Feat: add features to ctrl IME visuals; keep Windows the legacy way by default

crates/eframe/Cargo.toml

@@ -59,6 +59,8 @@ default_fonts = ["egui/default_fonts"]
 ## and `WebOptions::renderer`.
 glow = ["dep:egui_glow", "dep:glow", "dep:glutin-winit", "dep:glutin"]
 
+_override_legacy_ime_composition_visuals = ["egui/_override_legacy_ime_composition_visuals"]
+
 ## Enable saving app state to disk.
 persistence = ["dep:home", "egui-winit/serde", "egui/persistence", "ron", "serde"]
 
@@ -101,6 +103,10 @@ wgpu = ["wgpu_no_default_features", "egui-wgpu/default"]
 ## ```
 wgpu_no_default_features = ["dep:wgpu", "dep:egui-wgpu", "dep:pollster"]
 
+## Enable the new IME composition visuals on Windows. The legacy visuals remain
+## the default on Windows due to known issues with the new implementation.
+windows_new_ime_composition_visuals = ["egui/_override_legacy_ime_composition_visuals"]
+
 ## Enables compiling for x11.
 x11 = [
   "egui-winit/x11",
@@ -117,8 +123,6 @@ x11 = [
 __screenshot = []
 
 [dependencies]
-egui = { workspace = true, default-features = false, features = ["bytemuck"] }
-
 ahash.workspace = true
 document-features.workspace = true
 log.workspace = true
@@ -136,6 +140,10 @@ ron = { workspace = true, optional = true, features = ["integer128"] }
 serde = { workspace = true, optional = true }
 
 # -------------------------------------------
+# egui non-windows:
+[target.'cfg(not(target_os = "windows"))'.dependencies]
+egui = { workspace = true, default-features = false, features = ["bytemuck"] }
+
 # native:
 [target.'cfg(not(target_arch = "wasm32"))'.dependencies]
 egui-winit = { workspace = true, default-features = false, features = ["clipboard", "links"] }
@@ -183,6 +191,11 @@ objc2-app-kit = { workspace = true, default-features = false, features = [
 
 # windows:
 [target.'cfg(any(target_os = "windows"))'.dependencies]
+egui = { workspace = true, default-features = false, features = [
+  "bytemuck",
+  "legacy_ime_composition_visuals",
+] }
+
 windows-sys = { workspace = true, features = [
   "Win32_Foundation",
   "Win32_System_Com",

crates/egui/Cargo.toml

@@ -44,6 +44,21 @@ color-hex = ["epaint/color-hex"]
 ## If you plan on specifying your own fonts you may disable this feature.
 default_fonts = ["epaint/default_fonts"]
 
+## The legacy IME composition visuals have several shortcomings. Most notably,
+## they are visually identical to text selection, making it impossible to tell
+## the two apart if there is no candidate window (e.g. when using a Korean IME).
+## In addition, the cursor is always shown at the end of the composition no
+## matter where the actual cursor is, which makes composing Chinese and Japanese
+## text confusing.
+##
+## However, the new composition visuals are not yet fully reliable either. For
+## example, on Windows, `winit` currently reports an incorrect cursor position
+## for Korean IMEs: the cursor should be at the end of the composition, but
+## `winit` reports it at the beginning. Therefore, we keep the legacy visuals
+## as an option for now and plan to remove them once the new visuals work
+## correctly across all supported platforms.
+legacy_ime_composition_visuals = []
+
 ## [`mint`](https://docs.rs/mint) enables interoperability with other math libraries such as [`glam`](https://docs.rs/glam) and [`nalgebra`](https://docs.rs/nalgebra).
 mint = ["epaint/mint"]
 
@@ -62,6 +77,9 @@ serde = ["dep:serde", "epaint/serde", "accesskit/serde"]
 ## Change Vertex layout to be compatible with unity
 unity = ["epaint/unity"]
 
+## Override and disable the legacy_ime_composition_visuals feature.
+_override_legacy_ime_composition_visuals = []
+
 ## Override and disable the unity feature
 ## This exists, so that when testing with --all-features, snapshots render correctly.
 _override_unity = ["epaint/_override_unity"]

crates/egui/src/widgets/text_edit/builder.rs

@@ -827,11 +827,16 @@ impl TextEdit<'_> {
             false
         };
 
+        let should_paint_ime_visuals_the_legacy_way = cfg!(all(
+            feature = "legacy_ime_composition_visuals",
+            not(feature = "_override_legacy_ime_composition_visuals"),
+        ));
+
         if ui.is_rect_visible(inner_rect) {
             let has_focus = ui.memory(|mem| mem.has_focus(id));
 
             if has_focus
-                && state.cursor_purpose.is_selection()
+                && (state.cursor_purpose.is_selection() || should_paint_ime_visuals_the_legacy_way)
                 && let Some(cursor_range) = state.cursor.range(&galley)
             {
                 // Add text selection rectangles to the galley:
@@ -866,7 +871,12 @@ impl TextEdit<'_> {
                     let viewport_has_focus = ui.input(|i| i.focused);
                     if viewport_has_focus {
                         let time_since_last_interaction = now - state.last_interaction_time;
-                        match &state.cursor_purpose {
+                        let cursor_purpose = if should_paint_ime_visuals_the_legacy_way {
+                            &TextEditCursorPurpose::Selection
+                        } else {
+                            &state.cursor_purpose
+                        };
+                        match cursor_purpose {
                             TextEditCursorPurpose::Selection => {
                                 text_selection::visuals::paint_text_cursor(
                                     ui,