Text shaping 🚀

- Shapes text with rustybuzz
- Font fallback with family list
- Tofus are shown in the first font

Co-Authored-By: Martin <mhaug@live.de>

Cargo.toml

@@ -26,7 +26,8 @@ fontdock = { path = "../fontdock", default-features = false }
 image = { version = "0.23", default-features = false, features = ["jpeg", "png"] }
 miniz_oxide = "0.3"
 pdf-writer = { path = "../pdf-writer" }
-ttf-parser = "0.8.2"
+rustybuzz = "0.3"
+ttf-parser = "0.9"
 unicode-xid = "0.2"
 anyhow = { version = "1", optional = true }
 serde = { version = "1", features = ["derive"], optional = true }

src/env.rs

@@ -7,14 +7,15 @@ use std::fs;
 use std::io::Cursor;
 use std::path::{Path, PathBuf};
 
-use fontdock::{FaceFromVec, FaceId, FontSource};
+use fontdock::{FaceId, FontSource};
 use image::io::Reader as ImageReader;
 use image::{DynamicImage, GenericImageView, ImageFormat};
-use ttf_parser::Face;
 
 #[cfg(feature = "fs")]
 use fontdock::{FsIndex, FsSource};
 
+use crate::font::FaceBuf;
+
 /// Encapsulates all environment dependencies (fonts, resources).
 #[derive(Debug)]
 pub struct Env {
@@ -47,42 +48,6 @@ impl Env {
 /// A font loader that is backed by a dynamic source.
 pub type FontLoader = fontdock::FontLoader<Box<dyn FontSource<Face = FaceBuf>>>;
 
-/// An owned font face.
-pub struct FaceBuf {
-    data: Box<[u8]>,
-    face: Face<'static>,
-}
-
-impl FaceBuf {
-    /// Get a reference to the underlying face.
-    pub fn get(&self) -> &Face<'_> {
-        // We can't implement Deref because that would leak the internal 'static
-        // lifetime.
-        &self.face
-    }
-
-    /// The raw face data.
-    pub fn data(&self) -> &[u8] {
-        &self.data
-    }
-}
-
-impl FaceFromVec for FaceBuf {
-    fn from_vec(vec: Vec<u8>, i: u32) -> Option<Self> {
-        let data = vec.into_boxed_slice();
-
-        // SAFETY: The slices's location is stable in memory since we don't
-        //         touch it and it can't be touched from outside this type.
-        let slice: &'static [u8] =
-            unsafe { std::slice::from_raw_parts(data.as_ptr(), data.len()) };
-
-        Some(Self {
-            data,
-            face: Face::from_slice(slice, i).ok()?,
-        })
-    }
-}
-
 /// Simplify font loader construction from an [`FsIndex`].
 #[cfg(feature = "fs")]
 pub trait FsIndexExt {

src/exec/context.rs

@@ -1,7 +1,4 @@
 use std::mem;
-use std::rc::Rc;
-
-use fontdock::FontStyle;
 
 use super::{Exec, FontFamily, State};
 use crate::diag::{Diag, DiagSet, Pass};
@@ -87,7 +84,7 @@ impl<'a> ExecContext<'a> {
 
     /// Push a word space into the active paragraph.
     pub fn push_space(&mut self) {
-        let em = self.state.font.font_size();
+        let em = self.state.font.resolve_size();
         self.push(SpacingNode {
             amount: self.state.par.word_spacing.resolve(em),
             softness: 1,
@@ -103,19 +100,19 @@ impl<'a> ExecContext<'a> {
 
         while let Some(c) = scanner.eat_merging_crlf() {
             if is_newline(c) {
-                self.push(self.make_text_node(mem::take(&mut line)));
+                self.push(TextNode::new(mem::take(&mut line), &self.state));
                 self.push_linebreak();
             } else {
                 line.push(c);
             }
         }
 
-        self.push(self.make_text_node(line));
+        self.push(TextNode::new(line, &self.state));
     }
 
     /// Apply a forced line break.
     pub fn push_linebreak(&mut self) {
-        let em = self.state.font.font_size();
+        let em = self.state.font.resolve_size();
         self.push_into_stack(SpacingNode {
             amount: self.state.par.leading.resolve(em),
             softness: 2,
@@ -124,7 +121,7 @@ impl<'a> ExecContext<'a> {
 
     /// Apply a forced paragraph break.
     pub fn push_parbreak(&mut self) {
-        let em = self.state.font.font_size();
+        let em = self.state.font.resolve_size();
         self.push_into_stack(SpacingNode {
             amount: self.state.par.spacing.resolve(em),
             softness: 1,
@@ -154,36 +151,6 @@ impl<'a> ExecContext<'a> {
         result
     }
 
-    /// Construct a text node from the given string based on the active text
-    /// state.
-    pub fn make_text_node(&self, text: String) -> TextNode {
-        let mut variant = self.state.font.variant;
-
-        if self.state.font.strong {
-            variant.weight = variant.weight.thicken(300);
-        }
-
-        if self.state.font.emph {
-            variant.style = match variant.style {
-                FontStyle::Normal => FontStyle::Italic,
-                FontStyle::Italic => FontStyle::Normal,
-                FontStyle::Oblique => FontStyle::Normal,
-            }
-        }
-
-        TextNode {
-            text,
-            dir: self.state.dirs.cross,
-            aligns: self.state.aligns,
-            families: Rc::clone(&self.state.font.families),
-            variant,
-            font_size: self.state.font.font_size(),
-            top_edge: self.state.font.top_edge,
-            bottom_edge: self.state.font.bottom_edge,
-            color: self.state.font.color,
-        }
-    }
-
     /// Finish the active paragraph.
     fn finish_par(&mut self) {
         let mut par = mem::replace(&mut self.par, ParNode::new(&self.state));
@@ -292,7 +259,7 @@ impl StackNode {
 
 impl ParNode {
     fn new(state: &State) -> Self {
-        let em = state.font.font_size();
+        let em = state.font.resolve_size();
         Self {
             dirs: state.dirs,
             aligns: state.aligns,
@@ -301,3 +268,14 @@ impl ParNode {
         }
     }
 }
+
+impl TextNode {
+    fn new(text: String, state: &State) -> Self {
+        Self {
+            text,
+            dir: state.dirs.cross,
+            aligns: state.aligns,
+            props: state.font.resolve_props(),
+        }
+    }
+}

src/exec/state.rs

@@ -4,8 +4,9 @@ use std::rc::Rc;
 use fontdock::{FontStretch, FontStyle, FontVariant, FontWeight};
 
 use crate::color::{Color, RgbaColor};
+use crate::font::VerticalFontMetric;
 use crate::geom::*;
-use crate::layout::{Fill, VerticalFontMetric};
+use crate::layout::Fill;
 use crate::paper::{Paper, PaperClass, PAPER_A4};
 
 /// The evaluation state.
@@ -100,7 +101,7 @@ impl Default for ParState {
 #[derive(Debug, Clone, PartialEq)]
 pub struct FontState {
     /// A list of font families with generic class definitions.
-    pub families: Rc<FamilyMap>,
+    pub families: Rc<FamilyList>,
     /// The selected font variant.
     pub variant: FontVariant,
     /// The font size.
@@ -111,32 +112,58 @@ pub struct FontState {
     pub top_edge: VerticalFontMetric,
     /// The bottom end of the text bounding box.
     pub bottom_edge: VerticalFontMetric,
+    /// The glyph fill color / texture.
+    pub color: Fill,
     /// Whether the strong toggle is active or inactive. This determines
     /// whether the next `*` adds or removes font weight.
     pub strong: bool,
     /// Whether the emphasis toggle is active or inactive. This determines
     /// whether the next `_` makes italic or non-italic.
     pub emph: bool,
-    /// The glyph fill color / texture.
-    pub color: Fill,
 }
 
 impl FontState {
-    /// Access the `families` mutably.
-    pub fn families_mut(&mut self) -> &mut FamilyMap {
-        Rc::make_mut(&mut self.families)
+    /// The resolved font size.
+    pub fn resolve_size(&self) -> Length {
+        self.scale.resolve(self.size)
     }
 
-    /// The absolute font size.
-    pub fn font_size(&self) -> Length {
-        self.scale.resolve(self.size)
+    /// Resolve font properties.
+    pub fn resolve_props(&self) -> FontProps {
+        let mut variant = self.variant;
+
+        if self.strong {
+            variant.weight = variant.weight.thicken(300);
+        }
+
+        if self.emph {
+            variant.style = match variant.style {
+                FontStyle::Normal => FontStyle::Italic,
+                FontStyle::Italic => FontStyle::Normal,
+                FontStyle::Oblique => FontStyle::Normal,
+            }
+        }
+
+        FontProps {
+            families: Rc::clone(&self.families),
+            variant,
+            size: self.resolve_size(),
+            top_edge: self.top_edge,
+            bottom_edge: self.bottom_edge,
+            color: self.color,
+        }
+    }
+
+    /// Access the `families` mutably.
+    pub fn families_mut(&mut self) -> &mut FamilyList {
+        Rc::make_mut(&mut self.families)
     }
 }
 
 impl Default for FontState {
     fn default() -> Self {
         Self {
-            families: Rc::new(FamilyMap::default()),
+            families: Rc::new(FamilyList::default()),
             variant: FontVariant {
                 style: FontStyle::Normal,
                 weight: FontWeight::REGULAR,
@@ -146,16 +173,33 @@ impl Default for FontState {
             top_edge: VerticalFontMetric::CapHeight,
             bottom_edge: VerticalFontMetric::Baseline,
             scale: Linear::ONE,
+            color: Fill::Color(Color::Rgba(RgbaColor::BLACK)),
             strong: false,
             emph: false,
-            color: Fill::Color(Color::Rgba(RgbaColor::BLACK)),
         }
     }
 }
 
+/// Properties used for font selection and layout.
+#[derive(Debug, Clone, PartialEq)]
+pub struct FontProps {
+    /// The list of font families to use for shaping.
+    pub families: Rc<FamilyList>,
+    /// Which variant of the font to use.
+    pub variant: FontVariant,
+    /// The font size.
+    pub size: Length,
+    /// What line to consider the top edge of text.
+    pub top_edge: VerticalFontMetric,
+    /// What line to consider the bottom edge of text.
+    pub bottom_edge: VerticalFontMetric,
+    /// The color of the text.
+    pub color: Fill,
+}
+
 /// Font family definitions.
 #[derive(Debug, Clone, Eq, PartialEq, Ord, PartialOrd)]
-pub struct FamilyMap {
+pub struct FamilyList {
     /// The user-defined list of font families.
     pub list: Vec<FontFamily>,
     /// Definition of serif font families.
@@ -168,9 +212,9 @@ pub struct FamilyMap {
     pub base: Vec<String>,
 }
 
-impl FamilyMap {
+impl FamilyList {
     /// Flat iterator over this map's family names.
-    pub fn iter(&self) -> impl Iterator<Item = &str> {
+    pub fn iter(&self) -> impl Iterator<Item = &str> + Clone {
         self.list
             .iter()
             .flat_map(move |family: &FontFamily| {
@@ -186,7 +230,7 @@ impl FamilyMap {
     }
 }
 
-impl Default for FamilyMap {
+impl Default for FamilyList {
     fn default() -> Self {
         Self {
             list: vec![FontFamily::Serif],

src/export/pdf.rs

@@ -187,14 +187,15 @@ impl<'a> PdfExporter<'a> {
 
                     // Then, also check if we need to issue a font switching
                     // action.
-                    if shaped.face != face || shaped.font_size != size {
+                    if shaped.face != face || shaped.size != size {
                         face = shaped.face;
-                        size = shaped.font_size;
+                        size = shaped.size;
 
                         let name = format!("F{}", self.fonts.map(shaped.face));
                         text.font(Name(name.as_bytes()), size.to_pt() as f32);
                     }
 
+                    // TODO: Respect individual glyph offsets.
                     text.matrix(1.0, 0.0, 0.0, 1.0, x, y);
                     text.show(&shaped.encode_glyphs_be());
                 }
@@ -206,10 +207,10 @@ impl<'a> PdfExporter<'a> {
 
     fn write_fonts(&mut self) {
         for (refs, face_id) in self.refs.fonts().zip(self.fonts.layout_indices()) {
-            let owned_face = self.env.fonts.face(face_id);
-            let face = owned_face.get();
+            let face = self.env.fonts.face(face_id);
+            let ttf = face.ttf();
 
-            let name = face
+            let name = ttf
                 .names()
                 .find(|entry| {
                     entry.name_id() == name_id::POST_SCRIPT_NAME && entry.is_unicode()
@@ -228,18 +229,18 @@ impl<'a> PdfExporter<'a> {
 
             let mut flags = FontFlags::empty();
             flags.set(FontFlags::SERIF, name.contains("Serif"));
-            flags.set(FontFlags::FIXED_PITCH, face.is_monospaced());
-            flags.set(FontFlags::ITALIC, face.is_italic());
+            flags.set(FontFlags::FIXED_PITCH, ttf.is_monospaced());
+            flags.set(FontFlags::ITALIC, ttf.is_italic());
             flags.insert(FontFlags::SYMBOLIC);
             flags.insert(FontFlags::SMALL_CAP);
 
             // Convert from OpenType font units to PDF glyph units.
-            let em_per_unit = 1.0 / face.units_per_em().unwrap_or(1000) as f32;
+            let em_per_unit = 1.0 / ttf.units_per_em().unwrap_or(1000) as f32;
             let convert = |font_unit: f32| (1000.0 * em_per_unit * font_unit).round();
             let convert_i16 = |font_unit: i16| convert(font_unit as f32);
             let convert_u16 = |font_unit: u16| convert(font_unit as f32);
 
-            let global_bbox = face.global_bounding_box();
+            let global_bbox = ttf.global_bounding_box();
             let bbox = Rect::new(
                 convert_i16(global_bbox.x_min),
                 convert_i16(global_bbox.y_min),
@@ -247,11 +248,11 @@ impl<'a> PdfExporter<'a> {
                 convert_i16(global_bbox.y_max),
             );
 
-            let italic_angle = face.italic_angle().unwrap_or(0.0);
-            let ascender = convert_i16(face.typographic_ascender().unwrap_or(0));
-            let descender = convert_i16(face.typographic_descender().unwrap_or(0));
-            let cap_height = face.capital_height().map(convert_i16);
-            let stem_v = 10.0 + 0.244 * (f32::from(face.weight().to_number()) - 50.0);
+            let italic_angle = ttf.italic_angle().unwrap_or(0.0);
+            let ascender = convert_i16(ttf.typographic_ascender().unwrap_or(0));
+            let descender = convert_i16(ttf.typographic_descender().unwrap_or(0));
+            let cap_height = ttf.capital_height().map(convert_i16);
+            let stem_v = 10.0 + 0.244 * (f32::from(ttf.weight().to_number()) - 50.0);
 
             // Write the base font object referencing the CID font.
             self.writer
@@ -269,9 +270,9 @@ impl<'a> PdfExporter<'a> {
                 .font_descriptor(refs.font_descriptor)
                 .widths()
                 .individual(0, {
-                    let num_glyphs = face.number_of_glyphs();
+                    let num_glyphs = ttf.number_of_glyphs();
                     (0 .. num_glyphs).map(|g| {
-                        let advance = face.glyph_hor_advance(GlyphId(g));
+                        let advance = ttf.glyph_hor_advance(GlyphId(g));
                         convert_u16(advance.unwrap_or(0))
                     })
                 });
@@ -294,10 +295,10 @@ impl<'a> PdfExporter<'a> {
             self.writer
                 .cmap(refs.cmap, &{
                     let mut cmap = UnicodeCmap::new(cmap_name, system_info);
-                    for subtable in face.character_mapping_subtables() {
+                    for subtable in ttf.character_mapping_subtables() {
                         subtable.codepoints(|n| {
                             if let Some(c) = std::char::from_u32(n) {
-                                if let Some(g) = face.glyph_index(c) {
+                                if let Some(g) = ttf.glyph_index(c) {
                                     cmap.pair(g.0, c);
                                 }
                             }
@@ -309,7 +310,7 @@ impl<'a> PdfExporter<'a> {
                 .system_info(system_info);
 
             // Write the face's bytes.
-            self.writer.stream(refs.data, owned_face.data());
+            self.writer.stream(refs.data, face.data());
         }
     }
 

src/font.rs

@@ -0,0 +1,115 @@
+//! Font handling.
+
+use std::fmt::{self, Display, Formatter};
+
+use fontdock::FaceFromVec;
+
+/// An owned font face.
+pub struct FaceBuf {
+    data: Box<[u8]>,
+    ttf: ttf_parser::Face<'static>,
+    buzz: rustybuzz::Face<'static>,
+}
+
+impl FaceBuf {
+    /// The raw face data.
+    pub fn data(&self) -> &[u8] {
+        &self.data
+    }
+
+    /// Get a reference to the underlying ttf-parser face.
+    pub fn ttf(&self) -> &ttf_parser::Face<'_> {
+        // We can't implement Deref because that would leak the internal 'static
+        // lifetime.
+        &self.ttf
+    }
+
+    /// Get a reference to the underlying rustybuzz face.
+    pub fn buzz(&self) -> &rustybuzz::Face<'_> {
+        // We can't implement Deref because that would leak the internal 'static
+        // lifetime.
+        &self.buzz
+    }
+}
+
+impl FaceFromVec for FaceBuf {
+    fn from_vec(vec: Vec<u8>, i: u32) -> Option<Self> {
+        let data = vec.into_boxed_slice();
+
+        // SAFETY: The slices's location is stable in memory since we don't
+        //         touch it and it can't be touched from outside this type.
+        let slice: &'static [u8] =
+            unsafe { std::slice::from_raw_parts(data.as_ptr(), data.len()) };
+
+        Some(Self {
+            data,
+            ttf: ttf_parser::Face::from_slice(slice, i).ok()?,
+            buzz: rustybuzz::Face::from_slice(slice, i)?,
+        })
+    }
+}
+
+/// Identifies a vertical metric of a font.
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd)]
+pub enum VerticalFontMetric {
+    /// The distance from the baseline to the typographic ascender.
+    ///
+    /// Corresponds to the typographic ascender from the `OS/2` table if present
+    /// and falls back to the ascender from the `hhea` table otherwise.
+    Ascender,
+    /// The approximate height of uppercase letters.
+    CapHeight,
+    /// The approximate height of non-ascending lowercase letters.
+    XHeight,
+    /// The baseline on which the letters rest.
+    Baseline,
+    /// The distance from the baseline to the typographic descender.
+    ///
+    /// Corresponds to the typographic descender from the `OS/2` table if
+    /// present and falls back to the descender from the `hhea` table otherwise.
+    Descender,
+}
+
+impl VerticalFontMetric {
+    /// Look up the metric in the given font face.
+    pub fn lookup(self, face: &ttf_parser::Face) -> i16 {
+        match self {
+            VerticalFontMetric::Ascender => lookup_ascender(face),
+            VerticalFontMetric::CapHeight => face
+                .capital_height()
+                .filter(|&h| h > 0)
+                .unwrap_or_else(|| lookup_ascender(face)),
+            VerticalFontMetric::XHeight => face
+                .x_height()
+                .filter(|&h| h > 0)
+                .unwrap_or_else(|| lookup_ascender(face)),
+            VerticalFontMetric::Baseline => 0,
+            VerticalFontMetric::Descender => lookup_descender(face),
+        }
+    }
+}
+
+/// The ascender of the face.
+fn lookup_ascender(face: &ttf_parser::Face) -> i16 {
+    // We prefer the typographic ascender over the Windows ascender because
+    // it can be overly large if the font has large glyphs.
+    face.typographic_ascender().unwrap_or_else(|| face.ascender())
+}
+
+/// The descender of the face.
+fn lookup_descender(face: &ttf_parser::Face) -> i16 {
+    // See `lookup_ascender` for reason.
+    face.typographic_descender().unwrap_or_else(|| face.descender())
+}
+
+impl Display for VerticalFontMetric {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        f.pad(match self {
+            Self::Ascender => "ascender",
+            Self::CapHeight => "cap-height",
+            Self::XHeight => "x-height",
+            Self::Baseline => "baseline",
+            Self::Descender => "descender",
+        })
+    }
+}

src/layout/frame.rs

@@ -1,7 +1,9 @@
-use super::Shaped;
+use fontdock::FaceId;
+use ttf_parser::GlyphId;
+
 use crate::color::Color;
 use crate::env::ResourceId;
-use crate::geom::{Path, Point, Size};
+use crate::geom::{Length, Path, Point, Size};
 
 /// A finished layout with elements at fixed positions.
 #[derive(Debug, Clone, PartialEq)]
@@ -36,13 +38,67 @@ impl Frame {
 #[derive(Debug, Clone, PartialEq)]
 pub enum Element {
     /// Shaped text.
-    Text(Shaped),
+    Text(ShapedText),
     /// A geometric shape.
     Geometry(Geometry),
     /// A raster image.
     Image(Image),
 }
 
+/// A shaped run of text.
+#[derive(Debug, Clone, PartialEq)]
+pub struct ShapedText {
+    /// The font face the text was shaped with.
+    pub face: FaceId,
+    /// The font size.
+    pub size: Length,
+    /// The width.
+    pub width: Length,
+    /// The extent to the top.
+    pub top: Length,
+    /// The extent to the bottom.
+    pub bottom: Length,
+    /// The glyph fill color / texture.
+    pub color: Fill,
+    /// The shaped glyphs.
+    pub glyphs: Vec<GlyphId>,
+    /// The horizontal offsets of the glyphs. This is indexed parallel to
+    /// `glyphs`. Vertical offsets are not yet supported.
+    pub offsets: Vec<Length>,
+}
+
+impl ShapedText {
+    /// Create a new shape run with `width` zero and empty `glyphs` and `offsets`.
+    pub fn new(
+        face: FaceId,
+        size: Length,
+        top: Length,
+        bottom: Length,
+        color: Fill,
+    ) -> Self {
+        Self {
+            face,
+            size,
+            width: Length::ZERO,
+            top,
+            bottom,
+            glyphs: vec![],
+            offsets: vec![],
+            color,
+        }
+    }
+
+    /// Encode the glyph ids into a big-endian byte buffer.
+    pub fn encode_glyphs_be(&self) -> Vec<u8> {
+        let mut bytes = Vec::with_capacity(2 * self.glyphs.len());
+        for &GlyphId(g) in &self.glyphs {
+            bytes.push((g >> 8) as u8);
+            bytes.push((g & 0xff) as u8);
+        }
+        bytes
+    }
+}
+
 /// A shape with some kind of fill.
 #[derive(Debug, Clone, PartialEq)]
 pub struct Geometry {

src/layout/shaping.rs

@@ -1,205 +1,129 @@
-//! Super-basic text shaping.
-//!
-//! This is really only suited for simple Latin text. It picks the most suitable
-//! font for each individual character. When the direction is right-to-left, the
-//! word is spelled backwards. Vertical shaping is not supported.
-
-use std::fmt::{self, Debug, Display, Formatter};
-
-use fontdock::{FaceId, FontVariant};
-use ttf_parser::{Face, GlyphId};
+use fontdock::FaceId;
+use rustybuzz::UnicodeBuffer;
+use ttf_parser::GlyphId;
 
+use super::{Element, Frame, ShapedText};
 use crate::env::FontLoader;
-use crate::exec::FamilyMap;
-use crate::geom::{Dir, Length, Point, Size};
-use crate::layout::{Element, Fill, Frame};
+use crate::exec::FontProps;
+use crate::geom::{Length, Point, Size};
 
-/// A shaped run of text.
-#[derive(Clone, PartialEq)]
-pub struct Shaped {
-    /// The shaped text.
-    pub text: String,
-    /// The font face the text was shaped with.
-    pub face: FaceId,
-    /// The shaped glyphs.
-    pub glyphs: Vec<GlyphId>,
-    /// The horizontal offsets of the glyphs. This is indexed parallel to
-    /// `glyphs`. Vertical offsets are not yet supported.
-    pub offsets: Vec<Length>,
-    /// The font size.
-    pub font_size: Length,
-    /// The glyph fill color / texture.
-    pub color: Fill,
-}
-
-impl Shaped {
-    /// Create a new shape run with empty `text`, `glyphs` and `offsets`.
-    pub fn new(face: FaceId, font_size: Length, color: Fill) -> Self {
-        Self {
-            text: String::new(),
-            face,
-            glyphs: vec![],
-            offsets: vec![],
-            font_size,
-            color,
-        }
-    }
-
-    /// Encode the glyph ids into a big-endian byte buffer.
-    pub fn encode_glyphs_be(&self) -> Vec<u8> {
-        let mut bytes = Vec::with_capacity(2 * self.glyphs.len());
-        for &GlyphId(g) in &self.glyphs {
-            bytes.push((g >> 8) as u8);
-            bytes.push((g & 0xff) as u8);
-        }
-        bytes
-    }
-}
-
-impl Debug for Shaped {
-    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
-        Debug::fmt(&self.text, f)
-    }
-}
-
-/// Identifies a vertical metric of a font.
-#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd)]
-pub enum VerticalFontMetric {
-    /// The distance from the baseline to the typographic ascender.
-    ///
-    /// Corresponds to the typographic ascender from the `OS/2` table if present
-    /// and falls back to the ascender from the `hhea` table otherwise.
-    Ascender,
-    /// The approximate height of uppercase letters.
-    CapHeight,
-    /// The approximate height of non-ascending lowercase letters.
-    XHeight,
-    /// The baseline on which the letters rest.
-    Baseline,
-    /// The distance from the baseline to the typographic descender.
-    ///
-    /// Corresponds to the typographic descender from the `OS/2` table if
-    /// present and falls back to the descender from the `hhea` table otherwise.
-    Descender,
-}
-
-impl Display for VerticalFontMetric {
-    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
-        f.pad(match self {
-            Self::Ascender => "ascender",
-            Self::CapHeight => "cap-height",
-            Self::XHeight => "x-height",
-            Self::Baseline => "baseline",
-            Self::Descender => "descender",
-        })
-    }
-}
-
-/// Shape text into a frame containing [`Shaped`] runs.
-pub fn shape(
-    text: &str,
-    dir: Dir,
-    families: &FamilyMap,
-    variant: FontVariant,
-    font_size: Length,
-    top_edge: VerticalFontMetric,
-    bottom_edge: VerticalFontMetric,
-    color: Fill,
-    loader: &mut FontLoader,
-) -> Frame {
+/// Shape text into a frame containing shaped [`ShapedText`] runs.
+pub fn shape(text: &str, loader: &mut FontLoader, props: &FontProps) -> Frame {
     let mut frame = Frame::new(Size::new(Length::ZERO, Length::ZERO));
-    let mut shaped = Shaped::new(FaceId::MAX, font_size, color);
-    let mut width = Length::ZERO;
-    let mut top = Length::ZERO;
-    let mut bottom = Length::ZERO;
-
-    // Create an iterator with conditional direction.
-    let mut forwards = text.chars();
-    let mut backwards = text.chars().rev();
-    let chars: &mut dyn Iterator<Item = char> = if dir.is_positive() {
-        &mut forwards
-    } else {
-        &mut backwards
-    };
-
-    for c in chars {
-        for family in families.iter() {
-            if let Some(id) = loader.query(family, variant) {
-                let face = loader.face(id).get();
-                let (glyph, glyph_width) = match lookup_glyph(face, c) {
-                    Some(v) => v,
-                    None => continue,
-                };
-
-                let units_per_em = f64::from(face.units_per_em().unwrap_or(1000));
-                let convert = |units| units / units_per_em * font_size;
-
-                // Flush the buffer and reset the metrics if we use a new font face.
-                if shaped.face != id {
-                    place(&mut frame, shaped, width, top, bottom);
-
-                    shaped = Shaped::new(id, font_size, color);
-                    width = Length::ZERO;
-                    top = convert(f64::from(lookup_metric(face, top_edge)));
-                    bottom = convert(f64::from(lookup_metric(face, bottom_edge)));
-                }
-
-                shaped.text.push(c);
-                shaped.glyphs.push(glyph);
-                shaped.offsets.push(width);
-                width += convert(f64::from(glyph_width));
-                break;
-            }
-        }
-    }
-
-    place(&mut frame, shaped, width, top, bottom);
-
+    shape_segment(&mut frame, text, props.families.iter(), None, loader, props);
     frame
 }
 
+/// Shape text into a frame with font fallback using the `families` iterator.
+fn shape_segment<'a>(
+    frame: &mut Frame,
+    text: &str,
+    mut families: impl Iterator<Item = &'a str> + Clone,
+    mut first: Option<FaceId>,
+    loader: &mut FontLoader,
+    props: &FontProps,
+) {
+    // Select the font family.
+    let (id, fallback) = loop {
+        // Try to load the next available font family.
+        match families.next() {
+            Some(family) => match loader.query(family, props.variant) {
+                Some(id) => break (id, true),
+                None => {}
+            },
+            // We're out of families, so we don't do any more fallback and just
+            // shape the tofus with the first face we originally used.
+            None => match first {
+                Some(id) => break (id, false),
+                None => return,
+            },
+        }
+    };
+
+    // Register that this is the first available font.
+    let face = loader.face(id);
+    if first.is_none() {
+        first = Some(id);
+    }
+
+    // Find out some metrics and prepare the shaped text container.
+    let ttf = face.ttf();
+    let units_per_em = f64::from(ttf.units_per_em().unwrap_or(1000));
+    let convert = |units| f64::from(units) / units_per_em * props.size;
+    let top = convert(i32::from(props.top_edge.lookup(ttf)));
+    let bottom = convert(i32::from(props.bottom_edge.lookup(ttf)));
+    let mut shaped = ShapedText::new(id, props.size, top, bottom, props.color);
+
+    // Fill the buffer with our text.
+    let mut buffer = UnicodeBuffer::new();
+    buffer.push_str(text);
+    buffer.guess_segment_properties();
+
+    // Find out the text direction.
+    // TODO: Replace this once we do BiDi.
+    let rtl = matches!(buffer.direction(), rustybuzz::Direction::RightToLeft);
+
+    // Shape!
+    let glyphs = rustybuzz::shape(face.buzz(), &[], buffer);
+    let info = glyphs.glyph_infos();
+    let pos = glyphs.glyph_positions();
+    let mut iter = info.iter().zip(pos).peekable();
+
+    while let Some((info, pos)) = iter.next() {
+        // Do font fallback if the glyph is a tofu.
+        if info.codepoint == 0 && fallback {
+            // Flush what we have so far.
+            if !shaped.glyphs.is_empty() {
+                place(frame, shaped);
+                shaped = ShapedText::new(id, props.size, top, bottom, props.color);
+            }
+
+            // Determine the start and end cluster index of the tofu sequence.
+            let mut start = info.cluster as usize;
+            let mut end = info.cluster as usize;
+            while let Some((info, _)) = iter.peek() {
+                if info.codepoint != 0 {
+                    break;
+                }
+                end = info.cluster as usize;
+                iter.next();
+            }
+
+            // Because Harfbuzz outputs glyphs in visual order, the start
+            // cluster actually corresponds to the last codepoint in
+            // right-to-left text.
+            if rtl {
+                assert!(end <= start);
+                std::mem::swap(&mut start, &mut end);
+            }
+
+            // The end cluster index points right before the last character that
+            // mapped to the tofu sequence. So we have to offset the end by one
+            // char.
+            let offset = text[end ..].chars().next().unwrap().len_utf8();
+            let range = start .. end + offset;
+
+            // Recursively shape the tofu sequence with the next family.
+            shape_segment(frame, &text[range], families.clone(), first, loader, props);
+        } else {
+            // Add the glyph to the shaped output.
+            // TODO: Don't ignore y_advance and y_offset.
+            let glyph = GlyphId(info.codepoint as u16);
+            shaped.glyphs.push(glyph);
+            shaped.offsets.push(shaped.width + convert(pos.x_offset));
+            shaped.width += convert(pos.x_advance);
+        }
+    }
+
+    if !shaped.glyphs.is_empty() {
+        place(frame, shaped)
+    }
+}
+
 /// Place shaped text into a frame.
-fn place(frame: &mut Frame, shaped: Shaped, width: Length, top: Length, bottom: Length) {
-    if !shaped.text.is_empty() {
-        frame.push(Point::new(frame.size.width, top), Element::Text(shaped));
-        frame.size.width += width;
-        frame.size.height = frame.size.height.max(top - bottom);
-    }
-}
-
-/// Look up the glyph for `c` and returns its index alongside its advance width.
-fn lookup_glyph(face: &Face, c: char) -> Option<(GlyphId, u16)> {
-    let glyph = face.glyph_index(c)?;
-    let width = face.glyph_hor_advance(glyph)?;
-    Some((glyph, width))
-}
-
-/// Look up a vertical metric.
-fn lookup_metric(face: &Face, metric: VerticalFontMetric) -> i16 {
-    match metric {
-        VerticalFontMetric::Ascender => lookup_ascender(face),
-        VerticalFontMetric::CapHeight => face
-            .capital_height()
-            .filter(|&h| h > 0)
-            .unwrap_or_else(|| lookup_ascender(face)),
-        VerticalFontMetric::XHeight => face
-            .x_height()
-            .filter(|&h| h > 0)
-            .unwrap_or_else(|| lookup_ascender(face)),
-        VerticalFontMetric::Baseline => 0,
-        VerticalFontMetric::Descender => lookup_descender(face),
-    }
-}
-
-/// The ascender of the face.
-fn lookup_ascender(face: &Face) -> i16 {
-    // We prefer the typographic ascender over the Windows ascender because
-    // it can be overly large if the font has large glyphs.
-    face.typographic_ascender().unwrap_or_else(|| face.ascender())
-}
-
-/// The descender of the face.
-fn lookup_descender(face: &Face) -> i16 {
-    // See `lookup_ascender` for reason.
-    face.typographic_descender().unwrap_or_else(|| face.descender())
+fn place(frame: &mut Frame, shaped: ShapedText) {
+    let offset = frame.size.width;
+    frame.size.width += shaped.width;
+    frame.size.height = frame.size.height.max(shaped.top - shaped.bottom);
+    frame.push(Point::new(offset, shaped.top), Element::Text(shaped));
 }

src/layout/text.rs

@@ -1,50 +1,25 @@
 use std::fmt::{self, Debug, Formatter};
-use std::rc::Rc;
-
-use fontdock::FontVariant;
 
 use super::*;
-use crate::exec::FamilyMap;
+use crate::exec::FontProps;
 
 /// A consecutive, styled run of text.
 #[derive(Clone, PartialEq)]
 pub struct TextNode {
-    /// The text.
-    pub text: String,
     /// The text direction.
     pub dir: Dir,
     /// How to align this text node in its parent.
     pub aligns: LayoutAligns,
-    /// The list of font families for shaping.
-    pub families: Rc<FamilyMap>,
-    /// The font variant,
-    pub variant: FontVariant,
-    /// The font size.
-    pub font_size: Length,
-    /// The top end of the text bounding box.
-    pub top_edge: VerticalFontMetric,
-    /// The bottom end of the text bounding box.
-    pub bottom_edge: VerticalFontMetric,
-    /// The glyph fill.
-    pub color: Fill,
+    /// The text.
+    pub text: String,
+    /// Properties used for font selection and layout.
+    pub props: FontProps,
 }
 
 impl Layout for TextNode {
     fn layout(&self, ctx: &mut LayoutContext, _: &Areas) -> Fragment {
-        Fragment::Frame(
-            shape(
-                &self.text,
-                self.dir,
-                &self.families,
-                self.variant,
-                self.font_size,
-                self.top_edge,
-                self.bottom_edge,
-                self.color,
-                &mut ctx.env.fonts,
-            ),
-            self.aligns,
-        )
+        let frame = shape(&self.text, &mut ctx.env.fonts, &self.props);
+        Fragment::Frame(frame, self.aligns)
     }
 }
 

src/lib.rs

@@ -37,6 +37,7 @@ pub mod color;
 pub mod env;
 pub mod exec;
 pub mod export;
+pub mod font;
 pub mod geom;
 pub mod layout;
 pub mod library;

src/library/mod.rs

@@ -32,8 +32,8 @@ use fontdock::{FontStyle, FontWeight};
 use crate::eval::{AnyValue, FuncValue, Scope};
 use crate::eval::{EvalContext, FuncArgs, TemplateValue, Value};
 use crate::exec::{Exec, ExecContext, FontFamily};
+use crate::font::VerticalFontMetric;
 use crate::geom::*;
-use crate::layout::VerticalFontMetric;
 use crate::syntax::{Node, Spanned};
 
 /// Construct a scope containing all standard library definitions.

src/library/spacing.rs

@@ -27,7 +27,7 @@ fn spacing_impl(ctx: &mut EvalContext, args: &mut FuncArgs, axis: SpecAxis) -> V
     let spacing: Option<Linear> = args.require(ctx, "spacing");
     Value::template("spacing", move |ctx| {
         if let Some(linear) = spacing {
-            let amount = linear.resolve(ctx.state.font.font_size());
+            let amount = linear.resolve(ctx.state.font.resolve_size());
             let spacing = SpacingNode { amount, softness: 0 };
             if axis == ctx.state.dirs.main.axis() {
                 ctx.push_into_stack(spacing);

tests/typ/text/complex.typ

@@ -0,0 +1,38 @@
+// Test complex text shaping.
+
+---
+// Test ligatures.
+
+// This should create an "fi" ligature.
+Le fira
+
+// This should just shape nicely.
+#font("Noto Sans Arabic")
+منش إلا بسم الله
+
+// This should form a three-member family.
+#font("Twitter Color Emoji")
+👩‍👩‍👦 🤚🏿
+
+// These two shouldn't be affected by a zero-width joiner.
+🏞‍🌋
+
+---
+// Test font fallback.
+
+#font("EB Garamond", "Noto Sans Arabic", "Twitter Color Emoji")
+
+// Font fallback for emoji.
+A😀B
+
+// Font fallback for entire text.
+منش إلا بسم الله
+
+// Font fallback in right-to-left text.
+ب🐈😀سم
+
+// Multi-layer font fallback.
+Aب😀🏞سمB
+
+// Tofus are rendered with the first font.
+A🐈中文B

tests/typeset.rs

@@ -21,7 +21,7 @@ use typst::eval::{EvalContext, FuncArgs, FuncValue, Scope, Value};
 use typst::exec::State;
 use typst::export::pdf;
 use typst::geom::{self, Length, Point, Sides, Size};
-use typst::layout::{Element, Fill, Frame, Geometry, Image, Shape, Shaped};
+use typst::layout::{Element, Fill, Frame, Geometry, Image, Shape, ShapedText};
 use typst::library;
 use typst::parse::{LineMap, Scanner};
 use typst::pretty::pretty;
@@ -391,15 +391,18 @@ fn draw(env: &Env, frames: &[Frame], pixel_per_pt: f32) -> Pixmap {
 
         for &(pos, ref element) in &frame.elements {
             let pos = origin + pos;
+            let x = pos.x.to_pt() as f32;
+            let y = pos.y.to_pt() as f32;
+            let ts = ts.pre_translate(x, y);
             match element {
                 Element::Text(shaped) => {
-                    draw_text(&mut canvas, env, ts, pos, shaped);
+                    draw_text(&mut canvas, env, ts, shaped);
                 }
                 Element::Image(image) => {
-                    draw_image(&mut canvas, env, ts, pos, image);
+                    draw_image(&mut canvas, env, ts, image);
                 }
                 Element::Geometry(geom) => {
-                    draw_geometry(&mut canvas, ts, pos, geom);
+                    draw_geometry(&mut canvas, ts, geom);
                 }
             }
         }
@@ -410,18 +413,18 @@ fn draw(env: &Env, frames: &[Frame], pixel_per_pt: f32) -> Pixmap {
     canvas
 }
 
-fn draw_text(canvas: &mut Pixmap, env: &Env, ts: Transform, pos: Point, shaped: &Shaped) {
-    let face = env.fonts.face(shaped.face).get();
+fn draw_text(canvas: &mut Pixmap, env: &Env, ts: Transform, shaped: &ShapedText) {
+    let ttf = env.fonts.face(shaped.face).ttf();
 
     for (&glyph, &offset) in shaped.glyphs.iter().zip(&shaped.offsets) {
-        let units_per_em = face.units_per_em().unwrap_or(1000);
+        let units_per_em = ttf.units_per_em().unwrap_or(1000);
 
-        let x = (pos.x + offset).to_pt() as f32;
-        let y = pos.y.to_pt() as f32;
-        let scale = (shaped.font_size / units_per_em as f64).to_pt() as f32;
+        let x = offset.to_pt() as f32;
+        let s = (shaped.size / units_per_em as f64).to_pt() as f32;
+        let ts = ts.pre_translate(x, 0.0);
 
         // Try drawing SVG if present.
-        if let Some(tree) = face
+        if let Some(tree) = ttf
             .glyph_svg_image(glyph)
             .and_then(|data| std::str::from_utf8(data).ok())
             .map(|svg| {
@@ -433,11 +436,9 @@ fn draw_text(canvas: &mut Pixmap, env: &Env, ts: Transform, pos: Point, shaped:
             for child in tree.root().children() {
                 if let usvg::NodeKind::Path(node) = &*child.borrow() {
                     let path = convert_usvg_path(&node.data);
-                    let transform = convert_usvg_transform(node.transform);
-                    let ts = transform
-                        .post_concat(Transform::from_row(scale, 0.0, 0.0, scale, x, y))
+                    let ts = convert_usvg_transform(node.transform)
+                        .post_scale(s, s)
                         .post_concat(ts);
-
                     if let Some(fill) = &node.fill {
                         let (paint, fill_rule) = convert_usvg_fill(fill);
                         canvas.fill_path(&path, &paint, fill_rule, ts, None);
@@ -450,9 +451,9 @@ fn draw_text(canvas: &mut Pixmap, env: &Env, ts: Transform, pos: Point, shaped:
 
         // Otherwise, draw normal outline.
         let mut builder = WrappedPathBuilder(tiny_skia::PathBuilder::new());
-        if face.outline_glyph(glyph, &mut builder).is_some() {
+        if ttf.outline_glyph(glyph, &mut builder).is_some() {
             let path = builder.0.finish().unwrap();
-            let ts = Transform::from_row(scale, 0.0, 0.0, -scale, x, y).post_concat(ts);
+            let ts = ts.pre_scale(s, -s);
             let mut paint = convert_typst_fill(shaped.color);
             paint.anti_alias = true;
             canvas.fill_path(&path, &paint, FillRule::default(), ts, None);
@@ -460,11 +461,7 @@ fn draw_text(canvas: &mut Pixmap, env: &Env, ts: Transform, pos: Point, shaped:
     }
 }
 
-fn draw_geometry(canvas: &mut Pixmap, ts: Transform, pos: Point, element: &Geometry) {
-    let x = pos.x.to_pt() as f32;
-    let y = pos.y.to_pt() as f32;
-    let ts = Transform::from_translate(x, y).post_concat(ts);
-
+fn draw_geometry(canvas: &mut Pixmap, ts: Transform, element: &Geometry) {
     let paint = convert_typst_fill(element.fill);
     let rule = FillRule::default();
 
@@ -486,13 +483,7 @@ fn draw_geometry(canvas: &mut Pixmap, ts: Transform, pos: Point, element: &Geome
     };
 }
 
-fn draw_image(
-    canvas: &mut Pixmap,
-    env: &Env,
-    ts: Transform,
-    pos: Point,
-    element: &Image,
-) {
+fn draw_image(canvas: &mut Pixmap, env: &Env, ts: Transform, element: &Image) {
     let img = &env.resources.loaded::<ImageResource>(element.res);
 
     let mut pixmap = Pixmap::new(img.buf.width(), img.buf.height()).unwrap();
@@ -501,8 +492,6 @@ fn draw_image(
         *dest = ColorU8::from_rgba(r, g, b, a).premultiply();
     }
 
-    let x = pos.x.to_pt() as f32;
-    let y = pos.y.to_pt() as f32;
     let view_width = element.size.width.to_pt() as f32;
     let view_height = element.size.height.to_pt() as f32;
     let scale_x = view_width as f32 / pixmap.width() as f32;
@@ -514,10 +503,10 @@ fn draw_image(
         SpreadMode::Pad,
         FilterQuality::Bilinear,
         1.0,
-        Transform::from_row(scale_x, 0.0, 0.0, scale_y, x, y),
+        Transform::from_row(scale_x, 0.0, 0.0, scale_y, 0.0, 0.0),
     );
 
-    let rect = Rect::from_xywh(x, y, view_width, view_height).unwrap();
+    let rect = Rect::from_xywh(0.0, 0.0, view_width, view_height).unwrap();
     canvas.fill_rect(rect, &paint, ts, None);
 }