Merge pull request #1045 from vbasky/fix/926-underline-baseline

Underline follows baseline shift on whole-style text

crates/text/src/layout.rs

@@ -682,7 +682,8 @@ pub fn layout_rich_uncached(text: &str, style: &TextStyle, runs: &[StyleRun], pa
                 lay.underline_runs.push(*si);
             }
         } else if style.underline && pl.content > 0.0 {
-            lay.underlines.push([x, baseline + pm.underline_pos, x + pl.content, baseline + pm.underline_pos + pm.underline_thickness]);
+            let y = baseline - style.baseline_shift + pm.underline_pos;
+            lay.underlines.push([x, y, x + pl.content, y + pm.underline_thickness]);
             lay.underline_runs.push(0);
         }
         lay.lines.push(Line {

crates/text/tests/underline_shift.rs

@@ -0,0 +1,25 @@
+//! Whole-style underline must follow `baseline_shift` the same way character-style runs do.
+use filmcraft_text::{ParagraphStyle, StyleRun, TextStyle, layout, layout_rich};
+
+fn style(shift: f32) -> TextStyle {
+    TextStyle { size: 100.0, underline: true, baseline_shift: shift, ..Default::default() }
+}
+
+fn underline_y(shift: f32) -> (f32, f32) {
+    let para = ParagraphStyle::default();
+    let s = style(shift);
+    let plain = layout("Hi", &s, &para);
+    let rich = layout_rich("Hi", &s, &[StyleRun { range: 0..2, style: s.clone() }], &para);
+    (plain.underlines[0][1], rich.underlines[0][1])
+}
+
+#[test]
+fn whole_style_underline_follows_baseline_shift() {
+    let (p0, r0) = underline_y(0.0);
+    for shift in [40.0, -40.0] {
+        let (plain, rich) = underline_y(shift);
+        assert!((plain - rich).abs() < 1e-3, "plain {plain} vs rich {rich} at shift {shift}");
+        assert!((plain - (p0 - shift)).abs() < 1e-3, "plain underline y {plain} should move with shift {shift}");
+        assert!((rich - (r0 - shift)).abs() < 1e-3, "rich underline y {rich} should move with shift {shift}");
+    }
+}