render: preserve numeric font weights

crates/obscura-render/src/dom.rs

@@ -488,7 +488,7 @@ pub fn layout_dom_with_resources(
         struct Inherited {
             color: Option<[u8; 4]>,
             font_size: Option<f32>,
-            font_weight: Option<String>,
+            font_weight: u16,
             font_family: Option<String>,
             text_align: Option<taffy::AlignItems>,
             legacy_center: bool,
@@ -518,7 +518,7 @@ pub fn layout_dom_with_resources(
                 Inherited {
                     color: None,
                     font_size: None,
-                    font_weight: None,
+                    font_weight: 400,
                     font_family: None,
                     text_align: None,
                     legacy_center: false,
@@ -776,7 +776,12 @@ pub fn layout_dom_with_resources(
                         crate::Dimension::Px(_) | crate::Dimension::Percent(_)
                     );
                 }
-                match &style.font_weight { Some(w) => inh.font_weight = Some(w.clone()), None => style.font_weight = inh.font_weight.clone() }
+                let computed_weight = crate::style::computed_font_weight(
+                    style.font_weight.as_deref(),
+                    inh.font_weight,
+                );
+                style.font_weight = Some(computed_weight.to_string());
+                inh.font_weight = computed_weight;
                 match &style.font_family { Some(f) => inh.font_family = Some(f.clone()), None => style.font_family = inh.font_family.clone() }
                 let is_table = tree
                     .get_node(id)
@@ -2740,7 +2745,7 @@ fn build_text_words(
     if let Some(parent_id) = node.parent {
         if let Some(p_style) = styles.get(&parent_id) {
             fsize = p_style.font_size.unwrap_or(16.0);
-            is_bold = p_style.font_weight.as_deref() == Some("bold");
+            is_bold = crate::style::used_font_weight(p_style) >= 600;
             family = p_style.font_family.as_deref();
             line_height = crate::inline::used_line_height(p_style);
             transform = p_style
@@ -2839,7 +2844,7 @@ fn build_pseudo_content(
     words: &mut HashMap<taffy::NodeId, (NodeId, String)>,
 ) -> Vec<taffy::NodeId> {
     let fsize = style.font_size.unwrap_or(16.0);
-    let is_bold = style.font_weight.as_deref() == Some("bold");
+    let is_bold = crate::style::used_font_weight(style) >= 600;
     build_word_leaves(
         id,
         content,

crates/obscura-render/src/inline.rs

@@ -78,10 +78,18 @@ fn resolve_font_family(fam: Option<&str>) -> &'static str {
     FAMILY
 }
 
-fn resolve_loaded_font_family(
+#[derive(Clone)]
+struct LoadedFamily {
+    name: Arc<str>,
+    weights: Vec<u16>,
+    variable: bool,
+}
+
+fn resolve_loaded_font(
     fam: Option<&str>,
-    loaded: &HashMap<String, Arc<str>>,
+    requested_weight: u16,
-) -> Arc<str> {
+    loaded: &HashMap<String, LoadedFamily>,
+) -> (Arc<str>, u16) {
     if let Some(stack) = fam {
         for token in stack.split(',') {
             let name = token
@@ -89,11 +97,81 @@ fn resolve_loaded_font_family(
                 .trim_matches(|c| c == '"' || c == '\'')
                 .trim();
             if let Some(family) = loaded.get(&name.to_ascii_lowercase()) {
-                return Arc::clone(family);
+                let weight = if family.variable {
+                    requested_weight
+                } else {
+                    match_font_weight(requested_weight, &family.weights)
+                };
+                return (Arc::clone(&family.name), weight);
             }
         }
     }
-    Arc::from(resolve_font_family(fam))
+    let fallback = resolve_font_family(fam);
+    let weights: &[u16] = &[400, 700];
+    (Arc::from(fallback), match_font_weight(requested_weight, weights))
+}
+
+/// CSS Fonts' asymmetric missing-weight search. In particular, 600 selects
+/// 700 (not 400) when a family only provides regular and bold faces.
+fn match_font_weight(requested: u16, available: &[u16]) -> u16 {
+    if available.contains(&requested) {
+        return requested;
+    }
+    let mut weights = available.to_vec();
+    weights.sort_unstable();
+    weights.dedup();
+    if weights.is_empty() {
+        return requested;
+    }
+    if (400..=500).contains(&requested) {
+        weights
+            .iter()
+            .copied()
+            .filter(|weight| *weight >= requested && *weight <= 500)
+            .min()
+            .or_else(|| weights.iter().copied().filter(|weight| *weight < requested).max())
+            .or_else(|| weights.iter().copied().filter(|weight| *weight > 500).min())
+            .unwrap_or(requested)
+    } else if requested < 400 {
+        weights
+            .iter()
+            .copied()
+            .filter(|weight| *weight <= requested)
+            .max()
+            .or_else(|| weights.iter().copied().filter(|weight| *weight > requested).min())
+            .unwrap_or(requested)
+    } else {
+        weights
+            .iter()
+            .copied()
+            .filter(|weight| *weight >= requested)
+            .min()
+            .or_else(|| weights.iter().copied().filter(|weight| *weight < requested).max())
+            .unwrap_or(requested)
+    }
+}
+
+fn face_is_variable(data: &[u8], face_index: u32) -> bool {
+    let base = if data.get(..4) == Some(b"ttcf") {
+        let offset = 12usize.saturating_add(face_index as usize * 4);
+        data.get(offset..offset + 4)
+            .and_then(|bytes| bytes.try_into().ok())
+            .map(u32::from_be_bytes)
+            .unwrap_or(0) as usize
+    } else {
+        0
+    };
+    let Some(count) = data
+        .get(base + 4..base + 6)
+        .and_then(|bytes| bytes.try_into().ok())
+        .map(u16::from_be_bytes)
+    else {
+        return false;
+    };
+    (0..count as usize).any(|index| {
+        let start = base + 12 + index * 16;
+        data.get(start..start + 4) == Some(b"fvar")
+    })
 }
 /// Resolve `line-height: normal` from the selected face's horizontal header.
 ///
@@ -166,7 +244,7 @@ pub struct InlineItem {
 /// [`crate::DomLayout`] so paint can rasterize the shaped glyphs.
 pub struct TextEngine {
     font_system: FontSystem,
-    loaded_families: HashMap<String, Arc<str>>,
+    loaded_families: HashMap<String, LoadedFamily>,
     swash: SwashCache,
     items: Vec<InlineItem>,
     replaced: Vec<ReplacedItem>,
@@ -256,11 +334,24 @@ impl TextEngine {
             )));
         }
         let mut loaded_families = HashMap::new();
-        for face in db.faces() {
+        let faces: Vec<_> = db
-            for (name, _) in &face.families {
+            .faces()
-                loaded_families
+            .map(|face| (face.id, face.families.clone(), face.weight.0))
+            .collect();
+        for (id, names, weight) in faces {
+            let variable = db
+                .with_face_data(id, face_is_variable)
+                .unwrap_or(false);
+            for (name, _) in names {
+                let family = loaded_families
                     .entry(name.to_ascii_lowercase())
-                    .or_insert_with(|| Arc::from(name.as_str()));
+                    .or_insert_with(|| LoadedFamily {
+                        name: Arc::from(name.as_str()),
+                        weights: Vec::new(),
+                        variable: false,
+                    });
+                family.weights.push(weight);
+                family.variable |= variable;
             }
         }
         db.set_sans_serif_family(FAMILY);
@@ -293,9 +384,15 @@ impl TextEngine {
         }
         let base = styles.get(&id)?;
         let mut collector = Collector { last_was_space: true, clip_fills: Vec::new() };
+        let (family, weight) = resolve_loaded_font(
+            base.font_family.as_deref(),
+            crate::style::used_font_weight(base),
+            &self.loaded_families,
+        );
         let ctx = base_span_ctx(
             base,
-            resolve_loaded_font_family(base.font_family.as_deref(), &self.loaded_families),
+            family,
+            weight,
             &mut collector,
         );
         let mut spans: Vec<(String, SpanAttrs)> = Vec::new();
@@ -336,9 +433,15 @@ impl TextEngine {
         }
         let base = styles.get(&parent)?;
         let mut collector = Collector { last_was_space: true, clip_fills: Vec::new() };
+        let (family, weight) = resolve_loaded_font(
+            base.font_family.as_deref(),
+            crate::style::used_font_weight(base),
+            &self.loaded_families,
+        );
         let ctx = base_span_ctx(
             base,
-            resolve_loaded_font_family(base.font_family.as_deref(), &self.loaded_families),
+            family,
+            weight,
             &mut collector,
         );
         let mut spans: Vec<(String, SpanAttrs)> = Vec::new();
@@ -509,7 +612,7 @@ impl TextEngine {
 /// A run of same-styled inline text.
 #[derive(Clone, PartialEq)]
 struct SpanAttrs {
-    bold: bool,
+    weight: u16,
     italic: bool,
     underline: bool,
     color: [u8; 4],
@@ -520,7 +623,7 @@ struct SpanAttrs {
 impl SpanAttrs {
     fn to_attrs(&self) -> Attrs<'_> {
         let mut a = Attrs::new().family(Family::Name(self.family.as_ref()));
-        a = a.weight(if self.bold { Weight::BOLD } else { Weight::NORMAL });
+        a = a.weight(Weight(self.weight));
         a = a.style(if self.italic { Style::Italic } else { Style::Normal });
         // Clip-text glyphs must be shaped with an opaque fill so their coverage
         // reaches paint; the real gradient is selected through metadata.
@@ -537,7 +640,7 @@ impl SpanAttrs {
 #[derive(Clone)]
 struct SpanCtx {
     color: [u8; 4],
-    bold: bool,
+    weight: u16,
     italic: bool,
     underline: bool,
     transform: TextTransform,
@@ -566,6 +669,7 @@ struct Collector {
 fn base_span_ctx(
     base: &LayoutStyle,
     family: Arc<str>,
+    weight: u16,
     collector: &mut Collector,
 ) -> SpanCtx {
     let clip_fill = clip_text_fill(base).map(|fill| {
@@ -575,7 +679,7 @@ fn base_span_ctx(
     });
     SpanCtx {
         color: base.color.unwrap_or([0, 0, 0, 255]),
-        bold: base.font_weight.as_deref() == Some("bold"),
+        weight,
         italic: base.font_style_italic.unwrap_or(false),
         underline: base.underline.unwrap_or(false),
         transform: base.text_transform.unwrap_or(TextTransform::None),
@@ -591,7 +695,7 @@ fn collect_spans(
     ctx: SpanCtx,
     out: &mut Vec<(String, SpanAttrs)>,
     c: &mut Collector,
-    loaded_families: &HashMap<String, Arc<str>>,
+    loaded_families: &HashMap<String, LoadedFamily>,
 ) {
     for cid in tree.children(id) {
         collect_node_spans(
@@ -617,13 +721,13 @@ fn collect_node_spans(
     ctx: SpanCtx,
     out: &mut Vec<(String, SpanAttrs)>,
     c: &mut Collector,
-    loaded_families: &HashMap<String, Arc<str>>,
+    loaded_families: &HashMap<String, LoadedFamily>,
 ) {
     let Some(node) = tree.get_node(cid) else { return };
     match &node.data {
         obscura_dom::tree::NodeData::Text { contents } => {
             let attrs = SpanAttrs {
-                bold: ctx.bold,
+                weight: ctx.weight,
                 italic: ctx.italic,
                 underline: ctx.underline,
                 color: ctx.color,
@@ -640,7 +744,7 @@ fn collect_node_spans(
             }
             if elem.local.as_ref() == "br" {
                 out.push(("\n".to_string(), SpanAttrs {
-                    bold: ctx.bold,
+                    weight: ctx.weight,
                     italic: ctx.italic,
                     underline: ctx.underline,
                     color: ctx.color,
@@ -662,20 +766,28 @@ fn collect_node_spans(
             let clip_fill = own_clip_fill.or_else(|| {
                 if color[3] == 0 { ctx.clip_fill } else { None }
             });
+            let requested_weight = style
+                .map(crate::style::used_font_weight)
+                .unwrap_or(ctx.weight);
+            let (family, weight) = style
+                .and_then(|style| style.font_family.as_deref())
+                .map(|family| {
+                    resolve_loaded_font(
+                        Some(family),
+                        requested_weight,
+                        loaded_families,
+                    )
+                })
+                .unwrap_or_else(|| (Arc::clone(&ctx.family), requested_weight));
             let child = SpanCtx {
                 color,
-                bold: ctx.bold || style.map(|s| s.font_weight.as_deref() == Some("bold")).unwrap_or(false),
+                weight,
                 italic: ctx.italic || style.and_then(|s| s.font_style_italic).unwrap_or(false),
                 // Underline propagates in: an ancestor's underline covers
                 // descendant text; an element only sets its own via CSS.
                 underline: ctx.underline || style.and_then(|s| s.underline).unwrap_or(false),
                 transform: style.and_then(|s| s.text_transform).unwrap_or(ctx.transform),
-                family: style
+                family,
-                    .and_then(|s| s.font_family.as_deref())
-                    .map(|family| {
-                        resolve_loaded_font_family(Some(family), loaded_families)
-                    })
-                    .unwrap_or_else(|| Arc::clone(&ctx.family)),
                 clip_fill,
             };
             collect_spans(
@@ -1103,6 +1215,15 @@ mod tests {
         assert_eq!(normal_line_height(13.0, MONO_FAMILY), 15.0);
     }
 
+    #[test]
+    fn missing_font_weights_follow_css_search_order() {
+        assert_eq!(match_font_weight(500, &[400, 700]), 400);
+        assert_eq!(match_font_weight(600, &[400, 500, 700]), 700);
+        assert_eq!(match_font_weight(300, &[100, 400, 700]), 100);
+        assert_eq!(match_font_weight(800, &[400, 700]), 700);
+        assert_eq!(match_font_weight(500, &[400, 500, 700]), 500);
+    }
+
     #[test]
     fn clip_fill_only_for_transparent_clip_text() {
         let mut s = LayoutStyle::default();

crates/obscura-render/src/lib.rs

@@ -312,6 +312,9 @@ pub struct LayoutStyle {
     /// eagerly treating `9vw` as the number 9 made responsive headings pin to
     /// the minimum arm of their clamp.
     pub font_size_expression: Option<String>,
+    /// Specified CSS font weight during cascade (`1..1000`, `bolder`, or
+    /// `lighter`), normalized to its numeric computed value by the inheritance
+    /// pass before layout and shaping.
     pub font_weight: Option<String>,
     /// The computed `font-family` list, lowercased. Inherited. The text engine
     /// resolves it to a bundled face (Liberation Sans/Serif/Mono) the way

crates/obscura-render/src/paint.rs

@@ -449,7 +449,7 @@ pub fn paint_dom(tree: &DomTree, viewport: (f32, f32), base_url: Option<&str>) -
         if let Some(runs) = laid.text_runs.get(&nid) {
             let color = style.color.unwrap_or([0, 0, 0, 255]);
             let fsize = style.font_size.unwrap_or(16.0);
-            let is_bold = style.font_weight.as_deref() == Some("bold");
+            let is_bold = crate::style::used_font_weight(style) >= 600;
             for (word_rect, word) in runs {
                 draw_text(
                     &mut pixmap,
@@ -721,7 +721,7 @@ fn paint_text_node(
     }
     let color = clip_text_fill_color(style).unwrap_or_else(|| style.color.unwrap_or([0, 0, 0, 255]));
     let fsize = style.font_size.unwrap_or(16.0);
-    let is_bold = style.font_weight.as_deref() == Some("bold");
+    let is_bold = crate::style::used_font_weight(style) >= 600;
     // A text node has no transform of its own, but any transformed element
     // ancestor offsets it (the accumulation covers text nodes too). The clip
     // is already in screen space and stays put.

crates/obscura-render/src/style.rs

@@ -495,11 +495,9 @@ fn apply_value(style: &mut LayoutStyle, name: &str, value: &str) {
         }
         "font" => apply_font_shorthand(style, value),
         "font-weight" => {
-            // Normalize to "bold"/"normal" (consumers test for "bold"). Numeric
+            if let Some(weight) = specified_font_weight(value) {
-            // >= 600 and `bold`/`bolder` are bold; others normal.
+                style.font_weight = Some(weight);
-            let v = value.trim().to_ascii_lowercase();
+            }
-            let bold = v == "bold" || v == "bolder" || v.parse::<u32>().map(|n| n >= 600).unwrap_or(false);
-            style.font_weight = Some(if bold { "bold".to_string() } else { "normal".to_string() });
         }
         "font-family" => {
             let v = value.trim().to_ascii_lowercase();
@@ -2513,18 +2511,15 @@ fn apply_font_shorthand(style: &mut LayoutStyle, value: &str) {
 
     // The shorthand resets every constituent before applying supplied values.
     style.font_style_italic = Some(false);
-    style.font_weight = Some("normal".to_string());
+    style.font_weight = Some("400".to_string());
     style.line_height = Some(crate::LineHeight::Normal);
     style.line_height_expression = None;
     for token in &tokens[..size_index] {
         let lower = token.to_ascii_lowercase();
         if lower == "italic" || lower.starts_with("oblique") {
             style.font_style_italic = Some(true);
-        } else if lower == "bold"
+        } else if let Some(weight) = specified_font_weight(&lower) {
-            || lower == "bolder"
+            style.font_weight = Some(weight);
-            || lower.parse::<u32>().map(|weight| weight >= 600).unwrap_or(false)
-        {
-            style.font_weight = Some("bold".to_string());
         }
     }
     apply_font_size(style, size);
@@ -2534,6 +2529,54 @@ fn apply_font_shorthand(style: &mut LayoutStyle, value: &str) {
     style.font_family = Some(tokens[family_index..].join(" ").to_ascii_lowercase());
 }
 
+/// Normalize a specified CSS font weight while preserving relative keywords
+/// until the top-down inheritance pass can see the parent's computed weight.
+fn specified_font_weight(value: &str) -> Option<String> {
+    let lower = value.trim().to_ascii_lowercase();
+    match lower.as_str() {
+        "normal" => Some("400".to_string()),
+        "bold" => Some("700".to_string()),
+        "bolder" | "lighter" => Some(lower),
+        _ => lower
+            .parse::<f32>()
+            .ok()
+            .filter(|weight| weight.is_finite() && (1.0..=1000.0).contains(weight))
+            .map(|weight| weight.round().to_string()),
+    }
+}
+
+/// Resolve `font-weight` to the numeric computed value defined by CSS Fonts.
+/// Relative keywords use the inherited weight table rather than a binary
+/// normal/bold threshold.
+pub(crate) fn computed_font_weight(specified: Option<&str>, inherited: u16) -> u16 {
+    match specified {
+        None => inherited,
+        Some("normal") => 400,
+        Some("bold") => 700,
+        Some("bolder") if inherited < 100 => 400,
+        Some("bolder") if inherited < 350 => 400,
+        Some("bolder") if inherited < 550 => 700,
+        Some("bolder") if inherited < 900 => 900,
+        Some("bolder") => inherited,
+        Some("lighter") if inherited < 100 => inherited,
+        Some("lighter") if inherited < 350 => 100,
+        Some("lighter") if inherited < 550 => 100,
+        Some("lighter") if inherited < 750 => 400,
+        Some("lighter") if inherited < 900 => 700,
+        Some("lighter") => 700,
+        Some(weight) => weight
+            .parse::<f32>()
+            .ok()
+            .filter(|weight| weight.is_finite())
+            .map(|weight| weight.round().clamp(1.0, 1000.0) as u16)
+            .unwrap_or(inherited),
+    }
+}
+
+pub(crate) fn used_font_weight(style: &LayoutStyle) -> u16 {
+    computed_font_weight(style.font_weight.as_deref(), 400)
+}
+
 fn is_font_size_token(value: &str) -> bool {
     let lower = value.trim().to_ascii_lowercase();
     if lower == "0" || font_size_keyword(&lower).is_some() {
@@ -3504,7 +3547,7 @@ mod tests {
         );
         assert_eq!(s.font_size, Some(64.0));
         assert_eq!(s.line_height, Some(crate::LineHeight::Px(60.0)));
-        assert_eq!(s.font_weight.as_deref(), Some("normal"));
+        assert_eq!(s.font_weight.as_deref(), Some("500"));
         assert_eq!(s.font_style_italic, Some(false));
         assert_eq!(s.font_family.as_deref(), Some("\"google sans\", sans-serif"));
 
@@ -3514,10 +3557,32 @@ mod tests {
         );
         assert_eq!(reset.font_size, Some(20.0));
         assert_eq!(reset.line_height, Some(crate::LineHeight::Normal));
-        assert_eq!(reset.font_weight.as_deref(), Some("normal"));
+        assert_eq!(reset.font_weight.as_deref(), Some("400"));
         assert_eq!(reset.font_style_italic, Some(false));
     }
 
+    #[test]
+    fn font_weight_preserves_numeric_values_and_resolves_relative_keywords() {
+        let medium = compute_style("div", Some("font-weight:500"));
+        assert_eq!(medium.font_weight.as_deref(), Some("500"));
+        let semibold = compute_style("div", Some("font-weight:600"));
+        assert_eq!(semibold.font_weight.as_deref(), Some("600"));
+        let normal = compute_style("strong", Some("font-weight:normal"));
+        assert_eq!(normal.font_weight.as_deref(), Some("400"));
+
+        assert_eq!(computed_font_weight(Some("bolder"), 99), 400);
+        assert_eq!(computed_font_weight(Some("bolder"), 349), 400);
+        assert_eq!(computed_font_weight(Some("bolder"), 350), 700);
+        assert_eq!(computed_font_weight(Some("bolder"), 550), 900);
+        assert_eq!(computed_font_weight(Some("bolder"), 900), 900);
+        assert_eq!(computed_font_weight(Some("lighter"), 99), 99);
+        assert_eq!(computed_font_weight(Some("lighter"), 100), 100);
+        assert_eq!(computed_font_weight(Some("lighter"), 350), 100);
+        assert_eq!(computed_font_weight(Some("lighter"), 550), 400);
+        assert_eq!(computed_font_weight(Some("lighter"), 750), 700);
+        assert_eq!(computed_font_weight(Some("lighter"), 900), 700);
+    }
+
     #[test]
     fn containing_block_property_triggers_are_independent() {
         let s = compute_style("div", Some("transform:rotate(0deg);filter:none"));

crates/obscura-render/tests/layout_test.rs

@@ -1113,6 +1113,31 @@ fn length_line_height_computes_before_inheritance() {
     );
 }
 
+#[test]
+fn font_weight_computes_numerically_through_inheritance() {
+    let tree = parse_html(
+        r#"
+        <div id="medium" style="font-weight:500">
+          <span id="inherited">medium</span>
+          <strong id="normal" style="font-weight:normal">normal</strong>
+          <span id="bolder" style="font-weight:bolder">bolder</span>
+          <span id="lighter" style="font-weight:lighter">lighter</span>
+        </div>
+        "#,
+    );
+    let layout = layout_dom(&tree, (900.0, 1000.0));
+    let weight = |id| {
+        layout.styles[&tree.get_element_by_id(id).unwrap()]
+            .font_weight
+            .as_deref()
+    };
+    assert_eq!(weight("medium"), Some("500"));
+    assert_eq!(weight("inherited"), Some("500"));
+    assert_eq!(weight("normal"), Some("400"));
+    assert_eq!(weight("bolder"), Some("700"));
+    assert_eq!(weight("lighter"), Some("100"));
+}
+
 #[test]
 fn contextual_right_inset_uses_root_font_tokens() {
     let tree = parse_html(