Inherit dominant-baseline into nested <tspan> elements

CHANGELOG.md

@@ -10,6 +10,10 @@ This changelog also contains important changes in dependencies.
 
 This release has an MSRV of 1.87.0 for `usvg` and `resvg` and the C API.
 
+### Fixed
+- `dominant-baseline` is now correctly inherited by nested `<tspan>` elements,
+  so a nested span stays on the same baseline as its siblings. (#864)
+
 ## [0.47.0] 2026-02-05
 
 This release has an MSRV of 1.87.0 for `usvg` and `resvg` and the C API.

crates/resvg/tests/integration/render.rs

@@ -1402,6 +1402,7 @@ use crate::render;
 #[test] fn text_dominant_baseline_hanging() { assert_eq!(render("tests/text/dominant-baseline/hanging"), 0); }
 #[test] fn text_dominant_baseline_ideographic() { assert_eq!(render("tests/text/dominant-baseline/ideographic"), 0); }
 #[test] fn text_dominant_baseline_inherit() { assert_eq!(render("tests/text/dominant-baseline/inherit"), 0); }
+#[test] fn text_dominant_baseline_inherited_through_nested_tspan() { assert_eq!(render("tests/text/dominant-baseline/inherited-through-nested-tspan"), 0); }
 #[test] fn text_dominant_baseline_mathematical() { assert_eq!(render("tests/text/dominant-baseline/mathematical"), 0); }
 #[test] fn text_dominant_baseline_middle() { assert_eq!(render("tests/text/dominant-baseline/middle"), 0); }
 #[test] fn text_dominant_baseline_nested() { assert_eq!(render("tests/text/dominant-baseline/nested"), 0); }

crates/usvg/src/parser/svgtree/mod.rs

@@ -823,11 +823,15 @@ impl AId {
 fn is_non_inheritable(id: AId) -> bool {
     matches!(
         id,
+        // `dominant-baseline` is intentionally *not* listed here: unlike
+        // `alignment-baseline` and `baseline-shift`, it is an inherited property
+        // (CSS Inline Layout 3 / SVG 2, matching Chromium and Inkscape). Treating
+        // it as non-inheritable broke nested `<tspan>`s, whose direct parent does
+        // not carry the value (https://github.com/linebender/resvg/issues/864).
         AId::AlignmentBaseline
             | AId::BaselineShift
             | AId::ClipPath
             | AId::Display
-            | AId::DominantBaseline
             | AId::Filter
             | AId::FloodColor
             | AId::FloodOpacity

crates/usvg/tests/text.rs

@@ -0,0 +1,100 @@
+// Copyright 2024 the Resvg Authors
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+use std::sync::Arc;
+
+use once_cell::sync::Lazy;
+use usvg::{DominantBaseline, Group, Node, Text};
+
+static GLOBAL_FONTDB: Lazy<Arc<usvg::fontdb::Database>> = Lazy::new(|| {
+    let mut fontdb = usvg::fontdb::Database::new();
+    fontdb.load_fonts_dir("../resvg/tests/fonts");
+    fontdb.set_serif_family("Noto Serif");
+    fontdb.set_sans_serif_family("Noto Sans");
+    fontdb.set_cursive_family("Yellowtail");
+    fontdb.set_fantasy_family("Sedgwick Ave Display");
+    fontdb.set_monospace_family("Noto Mono");
+    Arc::new(fontdb)
+});
+
+fn parse(svg: &str) -> usvg::Tree {
+    let opt = usvg::Options {
+        fontdb: GLOBAL_FONTDB.clone(),
+        ..Default::default()
+    };
+    usvg::Tree::from_str(svg, &opt).unwrap()
+}
+
+fn first_text(group: &Group) -> Option<&Text> {
+    for node in group.children() {
+        match node {
+            Node::Text(t) => return Some(t),
+            Node::Group(g) => {
+                if let Some(t) = first_text(g) {
+                    return Some(t);
+                }
+            }
+            _ => {}
+        }
+    }
+    None
+}
+
+// Regression test for https://github.com/linebender/resvg/issues/864
+//
+// `dominant-baseline` is an inherited property (CSS Inline Layout 3 / SVG 2),
+// so a nested `<tspan>` that does not set it must inherit the value from an
+// ancestor `<text>` — even when its direct parent `<tspan>` doesn't carry it.
+// Previously the nested span fell back to `Auto`, placing it on the alphabetic
+// baseline while its sibling text used `text-after-edge`, so the two were no
+// longer on the same line.
+#[test]
+fn nested_tspan_inherits_dominant_baseline() {
+    let svg = "<svg xmlns='http://www.w3.org/2000/svg' width='400' height='200'>
+        <text x='20' y='150' font-family='Noto Sans' dominant-baseline='text-after-edge'>
+            <tspan x='20' font-size='40'><tspan>hello</tspan> world</tspan>
+        </text>
+    </svg>";
+
+    let tree = parse(svg);
+    let text = first_text(tree.root()).expect("a text node");
+
+    let chunk = text
+        .chunks()
+        .iter()
+        .find(|c| c.text() == "hello world")
+        .expect("the 'hello world' chunk");
+
+    // Two spans: the nested `<tspan>hello` and the trailing ` world`.
+    assert_eq!(chunk.spans().len(), 2);
+    for span in chunk.spans() {
+        assert_eq!(
+            span.dominant_baseline(),
+            DominantBaseline::TextAfterEdge,
+            "span {:?} did not inherit dominant-baseline from <text>",
+            &chunk.text()[span.start()..span.end()]
+        );
+    }
+}
+
+// A nested `<tspan>` setting its own `dominant-baseline` still overrides the
+// inherited one, and deeper descendants inherit the nested value.
+#[test]
+fn nested_tspan_dominant_baseline_override() {
+    let svg = "<svg xmlns='http://www.w3.org/2000/svg' width='400' height='200'>
+        <text x='20' y='150' font-family='Noto Sans' dominant-baseline='text-after-edge'>
+            <tspan x='20' font-size='40' dominant-baseline='hanging'><tspan>hi</tspan></tspan>
+        </text>
+    </svg>";
+
+    let tree = parse(svg);
+    let text = first_text(tree.root()).expect("a text node");
+    let chunk = text
+        .chunks()
+        .iter()
+        .find(|c| c.text() == "hi")
+        .expect("the 'hi' chunk");
+
+    let span = &chunk.spans()[0];
+    assert_eq!(span.dominant_baseline(), DominantBaseline::Hanging);
+}