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Implement proper visuals for IME composition (#8083)

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This PR adds visual support for IME composition, including the cursor
and conversion segment.
These visuals works (mostly) well on native platforms (`egui-winit`). On
the web (`eframe/web`), support is limited by browser capabilities:
Chromium works well, Firefox shows partial improvement, and Safari
remains subpar.

> [!NOTE]
>
> For `eframe` on Windows, this feature is currently gated behind the
`windows_new_ime_composition_visuals` feature flag.

## Details

We extend `egui::ImeEvent::Preedit(String)` to `egui::ImeEvent::Preedit
{ text: String, active_range_chars: Option<std::ops::Range<usize>> }`.
The new `active_range_chars` field enables rendering of:
- the cursor (when the range is empty), and
- the conversion segment (when the range is non-empty)

in IME composition.

In `egui-winit`, we now use the range provided by
`winit::event::Ime::Preedit` instead of ignoring it.

In `eframe/web`, we derive the range from `selectionStart` and
`selectionEnd` on the text agent. This mapping is fully accurate only in
Chromium, but represents the best available approach for now.

## Demonstrations

### Chinese IMEs (Shuangpin)

We can see where the cursor is now.

| What | With this PR | Without this PR |
|-|-|-|
| macOS builtin |<video
src=https://github.com/user-attachments/assets/487c7e7c-ef6d-4a86-8dbc-8c71871b4470
/>|<video
src=https://github.com/user-attachments/assets/49bd5a60-4b90-4e4a-99e0-cd01d3f7030c
/>|
| macOS builtin (light)|<video
src=https://github.com/user-attachments/assets/e84546f6-947b-4cea-a87e-fda903f49164
/>|——|
| Windows builtin |<video
src=https://github.com/user-attachments/assets/fd331884-1f0c-4822-a99e-8140aed54815
/>|——|
| Wayland iBus Intelligent Pinyin |<video
src=https://github.com/user-attachments/assets/b6796c75-1c4e-45e5-b43a-5d8dea320485
/>|——|
| Chromium (Chrome) macOS | Identical to `macOS builtin`. |——|
| Safari macOS | We can now differentiate between IME composition and
text selection, but we still can't tell where the cursor is. |——|
| Firefox (Zen) macOS | Identical to `macOS builtin`. |——|

### Japanese IMEs

We can see where the conversion segment is now.

| What | With this PR | Without this PR |
|-|-|-|
| macOS builtin |<video
src=https://github.com/user-attachments/assets/f2994cd4-a966-4ff0-9590-d263c202ec76
/>|<video
src=https://github.com/user-attachments/assets/7cf5ff35-003d-4f60-8fbf-15c725c3ecb9
/>|
| macOS builtin (light)|<video
src=https://github.com/user-attachments/assets/6f562bdd-12fc-4486-b37b-8fcf11643295
/>|——|
| Windows builtin |<video
src=https://github.com/user-attachments/assets/f0905659-5335-4034-abda-c25cf8f2fd57
/>|——|
| Wayland iBus Anthy |<video
src=https://github.com/user-attachments/assets/94cd3a24-3158-4d79-ae02-d9b30fdfa738
/>|——|
| Chromium (Chrome) macOS | Identical to `macOS builtin`. |——|
| Safari macOS | We can now differentiate between IME composition and
text selection, but we still can't tell where the conversion segment is.
|——|
| Firefox (Zen) macOS | (Limited improvement.) <video
src=https://github.com/user-attachments/assets/3daf9b63-6e75-467b-8515-31c2a44adf61
/> |——|

### Korean IMEs

We can clearly tell whether we are in composition (in contrast to
selection) now.

| What | With this PR | Without this PR |
|-|-|-|
|macOS builtin|<video
src=https://github.com/user-attachments/assets/73ca28c7-22a0-493f-8f4d-c6e59a2dec54
/>|<video
src=https://github.com/user-attachments/assets/f582de7d-7ec0-48fe-910f-0139ef1620d3
/>|
|macOS builtin (light)|<video
src=https://github.com/user-attachments/assets/269f03bd-6f95-498b-9fb1-1adcb043c738
/>|——|
| Windows builtin| (With a workaround for [this `winit`
bug](https://github.com/emilk/egui/pull/8083#issuecomment-4206742668)
applied.) <video
src=https://github.com/user-attachments/assets/1e82583d-0c41-4f1c-98cf-0606bee5af05
/>|——|
| Wayland iBus Hangul |<video
src=https://github.com/user-attachments/assets/8c9a0de1-9027-4b37-93a3-e9da0251d176
/>|——|
| Chromium (Chrome) macOS | Identical to `macOS builtin`. |——|
| Safari macOS | Identical to `Windows builtin`. |——|
| Firefox (Zen) macOS | Identical to `macOS builtin`. (ignoring the fact
that the composition breaks when typing the second Hangul. (This bug
predates this PR.)) |——|

---------

Co-authored-by: lucasmerlin <hi@lucasmerlin.me>
This commit is contained in:
Umaĵo
2026-06-26 00:21:19 +08:00
committed by GitHub
parent a8d09eb60d
commit 5bf62ca4b3
11 changed files with 480 additions and 37 deletions
Download Patch File Download Diff File Expand all files Collapse all files

3
crates/egui_kittest/tests/snapshots/test_ime_composition_visuals_cursor.png Normal file
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@@ -0,0 +1,3 @@
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size 9065

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crates/egui_kittest/tests/snapshots/test_ime_composition_visuals_segment.png Normal file
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@@ -0,0 +1,3 @@
version https://git-lfs.github.com/spec/v1
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size 9005

44
crates/egui_kittest/tests/tests.rs
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@@ -218,3 +218,47 @@ fn test_remove_cursor() {
"The button appearance should change"
);
}
#[test]
fn test_ime_composition_visuals() {
let mut harness = Harness::new_ui_state(
|ui, state| {
egui::TextEdit::multiline(state)
.desired_width(120.0)
.desired_rows(5)
.show(ui);
},
"Hello. Bye.".to_owned(),
);
harness.fit_contents();
let text_edit = harness.get_by_role(egui::accesskit::Role::MultilineTextInput);
text_edit.focus();
harness.run();
harness.key_press(egui::Key::Home);
for _ in 0.."Hello. ".len() {
harness.key_press(egui::Key::ArrowRight);
}
let text = "Have you ever seen an IME composing English text? You now see it. ";
let text_index_1 = "Have you ever ".chars().count();
let text_index_2 = "Have you ever seen an IME composing English text? "
.chars()
.count();
harness.event(egui::Event::Ime(egui::ImeEvent::Preedit {
text: text.to_owned(),
active_range_chars: Some(text_index_1..text_index_2),
}));
harness.run();
harness.snapshot("test_ime_composition_visuals_segment");
harness.event(egui::Event::Ime(egui::ImeEvent::Preedit {
text: text.to_owned(),
active_range_chars: Some(text_index_2..text_index_2),
}));
harness.run();
harness.snapshot("test_ime_composition_visuals_cursor");
}