Improve IME documentation

examples/ime.rs

@@ -13,8 +13,8 @@ fn main() {
         .init()
         .unwrap();
 
-    println!("Ime position will system default");
-    println!("Click to set ime position to cursor's");
+    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();

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.
@@ -272,6 +275,8 @@ pub enum WindowEvent<'a> {
 
     /// 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),
@@ -634,11 +639,49 @@ pub struct KeyboardInput {
     pub modifiers: ModifiersState,
 }
 
-/// Describes an event from input method.
+/// 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.
@@ -650,9 +693,16 @@ pub enum Ime {
     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,
 }
 

src/window.rs

@@ -814,6 +814,13 @@ impl Window {
 
     /// Sets location of IME candidate box in client area coordinates relative to the top left.
     ///
+    /// This is the window / popup / overlay that allows you to select the desired characters.
+    /// The look of this box may differ between input devices, even on the same platform.
+    ///
+    /// (Apple's official term is "candidate window", see their [chinese] and [japanese] guides).
+    ///
+    /// ## Example
+    ///
     /// ```no_run
     /// # use winit::dpi::{LogicalPosition, PhysicalPosition};
     /// # use winit::event_loop::EventLoop;
@@ -830,6 +837,9 @@ impl Window {
     /// ## Platform-specific
     ///
     /// - **iOS / Android / Web:** Unsupported.
+    ///
+    /// [chinese]: https://support.apple.com/guide/chinese-input-method/use-the-candidate-window-cim12992/104/mac/12.0
+    /// [japanese]: https://support.apple.com/guide/japanese-input-method/use-the-candidate-window-jpim10262/6.3/mac/12.0
     #[inline]
     pub fn set_ime_position<P: Into<Position>>(&self, position: P) {
         self.window.set_ime_position(position.into())