Support different kinds of underline rendering (updated)

book/src/themes.md

@@ -13,10 +13,10 @@ The default theme.toml can be found [here](https://github.com/helix-editor/helix
 Each line in the theme file is specified as below:
 
 ```toml
-key = { fg = "#ffffff", bg = "#000000", modifiers = ["bold", "italic"] }
+key = { fg = "#ffffff", bg = "#000000", underline-color = "#ff0000", underline-style = "curl", modifiers = ["bold", "italic"] }
 ```
 
-where `key` represents what you want to style, `fg` specifies the foreground color, `bg` the background color, and `modifiers` is a list of style modifiers. `bg` and `modifiers` can be omitted to defer to the defaults.
+where `key` represents what you want to style, `fg` specifies the foreground color, `bg` the background color, `underline_style` the underline style, `underline_color` the underline color (only meaningful if an underline style is enabled), and `modifiers` is a list of style modifiers. `bg`, `underline` and `modifiers` can be omitted to defer to the defaults.
 
 To specify only the foreground color:
 
@@ -77,17 +77,35 @@ The following values may be used as modifiers.
 
 Less common modifiers might not be supported by your terminal emulator.
 
+| Modifier             |
+| ---                  |
+| `bold`               |
+| `dim`                |
+| `italic`             |
+| `underlined`         |
+| `slow_blink`         |
+| `rapid_blink`        |
+| `reversed`           |
+| `hidden`             |
+| `crossed_out`        |
+
+> Note: The `underlined` modifier is deprecated and only available for backwards compatability.
+> It's behaviour is equivalent to `underline-style="line"`
+
+### Underline Style
+
+One of the following values may be used as an `underline-style`. 
+
+Some styles might not be supported by your terminal emulator.
+
 | Modifier       |
 | ---            |
-| `bold`         |
-| `dim`          |
-| `italic`       |
-| `underlined`   |
-| `slow_blink`   |
-| `rapid_blink`  |
-| `reversed`     |
-| `hidden`       |
-| `crossed_out`  |
+| `line`         |
+| `curl`         |
+| `dashed`       |
+| `dot`          |
+| `double_line`  |
+
 
 ### Scopes
 

helix-tui/Cargo.toml

@@ -20,6 +20,7 @@ bitflags = "1.3"
 cassowary = "0.3"
 unicode-segmentation = "1.10"
 crossterm = { version = "0.25", optional = true }
+termini = "0.1"
 serde = { version = "1", "optional" = true, features = ["derive"]}
 helix-view = { version = "0.6", path = "../helix-view", features = ["term"] }
 helix-core = { version = "0.6", path = "../helix-core" }

helix-tui/src/backend/crossterm.rs

@@ -7,20 +7,56 @@ use crossterm::{
         SetForegroundColor,
     },
     terminal::{self, Clear, ClearType},
+    Command,
 };
-use helix_view::graphics::{Color, CursorKind, Modifier, Rect};
-use std::io::{self, Write};
+use helix_view::graphics::{Color, CursorKind, Modifier, Rect, UnderlineStyle};
+use std::{
+    fmt,
+    io::{self, Write},
+};
+fn vte_version() -> Option<usize> {
+    std::env::var("VTE_VERSION").ok()?.parse().ok()
+}
+
+/// Describes terminal capabilities like extended underline, truecolor, etc.
+#[derive(Copy, Clone, Debug, Default)]
+struct Capabilities {
+    /// Support for undercurled, underdashed, etc.
+    has_extended_underlines: bool,
+}
+
+impl Capabilities {
+    /// Detect capabilities from the terminfo database located based
+    /// on the $TERM environment variable. If detection fails, returns
+    /// a default value where no capability is supported.
+    pub fn from_env_or_default() -> Self {
+        match termini::TermInfo::from_env() {
+            Err(_) => Capabilities::default(),
+            Ok(t) => Capabilities {
+                // Smulx, VTE: https://unix.stackexchange.com/a/696253/246284
+                // Su (used by kitty): https://sw.kovidgoyal.net/kitty/underlines
+                has_extended_underlines: t.extended_cap("Smulx").is_some()
+                    || t.extended_cap("Su").is_some()
+                    || vte_version() >= Some(5102),
+            },
+        }
+    }
+}
 
 pub struct CrosstermBackend<W: Write> {
     buffer: W,
+    capabilities: Capabilities,
 }
 
 impl<W> CrosstermBackend<W>
 where
     W: Write,
 {
     pub fn new(buffer: W) -> CrosstermBackend<W> {
-        CrosstermBackend { buffer }
+        CrosstermBackend {
+            buffer,
+            capabilities: Capabilities::from_env_or_default(),
+        }
     }
 }
 
@@ -47,6 +83,8 @@ where
     {
         let mut fg = Color::Reset;
         let mut bg = Color::Reset;
+        let mut underline_color = Color::Reset;
+        let mut underline_style = UnderlineStyle::Reset;
         let mut modifier = Modifier::empty();
         let mut last_pos: Option<(u16, u16)> = None;
         for (x, y, cell) in content {
@@ -74,11 +112,32 @@ where
                 bg = cell.bg;
             }
 
+            let mut new_underline_style = cell.underline_style;
+            if !self.capabilities.has_extended_underlines {
+                match new_underline_style {
+                    UnderlineStyle::Reset | UnderlineStyle::Line => (),
+                    _ => new_underline_style = UnderlineStyle::Line,
+                }
+
+                if cell.underline_color != underline_color {
+                    let color = CColor::from(cell.underline_color);
+                    map_error(queue!(self.buffer, SetUnderlineColor(color)))?;
+                    underline_color = cell.underline_color;
+                }
+            }
+
+            if new_underline_style != underline_style {
+                let attr = CAttribute::from(cell.underline_style);
+                map_error(queue!(self.buffer, SetAttribute(attr)))?;
+                underline_style = new_underline_style;
+            }
+
             map_error(queue!(self.buffer, Print(&cell.symbol)))?;
         }
 
         map_error(queue!(
             self.buffer,
+            SetUnderlineColor(CColor::Reset),
             SetForegroundColor(CColor::Reset),
             SetBackgroundColor(CColor::Reset),
             SetAttribute(CAttribute::Reset)
@@ -153,9 +212,6 @@ impl ModifierDiff {
         if removed.contains(Modifier::ITALIC) {
             map_error(queue!(w, SetAttribute(CAttribute::NoItalic)))?;
         }
-        if removed.contains(Modifier::UNDERLINED) {
-            map_error(queue!(w, SetAttribute(CAttribute::NoUnderline)))?;
-        }
         if removed.contains(Modifier::DIM) {
             map_error(queue!(w, SetAttribute(CAttribute::NormalIntensity)))?;
         }
@@ -176,9 +232,6 @@ impl ModifierDiff {
         if added.contains(Modifier::ITALIC) {
             map_error(queue!(w, SetAttribute(CAttribute::Italic)))?;
         }
-        if added.contains(Modifier::UNDERLINED) {
-            map_error(queue!(w, SetAttribute(CAttribute::Underlined)))?;
-        }
         if added.contains(Modifier::DIM) {
             map_error(queue!(w, SetAttribute(CAttribute::Dim)))?;
         }
@@ -195,3 +248,58 @@ impl ModifierDiff {
         Ok(())
     }
 }
+
+/// Crossterm uses semicolon as a seperator for colors
+/// this is actually not spec compliant (altough commonly supported)
+/// However the correct approach is to use colons as a seperator.
+/// This usually doesn't make a difference for emulators that do support colored underlines.
+/// However terminals that do not support colored underlines will ignore underlines colors with colons
+/// while escape sequences with semicolons are always processed which leads to weird visual artifacts.
+/// See [this nvim issue](https://github.com/neovim/neovim/issues/9270) for details
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct SetUnderlineColor(pub CColor);
+
+impl Command for SetUnderlineColor {
+    fn write_ansi(&self, f: &mut impl fmt::Write) -> fmt::Result {
+        let color = self.0;
+
+        if color == CColor::Reset {
+            write!(f, "\x1b[59m")?;
+            return Ok(());
+        }
+        f.write_str("\x1b[58:")?;
+
+        let res = match color {
+            CColor::Black => f.write_str("5:0"),
+            CColor::DarkGrey => f.write_str("5:8"),
+            CColor::Red => f.write_str("5:9"),
+            CColor::DarkRed => f.write_str("5:1"),
+            CColor::Green => f.write_str("5:10"),
+            CColor::DarkGreen => f.write_str("5:2"),
+            CColor::Yellow => f.write_str("5:11"),
+            CColor::DarkYellow => f.write_str("5:3"),
+            CColor::Blue => f.write_str("5:12"),
+            CColor::DarkBlue => f.write_str("5:4"),
+            CColor::Magenta => f.write_str("5:13"),
+            CColor::DarkMagenta => f.write_str("5:5"),
+            CColor::Cyan => f.write_str("5:14"),
+            CColor::DarkCyan => f.write_str("5:6"),
+            CColor::White => f.write_str("5:15"),
+            CColor::Grey => f.write_str("5:7"),
+            CColor::Rgb { r, g, b } => write!(f, "2::{}:{}:{}", r, g, b),
+            CColor::AnsiValue(val) => write!(f, "5:{}", val),
+            _ => Ok(()),
+        };
+        res?;
+        write!(f, "m")?;
+        Ok(())
+    }
+
+    #[cfg(windows)]
+    fn execute_winapi(&self) -> crossterm::Result<()> {
+        Err(std::io::Error::new(
+            std::io::ErrorKind::Other,
+            "SetUnderlineColor not supported by winapi.",
+        ))
+    }
+}

helix-tui/src/buffer.rs

@@ -3,14 +3,16 @@ use helix_core::unicode::width::UnicodeWidthStr;
 use std::cmp::min;
 use unicode_segmentation::UnicodeSegmentation;
 
-use helix_view::graphics::{Color, Modifier, Rect, Style};
+use helix_view::graphics::{Color, Modifier, Rect, Style, UnderlineStyle};
 
 /// A buffer cell
 #[derive(Debug, Clone, PartialEq)]
 pub struct Cell {
     pub symbol: String,
     pub fg: Color,
     pub bg: Color,
+    pub underline_color: Color,
+    pub underline_style: UnderlineStyle,
     pub modifier: Modifier,
 }
 
@@ -44,6 +46,13 @@ impl Cell {
         if let Some(c) = style.bg {
             self.bg = c;
         }
+        if let Some(c) = style.underline_color {
+            self.underline_color = c;
+        }
+        if let Some(style) = style.underline_style {
+            self.underline_style = style;
+        }
+
         self.modifier.insert(style.add_modifier);
         self.modifier.remove(style.sub_modifier);
         self
@@ -53,6 +62,8 @@ impl Cell {
         Style::default()
             .fg(self.fg)
             .bg(self.bg)
+            .underline_color(self.underline_color)
+            .underline_style(self.underline_style)
             .add_modifier(self.modifier)
     }
 
@@ -61,6 +72,8 @@ impl Cell {
         self.symbol.push(' ');
         self.fg = Color::Reset;
         self.bg = Color::Reset;
+        self.underline_color = Color::Reset;
+        self.underline_style = UnderlineStyle::Reset;
         self.modifier = Modifier::empty();
     }
 }
@@ -71,6 +84,8 @@ impl Default for Cell {
             symbol: " ".into(),
             fg: Color::Reset,
             bg: Color::Reset,
+            underline_color: Color::Reset,
+            underline_style: UnderlineStyle::Reset,
             modifier: Modifier::empty(),
         }
     }
@@ -87,7 +102,7 @@ impl Default for Cell {
 ///
 /// ```
 /// use helix_tui::buffer::{Buffer, Cell};
-/// use helix_view::graphics::{Rect, Color, Style, Modifier};
+/// use helix_view::graphics::{Rect, Color, UnderlineStyle, Style, Modifier};
 ///
 /// let mut buf = Buffer::empty(Rect{x: 0, y: 0, width: 10, height: 5});
 /// buf[(0, 2)].set_symbol("x");
@@ -97,7 +112,9 @@ impl Default for Cell {
 ///     symbol: String::from("r"),
 ///     fg: Color::Red,
 ///     bg: Color::White,
-///     modifier: Modifier::empty()
+///     underline_color: Color::Reset,
+///     underline_style: UnderlineStyle::Reset,
+///     modifier: Modifier::empty(),
 /// });
 /// buf[(5, 0)].set_char('x');
 /// assert_eq!(buf[(5, 0)].symbol, "x");

helix-tui/src/text.rs

@@ -134,6 +134,8 @@ impl<'a> Span<'a> {
     ///             style: Style {
     ///                 fg: Some(Color::Yellow),
     ///                 bg: Some(Color::Black),
+    ///                 underline_color: None,
+    ///                 underline_style: None,
     ///                 add_modifier: Modifier::empty(),
     ///                 sub_modifier: Modifier::empty(),
     ///             },
@@ -143,6 +145,8 @@ impl<'a> Span<'a> {
     ///             style: Style {
     ///                 fg: Some(Color::Yellow),
     ///                 bg: Some(Color::Black),
+    ///                 underline_color: None,
+    ///                 underline_style: None,
     ///                 add_modifier: Modifier::empty(),
     ///                 sub_modifier: Modifier::empty(),
     ///             },
@@ -152,6 +156,8 @@ impl<'a> Span<'a> {
     ///             style: Style {
     ///                 fg: Some(Color::Yellow),
     ///                 bg: Some(Color::Black),
+    ///                 underline_color: None,
+    ///                 underline_style: None,
     ///                 add_modifier: Modifier::empty(),
     ///                 sub_modifier: Modifier::empty(),
     ///             },
@@ -161,6 +167,8 @@ impl<'a> Span<'a> {
     ///             style: Style {
     ///                 fg: Some(Color::Yellow),
     ///                 bg: Some(Color::Black),
+    ///                 underline_color: None,
+    ///                 underline_style: None,
     ///                 add_modifier: Modifier::empty(),
     ///                 sub_modifier: Modifier::empty(),
     ///             },