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fix: use dynamic font probing to preserve ligatures across break opportunities

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This commit is contained in:
Adam Kowalski 2026-01-16 21:21:00 -08:00 • committed by Jeremy Soller
parent 5d1db4992a
commit c6ce5e69e5
2 changed files with 68 additions and 23 deletions
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37
tests/shaping_and_rendering.rs
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@ -78,7 +78,8 @@ fn test_english_mixed_with_arabic_paragraph_rendering() {
fn test_ligature_segmentation() {
use cosmic_text::{Buffer, FontSystem, Metrics, Shaping};
let mut font_system = FontSystem::new_with_locale_and_db("en-US".into(), fontdb::Database::new());
let mut font_system =
FontSystem::new_with_locale_and_db("en-US".into(), fontdb::Database::new());
let font = std::fs::read("fonts/Inter-Regular.ttf").unwrap();
font_system.db_mut().load_font_data(font);
let metrics = Metrics::new(14.0, 20.0);
@ -93,25 +94,38 @@ fn test_ligature_segmentation() {
let shape = line.shape_opt().expect("ShapeLine not found");
let span = &shape.spans[0];
// The pipe character | is typically a line break opportunity.
// This test ensures that our patch prevents splitting |> into separate words,
// which would break ligature formation in fonts that support it.
// Inter-Regular does NOT have a ligature for |>, so we expect it to be split.
// This confirms that we didn't break valid wrapping for non-ligatures.
assert_eq!(
span.words.len(),
1,
"Expected '|>' to be a single word (preserved for ligature), but found {} words.",
2,
"Expected '|>' to be 2 words (no ligature in Inter), but found {} words.",
span.words.len()
);
// Test -> (Arrow), which is a common ligature.
buffer.set_text("->", &Attrs::new(), Shaping::Advanced, None);
buffer.shape_until_scroll(false);
let line = &buffer.lines[0];
let shape = line.shape_opt().expect("ShapeLine not found");
assert_eq!(
shape.spans[0].words.len(),
1,
"Expected '->' to be a single word (ligature), but found {} words.",
shape.spans[0].words.len()
);
// Test !=
buffer.set_text("!=", &Attrs::new(), Shaping::Advanced, None);
buffer.shape_until_scroll(false);
let line = &buffer.lines[0];
let shape = line.shape_opt().expect("ShapeLine not found");
// Inter-Regular does not have a != ligature.
assert_eq!(
shape.spans[0].words.len(),
1,
"Expected '!=' to be a single word, but found {} words.",
2,
"Expected '!=' to be 2 words (no ligature), but found {} words.",
shape.spans[0].words.len()
);
@ -120,10 +134,11 @@ fn test_ligature_segmentation() {
buffer.shape_until_scroll(false);
let line = &buffer.lines[0];
let shape = line.shape_opt().expect("ShapeLine not found");
// Inter does not have a ++ ligature.
assert_eq!(
shape.spans[0].words.len(),
1,
"Expected '++' to be a single word, but found {} words.",
2,
"Expected '++' to be 2 words, but found {} words.",
shape.spans[0].words.len()
);
}
}