typography and documents: formula and diagram SVG for export; a diagram label without a font is an error

src/documents/diagram.rs

@@ -1,6 +1,6 @@
 use std::{
     panic::{AssertUnwindSafe, catch_unwind},
-    sync::Arc,
+    sync::{Arc, OnceLock},
 };
 
 use gpui::{
@@ -95,6 +95,72 @@ fn svg(chart: &Chart) -> Result<String, SharedString> {
     }
 }
 
+/// `source` as light SVG of plain paths, for export.
+pub fn diagram_svg(source: &str) -> Result<String, SharedString> {
+    let chart = Chart {
+        source: source.to_owned().into(),
+        dark: false,
+        ground: "#ffffff".into(),
+        ink: "#000000".into(),
+        scale: 100,
+    };
+    let drawn = svg(&chart)?;
+    // Markers and text become paths any reader draws.
+    let options = usvg::Options {
+        fontdb: fonts(),
+        ..usvg::Options::default()
+    };
+    let tree = usvg::Tree::from_data(drawn.as_bytes(), &options)
+        .map_err(|error| SharedString::from(format!("{error}")))?;
+    // A label without a font vanishes: say so.
+    let (written, kept) = (labels(&drawn)?, texts(tree.root()));
+    if kept < written {
+        log::error!("diagram: {kept} of {written} labels found a font");
+        return Err("no installed font could set this diagram's labels".into());
+    }
+    Ok(tree.to_string(&usvg::WriteOptions::default()))
+}
+
+/// The `<text>` elements holding words.
+fn labels(svg: &str) -> Result<usize, SharedString> {
+    let doc = usvg::roxmltree::Document::parse(svg)
+        .map_err(|error| SharedString::from(format!("{error}")))?;
+    let worded = |node: &usvg::roxmltree::Node| {
+        node.descendants()
+            .any(|word| word.text().is_some_and(|text| !text.trim().is_empty()))
+    };
+    Ok(doc
+        .descendants()
+        .filter(|node| node.has_tag_name("text") && worded(node))
+        .count())
+}
+
+/// Text nodes usvg set.
+fn texts(group: &usvg::Group) -> usize {
+    group
+        .children()
+        .iter()
+        .map(|node| match node {
+            usvg::Node::Group(inner) => texts(inner),
+            usvg::Node::Text(_) => 1,
+            _ => 0,
+        })
+        .sum()
+}
+
+/// The system's fonts, read once.
+fn fonts() -> Arc<usvg::fontdb::Database> {
+    static FONTS: OnceLock<Arc<usvg::fontdb::Database>> = OnceLock::new();
+    FONTS
+        .get_or_init(|| {
+            let mut fonts = usvg::fontdb::Database::new();
+            fonts.load_system_fonts();
+            log::info!("diagram: {} system font faces for export", fonts.len());
+            Arc::new(fonts)
+        })
+        .clone()
+}
+
 /// `#rrggbb` of a theme color.
 fn hex(color: Hsla) -> SharedString {
     let rgb = color.to_rgb();
@@ -182,6 +248,17 @@ mod tests {
         assert!(!why.is_empty());
     }
 
+    #[test]
+    fn an_exported_diagram_is_plain_paths() {
+        let svg = diagram_svg(
+            "flowchart LR
+  A[Start] --> B",
+        )
+        .expect("draws");
+        assert!(svg.contains("<path"), "{svg}");
+        assert!(!svg.contains("<marker") && !svg.contains("<text"), "{svg}");
+    }
+
     #[test]
     fn colors_write_as_hex() {
         assert_eq!(hex(gpui::rgb(0x2c2c2c).into()), "#2c2c2c");

src/documents/mod.rs

@@ -33,7 +33,7 @@ pub(crate) use blocks::source;
 pub use blocks::{Align, BlockData, BlockEditor, BlockEvent, BlockKind, Media};
 pub use contents::outline;
 pub use counts::{ReadingTime, WordCount};
-pub use diagram::Diagram;
+pub use diagram::{Diagram, diagram_svg};
 pub use document::{
     Attachment, DocumentEvent, DocumentHeading, DocumentLook, LARGEST_READ, MarkdownDocument,
     TableEdit, TableRefusal,

src/typography/math.rs

@@ -116,6 +116,18 @@ impl Asset for Typesetter {
     }
 }
 
+/// `source` as black outlined SVG, for export.
+pub fn formula_svg(source: &str, display: bool) -> Result<String, MathError> {
+    let formula = Formula {
+        source: source.to_owned().into(),
+        display,
+        rgba: 0x0000_00ff,
+        font: 1600,
+        scale: 100,
+    };
+    svg(&formula).map(|(svg, _)| svg)
+}
+
 /// The formula as outlined SVG holding all ink; its size.
 fn svg(formula: &Formula) -> Result<(String, Size<Pixels>), MathError> {
     let ast = parsed(&formula.source)?;

src/typography/math/tests.rs

@@ -177,3 +177,11 @@ fn a_shared_formula_stays_until_its_last_holder_leaves(cx: &mut gpui::TestAppCon
     flush(cx);
     assert!(!cached("c^2", cx), "the last holder freed it");
 }
+
+#[test]
+fn an_exported_formula_is_black_outlines() {
+    let svg = formula_svg(r"\sqrt{x}", true).expect("typesets");
+    assert!(svg.starts_with("<svg") && !svg.contains("<text"), "{svg}");
+    assert!(svg.contains("0,0,0"), "black: {svg}");
+    assert!(formula_svg(r"\frac{", false).is_err());
+}

src/typography/mod.rs

@@ -26,7 +26,7 @@ pub use formatted::{
 pub use inline::{Blockquote, Code, Highlight, Kbd, KbdCombo};
 pub use link::{ExternalLink, Link};
 pub(crate) use math::failed;
-pub use math::{Latex, MathError};
+pub use math::{Latex, MathError, formula_svg};
 pub use rolling::AnimatedNumber;
 pub use select::SelectableText;
 pub use text::{Caption, Heading, Label, Overline, Paragraph, Subtitle, Title, literal, tabular};