Fix #3209: SVG export writes type sizes and spacing in CSS with px

With Styling set to Internal CSS, Inline Style or Style Entities, font-size
and letter-spacing were written as bare numbers. Only presentation attributes
take a bare number; in CSS a browser drops them, so the type was drawn at its
default size. They are now written in px, SVG's user unit, and presentation
attributes keep bare numbers.

crates/svg/src/export/output.rs

@@ -292,14 +292,18 @@ impl Writer<'_> {
         format!("matrix({} {} {} {} {} {})", self.num(c[0]), self.num(c[1]), self.num(c[2]), self.num(c[3]), self.num(c[4]), self.num(c[5]))
     }
 
+    /// How style properties are written: the styling option, but SVG Tiny has presentation
+    /// attributes alone.
+    pub(super) fn styling(&self) -> Styling {
+        if self.tiny() { Styling::PresentationAttributes } else { self.opts.styling }
+    }
+
     /// Style properties as attributes, an inline style, or a CSS class, per the styling option.
     pub(super) fn attrs(&mut self, props: &Props) -> String {
         if props.is_empty() {
             return String::new();
         }
-        // SVG Tiny has presentation attributes alone.
-        let styling = if self.tiny() { Styling::PresentationAttributes } else { self.opts.styling };
-        match styling {
+        match self.styling() {
             Styling::PresentationAttributes => {
                 // CSS-only properties go in a style attribute (SVG Tiny has none: left out).
                 let (style, attrs): (Vec<_>, Vec<_>) = props.iter().partition(|(k, _)| {

crates/svg/src/export/text.rs

@@ -1,8 +1,8 @@
 use super::output::xml_text;
 use super::{
     Affine, AppearanceItem, Arc, BTreeSet, BezPath, BlendMode, CharStyle, FillRule, FontDb, FontFace, GradientKind, HashMap, Justify, Node, NodeId,
-    NodeKind, Paint, PathData, Props, Rect, StrokeAlign, TextKind, TextObject, Writer, base64_encode, css, css_string, fmt_num, font_descriptor,
-    xml_escape,
+    NodeKind, Paint, PathData, Props, Rect, StrokeAlign, Styling, TextKind, TextObject, Writer, base64_encode, css, css_string, fmt_num,
+    font_descriptor, xml_escape,
 };
 
 /// `chars` (sorted) as a CSS `unicode-range` (`U+41-5A,U+61`).
@@ -36,7 +36,10 @@ impl Writer<'_> {
     /// (as on the canvas).
     fn char_props(&mut self, st: &CharStyle, space: (Rect, Affine)) -> Props {
         let decimals = self.opts.decimals;
-        let len = |v: f64| fmt_num(v, decimals);
+        // Only presentation attributes take a bare number (in user units). Written as CSS, a
+        // length needs its unit, a user unit being a `px`: a browser drops `font-size:8.6` (#3209).
+        let unit = if self.styling() == Styling::PresentationAttributes { "" } else { "px" };
+        let len = |v: f64| format!("{}{unit}", fmt_num(v, decimals));
         let mut p = css::font_props(st, &len);
         // Character paints resolve in the text's space (`to_user` maps it into user space).
         let (bounds, to_user) = space;

crates/svg/tests/it/css_rules.rs

@@ -228,8 +228,16 @@ fn shared_properties_read_as_svg_export_writes_them() {
         let decl = format!("{k}:{v}").replace('"', """).replace('\'', "'");
         assert!(style.contains(&decl), "{decl} as in SVG export: {style}");
     }
-    // Lengths are the same numbers, with units on the web.
-    assert!(style.contains("font-size:18") && prop(&r, "font-size") == Some("18px"), "{style}");
+    // Lengths are the same, with units: CSS takes a bare number only for 0, and a browser drops
+    // `font-size:18`, leaving the type at its default size (#3209). Presentation attributes take
+    // bare numbers (`text_layout`).
+    let spacing = prop(&r, "letter-spacing").unwrap_or_default();
+    assert!(prop(&r, "font-size") == Some("18px") && spacing.ends_with("px"), "{r:?}");
+    for decl in ["font-size:18px".to_string(), format!("letter-spacing:{spacing}")] {
+        assert!(style.contains(&decl), "{decl} as in SVG export: {style}");
+    }
+    let inline = export(&d, &ExportOptions { styling: Styling::InlineStyle, ..ExportOptions::default() });
+    assert!(inline.contains("font-size:18px") && inline.contains(&format!("letter-spacing:{spacing}")), "{inline}");
 }
 
 #[test]