Render: slide backgrounds are laid over white

PowerPoint shows white around a background picture stretched into part of
the slide and under a see-through background colour. DeckCraft left those
areas transparent, which exports and the slide show draw black.

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/pptx/src/read/dml.rs

@@ -77,6 +77,12 @@ pub fn fill_el(imp: &mut Imp, part: &Part, f: &El) -> Option<Fill> {
         "solidFill" => Fill::Solid { color: color(f).unwrap_or(ColorRef::rgb(Rgba::BLACK)) },
         "gradFill" => Fill::Gradient(gradient(f)),
         "blipFill" => match blip_fill(imp, part, f) {
+            // A picture filling a shape or background with neither `a:stretch` nor `a:tile` is
+            // tiled at its own size, as PowerPoint draws it.
+            Some(mut p) if f.child("stretch").is_none() && f.child("tile").is_none() => {
+                p.mode = PictureMode::Tile { tx: 0.0, ty: 0.0, sx: 1.0, sy: 1.0, flip: "none".into(), align: "tl".into() };
+                Fill::Picture(p)
+            }
             Some(p) => Fill::Picture(p),
             None => Fill::None,
         },

crates/pptx/src/read/mod.rs

@@ -14,7 +14,7 @@ use std::sync::Arc;
 use deckcraft_geom::{Size, emu_to_pt};
 use deckcraft_model::text::TextBody;
 use deckcraft_model::{
-    Background, Comment, CustomShow, HeaderFooter, Layout, LayoutId, LayoutType, Master, MasterId, MediaId, MediaItem, PhType, Presentation,
+    Background, Comment, CustomShow, Geom, HeaderFooter, Layout, LayoutId, LayoutType, Master, MasterId, MediaId, MediaItem, PhType, Presentation,
     Properties, Section, ShowSettings, Slide, SlideId, defaults,
 };
 
@@ -387,6 +387,7 @@ pub fn import(bytes: &[u8]) -> Result<Presentation, PptxError> {
         p.props.company = d.root.child("Company").map(|c| c.text()).unwrap_or_default();
     }
 
+    inherit_placeholder_geometry(&mut p);
     p.header_footer = header_footer(&p);
     p.media = std::mem::take(&mut imp.media);
     p.next_id = imp.next;
@@ -419,6 +420,91 @@ pub fn color_map(cm: &El) -> Vec<(String, String)> {
     cm.attrs.iter().filter(|(k, _)| !k.starts_with("xmlns")).map(|(k, v)| (k.clone(), v.clone())).collect()
 }
 
+/// Placeholders read without a geometry (an empty custom geometry, see `shapes::sp`) take the
+/// geometry of the layout or master placeholder they inherit from, as PowerPoint draws them: a
+/// layout's picture placeholder cut into a shape keeps that shape on the slide. Anything left
+/// is a rectangle.
+fn inherit_placeholder_geometry(p: &mut Presentation) {
+    let unset = |g: &Geom| matches!(g, Geom::Custom { paths } if paths.is_empty());
+    // Masters first, then layouts (from their masters), then slides (from layouts and masters).
+    for m in &mut p.masters {
+        let m = Arc::make_mut(m);
+        walk_shapes_mut(&mut m.shapes, &mut |s| {
+            if unset(&s.geom) {
+                s.geom = Geom::default();
+            }
+        });
+    }
+    let mut layout_geoms: Vec<(LayoutId, usize, Geom)> = vec![];
+    for m in &p.masters {
+        for l in &m.layouts {
+            let ctx = deckcraft_model::resolve::Ctx::for_layout(p, m, l);
+            for (i, s) in l.shapes.iter().enumerate() {
+                if unset(&s.geom) {
+                    let (_, mp) = deckcraft_model::resolve::parents(&ctx, s);
+                    layout_geoms.push((l.id, i, mp.map(|m| m.geom.clone()).filter(|g| !unset(g)).unwrap_or_default()));
+                }
+            }
+        }
+    }
+    for m in &mut p.masters {
+        let m = Arc::make_mut(m);
+        for l in &mut m.layouts {
+            for (id, i, g) in layout_geoms.iter().filter(|(id, _, _)| *id == l.id) {
+                let _ = id;
+                if let Some(s) = l.shapes.get_mut(*i) {
+                    s.geom = g.clone();
+                }
+            }
+        }
+    }
+    let mut slide_geoms: Vec<(usize, usize, Geom)> = vec![];
+    for (si, sl) in p.slides.iter().enumerate() {
+        let Some(ctx) = deckcraft_model::resolve::Ctx::for_slide(p, sl) else { continue };
+        for (i, s) in sl.shapes.iter().enumerate() {
+            if unset(&s.geom) {
+                let (lp, mp) = deckcraft_model::resolve::parents(&ctx, s);
+                let g = lp.map(|l| l.geom.clone()).filter(|g| !unset(g)).or_else(|| mp.map(|m| m.geom.clone()).filter(|g| !unset(g)));
+                slide_geoms.push((si, i, g.unwrap_or_default()));
+            }
+        }
+    }
+    for (si, i, g) in slide_geoms {
+        if let Some(sl) = p.slides.get_mut(si)
+            && let Some(s) = Arc::make_mut(sl).shapes.get_mut(i)
+        {
+            s.geom = g;
+        }
+    }
+    // Placeholders inside groups (rare) and anything still unset: rectangles.
+    for sl in &mut p.slides {
+        walk_shapes_mut(&mut Arc::make_mut(sl).shapes, &mut |s| {
+            if unset(&s.geom) {
+                s.geom = Geom::default();
+            }
+        });
+    }
+    for m in &mut p.masters {
+        for l in &mut Arc::make_mut(m).layouts {
+            walk_shapes_mut(&mut l.shapes, &mut |s| {
+                if unset(&s.geom) {
+                    s.geom = Geom::default();
+                }
+            });
+        }
+    }
+}
+
+/// Every shape, groups included.
+fn walk_shapes_mut(shapes: &mut [deckcraft_model::Shape], f: &mut dyn FnMut(&mut deckcraft_model::Shape)) {
+    for s in shapes {
+        f(s);
+        if let deckcraft_model::ShapeKind::Group { children, .. } = &mut s.kind {
+            walk_shapes_mut(children, f);
+        }
+    }
+}
+
 fn background(imp: &mut Imp, part: &Part, csld: &El) -> Option<Background> {
     let bg = csld.child("bg")?;
     if let Some(pr) = bg.child("bgPr") {

crates/pptx/src/read/shapes.rs

@@ -180,6 +180,15 @@ fn preset_geom(pg: &El) -> Geom {
     Geom::Preset { name, adj }
 }
 
+/// A placeholder whose `spPr` names no geometry takes its layout's (or master's) placeholder's:
+/// marked here with an empty custom geometry, filled in once the layouts are read
+/// (`inherit_placeholder_geometry`).
+fn mark_inherited_geometry(s: &mut Shape, pr: Option<&El>) {
+    if s.ph.is_some() && pr.is_none_or(|pr| pr.child("prstGeom").is_none() && pr.child("custGeom").is_none()) {
+        s.geom = Geom::Custom { paths: vec![] };
+    }
+}
+
 /// `spPr` → transform, geometry, fill, line, effects.
 fn sp_pr(imp: &mut Imp, part: &Part, s: &mut Shape, pr: &El) {
     if let Some(x) = pr.child("xfrm") {
@@ -229,6 +238,7 @@ fn sp(imp: &mut Imp, part: &Part, ctx: &mut IdCtx, e: &El) -> Shape {
     if let Some(pr) = e.child("spPr") {
         sp_pr(imp, part, &mut s, pr);
     }
+    mark_inherited_geometry(&mut s, e.child("spPr"));
     if e.bool("useBgFill") == Some(true) {
         s.fill = Some(Fill::Background);
     }

crates/pptx/tests/fills.rs

@@ -0,0 +1,81 @@
+//! Fills read from decks written by other tools.
+
+use std::io::{Cursor, Read, Write};
+
+use deckcraft_geom::Xfrm;
+use deckcraft_model::style::{Fill, PictureFill, PictureMode};
+use deckcraft_model::{Shape, ShapeId, defaults};
+
+/// `bytes` with `edit` applied to every slide part.
+fn edit_slides(bytes: &[u8], edit: impl Fn(String) -> String) -> Vec<u8> {
+    let mut z = zip::ZipArchive::new(Cursor::new(bytes)).expect("zip");
+    let mut out = zip::ZipWriter::new(Cursor::new(Vec::new()));
+    let o = zip::write::SimpleFileOptions::default();
+    for i in 0..z.len() {
+        let mut f = z.by_index(i).expect("entry");
+        let mut d = vec![];
+        f.read_to_end(&mut d).expect("read");
+        let name = f.name().to_string();
+        if name.starts_with("ppt/slides/slide") && name.ends_with(".xml") {
+            d = edit(String::from_utf8(d).expect("utf8")).into_bytes();
+        }
+        out.start_file(name, o).expect("start");
+        out.write_all(&d).expect("write");
+    }
+    out.finish().expect("finish").into_inner()
+}
+
+fn png() -> Vec<u8> {
+    let mut out = Cursor::new(vec![]);
+    image::DynamicImage::ImageRgb8(image::RgbImage::from_pixel(4, 4, image::Rgb([10, 200, 30])))
+        .write_to(&mut out, image::ImageFormat::Png)
+        .expect("png");
+    out.into_inner()
+}
+
+/// A deck with one shape filled with a stretched picture, exported.
+fn deck() -> Vec<u8> {
+    let mut p = defaults::new_presentation(None);
+    let media = p.add_media("tile.png", "image/png", png());
+    let id = ShapeId(p.alloc_id());
+    let first = p.slides[0].id;
+    p.slide_mut(first).expect("slide").shapes.push(Shape {
+        id,
+        name: "Textured".into(),
+        xfrm: Some(Xfrm::new(10.0, 10.0, 200.0, 100.0)),
+        fill: Some(Fill::Picture(PictureFill { media, ..Default::default() })),
+        ..Default::default()
+    });
+    deckcraft_pptx::export(&p).expect("export")
+}
+
+fn textured_mode(bytes: &[u8]) -> PictureMode {
+    let q = deckcraft_pptx::import(bytes).expect("import");
+    let s = q.slides[0].shapes.iter().find(|s| s.name == "Textured").expect("shape");
+    match &s.fill {
+        Some(Fill::Picture(pf)) => pf.mode.clone(),
+        other => panic!("{other:?}"),
+    }
+}
+
+#[test]
+fn a_shape_picture_fill_without_stretch_or_tile_tiles() {
+    // tdf#128596: `<a:blipFill><a:blip/></a:blipFill>` on a shape, as some tools write it;
+    // PowerPoint tiles the picture at its own size.
+    let bare = edit_slides(&deck(), |s| {
+        let s = regex_free_strip(&s, "<a:stretch>", "</a:stretch>");
+        assert!(!s.contains("<a:stretch"), "the test deck lost its stretch");
+        s
+    });
+    assert!(matches!(textured_mode(&bare), PictureMode::Tile { sx, sy, .. } if sx == 1.0 && sy == 1.0));
+    // An explicit stretch is still a stretch.
+    assert!(matches!(textured_mode(&deck()), PictureMode::Stretch { .. }));
+}
+
+/// `s` without the first `open`…`close` span inside a `blipFill`.
+fn regex_free_strip(s: &str, open: &str, close: &str) -> String {
+    let Some(b) = s.find("<a:blipFill") else { return s.to_string() };
+    let Some(i) = s[b..].find(open).map(|i| i + b) else { return s.to_string() };
+    let Some(j) = s[i..].find(close).map(|j| j + i + close.len()) else { return s.to_string() };
+    format!("{}{}", &s[..i], &s[j..])
+}

crates/pptx/tests/placeholders.rs

@@ -0,0 +1,64 @@
+//! Placeholder inheritance in decks written by PowerPoint.
+
+use std::io::{Cursor, Read, Write};
+
+use deckcraft_model::{Geom, defaults};
+
+/// `bytes` with `edit` applied to every slide part.
+fn edit_slides(bytes: &[u8], edit: impl Fn(String) -> String) -> Vec<u8> {
+    let mut z = zip::ZipArchive::new(Cursor::new(bytes)).expect("zip");
+    let mut out = zip::ZipWriter::new(Cursor::new(Vec::new()));
+    let o = zip::write::SimpleFileOptions::default();
+    for i in 0..z.len() {
+        let mut f = z.by_index(i).expect("entry");
+        let mut d = vec![];
+        f.read_to_end(&mut d).expect("read");
+        let name = f.name().to_string();
+        if name.starts_with("ppt/slides/slide") && name.ends_with(".xml") {
+            d = edit(String::from_utf8(d).expect("utf8")).into_bytes();
+        }
+        out.start_file(name, o).expect("start");
+        out.write_all(&d).expect("write");
+    }
+    out.finish().expect("finish").into_inner()
+}
+
+#[test]
+fn a_placeholder_without_geometry_takes_its_layouts() {
+    // PowerPoint leaves a slide placeholder's spPr empty and draws it with the layout
+    // placeholder's geometry (a picture placeholder cut into a shape keeps the shape).
+    let mut p = defaults::new_presentation(None);
+    let layout = p.slides[0].layout;
+    let m = std::sync::Arc::make_mut(&mut p.masters[0]);
+    let l = m.layouts.iter_mut().find(|l| l.id == layout).expect("layout");
+    for s in &mut l.shapes {
+        if s.ph.is_some() {
+            s.geom = Geom::Preset { name: "ellipse".into(), adj: vec![] };
+        }
+    }
+    let bytes = deckcraft_pptx::export(&p).expect("export");
+    // Strip the slide's own geometry, as PowerPoint writes inheriting placeholders.
+    let bare = edit_slides(&bytes, |s| {
+        let mut s = s;
+        while let Some(i) = s.find("<a:prstGeom") {
+            let Some(j) = s[i..].find("</a:prstGeom>").map(|j| j + i + "</a:prstGeom>".len()) else { break };
+            s.replace_range(i..j, "");
+        }
+        s
+    });
+    let q = deckcraft_pptx::import(&bare).expect("import");
+    let phs: Vec<_> = q.slides[0].shapes.iter().filter(|s| s.ph.is_some()).collect();
+    assert!(!phs.is_empty());
+    for s in phs {
+        assert!(matches!(&s.geom, Geom::Preset { name, .. } if name == "ellipse"), "{:?}", s.geom);
+    }
+    // A placeholder with its own geometry keeps it.
+    let first = p.slides[0].id;
+    for s in &mut p.slide_mut(first).expect("slide").shapes {
+        if s.ph.is_some() {
+            s.geom = Geom::Preset { name: "triangle".into(), adj: vec![] };
+        }
+    }
+    let q = deckcraft_pptx::import(&deckcraft_pptx::export(&p).expect("export")).expect("import");
+    assert!(q.slides[0].shapes.iter().filter(|s| s.ph.is_some()).all(|s| matches!(&s.geom, Geom::Preset { name, .. } if name == "triangle")));
+}

crates/render/src/lib.rs

@@ -13,6 +13,7 @@ mod morph_path;
 mod morph_text;
 mod paint;
 mod placed;
+mod ramp;
 mod table;
 
 use std::collections::HashMap;
@@ -221,11 +222,14 @@ pub struct Renderer {
     resources: Resources,
     /// Outlines morphing in the frame being drawn by `blend`.
     paths: Vec<PathMorph>,
+    /// The background of the slide (layout, master) being drawn, its placeholder colour and the
+    /// slide's view transform: shapes filled with the background (`useBgFill`) show it through.
+    bg: Option<(Fill, Option<Rgba>, Affine)>,
 }
 
 impl Default for Renderer {
     fn default() -> Self {
-        Renderer { resources: Resources::new(), paths: Vec::new() }
+        Renderer { resources: Resources::new(), paths: Vec::new(), bg: None }
     }
 }
 
@@ -588,7 +592,12 @@ impl Renderer {
         let r = Rect::new(0.0, 0.0, f.pres.slide_size.width, f.pres.slide_size.height);
         ctx.set_transform(view);
         let path = r.to_path(0.1);
+        // PowerPoint lays every background over white: a picture stretched into part of the
+        // slide, or a see-through colour, leaves white around and under it.
+        ctx.set_paint(color(Rgba::WHITE, 1.0));
+        ctx.fill_path(&path);
         paint::fill_path(ctx, rctx, &fill, ph, &path, r, view, FillMode::Norm, 1.0, f.pres);
+        self.bg = Some((fill, ph, view));
     }
 
     fn shape(&mut self, ctx: &mut RenderContext, f: &Frame, rctx: &Ctx, s: &Shape, parent: Affine, depth: usize) {
@@ -710,7 +719,16 @@ impl Renderer {
                         }
                         ctx.set_transform(m);
                         ctx.set_fill_rule(if sp.even_odd { peniko::Fill::EvenOdd } else { peniko::Fill::NonZero });
-                        paint::fill_path(ctx, rctx, fl, fill_ph, &sp.path, Rect::new(0.0, 0.0, w, h), m, sp.fill, fade(i).fill, f.pres);
+                        match (fl, &self.bg) {
+                            // `useBgFill`: the slide's background, laid out on the slide (not the
+                            // shape), shows through the shape.
+                            (Fill::Background, Some((bg, ph, view))) => {
+                                let slide = Rect::new(0.0, 0.0, f.pres.slide_size.width, f.pres.slide_size.height);
+                                let path = (view.inverse() * m) * sp.path.clone();
+                                paint::fill_path(ctx, rctx, bg, *ph, &path, slide, *view, sp.fill, fade(i).fill, f.pres);
+                            }
+                            _ => paint::fill_path(ctx, rctx, fl, fill_ph, &sp.path, Rect::new(0.0, 0.0, w, h), m, sp.fill, fade(i).fill, f.pres),
+                        }
                         ctx.set_fill_rule(peniko::Fill::NonZero);
                     }
                 }

crates/render/src/paint.rs

@@ -35,10 +35,11 @@ pub fn fill_path(
             if g.stops.is_empty() {
                 return;
             }
-            let mut stops: Vec<(f32, peniko::Color)> =
-                g.stops.iter().map(|s| (s.pos.clamp(0.0, 1.0) as f32, color(shade(rctx.color(&s.color, ph), mode), alpha))).collect();
+            let mut stops: Vec<(f64, Rgba)> = g.stops.iter().map(|s| (s.pos.clamp(0.0, 1.0), shade(rctx.color(&s.color, ph), mode))).collect();
             stops.sort_by(|a, b| a.0.total_cmp(&b.0));
-            let stops: Vec<peniko::ColorStop> = stops.into_iter().map(|(o, c)| peniko::ColorStop { offset: o, color: c.into() }).collect();
+            // PowerPoint's ramp between stops (linear light, S-shaped), see `ramp`.
+            let stops: Vec<peniko::ColorStop> =
+                crate::ramp::expand(&stops).into_iter().map(|(o, c)| peniko::ColorStop { offset: o as f32, color: color(c, alpha).into() }).collect();
             let grad = match &g.shape {
                 GradientShape::Linear { angle, .. } => {
                     // Angle measured clockwise from left→right; span the bounds along that direction.

crates/render/src/ramp.rs

@@ -0,0 +1,128 @@
+//! Gradient colour ramps as PowerPoint draws them.
+//!
+//! A gradient of exactly two stops, at 0 % and 100 % (what a two-colour gradient is), is not
+//! blended linearly in sRGB by PowerPoint: it mixes the colours in linear light, and the second
+//! colour's share follows an S-shaped curve of the position. Black to white is 105 (not 64) a
+//! quarter of the way, 186 (not 128) half way and 238 (not 191) three quarters of the way, in any
+//! direction, on shapes and on slide backgrounds. Gradients with three or more stops, or with a
+//! stop moved off an end, blend linearly in sRGB (measured from PowerPoint's own slide export).
+//! The renderer interpolates linearly in sRGB, so a two-colour gradient is expanded into short
+//! pieces whose colours follow PowerPoint's ramp.
+
+use deckcraft_color::Rgba;
+
+/// The next stop's share of the linear-light mix at sixteenths of a segment (0 at the first stop,
+/// 1 at the second). Measured, then made symmetric: `w(1 - t) = 1 - w(t)`.
+const WEIGHT: [f64; 17] =
+    [0.0, 0.0205, 0.0469, 0.0878, 0.1431, 0.2143, 0.2989, 0.3972, 0.5, 0.6028, 0.7011, 0.7857, 0.8569, 0.9122, 0.9531, 0.9795, 1.0];
+
+/// Pieces each segment between two stops is cut into.
+const PIECES: usize = 16;
+
+/// The next stop's share at `t` (0..1) between two stops.
+pub fn weight(t: f64) -> f64 {
+    if !t.is_finite() {
+        return 0.0;
+    }
+    let x = t.clamp(0.0, 1.0) * (WEIGHT.len() - 1) as f64;
+    let i = (x.floor() as usize).min(WEIGHT.len() - 2);
+    let f = x - i as f64;
+    let (a, b) = (WEIGHT.get(i).copied().unwrap_or(0.0), WEIGHT.get(i + 1).copied().unwrap_or(1.0));
+    a + (b - a) * f
+}
+
+fn to_linear(v: u8) -> f64 {
+    let v = v as f64 / 255.0;
+    if v <= 0.04045 { v / 12.92 } else { ((v + 0.055) / 1.055).powf(2.4) }
+}
+
+fn to_srgb(v: f64) -> u8 {
+    let v = v.clamp(0.0, 1.0);
+    let s = if v <= 0.0031308 { v * 12.92 } else { 1.055 * v.powf(1.0 / 2.4) - 0.055 };
+    (s * 255.0).round().clamp(0.0, 255.0) as u8
+}
+
+/// The colour at `t` between stops `a` and `b`. Alpha mixes by the same share.
+pub fn mix(a: Rgba, b: Rgba, t: f64) -> Rgba {
+    let w = weight(t);
+    let ch = |x: u8, y: u8| to_srgb(to_linear(x) + (to_linear(y) - to_linear(x)) * w);
+    Rgba { r: ch(a.r, b.r), g: ch(a.g, b.g), b: ch(a.b, b.b), a: (a.a as f64 + (b.a as f64 - a.a as f64) * w).round().clamp(0.0, 255.0) as u8 }
+}
+
+/// Sorted stops (position 0..1, colour) as a renderer interpolating linearly in sRGB should get
+/// them: a two-colour gradient (two stops, at 0 and 1) expanded to follow PowerPoint's ramp,
+/// anything else unchanged.
+pub fn expand(stops: &[(f64, Rgba)]) -> Vec<(f64, Rgba)> {
+    let two_colour = matches!(stops, [(p, _), (q, _)] if *p <= 1e-6 && *q >= 1.0 - 1e-6);
+    if !two_colour {
+        return stops.to_vec();
+    }
+    let mut out = Vec::with_capacity(stops.len() * PIECES + 1);
+    for (i, &(p, c)) in stops.iter().enumerate() {
+        out.push((p, c));
+        let Some(&(q, d)) = stops.get(i + 1) else { continue };
+        if q - p <= 1e-6 || c == d {
+            continue;
+        }
+        for k in 1..PIECES {
+            let t = k as f64 / PIECES as f64;
+            out.push((p + (q - p) * t, mix(c, d, t)));
+        }
+    }
+    out
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn black_to_white_follows_powerpoint() {
+        // PowerPoint's export: 105 at a quarter, 186 half way, 238 at three quarters.
+        let (k, w) = (Rgba::rgb(0, 0, 0), Rgba::rgb(255, 255, 255));
+        for (t, want) in [(0.25, 105), (0.5, 186), (0.75, 238)] {
+            let got = mix(k, w, t).r as i32;
+            assert!((got - want).abs() <= 3, "{t}: {got} vs {want}");
+        }
+    }
+
+    #[test]
+    fn colour_pairs_follow_powerpoint() {
+        // Blue (4472C4) to orange (ED7D31) half way: PowerPoint draws (178, 120, 146).
+        let m = mix(Rgba::rgb(68, 114, 196), Rgba::rgb(237, 125, 49), 0.5);
+        assert!((m.r as i32 - 178).abs() <= 3 && (m.g as i32 - 120).abs() <= 3 && (m.b as i32 - 146).abs() <= 3, "{m:?}");
+        // Red to blue a quarter of the way: (238, 0, 105).
+        let m = mix(Rgba::rgb(255, 0, 0), Rgba::rgb(0, 0, 255), 0.25);
+        assert!((m.r as i32 - 238).abs() <= 3 && (m.b as i32 - 105).abs() <= 3, "{m:?}");
+    }
+
+    #[test]
+    fn the_ends_are_the_stops_and_the_weight_is_symmetric() {
+        let (a, b) = (Rgba::rgb(10, 200, 30), Rgba::rgb(240, 20, 90));
+        assert_eq!(mix(a, b, 0.0), a);
+        assert_eq!(mix(a, b, 1.0), b);
+        for k in 0..=32 {
+            let t = k as f64 / 32.0;
+            assert!((weight(t) + weight(1.0 - t) - 1.0).abs() < 1e-9);
+            assert!(weight(t) <= weight((t + 0.01).min(1.0)), "monotonic");
+        }
+        assert_eq!(weight(f64::NAN), 0.0);
+    }
+
+    #[test]
+    fn expand_keeps_stops_and_hard_edges() {
+        let (r, g) = (Rgba::rgb(255, 0, 0), Rgba::rgb(0, 255, 0));
+        // Three or more stops, or a stop off an end, blend linearly in sRGB: unchanged.
+        let e = expand(&[(0.0, r), (0.5, r), (0.5, g), (1.0, g)]);
+        assert_eq!(e, vec![(0.0, r), (0.5, r), (0.5, g), (1.0, g)]);
+        assert_eq!(expand(&[(0.2, r), (1.0, g)]), vec![(0.2, r), (1.0, g)]);
+        assert_eq!(expand(&[(0.0, r), (0.5, g), (1.0, r)]).len(), 3);
+        // Two equal colours add nothing.
+        assert_eq!(expand(&[(0.0, r), (1.0, r)]), vec![(0.0, r), (1.0, r)]);
+        let e = expand(&[(0.0, r), (1.0, g)]);
+        assert_eq!(e.len(), PIECES + 1);
+        assert_eq!(e.first(), Some(&(0.0, r)));
+        assert_eq!(e.last(), Some(&(1.0, g)));
+        assert!(e.windows(2).all(|w| w[0].0 <= w[1].0));
+    }
+}

crates/render/src/tests.rs

@@ -523,3 +523,112 @@ fn hyperlinks_draw_in_the_hyperlink_colour_underlined() {
     let own = px(&run_deck(RunProps { link, fill: red.clone(), ..Default::default() }));
     assert_eq!(diff(&own, &px(&run_deck(RunProps { fill: red, underline: Some("sng".into()), ..Default::default() }))), 0);
 }
+
+#[test]
+fn a_linear_gradient_ramps_like_powerpoint() {
+    // Black to white, left to right: PowerPoint draws 105 a quarter of the way and 186 half way
+    // (linear-light mix, S-shaped), not 64 and 128.
+    use deckcraft_model::style::{Fill, Gradient, GradientShape, GradientStop};
+    let stop = |pos, c| GradientStop { pos, color: ColorRef::rgb(c) };
+    let sh = Shape {
+        id: ShapeId(700),
+        xfrm: Some(Xfrm::new(0.0, 0.0, 800.0, 100.0)),
+        fill: Some(Fill::Gradient(Gradient {
+            stops: vec![stop(0.0, deckcraft_color::Rgba::rgb(0, 0, 0)), stop(1.0, deckcraft_color::Rgba::rgb(255, 255, 255))],
+            shape: GradientShape::Linear { angle: 0.0, scaled: false },
+            rotate_with_shape: true,
+        })),
+        line: Some(deckcraft_model::style::Line { fill: Some(Fill::None), ..Default::default() }),
+        ..Default::default()
+    };
+    let p = deck_with(vec![sh]);
+    let img = render_slide(&p, 0, &RenderOpts { scale: 1.0, ..Default::default() });
+    for (x, want) in [(200, 105), (400, 186), (600, 238)] {
+        let got = img.pixel(x, 50)[0] as i32;
+        assert!((got - want).abs() <= 4, "x {x}: {got} vs {want}");
+    }
+}
+
+#[test]
+fn a_gradient_with_a_stop_off_the_end_stays_linear() {
+    // Stops at 20 % and 100 %: PowerPoint blends linearly in sRGB (96 at 50 %, 175 at 75 %).
+    use deckcraft_model::style::{Fill, Gradient, GradientShape, GradientStop};
+    let stop = |pos, c| GradientStop { pos, color: ColorRef::rgb(c) };
+    let sh = Shape {
+        id: ShapeId(701),
+        xfrm: Some(Xfrm::new(0.0, 0.0, 800.0, 100.0)),
+        fill: Some(Fill::Gradient(Gradient {
+            stops: vec![stop(0.2, deckcraft_color::Rgba::rgb(0, 0, 0)), stop(1.0, deckcraft_color::Rgba::rgb(255, 255, 255))],
+            shape: GradientShape::Linear { angle: 0.0, scaled: false },
+            rotate_with_shape: true,
+        })),
+        line: Some(deckcraft_model::style::Line { fill: Some(Fill::None), ..Default::default() }),
+        ..Default::default()
+    };
+    let p = deck_with(vec![sh]);
+    let img = render_slide(&p, 0, &RenderOpts { scale: 1.0, ..Default::default() });
+    for (x, want) in [(400, 96), (600, 175)] {
+        let got = img.pixel(x, 50)[0] as i32;
+        assert!((got - want).abs() <= 4, "x {x}: {got} vs {want}");
+    }
+}
+
+#[test]
+fn a_shape_filled_with_the_background_shows_the_slide_background() {
+    // `useBgFill`: PowerPoint paints the slide's background into the shape, laid out on the
+    // slide. A white panel covers a black-to-grey background; a shape on it with the background
+    // fill is a window onto that background.
+    use deckcraft_model::style::{Fill, Gradient, GradientShape, GradientStop};
+    let none = || Some(deckcraft_model::style::Line { fill: Some(Fill::None), ..Default::default() });
+    let panel = Shape {
+        id: ShapeId(710),
+        xfrm: Some(Xfrm::new(0.0, 0.0, 960.0, 540.0)),
+        fill: Some(Fill::solid(ColorRef::rgb(deckcraft_color::Rgba::rgb(255, 255, 255)))),
+        line: none(),
+        ..Default::default()
+    };
+    let window = Shape {
+        id: ShapeId(711),
+        xfrm: Some(Xfrm::new(100.0, 100.0, 760.0, 340.0)),
+        fill: Some(Fill::Background),
+        line: none(),
+        ..Default::default()
+    };
+    let mut p = deck_with(vec![panel, window]);
+    let stop = |pos, v| GradientStop { pos, color: ColorRef::rgb(deckcraft_color::Rgba::rgb(v, v, v)) };
+    std::sync::Arc::make_mut(&mut p.slides[0]).background = Some(deckcraft_model::Background::Fill {
+        fill: Fill::Gradient(Gradient {
+            stops: vec![stop(0.0, 0), stop(0.5, 0), stop(1.0, 200)],
+            shape: GradientShape::Linear { angle: 0.0, scaled: false },
+            rotate_with_shape: true,
+        }),
+    });
+    let img = render_slide(&p, 0, &RenderOpts { scale: 1.0, ..Default::default() });
+    assert_eq!(img.pixel(50, 50)[0], 255, "the panel stays white outside the window");
+    assert!(img.pixel(300, 270)[0] < 8, "the window shows the background's black half: {:?}", img.pixel(300, 270));
+    // Laid out on the slide: three quarters across the slide is half way from black to grey.
+    let v = img.pixel(720, 270)[0] as i32;
+    assert!((v - 100).abs() <= 6, "{v}");
+}
+
+#[test]
+fn a_background_is_laid_over_white() {
+    // A background picture stretched into the bottom-right quarter (fillRect l=50% t=50%), and a
+    // half-transparent colour: PowerPoint shows white around and under them, not transparency.
+    use deckcraft_model::style::{Fill, PictureFill, PictureMode};
+    let mut png = std::io::Cursor::new(Vec::new());
+    image::DynamicImage::ImageRgb8(image::RgbImage::from_pixel(4, 4, image::Rgb([0, 0, 200]))).write_to(&mut png, image::ImageFormat::Png).unwrap();
+    let mut p = deck_with(vec![]);
+    let media = p.add_media("bg.png", "image/png", png.into_inner());
+    let pf = PictureFill { media, mode: PictureMode::Stretch { fill_rect: [0.5, 0.5, 0.0, 0.0] }, ..Default::default() };
+    std::sync::Arc::make_mut(&mut p.slides[0]).background = Some(deckcraft_model::Background::Fill { fill: Fill::Picture(pf) });
+    let img = render_slide(&p, 0, &RenderOpts { scale: 0.5, ..Default::default() });
+    assert_eq!(img.pixel(20, 20), [255, 255, 255, 255], "white where the picture doesn't reach");
+    let q = img.pixel(400, 230);
+    assert!(q[2] > 190 && q[0] < 10 && q[3] == 255, "{q:?}");
+    let see_through = ColorRef::rgb(deckcraft_color::Rgba { r: 0, g: 0, b: 0, a: 128 });
+    std::sync::Arc::make_mut(&mut p.slides[0]).background = Some(deckcraft_model::Background::Fill { fill: Fill::solid(see_through) });
+    let img = render_slide(&p, 0, &RenderOpts { scale: 0.5, ..Default::default() });
+    let g = img.pixel(20, 20);
+    assert!(g[3] == 255 && (g[0] as i32 - 127).abs() <= 3, "half-transparent black over white is grey: {g:?}");
+}

crates/text/src/lib.rs

@@ -566,6 +566,9 @@ fn shape_cells(ctx: &Ctx, text: &str, char_style: &[usize], styles: &[Style], fa
     cells
 }
 
+/// Size of superscript and subscript text relative to the run's size.
+const SUB_SUPER: f64 = 0.66;
+
 /// Shape cells `range` (one item) and hang each cluster's glyphs on its first cell, sharing the
 /// cluster's advance among its graphemes (by the ligature's GDEF carets when it has them).
 #[allow(clippy::too_many_arguments)]
@@ -593,7 +596,11 @@ fn shape_item(
         let st = styles.get(cell.style);
         let size = st.map(|s| s.size).unwrap_or(18.0);
         let small = st.is_some_and(|s| s.caps == Caps::Small) && cell.ch.is_lowercase();
-        (if small { size * 0.8 } else { size }) / upem
+        let size = if small { size * 0.8 } else { size };
+        // Superscript and subscript glyphs are drawn at two thirds of the size, so they advance by
+        // two thirds too.
+        let size = if st.is_some_and(|s| s.baseline != 0.0) { size * SUB_SUPER } else { size };
+        size / upem
     };
     // Cluster heads in this item, ascending; each cluster spans to the next head.
     let mut heads: Vec<usize> = glyphs.iter().filter_map(|g| char_at_byte.get(&g.cluster).copied()).filter(|h| range.contains(h)).collect();
@@ -679,7 +686,8 @@ fn map_symbol_bullet(c: &str, font: Option<&str>) -> String {
         };
         return m.to_string();
     }
-    c.to_string()
+    // PowerPoint draws only the first character of a longer `buChar` ("••" draws one dot).
+    c.graphemes(true).next().unwrap_or("•").to_string()
 }
 
 fn measure_str(face: &FontFace, size: f64, s: &str) -> (f64, Vec<(u32, f64)>) {
@@ -694,9 +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.
@@ -909,7 +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)
         };
@@ -1155,7 +1178,7 @@ fn layout_scaled(ctx: &Ctx, shape: &Shape, body: &TextBody, bp: &BodyProps, opts
             let Some(st) = p.styles.get(cell.style) else { continue };
             let Some(&(cx, cx1)) = line.edges.get(k) else { continue };
             let base_y = line.baseline - st.baseline * st.size;
-            let size = if st.baseline != 0.0 { st.size * 0.66 } else { st.size };
+            let size = if st.baseline != 0.0 { st.size * SUB_SUPER } else { st.size };
             let size = if st.caps == Caps::Small && cell.ch.is_lowercase() { size * 0.8 } else { size };
             let key = (cell.style, cell.face);
             if key != cur_key {
@@ -1204,9 +1227,8 @@ fn layout_scaled(ctx: &Ctx, shape: &Shape, body: &TextBody, bp: &BodyProps, opts
                             }
                         }
                     }
-                    let k66 = if st.baseline != 0.0 { 0.66 } else { 1.0 };
                     for (gid, gx, gy) in &cell.glyphs {
-                        r.glyphs.push((*gid, cl + kash + gx * k66, base_y + gy));
+                        r.glyphs.push((*gid, cl + kash + gx, base_y + gy));
                         r.cells.push((ci, cell.ch));
                     }
                 }

crates/text/src/tests.rs

@@ -45,6 +45,20 @@ fn bullets_are_drawn_for_body_text() {
     assert_eq!(l.para_lines.len(), 2);
 }
 
+#[test]
+fn only_the_first_character_of_a_bullet_is_drawn() {
+    // "••" (seen in the wild) draws one dot in PowerPoint.
+    for (char, glyphs) in [("\u{2022}\u{2022}", 1), ("\u{2022}", 1), ("-->", 1)] {
+        let (p, mut sh) = setup("One", 600.0, 300.0);
+        sh.text.as_mut().unwrap().paragraphs[0].props.bullet = Some(Bullet::Char { char: char.into() });
+        let l = lay(&p, &sh, 600.0, 300.0);
+        let bullet = l.runs.iter().find(|r| r.chars == (0, 0)).expect("bullet run");
+        assert_eq!(bullet.glyphs.len(), glyphs, "{char:?}");
+    }
+    // The first grapheme cluster is kept whole.
+    assert_eq!(map_symbol_bullet("e\u{301}x", None), "e\u{301}");
+}
+
 #[test]
 fn shrink_on_overflow() {
     let text = (0..30).map(|i| format!("Line number {i}")).collect::<Vec<_>>().join("\n");
@@ -395,3 +409,114 @@ fn hostile_bidi_input_never_panics() {
         }
     }
 }
+
+/// Width of `word` laid out in a run with `baseline` (0 = normal, 0.3 = superscript …).
+fn run_width(word: &str, baseline: Option<f64>) -> f64 {
+    let mut run = Run::new(word);
+    run.props.size = Some(24.0);
+    run.props.baseline = baseline;
+    let (p, sh) = bidi_setup(vec![run], 2000.0, false, Align::Left);
+    let l = lay(&p, &sh, 2000.0, 300.0);
+    let line = &l.lines[0];
+    line.caret_x.last().unwrap() - line.caret_x.first().unwrap()
+}
+
+#[test]
+fn superscript_and_subscript_advance_at_their_drawn_size() {
+    // The glyphs are drawn at two thirds of the size; advancing by the full size spread the
+    // letters apart ("s u p e r").
+    let normal = run_width("superscript", None);
+    for b in [Some(0.3), Some(-0.25)] {
+        let w = run_width("superscript", b);
+        assert!((w / normal - SUB_SUPER).abs() < 0.02, "{b:?}: {w} vs {normal}");
+    }
+}
+
+#[test]
+fn superscript_glyphs_sit_inside_their_cells() {
+    let mut run = Run::new("super");
+    run.props.size = Some(24.0);
+    run.props.baseline = Some(0.3);
+    let (p, sh) = bidi_setup(vec![run], 2000.0, false, Align::Left);
+    let l = lay(&p, &sh, 2000.0, 300.0);
+    let line = &l.lines[0];
+    let r = l.runs.iter().find(|r| !r.cells.is_empty()).unwrap();
+    assert!((r.size - 24.0 * SUB_SUPER).abs() < 1e-6);
+    for (g, (ci, _)) in r.glyphs.iter().zip(&r.cells) {
+        let (x0, x1) = line.edges[*ci - line.start];
+        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);
+    }
+}