Text: note that the 1.2 line pitch was measured on one Windows install

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

crates/fonts/src/fontdb.rs

@@ -79,6 +79,10 @@ pub struct FontFace {
     /// values).
     pub cap_height: f64,
     pub x_height: f64,
+    /// Where the baseline sits in a line, as a share of the line's height from its top: the
+    /// Windows ascent over the Windows ascent plus descent (OS/2 `usWinAscent`/`usWinDescent`),
+    /// the split PowerPoint uses (computed by `line_split`).
+    pub line_split: f64,
     pub shaper: harfrust::ShaperData,
     /// Variable fonts: the named instance's axis settings (user units; empty = default instance),
     /// the normalised location and the shaper's view of it.
@@ -436,6 +440,23 @@ pub(crate) fn last_resort_face() -> Arc<FontFace> {
     .clone()
 }
 
+/// The share of a line above the baseline (`FontFace::line_split`): OS/2 `usWinAscent` over
+/// `usWinAscent + usWinDescent`, else the ascent over ascent plus descent. Fonts whose Windows
+/// extent is huge (Gabriola, Cambria Math: over 1.5 em) get 0.81, where PowerPoint puts their
+/// baseline (observed).
+fn line_split(f: &skrifa::FontRef, ascent: f64, descent: f64, upem: f64) -> f64 {
+    use skrifa::raw::TableProvider;
+    let (a, d) = match f.os2() {
+        Ok(os2) if os2.us_win_ascent() > 0 => (os2.us_win_ascent() as f64, os2.us_win_descent() as f64),
+        _ => (ascent, descent),
+    };
+    let total = a + d;
+    if !total.is_finite() || total <= 0.0 || a < 0.0 || d < 0.0 {
+        return 0.8;
+    }
+    if total > upem * 1.5 { 0.81 } else { (a / total).clamp(0.5, 1.0) }
+}
+
 fn make_face(bytes: FontBytes, index: u32, family: String, style: String, coords: Vec<([u8; 4], f32)>) -> Option<FontFace> {
     let data: &[u8] = match &bytes {
         FontBytes::Static(b) => b,
@@ -467,6 +488,7 @@ fn make_face(bytes: FontBytes, index: u32, family: String, style: String, coords
         descent: -(m.descent as f64),
         cap_height: m.cap_height.map(|v| v as f64).filter(|v| *v > 0.0).unwrap_or(m.ascent as f64 * 0.72),
         x_height: m.x_height.map(|v| v as f64).filter(|v| *v > 0.0).unwrap_or(m.ascent as f64 * 0.5),
+        line_split: line_split(&f, m.ascent as f64, -(m.descent as f64), m.units_per_em.max(1) as f64),
         shaper,
         coords,
         location,

crates/fonts/src/lib.rs

@@ -143,6 +143,17 @@ mod tests {
         assert!(f.upem > 0.0);
     }
 
+    #[test]
+    fn line_split_follows_the_windows_ascent_and_descent() {
+        use skrifa::raw::TableProvider;
+        let f = fontdb::last_resort_face();
+        let font = skrifa::FontRef::new(f.data()).unwrap();
+        let os2 = font.os2().unwrap();
+        let (a, d) = (os2.us_win_ascent() as f64, os2.us_win_descent() as f64);
+        assert!((f.line_split - a / (a + d)).abs() < 1e-9, "{} vs {}", f.line_split, a / (a + d));
+        assert!(f.line_split > 0.5 && f.line_split < 1.0);
+    }
+
     #[test]
     fn some_face_always_resolves() {
         let db = FontDb::with_font_dirs(Vec::new());

crates/text/src/lib.rs

@@ -702,9 +702,20 @@ fn measure_str(face: &FontFace, size: f64, s: &str) -> (f64, Vec<(u32, f64)>) {
     (x, out)
 }
 
+/// Single line spacing as a multiple of the font size. PowerPoint spaces single-spaced lines 1.2
+/// times the size apart in every font (observed on twenty Latin, CJK, Thai and Indic fonts at 18
+/// and 40 pt), whatever the font's own ascent and descent.
+///
+/// Caveat: this was measured on one Windows install of desktop PowerPoint. It may be a Windows or
+/// machine setting; PowerPoint on macOS or the web may space lines by the font's own metrics.
+/// Keep it a single tunable value, and re-measure on the other platform before changing it.
+const LINE_PITCH: f64 = 1.2;
+
+/// A line's height above and below the baseline at `size`: [`LINE_PITCH`] × size, split where
+/// the font's Windows ascent and descent put the baseline.
 fn line_metrics(face: &FontFace, size: f64) -> (f64, f64) {
-    let k = size / face.upem.max(1.0);
-    (face.ascent * k, face.descent * k)
+    let h = size * LINE_PITCH;
+    (h * face.line_split, h * (1.0 - face.line_split))
 }
 
 /// Break opportunities: allowed[i] = a line may start at char i.
@@ -917,7 +928,11 @@ fn layout_scaled(ctx: &Ctx, shape: &Shape, body: &TextBody, bp: &BodyProps, opts
         let bullet_w = p.bullet.as_ref().map(|(s, st)| measure_str(&st.face, st.size, s).0).unwrap_or(0.0);
         let first_x = if p.bullet.is_some() {
             let bx = (margin + indent).max(0.0);
-            if indent < 0.0 && bx + bullet_w <= margin { margin } else { bx + bullet_w + if indent >= 0.0 { 0.0 } else { 3.0 } }
+            // A hanging bullet's text starts at the margin. When the hang reaches left of the box
+            // (marL + indent < 0), PowerPoint pins the bullet to the box's edge and keeps the
+            // hang: the first line's text starts at -indent (later lines stay at the margin).
+            let stop = margin.max(-indent);
+            if indent < 0.0 && bx + bullet_w <= stop { stop } else { bx + bullet_w + if indent >= 0.0 { 0.0 } else { 3.0 } }
         } else {
             (margin + indent).max(0.0)
         };

crates/text/src/tests.rs

@@ -447,3 +447,76 @@ fn superscript_glyphs_sit_inside_their_cells() {
         assert!(g.1 >= x0 - 0.01 && g.1 < x1, "glyph at {} outside its cell {x0}..{x1}", g.1);
     }
 }
+
+/// A wrapping numbered paragraph with `marL` and `indent`; returns (bullet x, first line's text
+/// x, second line's text x).
+fn hanging(margin: f64, indent: f64, bullet: Bullet) -> (Option<f64>, f64, f64) {
+    let text = "Wrapping words go on and on so the paragraph needs at least two or three lines here";
+    let (p, mut sh) = setup(text, 300.0, 300.0);
+    let para = &mut sh.text.as_mut().unwrap().paragraphs[0];
+    para.props.bullet = Some(bullet);
+    para.props.margin_left = Some(margin);
+    para.props.indent = Some(indent);
+    let l = lay(&p, &sh, 300.0, 300.0);
+    assert!(l.lines.len() >= 2, "{} lines", l.lines.len());
+    let bx = l.runs.iter().find(|r| r.cells.is_empty() && !r.glyphs.is_empty()).map(|r| r.glyphs[0].1);
+    (bx, l.lines[0].caret_x[0], l.lines[1].caret_x[0])
+}
+
+#[test]
+fn a_hang_past_the_box_edge_keeps_its_width_on_the_first_line() {
+    // PowerPoint, marL 0 / indent -36pt: the number sits at the box's edge, the first line's text
+    // 36pt in, and the wrapped lines at the margin (observed with PowerPoint's slide export).
+    let num = || Bullet::AutoNum { scheme: "arabicPeriod".into(), start_at: 1 };
+    let (bx, first, rest) = hanging(0.0, -36.0, num());
+    assert!((first - rest - 36.0).abs() < 0.5, "first {first} rest {rest}");
+    assert!((bx.unwrap() - rest).abs() < 0.5, "bullet {bx:?} rest {rest}");
+    // marL 18 / indent -54: number at the edge, first line at 54, the rest at 18.
+    let (bx, first, rest) = hanging(18.0, -54.0, num());
+    assert!((first - rest - 36.0).abs() < 0.5, "first {first} rest {rest}");
+    assert!((rest - bx.unwrap() - 18.0).abs() < 0.5, "bullet {bx:?} rest {rest}");
+    // A character bullet behaves the same.
+    let (_, first, rest) = hanging(0.0, -36.0, Bullet::Char { char: "•".into() });
+    assert!((first - rest - 36.0).abs() < 0.5, "first {first} rest {rest}");
+    // Without a bullet the first line just starts at the edge.
+    let (_, first, rest) = hanging(0.0, -36.0, Bullet::None);
+    assert!((first - rest).abs() < 0.5, "first {first} rest {rest}");
+}
+
+#[test]
+fn an_ordinary_hang_still_puts_the_text_at_the_margin() {
+    let (bx, first, rest) = hanging(36.0, -36.0, Bullet::AutoNum { scheme: "arabicPeriod".into(), start_at: 1 });
+    assert!((first - rest).abs() < 0.5, "first {first} rest {rest}");
+    assert!((rest - bx.unwrap() - 36.0).abs() < 0.5);
+}
+
+#[test]
+fn single_spaced_lines_are_1_2_times_the_size_apart_whatever_the_font() {
+    // PowerPoint spaces single-spaced lines 1.2 × the font size apart in every font, with the
+    // baseline where the font's Windows ascent/descent split puts it (observed on twenty fonts).
+    for size in [18.0, 40.0] {
+        let mut run = Run::new("HHH");
+        run.props.size = Some(size);
+        let (p, mut sh) = bidi_setup(vec![run], 2000.0, false, Align::Left);
+        let t = sh.text.as_mut().unwrap();
+        t.body.autofit = Some(AutoFit::None);
+        let second = t.paragraphs[0].clone();
+        t.paragraphs.push(second.clone());
+        t.paragraphs.push(second);
+        for para in &mut t.paragraphs {
+            para.props.line_spacing = Some(Spacing::Pct(1.0));
+            para.props.space_before = Some(Spacing::Pts(0.0));
+            para.props.space_after = Some(Spacing::Pts(0.0));
+        }
+        let l = lay(&p, &sh, 2000.0, 600.0);
+        assert_eq!(l.lines.len(), 3);
+        // Each line is 1.2 × the size tall (the face is not compared across lines: another
+        // test's thread can load the family between them, see #252).
+        for line in &l.lines {
+            assert!((line.bottom - line.top - size * LINE_PITCH).abs() < 1e-6, "{size}: {}", line.bottom - line.top);
+        }
+        let face = &l.runs[0].face;
+        let first = &l.lines[0];
+        assert!((first.baseline - first.top - size * LINE_PITCH * face.line_split).abs() < 1e-6);
+    }
+}