModifiersChanged(modifiers)),
+            Ime(event) => Some(Ime(event)),
             #[allow(deprecated)]
             CursorMoved {
                 device_id,
@@ -627,6 +639,73 @@ pub struct KeyboardInput {
     pub modifiers: ModifiersState,
 }
 
+/// Describes [input method](https://en.wikipedia.org/wiki/Input_method) events.
+///
+/// This is also called a "composition event".
+///
+/// Most keypresses using a latin-like keyboard layout simply generate a [`WindowEvent::ReceivedCharacter`].
+/// However, one couldn't possibly have a key for every single unicode character that the user might want to type
+/// - so the solution operating systems employ is to allow the user to type these using _a sequence of keypresses_ instead.
+///
+/// A prominent example of this is accents - many keyboard layouts allow you to first click the "accent key", and then
+/// the character you want to apply the accent to. This will generate the following event sequence:
+/// ```ignore
+/// // Press "`" key
+/// Ime::Preedit("`", Some(0), Some(0))
+/// // Press "E" key
+/// Ime::Commit("é")
+/// ```
+///
+/// Additionally, certain input devices are configured to display a candidate box that allow the user to select the
+/// desired character interactively. (To properly position this box, you must use [`Window::set_ime_position`].)
+///
+/// An example of a keyboard layout which uses candidate boxes is pinyin. On a latin keybaord the following event
+/// sequence could be obtained:
+/// ```ignore
+/// // Press "A" key
+/// Ime::Preedit("a", Some(1), Some(1))
+/// // Press "B" key
+/// Ime::Preedit("a b", Some(3), Some(3))
+/// // Press left arrow key
+/// Ime::Preedit("a b", Some(1), Some(1))
+/// // Press space key
+/// Ime::Preedit("啊b", Some(3), Some(3))
+/// // Press space key
+/// Ime::Commit("啊不")
+/// ```
+///
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub enum Ime {
+    /// Notifies when the IME was enabled.
+    ///
+    /// After getting this event you could receive [`Preedit`](Self::Preedit) and
+    /// [`Commit`](Self::Commit) events. You should also start performing IME related requests
+    /// like [`Window::set_ime_position`].
+    Enabled,
+
+    /// Notifies when a new composing text should be set at the cursor position.
+    ///
+    /// The value represents a pair of the preedit string and the cursor begin position and end
+    /// position. When it's `None`, the cursor should be hidden.
+    ///
+    /// The cursor position is byte-wise indexed.
+    Preedit(String, Option<(usize, usize)>),
+
+    /// Notifies when text should be inserted into the editor widget.
+    ///
+    /// Any pending [`Preedit`](Self::Preedit) must be cleared.
+    Commit(String),
+
+    /// Notifies when the IME was disabled.
+    ///
+    /// After receiving this event you won't get any more [`Preedit`](Self::Preedit) or
+    /// [`Commit`](Self::Commit) events until the next [`Enabled`](Self::Enabled) event. You can
+    /// also stop issuing IME related requests like [`Window::set_ime_position`] and clear pending
+    /// preedit text.
+    Disabled,
+}
+
 /// Describes touch-screen input state.
 #[derive(Debug, Hash, PartialEq, Eq, Clone, Copy)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]

src/platform_impl/android/mod.rs

@@ -748,6 +748,8 @@ impl Window {
 
     pub fn set_ime_position(&self, _position: Position) {}
 
+    pub fn set_ime_allowed(&self, _allowed: bool) {}
+
     pub fn focus_window(&self) {}
 
     pub fn request_user_attention(&self, _request_type: Option<window::UserAttentionType>) {}

src/platform_impl/ios/window.rs

@@ -291,6 +291,10 @@ impl Inner {
         warn!("`Window::set_ime_position` is ignored on iOS")
     }
 
+    pub fn set_ime_allowed(&self, _allowed: bool) {
+        warn!("`Window::set_ime_allowed` is ignored on iOS")
+    }
+
     pub fn focus_window(&self) {
         warn!("`Window::set_focus` is ignored on iOS")
     }

src/platform_impl/linux/mod.rs

@@ -477,6 +477,11 @@ impl Window {
         x11_or_wayland!(match self; Window(w) => w.set_ime_position(position))
     }
 
+    #[inline]
+    pub fn set_ime_allowed(&self, allowed: bool) {
+        x11_or_wayland!(match self; Window(w) => w.set_ime_allowed(allowed))
+    }
+
     #[inline]
     pub fn focus_window(&self) {
         match self {

src/platform_impl/linux/wayland/event_loop/mod.rs

@@ -32,10 +32,9 @@ mod sink;
 mod state;
 
 pub use proxy::EventLoopProxy;
+pub use sink::EventSink;
 pub use state::WinitState;
 
-use sink::EventSink;
-
 type WinitDispatcher = calloop::Dispatcher<'static, WaylandSource, WinitState>;
 
 pub struct EventLoopWindowTarget<T> {