Implement multi-char cursor highlight

Use `end` of the cursor to draw a `HollowBlock` from `start` to `end`.
When cursor covers only a single character, use `Beam` cursor instead
of `HollowBlock`.

Fixes #8238.
Fixes #7849.

5 files changed, 49 insertions, 35 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index ca900247..e9d8d3ff 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -29,6 +29,7 @@ Notable changes to the `alacritty_terminal` crate are documented in its
     to the new `general` section
 - Moved config option `shell` to `terminal.shell`
 - `ctrl+shift+u` binding to open links to `ctrl+shift+o` to avoid collisions with IMEs
+- Use `Beam` cursor for single char cursor inside the IME preview
 
 ### Fixed
 
@@ -48,6 +49,7 @@ Notable changes to the `alacritty_terminal` crate are documented in its
 - Windows app icon now displays properly in old alt+tab on Windows
 - Alacritty not being properly activated with startup notify
 - Invalid URL highlights after terminal scrolling
+- Hollow block cursor not spanning multiple chars being edited inside the IME preview
 
 ## 0.13.2
 
diff --git a/alacritty/src/display/content.rs b/alacritty/src/display/content.rs
index 0e06b3ca..2fbbdec4 100644
--- a/alacritty/src/display/content.rs
+++ b/alacritty/src/display/content.rs
@@ -1,4 +1,5 @@
 use std::borrow::Cow;
+use std::num::NonZeroU32;
 use std::ops::Deref;
 use std::{cmp, mem};
 
@@ -134,8 +135,13 @@ impl<'a> RenderableContent<'a> {
             text_color = self.config.colors.primary.background;
         }
 
+        let width = if cell.flags.contains(Flags::WIDE_CHAR) {
+            NonZeroU32::new(2).unwrap()
+        } else {
+            NonZeroU32::new(1).unwrap()
+        };
         RenderableCursor {
-            is_wide: cell.flags.contains(Flags::WIDE_CHAR),
+            width,
             shape: self.cursor_shape,
             point: self.cursor_point,
             cursor_color,
@@ -396,7 +402,7 @@ pub struct RenderableCursor {
     shape: CursorShape,
     cursor_color: Rgb,
     text_color: Rgb,
-    is_wide: bool,
+    width: NonZeroU32,
     point: Point<usize>,
 }
 
@@ -405,15 +411,20 @@ impl RenderableCursor {
         let shape = CursorShape::Hidden;
         let cursor_color = Rgb::default();
         let text_color = Rgb::default();
-        let is_wide = false;
+        let width = NonZeroU32::new(1).unwrap();
         let point = Point::default();
-        Self { shape, cursor_color, text_color, is_wide, point }
+        Self { shape, cursor_color, text_color, width, point }
     }
 }
 
 impl RenderableCursor {
-    pub fn new(point: Point<usize>, shape: CursorShape, cursor_color: Rgb, is_wide: bool) -> Self {
-        Self { shape, cursor_color, text_color: cursor_color, is_wide, point }
+    pub fn new(
+        point: Point<usize>,
+        shape: CursorShape,
+        cursor_color: Rgb,
+        width: NonZeroU32,
+    ) -> Self {
+        Self { shape, cursor_color, text_color: cursor_color, width, point }
     }
 
     pub fn color(&self) -> Rgb {
@@ -424,8 +435,8 @@ impl RenderableCursor {
         self.shape
     }
 
-    pub fn is_wide(&self) -> bool {
-        self.is_wide
+    pub fn width(&self) -> NonZeroU32 {
+        self.width
     }
 
     pub fn point(&self) -> Point<usize> {
diff --git a/alacritty/src/display/cursor.rs b/alacritty/src/display/cursor.rs
index 65933ccc..b0e2d6c3 100644
--- a/alacritty/src/display/cursor.rs
+++ b/alacritty/src/display/cursor.rs
@@ -24,9 +24,7 @@ impl IntoRects for RenderableCursor {
 
         let thickness = (thickness * width).round().max(1.);
 
-        if self.is_wide() {
-            width *= 2.;
-        }
+        width *= self.width().get() as f32;
 
         match self.shape() {
             CursorShape::Beam => beam(x, y, height, thickness, self.color()),
diff --git a/alacritty/src/display/mod.rs b/alacritty/src/display/mod.rs
index 51553288..a8501da6 100644
--- a/alacritty/src/display/mod.rs
+++ b/alacritty/src/display/mod.rs
@@ -874,7 +874,9 @@ impl Display {
                 if self.ime.preedit().is_none() {
                     let fg = config.colors.footer_bar_foreground();
                     let shape = CursorShape::Underline;
-                    let cursor = RenderableCursor::new(Point::new(line, column), shape, fg, false);
+                    let cursor_width = NonZeroU32::new(1).unwrap();
+                    let cursor =
+                        RenderableCursor::new(Point::new(line, column), shape, fg, cursor_width);
                     rects.extend(cursor.rects(&size_info, config.cursor.thickness()));
                 }
 
@@ -1081,8 +1083,8 @@ impl Display {
 
         // Get the visible preedit.
         let visible_text: String = match (preedit.cursor_byte_offset, preedit.cursor_end_offset) {
-            (Some(byte_offset), Some(end_offset)) if end_offset > num_cols => StrShortener::new(
-                &preedit.text[byte_offset..],
+            (Some(byte_offset), Some(end_offset)) if end_offset.0 > num_cols => StrShortener::new(
+                &preedit.text[byte_offset.0..],
                 num_cols,
                 ShortenDirection::Right,
                 Some(SHORTENER),
@@ -1125,19 +1127,21 @@ impl Display {
         rects.extend(underline.rects(Flags::UNDERLINE, &metrics, &self.size_info));
 
         let ime_popup_point = match preedit.cursor_end_offset {
-            Some(cursor_end_offset) if cursor_end_offset != 0 => {
-                let is_wide = preedit.text[preedit.cursor_byte_offset.unwrap_or_default()..]
-                    .chars()
-                    .next()
-                    .map(|ch| ch.width() == Some(2))
-                    .unwrap_or_default();
+            Some(cursor_end_offset) => {
+                // Use hollow block when multiple characters are changed at once.
+                let (shape, width) = if let Some(width) =
+                    NonZeroU32::new((cursor_end_offset.0 - cursor_end_offset.1) as u32)
+                {
+                    (CursorShape::HollowBlock, width)
+                } else {
+                    (CursorShape::Beam, NonZeroU32::new(1).unwrap())
+                };
 
                 let cursor_column = Column(
-                    (end.column.0 as isize - cursor_end_offset as isize + 1).max(0) as usize,
+                    (end.column.0 as isize - cursor_end_offset.0 as isize + 1).max(0) as usize,
                 );
                 let cursor_point = Point::new(point.line, cursor_column);
-                let cursor =
-                    RenderableCursor::new(cursor_point, CursorShape::HollowBlock, fg, is_wide);
+                let cursor = RenderableCursor::new(cursor_point, shape, fg, width);
                 rects.extend(cursor.rects(&self.size_info, config.cursor.thickness()));
                 cursor_point
             },
@@ -1436,20 +1440,22 @@ pub struct Preedit {
     /// Byte offset for cursor start into the preedit text.
     ///
     /// `None` means that the cursor is invisible.
-    cursor_byte_offset: Option<usize>,
+    cursor_byte_offset: Option<(usize, usize)>,
 
-    /// The cursor offset from the end of the preedit in char width.
-    cursor_end_offset: Option<usize>,
+    /// The cursor offset from the end of the start of the preedit in char width.
+    cursor_end_offset: Option<(usize, usize)>,
 }
 
 impl Preedit {
-    pub fn new(text: String, cursor_byte_offset: Option<usize>) -> Self {
+    pub fn new(text: String, cursor_byte_offset: Option<(usize, usize)>) -> Self {
         let cursor_end_offset = if let Some(byte_offset) = cursor_byte_offset {
             // Convert byte offset into char offset.
-            let cursor_end_offset =
-                text[byte_offset..].chars().fold(0, |acc, ch| acc + ch.width().unwrap_or(1));
+            let start_to_end_offset =
+                text[byte_offset.0..].chars().fold(0, |acc, ch| acc + ch.width().unwrap_or(1));
+            let end_to_end_offset =
+                text[byte_offset.1..].chars().fold(0, |acc, ch| acc + ch.width().unwrap_or(1));
 
-            Some(cursor_end_offset)
+            Some((start_to_end_offset, end_to_end_offset))
         } else {
             None
         };
diff --git a/alacritty/src/event.rs b/alacritty/src/event.rs
index b4600ae3..46e9433c 100644
--- a/alacritty/src/event.rs
+++ b/alacritty/src/event.rs
@@ -1843,11 +1843,8 @@ impl input::Processor<EventProxy, ActionContext<'_, Notifier, EventProxy>> {
                             self.ctx.update_cursor_blinking();
                         },
                         Ime::Preedit(text, cursor_offset) => {
-                            let preedit = if text.is_empty() {
-                                None
-                            } else {
-                                Some(Preedit::new(text, cursor_offset.map(|offset| offset.0)))
-                            };
+                            let preedit =
+                                (!text.is_empty()).then(|| Preedit::new(text, cursor_offset));
 
                             if self.ctx.display.ime.preedit() != preedit.as_ref() {
                                 self.ctx.display.ime.set_preedit(preedit);