From b7015f17a49501e99642009ebadabcbefc0fbad0 Mon Sep 17 00:00:00 2001
From: Ogulcan Celik <ogulcancelik@gmail.com>
Date: Tue, 30 Jun 2026 15:55:13 +0300
Subject: fix: render ansi undercurl styles

refs #895
---
 src/protocol/render_ansi.rs | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

(limited to 'src/protocol/render_ansi.rs')

diff --git a/src/protocol/render_ansi.rs b/src/protocol/render_ansi.rs
index 12606bff..3346bb9c 100644
--- a/src/protocol/render_ansi.rs
+++ b/src/protocol/render_ansi.rs
@@ -31,7 +31,7 @@ use std::io::Write;
 
 use unicode_width::UnicodeWidthStr;
 
-use crate::protocol::{CellData, FrameData};
+use crate::protocol::{underline_style_from_modifier, CellData, FrameData};
 
 /// Bytes produced by a [`BlitEncoder`] for one terminal frame.
 pub(crate) struct EncodedBlit {
@@ -294,7 +294,13 @@ fn modifier_to_sgr_parts(val: u16) -> Vec<&'static str> {
         parts.push("3");
     }
     if val & UNDERLINED != 0 {
-        parts.push("4");
+        parts.push(match underline_style_from_modifier(val) {
+            2 => "4:2",
+            3 => "4:3",
+            4 => "4:4",
+            5 => "4:5",
+            _ => "4",
+        });
     }
     if val & SLOW_BLINK != 0 {
         parts.push("5");
@@ -842,6 +848,18 @@ mod tests {
         assert_eq!(build_sgr(0x00_00_00_00, 0x00_00_00_00, 0), "\x1b[0;39;49m");
     }
 
+    #[test]
+    fn build_sgr_preserves_curly_underline_style() {
+        let modifier = crate::protocol::modifier_to_u16(
+            crate::protocol::modifier_with_underline_style(ratatui::style::Modifier::UNDERLINED, 3),
+        );
+
+        assert_eq!(
+            build_sgr(0x00_00_00_00, 0x00_00_00_00, modifier),
+            "\x1b[0;4:3;39;49m"
+        );
+    }
+
     #[test]
     fn cells_equal_identical() {
         let a = make_cell("A", 2, 1, 0);
-- 
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