Render: shapes filled with the background (useBgFill) show it

A shape with useBgFill="1" is a window onto the slide's background, laid
out on the slide. DeckCraft drew nothing in it, so a master that covers the
background with a white panel and cuts a background-filled frame into it
(tdf93868) rendered all white.

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

crates/engine/src/cmd/design.rs

@@ -483,6 +483,7 @@ fn insert_layout(s: &mut Session, p: &Value) -> Result<Value> {
                 background: None,
                 show_master_shapes: true,
                 preserve: true,
+                color_map: None,
                 raw_ext: None,
             },
         );

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/model/src/defaults.rs

@@ -243,6 +243,7 @@ pub fn build_master(size: Size, theme: Theme, first_id: u32) -> (Master, u32) {
             background: None,
             show_master_shapes: true,
             preserve: true,
+            color_map: None,
             raw_ext: None,
         });
     };

crates/model/src/lib.rs

@@ -488,6 +488,10 @@ pub struct Slide {
     /// Speaker notes.
     pub notes: TextBody,
     pub comments: Vec<Comment>,
+    /// `clrMapOvr`: a colour map replacing the layout's or master's (`bg1`→`dk1`…); None follows
+    /// the layout.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub color_map: Option<Vec<(String, String)>>,
     /// Unmodelled XML kept for round-trip (custom data, tags).
     #[serde(skip_serializing_if = "Option::is_none")]
     pub raw_ext: Option<String>,
@@ -507,6 +511,7 @@ impl Default for Slide {
             animations: vec![],
             notes: TextBody::default(),
             comments: vec![],
+            color_map: None,
             raw_ext: None,
         }
     }
@@ -596,6 +601,10 @@ pub struct Layout {
     pub background: Option<Background>,
     pub show_master_shapes: bool,
     pub preserve: bool,
+    /// `clrMapOvr`: a colour map replacing the master's for this layout and the slides using it
+    /// (dark "section" layouts map `bg1` to `dk1`); None follows the master.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub color_map: Option<Vec<(String, String)>>,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub raw_ext: Option<String>,
 }
@@ -641,24 +650,17 @@ impl Master {
     }
     /// Resolve `bg1`/`tx1`/`bg2`/`tx2` through the colour map.
     pub fn map_slot(&self, slot: SchemeSlot) -> SchemeSlot {
-        let key = match slot {
-            SchemeSlot::Bg1 => "bg1",
-            SchemeSlot::Tx1 => "tx1",
-            SchemeSlot::Bg2 => "bg2",
-            SchemeSlot::Tx2 => "tx2",
-            other => return other,
-        };
-        self.color_map.iter().find(|(k, _)| k == key).and_then(|(_, v)| SchemeSlot::from_xml(v)).unwrap_or(match slot {
-            SchemeSlot::Bg1 => SchemeSlot::Lt1,
-            SchemeSlot::Tx1 => SchemeSlot::Dk1,
-            SchemeSlot::Bg2 => SchemeSlot::Lt2,
-            _ => SchemeSlot::Dk2,
-        })
+        map_slot(&self.color_map, slot)
     }
     /// The theme's colour scheme with the colour map applied (`bg1`… resolve to mapped colours).
     pub fn scheme(&self) -> ColorScheme {
+        self.scheme_with(&self.color_map)
+    }
+    /// The theme's colour scheme with `map` (a layout's or slide's override, or the master's own)
+    /// applied.
+    pub fn scheme_with(&self, map: &[(String, String)]) -> ColorScheme {
         let mut s = self.theme.colors.clone();
-        if self.color_map.is_empty() {
+        if map.is_empty() {
             return s;
         }
         let base = self.theme.colors.clone();
@@ -668,12 +670,30 @@ impl Master {
             (SchemeSlot::Bg2, SchemeSlot::Lt2),
             (SchemeSlot::Tx2, SchemeSlot::Dk2),
         ] {
-            s.set(slot, base.get(self.map_slot(alias)));
+            s.set(slot, base.get(map_slot(map, alias)));
         }
         s
     }
 }
 
+/// Resolve `bg1`/`tx1`/`bg2`/`tx2` through the colour map `map` (the default mapping when it has
+/// no entry).
+pub fn map_slot(map: &[(String, String)], slot: SchemeSlot) -> SchemeSlot {
+    let key = match slot {
+        SchemeSlot::Bg1 => "bg1",
+        SchemeSlot::Tx1 => "tx1",
+        SchemeSlot::Bg2 => "bg2",
+        SchemeSlot::Tx2 => "tx2",
+        other => return other,
+    };
+    map.iter().find(|(k, _)| k == key).and_then(|(_, v)| SchemeSlot::from_xml(v)).unwrap_or(match slot {
+        SchemeSlot::Bg1 => SchemeSlot::Lt1,
+        SchemeSlot::Tx1 => SchemeSlot::Dk1,
+        SchemeSlot::Bg2 => SchemeSlot::Lt2,
+        _ => SchemeSlot::Dk2,
+    })
+}
+
 #[derive(Clone, Debug, Default, PartialEq, Serialize, Deserialize)]
 #[serde(default, rename_all = "camelCase")]
 pub struct Section {

crates/model/src/resolve.rs

@@ -22,23 +22,27 @@ pub struct Ctx<'a> {
     pub layout: Option<&'a Layout>,
     pub owner: Owner,
     pub scheme: ColorScheme,
+    /// The colour map in force: the slide's override, else its layout's, else the master's.
+    pub color_map: Vec<(String, String)>,
 }
 
 impl<'a> Ctx<'a> {
     pub fn for_slide(pres: &'a Presentation, slide: &Slide) -> Option<Ctx<'a>> {
         let (master, layout) = pres.master_for(slide)?;
-        Some(Ctx { pres, master, layout, owner: Owner::Slide, scheme: master.scheme() })
+        let map = slide.color_map.as_ref().or(layout.and_then(|l| l.color_map.as_ref())).unwrap_or(&master.color_map).clone();
+        Some(Ctx { pres, master, layout, owner: Owner::Slide, scheme: master.scheme_with(&map), color_map: map })
     }
     pub fn for_layout(pres: &'a Presentation, master: &'a Master, layout: &'a Layout) -> Ctx<'a> {
-        Ctx { pres, master, layout: Some(layout), owner: Owner::Layout, scheme: master.scheme() }
+        let map = layout.color_map.as_ref().unwrap_or(&master.color_map).clone();
+        Ctx { pres, master, layout: Some(layout), owner: Owner::Layout, scheme: master.scheme_with(&map), color_map: map }
     }
     pub fn for_master(pres: &'a Presentation, master: &'a Master) -> Ctx<'a> {
-        Ctx { pres, master, layout: None, owner: Owner::Master, scheme: master.scheme() }
+        Ctx { pres, master, layout: None, owner: Owner::Master, scheme: master.scheme(), color_map: master.color_map.clone() }
     }
     pub fn color(&self, c: &ColorRef, ph: Option<Rgba>) -> Rgba {
         let c = match &c.base {
             crate::ColorBase::Scheme { slot } if matches!(slot, SchemeSlot::Bg1 | SchemeSlot::Tx1 | SchemeSlot::Bg2 | SchemeSlot::Tx2) => {
-                ColorRef { base: crate::ColorBase::Scheme { slot: self.master.map_slot(*slot) }, mods: c.mods.clone() }
+                ColorRef { base: crate::ColorBase::Scheme { slot: crate::map_slot(&self.color_map, *slot) }, mods: c.mods.clone() }
             }
             _ => c.clone(),
         };

crates/model/src/tests.rs

@@ -159,3 +159,31 @@ fn hyperlinked_runs_take_the_theme_hyperlink_look() {
     let dbl = resolve::run(&ctx, title, &para, &RunProps { link, underline: Some("dbl".into()), ..Default::default() });
     assert_eq!((dbl.fill, dbl.underline.as_deref()), (hlink, Some("dbl")));
 }
+
+#[test]
+fn a_layout_colour_map_override_applies_to_its_slides() {
+    // A dark "section" layout maps bg1→dk1 and tx1→lt1; a slide on it that keeps the master
+    // mapping (`masterClrMapping`) follows the layout, as PowerPoint draws it.
+    let mut p = Presentation::default();
+    let dark: Vec<(String, String)> =
+        [("bg1", "dk1"), ("tx1", "lt1"), ("bg2", "dk2"), ("tx2", "lt2")].iter().map(|(a, b)| (a.to_string(), b.to_string())).collect();
+    let layout = p.slides[0].layout;
+    let m = std::sync::Arc::make_mut(&mut p.masters[0]);
+    let colors = m.theme.colors.clone();
+    m.layouts.iter_mut().find(|l| l.id == layout).unwrap().color_map = Some(dark.clone());
+    let s: Slide = (*p.slides[0]).clone();
+    let ctx = Ctx::for_slide(&p, &s).unwrap();
+    assert_eq!(ctx.color(&ColorRef::scheme(SchemeSlot::Bg1), None), colors.get(SchemeSlot::Dk1));
+    assert_eq!(ctx.color(&ColorRef::scheme(SchemeSlot::Tx2), None), colors.get(SchemeSlot::Lt2));
+    assert_eq!(ctx.scheme.get(SchemeSlot::Lt1), colors.get(SchemeSlot::Dk1));
+    // The slide's own override wins over the layout's.
+    let mut own = s.clone();
+    own.color_map = Some([("bg1", "lt1"), ("tx1", "dk1")].iter().map(|(a, b)| (a.to_string(), b.to_string())).collect());
+    let ctx = Ctx::for_slide(&p, &own).unwrap();
+    assert_eq!(ctx.color(&ColorRef::scheme(SchemeSlot::Bg1), None), colors.get(SchemeSlot::Lt1));
+    // The layout itself draws with its override; the master keeps its own map.
+    let m = &p.masters[0];
+    let l = m.layout(layout).unwrap();
+    assert_eq!(Ctx::for_layout(&p, m, l).color(&ColorRef::scheme(SchemeSlot::Bg1), None), colors.get(SchemeSlot::Dk1));
+    assert_eq!(Ctx::for_master(&p, m).color(&ColorRef::scheme(SchemeSlot::Bg1), None), colors.get(SchemeSlot::Lt1));
+}

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

@@ -609,12 +609,18 @@ fn read_layout(imp: &mut Imp, part: &Part, doc: &Doc) -> Layout {
             l.shapes = shapes::sp_tree(imp, part, &mut ctx, tree, 0);
         }
     }
+    l.color_map = color_map_override(root);
     if let Some(ext) = root.child("extLst").filter(|e| !has_rel_refs(e)) {
         l.raw_ext = Some(ext.elements().map(|e| part.keep(e)).collect());
     }
     l
 }
 
+/// A layout's or slide's `clrMapOvr/overrideClrMapping` (None for `masterClrMapping` or none).
+fn color_map_override(root: &El) -> Option<Vec<(String, String)>> {
+    root.child("clrMapOvr")?.child("overrideClrMapping").map(color_map)
+}
+
 fn read_slide(imp: &mut Imp, part: &Part, doc: &Doc, id: SlideId, layout: LayoutId) -> Slide {
     let root = &doc.root;
     let mut s = Slide {
@@ -622,6 +628,7 @@ fn read_slide(imp: &mut Imp, part: &Part, doc: &Doc, id: SlideId, layout: Layout
         layout,
         hidden: root.bool("show") == Some(false),
         show_master_shapes: root.bool("showMasterSp").unwrap_or(true),
+        color_map: color_map_override(root),
         ..Default::default()
     };
     let mut ctx = shapes::IdCtx::default();

crates/pptx/src/write/mod.rs

@@ -227,6 +227,21 @@ const CLR_KEYS: [(&str, &str); 12] = [
 ];
 
 fn clr_map(w: &mut W, map: &[(String, String)]) {
+    w.empty("p:clrMap", clr_map_attrs(map));
+}
+
+/// `p:clrMapOvr`: the layout's or slide's own colour map, else `a:masterClrMapping`.
+fn clr_map_ovr(w: &mut W, map: Option<&[(String, String)]>) {
+    w.open0("p:clrMapOvr");
+    match map {
+        Some(m) => w.empty("a:overrideClrMapping", clr_map_attrs(m)),
+        None => w.empty0("a:masterClrMapping"),
+    }
+    w.close("p:clrMapOvr");
+}
+
+/// The twelve colour map attributes, each a theme slot (the default for anything else).
+fn clr_map_attrs(map: &[(String, String)]) -> A {
     let mut a = A::new();
     for (k, d) in CLR_KEYS {
         let v = map
@@ -237,7 +252,7 @@ fn clr_map(w: &mut W, map: &[(String, String)]) {
             .unwrap_or(d);
         a = a.a(k, v);
     }
-    w.empty("p:clrMap", a);
+    a
 }
 
 fn ext_list(w: &mut W, raw: Option<&str>) {
@@ -522,9 +537,7 @@ fn layout_xml(x: &mut Exp, o: &mut Out, l: &Layout) -> Vec<u8> {
         A::new().o("showMasterSp", (!l.show_master_shapes).then_some("0")).a("type", l.kind.xml()).t("preserve", l.preserve),
     );
     csld(&mut w, x, o, &l.name, l.background.as_ref(), &l.shapes);
-    w.open0("p:clrMapOvr");
-    w.empty0("a:masterClrMapping");
-    w.close("p:clrMapOvr");
+    clr_map_ovr(&mut w, l.color_map.as_deref());
     ext_list(&mut w, ext_children(l.raw_ext.as_deref()).as_deref());
     w.close("p:sldLayout");
     w.finish()
@@ -556,9 +569,7 @@ fn slide_xml(x: &mut Exp, o: &mut Out, s: &Slide) -> Vec<u8> {
     let mut w = W::new();
     root_open(&mut w, "p:sld", A::new().o("showMasterSp", (!s.show_master_shapes).then_some("0")).o("show", s.hidden.then_some("0")));
     let ids = csld(&mut w, x, o, &s.name, s.background.as_ref(), &s.shapes);
-    w.open0("p:clrMapOvr");
-    w.empty0("a:masterClrMapping");
-    w.close("p:clrMapOvr");
+    clr_map_ovr(&mut w, s.color_map.as_deref());
     if let Some(t) = &s.transition {
         timing::transition(&mut w, x, o, t);
     }

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/roundtrip.rs

@@ -730,3 +730,39 @@ fn date_fields_keep_their_type_and_saved_text() {
         assert_eq!(by_name(&q.slides[0], name).text, by_name(&p.slides[0], name).text, "{name}");
     }
 }
+
+#[test]
+fn colour_map_overrides_round_trip() {
+    let mut p = defaults::new_presentation(None);
+    let dark: Vec<(String, String)> =
+        [("bg1", "dk1"), ("tx1", "lt1"), ("bg2", "dk2"), ("tx2", "lt2")].iter().map(|(a, b)| (a.to_string(), b.to_string())).collect();
+    let layout = p.slides[0].layout;
+    std::sync::Arc::make_mut(&mut p.masters[0]).layouts.iter_mut().find(|l| l.id == layout).expect("layout").color_map = Some(dark.clone());
+    let first = p.slides[0].id;
+    p.slide_mut(first).expect("slide").color_map = Some(dark.clone());
+    let q = round(&p);
+    let get = |m: &Option<Vec<(String, String)>>, k: &str| m.as_ref().and_then(|m| m.iter().find(|(a, _)| a == k).map(|(_, v)| v.clone()));
+    let ql = q.masters[0].layouts.iter().find(|l| l.color_map.is_some()).expect("the layout keeps its override");
+    assert_eq!(get(&ql.color_map, "bg1").as_deref(), Some("dk1"));
+    assert_eq!(get(&q.slides[0].color_map, "tx1").as_deref(), Some("lt1"));
+    // Layouts and slides without one keep following the master.
+    assert!(q.masters[0].layouts.iter().filter(|l| l.color_map.is_none()).count() >= 1);
+}
+
+#[test]
+fn a_picture_duotone_round_trips() {
+    let mut p = defaults::new_presentation(None);
+    let img = p.add_media("image1.png", "image/png", png(4, 4, [128, 128, 128]));
+    let mut pic = shape(&mut p, "Duotone", 10.0, 10.0, 100.0, 100.0);
+    let mut pf = PictureFill { media: img, ..Default::default() };
+    pf.adjust.duotone = Some((ColorRef::scheme(SchemeSlot::Accent1).with(ColorTransform::Shade(30000)), ColorRef::rgb(Rgba::rgb(250, 240, 200))));
+    pic.kind = deckcraft_model::ShapeKind::Picture { fill: pf };
+    let first = p.slides[0].id;
+    p.slide_mut(first).expect("slide").shapes.push(pic);
+    let q = round(&p);
+    let sh = by_name(&q.slides[0], "Duotone");
+    let deckcraft_model::ShapeKind::Picture { fill } = &sh.kind else { panic!("picture") };
+    let (d, l) = fill.adjust.duotone.as_ref().expect("duotone kept");
+    assert!(matches!(d.base, deckcraft_model::ColorBase::Scheme { slot: SchemeSlot::Accent1 }));
+    assert!(matches!(l.base, deckcraft_model::ColorBase::Rgb { rgb } if rgb == Rgba::rgb(250, 240, 200)));
+}

crates/render/src/images.rs

@@ -79,9 +79,26 @@ fn adjust_key(a: &PictureAdjust) -> u64 {
     if let Some(c) = a.clear_color {
         mix(((c.r as u64) << 16) | ((c.g as u64) << 8) | c.b as u64 | 1 << 40);
     }
+    if let Some((d, l)) = duotone_rgb(a) {
+        for c in [d, l] {
+            mix(((c.r as u64) << 24) | ((c.g as u64) << 16) | ((c.b as u64) << 8) | c.a as u64 | 1 << 41);
+        }
+    }
     h
 }
 
+/// The duotone's dark and light colours. The painter resolves them to plain RGB first (see
+/// `paint::resolved`); a colour that is still a scheme reference falls back to black and white.
+fn duotone_rgb(a: &PictureAdjust) -> Option<(deckcraft_color::Rgba, deckcraft_color::Rgba)> {
+    use deckcraft_model::style::ColorBase;
+    let (d, l) = a.duotone.as_ref()?;
+    let rgb = |c: &deckcraft_model::style::ColorRef, or: deckcraft_color::Rgba| match &c.base {
+        ColorBase::Rgb { rgb } if c.mods.is_empty() => *rgb,
+        _ => or,
+    };
+    Some((rgb(d, deckcraft_color::Rgba::BLACK), rgb(l, deckcraft_color::Rgba::WHITE)))
+}
+
 /// Decode encoded bytes (PNG, JPEG, GIF, WebP, BMP, TIFF) to straight RGBA.
 pub fn decode(bytes: &[u8]) -> Option<image::RgbaImage> {
     if bytes.len() > 512 << 20 {
@@ -233,6 +250,7 @@ fn apply_adjust(img: &mut image::RgbaImage, a: &PictureAdjust) {
     if a.brightness == 0.0 && a.contrast == 0.0 && sat == 1.0 && !a.grayscale && a.clear_color.is_none() && a.duotone.is_none() {
         return;
     }
+    let duo = duotone_rgb(a);
     let b = a.brightness.clamp(-1.0, 1.0) * 255.0;
     let c = a.contrast.clamp(-1.0, 1.0);
     let cf = if c >= 0.0 { 1.0 / (1.0 - c * 0.99) } else { 1.0 + c };
@@ -252,6 +270,12 @@ fn apply_adjust(img: &mut image::RgbaImage, a: &PictureAdjust) {
             *v = y + (*v - y) * s;
             *v = (*v - 128.0) * cf + 128.0 + b;
         }
+        // Duotone: the pixel's luminance picks a colour between the dark and the light one.
+        if let Some((d, l)) = duo {
+            let t = ((0.299 * rgb[0] + 0.587 * rgb[1] + 0.114 * rgb[2]) / 255.0).clamp(0.0, 1.0);
+            rgb =
+                [d.r as f64 + (l.r as f64 - d.r as f64) * t, d.g as f64 + (l.g as f64 - d.g as f64) * t, d.b as f64 + (l.b as f64 - d.b as f64) * t];
+        }
         for (i, v) in rgb.iter().enumerate() {
             if let Some(ch) = p.0.get_mut(i) {
                 *ch = v.round().clamp(0.0, 255.0) as u8;
@@ -266,6 +290,25 @@ mod tests {
 
     use super::*;
 
+    #[test]
+    fn duotone_maps_luminance_between_its_two_colours() {
+        use deckcraft_color::Rgba;
+        use deckcraft_model::style::ColorRef;
+        let mut img = image::RgbaImage::from_fn(3, 1, |x, _| image::Rgba([[0, 0, 0, 255], [128, 128, 128, 200], [255, 255, 255, 255]][x as usize]));
+        let adj =
+            PictureAdjust { duotone: Some((ColorRef::rgb(Rgba::rgb(100, 40, 0)), ColorRef::rgb(Rgba::rgb(250, 240, 200)))), ..Default::default() };
+        apply_adjust(&mut img, &adj);
+        assert_eq!(img.get_pixel(0, 0).0, [100, 40, 0, 255], "black takes the dark colour");
+        assert_eq!(img.get_pixel(2, 0).0, [250, 240, 200, 255], "white takes the light colour");
+        let mid = img.get_pixel(1, 0).0;
+        assert!((mid[0] as i32 - 175).abs() <= 1 && (mid[1] as i32 - 140).abs() <= 1 && (mid[2] as i32 - 100).abs() <= 1, "{mid:?}");
+        assert_eq!(mid[3], 200, "alpha is kept");
+        // Different duotones are cached separately.
+        let other = PictureAdjust { duotone: Some((ColorRef::rgb(Rgba::rgb(0, 0, 0)), ColorRef::rgb(Rgba::rgb(255, 0, 0)))), ..Default::default() };
+        assert_ne!(adjust_key(&adj), adjust_key(&other));
+        assert_ne!(adjust_key(&adj), adjust_key(&PictureAdjust::default()));
+    }
+
     #[test]
     fn a_gif_of_many_tiny_frames_keeps_only_the_frame_cap() {
         use image::{Delay, Frame, Rgba, RgbaImage};

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 }
     }
 }
 
@@ -589,6 +593,7 @@ impl Renderer {
         ctx.set_transform(view);
         let path = r.to_path(0.1);
         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) {
@@ -683,7 +688,7 @@ impl Renderer {
                 let bounds = Rect::new(0.0, 0.0, w, h);
                 ctx.push_clip_layer(&outline);
                 let t = f.opts.gif_times.iter().find(|g| g.0 == s.id).map(|g| g.1);
-                paint::picture(ctx, f.pres, pf, bounds, m, t);
+                paint::picture(ctx, f.pres, &paint::resolved(rctx, pf, None), bounds, m, t);
                 ctx.pop_layer();
             }
             ShapeKind::Media(mc) => {
@@ -710,7 +715,16 @@ 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

@@ -3,7 +3,7 @@
 use deckcraft_color::Rgba;
 use deckcraft_geom::preset::FillMode;
 use deckcraft_model::resolve::Ctx;
-use deckcraft_model::style::{Fill, GradientShape, PictureFill, PictureMode};
+use deckcraft_model::style::{ColorRef, Fill, GradientShape, PictureFill, PictureMode};
 use deckcraft_model::{PhType, Presentation};
 use kurbo::{Affine, BezPath, Point, Rect, Shape as _};
 use vello_cpu::{RenderContext, peniko};
@@ -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.
@@ -65,7 +66,7 @@ pub fn fill_path(
         }
         Fill::Picture(pf) => {
             ctx.push_clip_layer(path);
-            picture(ctx, pres, pf, bounds, m, None);
+            picture(ctx, pres, &resolved(rctx, pf, ph), bounds, m, None);
             ctx.pop_layer();
         }
         Fill::Pattern(p) => {
@@ -120,6 +121,16 @@ fn p_rect(x: f64, y: f64, w: f64, h: f64) -> BezPath {
 }
 fn p_add(_a: &mut BezPath, _b: &mut BezPath) {}
 
+/// `pf` with its duotone colours resolved to plain RGB against the slide's colours and the
+/// placeholder colour `ph` (theme background pictures recolour with `phClr`), so the decoded-image
+/// cache can apply and key them without a colour scheme.
+pub fn resolved<'a>(rctx: &Ctx, pf: &'a PictureFill, ph: Option<Rgba>) -> std::borrow::Cow<'a, PictureFill> {
+    let Some((d, l)) = &pf.adjust.duotone else { return std::borrow::Cow::Borrowed(pf) };
+    let mut out = pf.clone();
+    out.adjust.duotone = Some((ColorRef::rgb(rctx.color(d, ph)), ColorRef::rgb(rctx.color(l, ph))));
+    std::borrow::Cow::Owned(out)
+}
+
 /// Draw a picture fill into `bounds` (shape-local) honouring crop and stretch/tile modes; an animated
 /// GIF shows its frame at `gif_time` seconds.
 pub fn picture(ctx: &mut RenderContext, pres: &Presentation, pf: &PictureFill, bounds: Rect, m: Affine, gif_time: Option<f64>) {

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 +523,90 @@ 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}");
+}

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);
+    }
+}