More robust glyph drawing (#5159)

6 files changed, 203 insertions, 123 deletions

diff --git a/crates/typst-pdf/src/color_font.rs b/crates/typst-pdf/src/color_font.rs
index 5182a059..f6fea396 100644
--- a/crates/typst-pdf/src/color_font.rs
+++ b/crates/typst-pdf/src/color_font.rs
@@ -12,10 +12,11 @@ use indexmap::IndexMap;
 use pdf_writer::types::UnicodeCmap;
 use pdf_writer::writers::WMode;
 use pdf_writer::{Filter, Finish, Name, Rect, Ref};
-use typst::diag::SourceResult;
+use typst::diag::{bail, error, SourceDiagnostic, SourceResult};
+use typst::foundations::Repr;
 use typst::layout::Em;
-use typst::text::color::frame_for_glyph;
-use typst::text::Font;
+use typst::text::color::glyph_frame;
+use typst::text::{Font, Glyph, TextItemView};
 
 use crate::content;
 use crate::font::{base_font_name, write_font_descriptor, CMAP_NAME, SYSTEM_INFO};
@@ -211,9 +212,10 @@ impl ColorFontMap<()> {
     pub fn get(
         &mut self,
         options: &PdfOptions,
-        font: &Font,
-        gid: u16,
+        text: &TextItemView,
+        glyph: &Glyph,
     ) -> SourceResult<(usize, u8)> {
+        let font = &text.item.font;
         let color_font = self.map.entry(font.clone()).or_insert_with(|| {
             let global_bbox = font.ttf().global_bounding_box();
             let bbox = Rect::new(
@@ -230,7 +232,7 @@ impl ColorFontMap<()> {
             }
         });
 
-        Ok(if let Some(index_of_glyph) = color_font.glyph_indices.get(&gid) {
+        Ok(if let Some(index_of_glyph) = color_font.glyph_indices.get(&glyph.id) {
             // If we already know this glyph, return it.
             (color_font.slice_ids[index_of_glyph / 256], *index_of_glyph as u8)
         } else {
@@ -242,9 +244,13 @@ impl ColorFontMap<()> {
                 self.total_slice_count += 1;
             }
 
-            let frame = frame_for_glyph(font, gid);
-            let width =
-                font.advance(gid).unwrap_or(Em::new(0.0)).get() * font.units_per_em();
+            let (frame, tofu) = glyph_frame(font, glyph.id);
+            if options.standards.pdfa && tofu {
+                bail!(failed_to_convert(text, glyph));
+            }
+
+            let width = font.advance(glyph.id).unwrap_or(Em::new(0.0)).get()
+                * font.units_per_em();
             let instructions = content::build(
                 options,
                 &mut self.resources,
@@ -252,8 +258,8 @@ impl ColorFontMap<()> {
                 None,
                 Some(width as f32),
             )?;
-            color_font.glyphs.push(ColorGlyph { gid, instructions });
-            color_font.glyph_indices.insert(gid, index);
+            color_font.glyphs.push(ColorGlyph { gid: glyph.id, instructions });
+            color_font.glyph_indices.insert(glyph.id, index);
 
             (color_font.slice_ids[index / 256], index as u8)
         })
@@ -321,3 +327,19 @@ pub struct ColorFontSlice {
     /// represent the subset of the TTF font we are interested in.
     pub subfont: usize,
 }
+
+/// The error when the glyph could not be converted.
+#[cold]
+fn failed_to_convert(text: &TextItemView, glyph: &Glyph) -> SourceDiagnostic {
+    let mut diag = error!(
+        glyph.span.0,
+        "the glyph for {} could not be exported",
+        text.glyph_text(glyph).repr()
+    );
+
+    if text.item.font.ttf().tables().cff2.is_some() {
+        diag.hint("CFF2 fonts are not currently supported");
+    }
+
+    diag
+}
diff --git a/crates/typst-pdf/src/content.rs b/crates/typst-pdf/src/content.rs
index 79323b6a..babb3e57 100644
--- a/crates/typst-pdf/src/content.rs
+++ b/crates/typst-pdf/src/content.rs
@@ -10,15 +10,15 @@ use pdf_writer::types::{
 };
 use pdf_writer::writers::PositionedItems;
 use pdf_writer::{Content, Finish, Name, Rect, Str};
-use typst::diag::{bail, SourceResult};
+use typst::diag::{bail, error, SourceDiagnostic, SourceResult};
 use typst::foundations::Repr;
 use typst::layout::{
     Abs, Em, Frame, FrameItem, GroupItem, Point, Ratio, Size, Transform,
 };
 use typst::model::Destination;
 use typst::syntax::Span;
-use typst::text::color::is_color_glyph;
-use typst::text::{Font, TextItem, TextItemView};
+use typst::text::color::should_outline;
+use typst::text::{Font, Glyph, TextItem, TextItemView};
 use typst::utils::{Deferred, Numeric, SliceExt};
 use typst::visualize::{
     FillRule, FixedStroke, Geometry, Image, LineCap, LineJoin, Paint, Path, PathItem,
@@ -418,46 +418,27 @@ fn write_group(ctx: &mut Builder, pos: Point, group: &GroupItem) -> SourceResult
 
 /// Encode a text run into the content stream.
 fn write_text(ctx: &mut Builder, pos: Point, text: &TextItem) -> SourceResult<()> {
-    if ctx.options.standards.pdfa {
-        let last_resort = text.font.info().is_last_resort();
-        for g in &text.glyphs {
-            if last_resort || g.id == 0 {
-                bail!(
-                    g.span.0,
-                    "the text {} could not be displayed with any font",
-                    TextItemView::full(text).glyph_text(g).repr(),
-                );
-            }
-        }
-    }
-
-    let ttf = text.font.ttf();
-    let tables = ttf.tables();
-
-    // If the text run contains either only color glyphs (used for emojis for
-    // example) or normal text we can render it directly
-    let has_color_glyphs = tables.sbix.is_some()
-        || tables.cbdt.is_some()
-        || tables.svg.is_some()
-        || tables.colr.is_some();
-    if !has_color_glyphs {
-        write_normal_text(ctx, pos, TextItemView::full(text))?;
-        return Ok(());
+    if ctx.options.standards.pdfa && text.font.info().is_last_resort() {
+        bail!(
+            Span::find(text.glyphs.iter().map(|g| g.span.0)),
+            "the text {} could not be displayed with any font",
+            &text.text,
+        );
     }
 
-    let color_glyph_count =
-        text.glyphs.iter().filter(|g| is_color_glyph(&text.font, g)).count();
+    let outline_glyphs =
+        text.glyphs.iter().filter(|g| should_outline(&text.font, g)).count();
 
-    if color_glyph_count == text.glyphs.len() {
-        write_color_glyphs(ctx, pos, TextItemView::full(text))?;
-    } else if color_glyph_count == 0 {
+    if outline_glyphs == text.glyphs.len() {
         write_normal_text(ctx, pos, TextItemView::full(text))?;
+    } else if outline_glyphs == 0 {
+        write_complex_glyphs(ctx, pos, TextItemView::full(text))?;
     } else {
-        // Otherwise we need to split it in smaller text runs
+        // Otherwise we need to split it into smaller text runs.
         let mut offset = 0;
         let mut position_in_run = Abs::zero();
-        for (color, sub_run) in
-            text.glyphs.group_by_key(|g| is_color_glyph(&text.font, g))
+        for (should_outline, sub_run) in
+            text.glyphs.group_by_key(|g| should_outline(&text.font, g))
         {
             let end = offset + sub_run.len();
 
@@ -468,11 +449,12 @@ fn write_text(ctx: &mut Builder, pos: Point, text: &TextItem) -> SourceResult<()
             let pos = pos + Point::new(position_in_run, Abs::zero());
             position_in_run += text_item_view.width();
             offset = end;
-            // Actually write the sub text-run
-            if color {
-                write_color_glyphs(ctx, pos, text_item_view)?;
-            } else {
+
+            // Actually write the sub text-run.
+            if should_outline {
                 write_normal_text(ctx, pos, text_item_view)?;
+            } else {
+                write_complex_glyphs(ctx, pos, text_item_view)?;
             }
         }
     }
@@ -534,6 +516,10 @@ fn write_normal_text(
 
     // Write the glyphs with kerning adjustments.
     for glyph in text.glyphs() {
+        if ctx.options.standards.pdfa && glyph.id == 0 {
+            bail!(tofu(&text, glyph));
+        }
+
         adjustment += glyph.x_offset;
 
         if !adjustment.is_zero() {
@@ -596,7 +582,7 @@ fn show_text(items: &mut PositionedItems, encoded: &[u8]) {
 }
 
 /// Encodes a text run made only of color glyphs into the content stream
-fn write_color_glyphs(
+fn write_complex_glyphs(
     ctx: &mut Builder,
     pos: Point,
     text: TextItemView,
@@ -621,12 +607,17 @@ fn write_color_glyphs(
         .or_default();
 
     for glyph in text.glyphs() {
+        if ctx.options.standards.pdfa && glyph.id == 0 {
+            bail!(tofu(&text, glyph));
+        }
+
         // Retrieve the Type3 font reference and the glyph index in the font.
         let color_fonts = ctx
             .resources
             .color_fonts
             .get_or_insert_with(|| Box::new(ColorFontMap::new()));
-        let (font, index) = color_fonts.get(ctx.options, &text.item.font, glyph.id)?;
+
+        let (font, index) = color_fonts.get(ctx.options, &text, glyph)?;
 
         if last_font != Some(font) {
             ctx.content.set_font(
@@ -824,3 +815,13 @@ fn to_pdf_line_join(join: LineJoin) -> LineJoinStyle {
         LineJoin::Bevel => LineJoinStyle::BevelJoin,
     }
 }
+
+/// The error when there is a tofu glyph.
+#[cold]
+fn tofu(text: &TextItemView, glyph: &Glyph) -> SourceDiagnostic {
+    error!(
+        glyph.span.0,
+        "the text {} could not be displayed with any font",
+        text.glyph_text(glyph).repr(),
+    )
+}
diff --git a/crates/typst-render/src/text.rs b/crates/typst-render/src/text.rs
index c4e83340..70d51642 100644
--- a/crates/typst-render/src/text.rs
+++ b/crates/typst-render/src/text.rs
@@ -4,7 +4,7 @@ use pixglyph::Bitmap;
 use tiny_skia as sk;
 use ttf_parser::{GlyphId, OutlineBuilder};
 use typst::layout::{Abs, Axes, Point, Size};
-use typst::text::color::{frame_for_glyph, is_color_glyph};
+use typst::text::color::{glyph_frame, should_outline};
 use typst::text::{Font, TextItem};
 use typst::visualize::{FixedStroke, Paint};
 
@@ -18,20 +18,19 @@ pub fn render_text(canvas: &mut sk::Pixmap, state: State, text: &TextItem) {
         let id = GlyphId(glyph.id);
         let offset = x + glyph.x_offset.at(text.size).to_f32();
 
-        if is_color_glyph(&text.font, glyph) {
+        if should_outline(&text.font, glyph) {
+            let state =
+                state.pre_translate(Point::new(Abs::raw(offset as _), Abs::raw(0.0)));
+            render_outline_glyph(canvas, state, text, id);
+        } else {
             let upem = text.font.units_per_em();
             let text_scale = Abs::raw(text.size.to_raw() / upem);
             let state = state
                 .pre_translate(Point::new(Abs::raw(offset as _), -text.size))
                 .pre_scale(Axes::new(text_scale, text_scale));
 
-            let glyph_frame = frame_for_glyph(&text.font, glyph.id);
-
+            let (glyph_frame, _) = glyph_frame(&text.font, glyph.id);
             crate::render_frame(canvas, state, &glyph_frame);
-        } else {
-            let state =
-                state.pre_translate(Point::new(Abs::raw(offset as _), Abs::raw(0.0)));
-            render_outline_glyph(canvas, state, text, id);
         }
 
         x += glyph.x_advance.at(text.size).to_f32();
diff --git a/crates/typst-syntax/src/span.rs b/crates/typst-syntax/src/span.rs
index 4d5dd9c3..85745f60 100644
--- a/crates/typst-syntax/src/span.rs
+++ b/crates/typst-syntax/src/span.rs
@@ -92,6 +92,13 @@ impl Span {
         }
     }
 
+    /// Find the first non-detached span in the iterator.
+    pub fn find(iter: impl IntoIterator<Item = Self>) -> Self {
+        iter.into_iter()
+            .find(|span| !span.is_detached())
+            .unwrap_or(Span::detached())
+    }
+
     /// Resolve a file location relative to this span's source.
     pub fn resolve_path(self, path: &str) -> Result<FileId, EcoString> {
         let Some(file) = self.id() else {
diff --git a/crates/typst/src/realize.rs b/crates/typst/src/realize.rs
index 7c199ff1..896c2a6a 100644
--- a/crates/typst/src/realize.rs
+++ b/crates/typst/src/realize.rs
@@ -1241,9 +1241,5 @@ fn destruct_space(buf: &mut [Pair], end: &mut usize, state: &mut SpaceState) {
 
 /// Finds the first non-detached span in the list.
 fn select_span(children: &[Pair]) -> Span {
-    children
-        .iter()
-        .map(|(c, _)| c.span())
-        .find(|span| !span.is_detached())
-        .unwrap_or(Span::detached())
+    Span::find(children.iter().map(|(c, _)| c.span()))
 }
diff --git a/crates/typst/src/text/font/color.rs b/crates/typst/src/text/font/color.rs
index 6b6ae9b0..0e6b0c1f 100644
--- a/crates/typst/src/text/font/color.rs
+++ b/crates/typst/src/text/font/color.rs
@@ -6,51 +6,138 @@ use ttf_parser::{GlyphId, RgbaColor};
 use usvg::tiny_skia_path;
 use xmlwriter::XmlWriter;
 
-use crate::layout::{Abs, Axes, Frame, FrameItem, Point, Size};
+use crate::layout::{Abs, Frame, FrameItem, Point, Size};
 use crate::syntax::Span;
 use crate::text::{Font, Glyph};
-use crate::visualize::Image;
+use crate::visualize::{FixedStroke, Geometry, Image};
 
-/// Tells if a glyph is a color glyph or not in a given font.
-pub fn is_color_glyph(font: &Font, g: &Glyph) -> bool {
+/// Whether this glyph should be rendered via simple outlining instead of via
+/// `glyph_frame`.
+pub fn should_outline(font: &Font, glyph: &Glyph) -> bool {
     let ttf = font.ttf();
-    let glyph_id = GlyphId(g.id);
-    ttf.glyph_raster_image(glyph_id, 160).is_some()
-        || ttf.glyph_svg_image(glyph_id).is_some()
-        || ttf.is_color_glyph(glyph_id)
+    let glyph_id = GlyphId(glyph.id);
+    (ttf.tables().glyf.is_some() || ttf.tables().cff.is_some())
+        && !ttf
+            .glyph_raster_image(glyph_id, u16::MAX)
+            .is_some_and(|img| img.format == ttf_parser::RasterImageFormat::PNG)
+        && !ttf.is_color_glyph(glyph_id)
+        && ttf.glyph_svg_image(glyph_id).is_none()
 }
 
-/// Returns a frame with the glyph drawn inside.
+/// Returns a frame representing a glyph and whether it is a fallback tofu
+/// frame.
+///
+/// Should only be called on glyphs for which [`should_outline`] returns false.
 ///
 /// The glyphs are sized in font units, [`text.item.size`] is not taken into
 /// account.
 #[comemo::memoize]
-pub fn frame_for_glyph(font: &Font, glyph_id: u16) -> Frame {
-    let ttf = font.ttf();
-    let upem = Abs::pt(ttf.units_per_em() as f64);
+pub fn glyph_frame(font: &Font, glyph_id: u16) -> (Frame, bool) {
+    let upem = Abs::pt(font.units_per_em());
     let glyph_id = GlyphId(glyph_id);
 
     let mut frame = Frame::soft(Size::splat(upem));
+    let mut tofu = false;
+
+    if draw_glyph(&mut frame, font, upem, glyph_id).is_none()
+        && font.ttf().glyph_index(' ') != Some(glyph_id)
+    {
+        // Generate a fallback tofu if the glyph couldn't be drawn, unless it is
+        // the space glyph. Then, an empty frame does the job. (This happens for
+        // some rare CBDT fonts, which don't define a bitmap for the space, but
+        // also don't have a glyf or CFF table.)
+        draw_fallback_tofu(&mut frame, font, upem, glyph_id);
+        tofu = true;
+    }
+
+    (frame, tofu)
+}
 
-    if let Some(raster_image) = ttf.glyph_raster_image(glyph_id, u16::MAX) {
-        draw_raster_glyph(&mut frame, font, upem, raster_image);
+/// Tries to draw a glyph.
+fn draw_glyph(
+    frame: &mut Frame,
+    font: &Font,
+    upem: Abs,
+    glyph_id: GlyphId,
+) -> Option<()> {
+    let ttf = font.ttf();
+    if let Some(raster_image) = ttf
+        .glyph_raster_image(glyph_id, u16::MAX)
+        .filter(|img| img.format == ttf_parser::RasterImageFormat::PNG)
+    {
+        draw_raster_glyph(frame, font, upem, raster_image)
     } else if ttf.is_color_glyph(glyph_id) {
-        draw_colr_glyph(&mut frame, upem, ttf, glyph_id);
+        draw_colr_glyph(frame, font, upem, glyph_id)
     } else if ttf.glyph_svg_image(glyph_id).is_some() {
-        draw_svg_glyph(&mut frame, upem, font, glyph_id);
+        draw_svg_glyph(frame, font, upem, glyph_id)
+    } else {
+        None
     }
+}
+
+/// Draws a fallback tofu box with the advance width of the glyph.
+fn draw_fallback_tofu(frame: &mut Frame, font: &Font, upem: Abs, glyph_id: GlyphId) {
+    let advance = font
+        .ttf()
+        .glyph_hor_advance(glyph_id)
+        .map(|advance| Abs::pt(advance as f64))
+        .unwrap_or(upem / 3.0);
+    let inset = 0.15 * advance;
+    let height = 0.7 * upem;
+    let pos = Point::new(inset, upem - height);
+    let size = Size::new(advance - inset * 2.0, height);
+    let thickness = upem / 20.0;
+    let stroke = FixedStroke { thickness, ..Default::default() };
+    let shape = Geometry::Rect(size).stroked(stroke);
+    frame.push(pos, FrameItem::Shape(shape, Span::detached()));
+}
+
+/// Draws a raster glyph in a frame.
+///
+/// Supports only PNG images.
+fn draw_raster_glyph(
+    frame: &mut Frame,
+    font: &Font,
+    upem: Abs,
+    raster_image: ttf_parser::RasterGlyphImage,
+) -> Option<()> {
+    let image = Image::new(
+        raster_image.data.into(),
+        typst::visualize::ImageFormat::Raster(typst::visualize::RasterFormat::Png),
+        None,
+    )
+    .ok()?;
+
+    // Apple Color emoji doesn't provide offset information (or at least
+    // not in a way ttf-parser understands), so we artificially shift their
+    // baseline to make it look good.
+    let y_offset = if font.info().family.to_lowercase() == "apple color emoji" {
+        20.0
+    } else {
+        -(raster_image.y as f64)
+    };
+
+    let position = Point::new(
+        upem * raster_image.x as f64 / raster_image.pixels_per_em as f64,
+        upem * y_offset / raster_image.pixels_per_em as f64,
+    );
+    let aspect_ratio = image.width() / image.height();
+    let size = Size::new(upem, upem * aspect_ratio);
+    frame.push(position, FrameItem::Image(image, size, Span::detached()));
 
-    frame
+    Some(())
 }
 
+/// Draws a glyph from the COLR table into the frame.
 fn draw_colr_glyph(
     frame: &mut Frame,
+    font: &Font,
     upem: Abs,
-    ttf: &ttf_parser::Face,
     glyph_id: GlyphId,
 ) -> Option<()> {
     let mut svg = XmlWriter::new(xmlwriter::Options::default());
 
+    let ttf = font.ttf();
     let width = ttf.global_bounding_box().width() as f64;
     let height = ttf.global_bounding_box().height() as f64;
     let x_min = ttf.global_bounding_box().x_min as f64;
@@ -87,8 +174,7 @@ fn draw_colr_glyph(
         transforms_stack: vec![ttf_parser::Transform::default()],
     };
 
-    ttf.paint_color_glyph(glyph_id, 0, RgbaColor::new(0, 0, 0, 255), &mut glyph_painter)
-        .unwrap();
+    ttf.paint_color_glyph(glyph_id, 0, RgbaColor::new(0, 0, 0, 255), &mut glyph_painter)?;
     svg.end_element();
 
     let data = svg.end_document().into_bytes();
@@ -98,54 +184,22 @@ fn draw_colr_glyph(
         typst::visualize::ImageFormat::Vector(typst::visualize::VectorFormat::Svg),
         None,
     )
-    .unwrap();
+    .ok()?;
 
     let y_shift = Abs::raw(upem.to_raw() - y_max);
 
     let position = Point::new(Abs::raw(x_min), y_shift);
-    let size = Axes::new(Abs::pt(width), Abs::pt(height));
+    let size = Size::new(Abs::pt(width), Abs::pt(height));
     frame.push(position, FrameItem::Image(image, size, Span::detached()));
 
     Some(())
 }
 
-/// Draws a raster glyph in a frame.
-fn draw_raster_glyph(
-    frame: &mut Frame,
-    font: &Font,
-    upem: Abs,
-    raster_image: ttf_parser::RasterGlyphImage,
-) {
-    let image = Image::new(
-        raster_image.data.into(),
-        typst::visualize::ImageFormat::Raster(typst::visualize::RasterFormat::Png),
-        None,
-    )
-    .unwrap();
-
-    // Apple Color emoji doesn't provide offset information (or at least
-    // not in a way ttf-parser understands), so we artificially shift their
-    // baseline to make it look good.
-    let y_offset = if font.info().family.to_lowercase() == "apple color emoji" {
-        20.0
-    } else {
-        -(raster_image.y as f64)
-    };
-
-    let position = Point::new(
-        upem * raster_image.x as f64 / raster_image.pixels_per_em as f64,
-        upem * y_offset / raster_image.pixels_per_em as f64,
-    );
-    let aspect_ratio = image.width() / image.height();
-    let size = Axes::new(upem, upem * aspect_ratio);
-    frame.push(position, FrameItem::Image(image, size, Span::detached()));
-}
-
 /// Draws an SVG glyph in a frame.
 fn draw_svg_glyph(
     frame: &mut Frame,
-    upem: Abs,
     font: &Font,
+    upem: Abs,
     glyph_id: GlyphId,
 ) -> Option<()> {
     // TODO: Our current conversion of the SVG table works for Twitter Color Emoji,
@@ -211,9 +265,10 @@ fn draw_svg_glyph(
         typst::visualize::ImageFormat::Vector(typst::visualize::VectorFormat::Svg),
         None,
     )
-    .unwrap();
+    .ok()?;
+
     let position = Point::new(Abs::pt(left), Abs::pt(top) + upem);
-    let size = Axes::new(Abs::pt(width), Abs::pt(height));
+    let size = Size::new(Abs::pt(width), Abs::pt(height));
     frame.push(position, FrameItem::Image(image, size, Span::detached()));
 
     Some(())