From 7e1dcceb460c2e9e39313326ec0d23d1c63cf0d3 Mon Sep 17 00:00:00 2001
From: Yangtse Su <yangtsesu@gmail.com>
Date: Mon, 19 Oct 2026 16:23:51 +0800
Subject: [PATCH 1/2] feat(core): span a character box with the font's metrics
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
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rofd's page text geometry built every character box from the font size - one size
above the baseline, stopping at it - while a PDF text box is built from the font's own
metrics (poppler's `TextWord::setInitialBounds`: `yMin = y - ascent`, `yMax = y -
descent`, the ascent/descent of the face). The mismatch cut the bottom off CJK glyphs
and Latin descenders, and it left the vertical extent of a box dependent on the glyph
inside it, so punctuation and Latin did not line up with CJK in one line. Measured on a
real government document (2464 glyphs over six embedded fonts, sizes 4.9-7.8 mm): 86%
of the scalars reach below the baseline - CJK overshoot 0.098-0.129 em, Latin
descenders up to 0.188 em - by a mean of 0.50 mm and up to 1.46 mm, while the box top
sat 1.45 mm above the painted top on average.

The provider seam that already resolves per-scalar advances now answers the whole
scalar geometry: `TextScalarMetrics` carries the advance of the glyph the positioner
selected plus the *face's* typographic ascent and descent, which are the same for every
glyph of that face at one size, so the boxes of a run share one band and cover the
glyphs. `ResolvedFont` reads that pair once from FreeType while validating the face,
`GlyphMetrics` exposes it beside the advance, and a face that declares no usable
metrics keeps the font-size footprint - as does a document loaded without a provider.
The provider is asked for every text object, even one whose runs all declare their own
deltas: the vertical extents come from the resolved font whatever a scalar declares.

Verified: cargo fmt --all -- --check; cargo clippy -p rofd-core -p rofd-render
-p rofd-ffi --all-targets -- -D warnings; cargo test for the three crates;
crates/rofd-ffi/tests/run_c_tests.sh (the export set is unchanged). The
pixel-level tests fail against the previous model and pass with this one -
`crates/rofd-render/tests/cairo_text.rs::semantic_character_boxes_cover_the_rendered_ink`
(the two scalars of one run now share top and bottom, and the band is strictly taller
than the ink) and
`crates/rofd-ffi/tests/semantic.rs::text_layout_rectangles_cover_the_rendered_ink_below_the_baseline`
(same band for A and 中) - and `crates/rofd-core/tests/semantic_text.rs` pins the
aligned band.
---
 crates/rofd-core/src/document.rs              |  69 ++---
 crates/rofd-core/src/lib.rs                   |   4 +-
 crates/rofd-core/src/semantic.rs              | 104 ++++---
 crates/rofd-core/tests/semantic_text.rs       | 118 ++++++--
 crates/rofd-ffi/include/rofd.h                |   9 +-
 crates/rofd-ffi/src/document.rs               |  10 +-
 crates/rofd-ffi/src/renderer.rs               |  29 +-
 crates/rofd-ffi/tests/semantic.rs             | 197 +++++++++++++
 crates/rofd-render/src/fonts.rs               | 258 +++++++++++++-----
 crates/rofd-render/src/lib.rs                 |   4 +-
 crates/rofd-render/tests/cairo_text.rs        |  84 +++++-
 crates/rofd-render/tests/fonts.rs             |  77 ++++--
 ...-09-poppler-style-c-semantic-api-design.md |  14 +-
 13 files changed, 758 insertions(+), 219 deletions(-)

diff --git a/crates/rofd-core/src/document.rs b/crates/rofd-core/src/document.rs
index 0ac4ac65..22c5168b 100644
--- a/crates/rofd-core/src/document.rs
+++ b/crates/rofd-core/src/document.rs
@@ -123,18 +123,18 @@ struct DocumentInner {
     bookmarks: OnceLock<crate::navigation::BookmarkData>,
     bookmark_initialization: Mutex<()>,
     navigation_warning_state: Mutex<NavigationWarningState>,
-    /// Font-resolved per-scalar advances for runs without explicit deltas, when the
-    /// loader supplied a provider (see [`crate::TextAdvanceProvider`]).
-    text_advances: Option<TextAdvances>,
+    /// Font-resolved per-scalar geometry for the page text index, when the loader
+    /// supplied a provider (see [`crate::TextMetricsProvider`]).
+    text_metrics: Option<TextMetricsSource>,
 }
 
-/// Debug-friendly owner of the optional text advance provider.
+/// Debug-friendly owner of the optional text metrics provider.
 #[derive(Clone)]
-struct TextAdvances(Arc<dyn crate::TextAdvanceProvider>);
+struct TextMetricsSource(Arc<dyn crate::TextMetricsProvider>);
 
-impl std::fmt::Debug for TextAdvances {
+impl std::fmt::Debug for TextMetricsSource {
     fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        formatter.write_str("TextAdvances(<provider>)")
+        formatter.write_str("TextMetricsSource(<provider>)")
     }
 }
 
@@ -242,15 +242,17 @@ impl Page {
         &self.data.layers
     }
 
-    /// Returns flattened source text and conservative character geometry in
-    /// physical-page millimetres, in effective paint order.
+    /// Returns flattened source text and per-character geometry in physical-page
+    /// millimetres, in effective paint order.
     ///
     /// Visible annotation appearances follow the page layers. Distinct nonempty
-    /// text objects are separated by synthesized newlines. Geometry uses validated
-    /// OFD positioning; a scalar whose run declares no `DeltaX` uses the advance of a
-    /// provider's font when the document was loaded with one, and the font size
-    /// otherwise. The complete result is cached and shared by cloned page handles.
-    /// Failed builds are not cached and may be retried on a later call.
+    /// text objects are separated by synthesized newlines. Geometry uses validated OFD
+    /// positioning; a scalar whose run declares no `DeltaX` advances by the advance of
+    /// a provider's font when the document was loaded with one, and its box spans that
+    /// font's ascent and descent around the baseline, so it covers the painted glyph.
+    /// Without a provider the font-size footprint stays in place. The complete result
+    /// is cached and shared by cloned page handles. Failed builds are not cached and
+    /// may be retried on a later call.
     pub fn text(&self) -> crate::Result<&crate::PageText> {
         if let Some(text) = self.data.semantic_text.get() {
             return Ok(text);
@@ -261,12 +263,12 @@ impl Page {
         if let Some(text) = self.data.semantic_text.get() {
             return Ok(text);
         }
-        let advances = self
+        let metrics = self
             ._document
-            .text_advances
+            .text_metrics
             .as_ref()
-            .map(|advances| advances.0.as_ref() as &dyn crate::TextAdvanceProvider);
-        let text = crate::semantic::build_page_text(self, advances)?;
+            .map(|metrics| metrics.0.as_ref() as &dyn crate::TextMetricsProvider);
+        let text = crate::semantic::build_page_text(self, metrics)?;
         Ok(self.data.semantic_text.get_or_init(|| text))
     }
 
@@ -358,39 +360,40 @@ impl Page {
 impl Document {
     /// Opens an OFD document from a host file path.
     pub fn open(path: impl AsRef<Path>, options: LoadOptions) -> Result<Self> {
-        Self::open_with_advances(path, options, None)
+        Self::open_with_metrics(path, options, None)
     }
 
-    /// Opens an OFD document from a host file path, resolving text advances through
-    /// `advances`.
-    pub fn open_with_advances(
+    /// Opens an OFD document from a host file path, resolving per-scalar text
+    /// geometry through `metrics`.
+    pub fn open_with_metrics(
         path: impl AsRef<Path>,
         options: LoadOptions,
-        advances: Option<Arc<dyn crate::TextAdvanceProvider>>,
+        metrics: Option<Arc<dyn crate::TextMetricsProvider>>,
     ) -> Result<Self> {
         let path = path.as_ref();
         let bytes = fs::read(path).map_err(|source| Error::Io {
             path: path.to_owned(),
             source,
         })?;
-        Self::from_bytes_with_advances(bytes, options, advances)
+        Self::from_bytes_with_metrics(bytes, options, metrics)
     }
 
     /// Opens an OFD document from owned bytes.
     pub fn from_bytes(bytes: Vec<u8>, options: LoadOptions) -> Result<Self> {
-        Self::from_bytes_with_advances(bytes, options, None)
+        Self::from_bytes_with_metrics(bytes, options, None)
     }
 
-    /// Opens an OFD document from owned bytes, resolving text advances through
-    /// `advances`.
+    /// Opens an OFD document from owned bytes, resolving per-scalar text geometry
+    /// through `metrics`.
     ///
-    /// Without a provider, runs that carry no explicit `DeltaX` keep the font-size
-    /// footprint; with one they use the font's advances, which is what a renderer
-    /// draws.
-    pub fn from_bytes_with_advances(
+    /// Without a provider, text geometry keeps the font-size footprint. With one, a
+    /// scalar whose run declares no `DeltaX` advances by the font's advance and its
+    /// box spans the font's extent around the baseline, which is what a renderer
+    /// paints.
+    pub fn from_bytes_with_metrics(
         bytes: Vec<u8>,
         options: LoadOptions,
-        advances: Option<Arc<dyn crate::TextAdvanceProvider>>,
+        metrics: Option<Arc<dyn crate::TextMetricsProvider>>,
     ) -> Result<Self> {
         let strictness = options.strictness;
         let limits = options.limits;
@@ -534,7 +537,7 @@ impl Document {
             container,
             document_path,
             limits,
-            text_advances: advances.map(TextAdvances),
+            text_metrics: metrics.map(TextMetricsSource),
             metadata: Metadata {
                 document_id: info.document_id,
                 title: info.title,
diff --git a/crates/rofd-core/src/lib.rs b/crates/rofd-core/src/lib.rs
index 027a3440..7f6435c5 100644
--- a/crates/rofd-core/src/lib.rs
+++ b/crates/rofd-core/src/lib.rs
@@ -36,8 +36,8 @@ pub use paint::{Color, LineCap, LineJoin, StrokeStyle};
 pub use path_data::{PathCommand, PathData};
 pub use resources::{FontResource, ImageFormat, ImageResource, ResourceIdentity, ResourceKind};
 pub use semantic::{
-    FindOptions, PageText, SelectionStyle, TextAdvanceProvider, TextChar, TextCharFlags,
-    TextGeometryPrecision, TextMatch, TextSelection,
+    FindOptions, PageText, SelectionStyle, TextChar, TextCharFlags, TextGeometryPrecision,
+    TextMatch, TextMetricsProvider, TextScalarMetrics, TextSelection,
 };
 pub use signature::{SealPicture, SealPictureKind, StampAnnotation};
 pub use text::{CharacterGlyphMap, GlyphTransform, TextCode, TextObject};
diff --git a/crates/rofd-core/src/semantic.rs b/crates/rofd-core/src/semantic.rs
index c7ee1959..8de2e11f 100644
--- a/crates/rofd-core/src/semantic.rs
+++ b/crates/rofd-core/src/semantic.rs
@@ -2,22 +2,46 @@ use std::ops::Range;
 
 use crate::{Error, Page, PageObject, Point, Rect, Result, TextObject, Transform};
 
-/// Supplies the horizontal advance of one scalar when a text run declares no
-/// `DeltaX` for it.
+/// Font-resolved geometry of one scalar of a text object, in millimetres.
 ///
-/// The OFD text model positions such a scalar by its font's advance, so geometry
-/// that resolves fonts matches what a renderer draws; this crate parses and indexes
-/// text without font access, which is why a provider is injected from outside
-/// (`rofd-render` implements it over the same font stack the renderer uses). A
-/// document loaded without a provider keeps the font-size footprint for those runs,
-/// which stays a valid conservative approximation.
-pub trait TextAdvanceProvider: Send + Sync {
-    /// Returns one advance in millimetres per scalar of `text`, concatenating its
-    /// runs in order, or `None` when the object's font cannot be resolved (the
+/// Every value is relative to the scalar's pen position, which is the baseline
+/// origin the OFD text model positions and a renderer paints from. The advance is the
+/// glyph's; the extents are its face's typographic ascent and descent, so the scalars
+/// of one face at one size share them and the boxes of different scripts and of
+/// punctuation stay aligned, the way a PDF text box built from font metrics does.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct TextScalarMetrics {
+    /// Horizontal advance the pen moves by after the scalar is painted.
+    pub advance_mm: f64,
+    /// Extent the face declares above the baseline.
+    pub ascent_mm: f64,
+    /// Extent the face declares below the baseline.
+    pub descent_mm: f64,
+}
+
+/// Supplies the font-resolved geometry of each scalar of one text object.
+///
+/// A scalar without an explicit `DeltaX` is positioned by its font's advance, and it
+/// is painted at the font's own extent around the baseline; this crate parses and
+/// indexes text without font access, which is why a provider is injected from outside
+/// (`rofd-render` implements it over the same font stack the renderer uses) whenever
+/// page geometry has to match what a renderer draws. A document loaded without a
+/// provider keeps the font-size footprint, which stays a valid conservative
+/// approximation.
+pub trait TextMetricsProvider: Send + Sync {
+    /// Returns one metrics entry in millimetres per scalar of `text`, concatenating
+    /// its runs in order, or `None` when the object's font cannot be resolved (the
     /// builder then keeps the font-size footprint).
     ///
-    /// Non-finite or negative values are ignored per scalar.
-    fn advances_mm(&self, page: &Page, text: &TextObject, size_mm: f64) -> Option<Vec<f64>>;
+    /// A scalar without a resolved glyph of its own keeps the conservative font-size
+    /// footprint: `size_mm` above the baseline and nothing below it. That covers both
+    /// a scalar no face owns and one whose glyph paints nothing, such as a space.
+    fn metrics_mm(
+        &self,
+        page: &Page,
+        text: &TextObject,
+        size_mm: f64,
+    ) -> Option<Vec<TextScalarMetrics>>;
 }
 
 /// Options for literal search in canonical page text.
@@ -482,9 +506,9 @@ fn union_rectangles(mut rectangles: impl Iterator<Item = Rect>) -> Result<Option
 
 pub(crate) fn build_page_text(
     page: &crate::Page,
-    advances: Option<&dyn TextAdvanceProvider>,
+    metrics: Option<&dyn TextMetricsProvider>,
 ) -> Result<PageText> {
-    let mut builder = TextBuilder::new(page, advances);
+    let mut builder = TextBuilder::new(page, metrics);
     for layer in page.layers() {
         builder.objects(layer.objects(), Transform::IDENTITY)?;
     }
@@ -499,7 +523,7 @@ pub(crate) fn build_page_text(
 struct TextBuilder<'a> {
     text: PageText,
     page: &'a Page,
-    advances: Option<&'a dyn TextAdvanceProvider>,
+    metrics: Option<&'a dyn TextMetricsProvider>,
     source_characters: usize,
     metadata_entries: usize,
     max_source_characters: usize,
@@ -507,12 +531,12 @@ struct TextBuilder<'a> {
 }
 
 impl<'a> TextBuilder<'a> {
-    fn new(page: &'a Page, advances: Option<&'a dyn TextAdvanceProvider>) -> Self {
+    fn new(page: &'a Page, metrics: Option<&'a dyn TextMetricsProvider>) -> Self {
         let limits = page.resource_limits();
         Self {
             text: PageText::default(),
             page,
-            advances,
+            metrics,
             source_characters: 0,
             metadata_entries: 0,
             max_source_characters: limits.max_text_characters_per_page,
@@ -552,27 +576,35 @@ impl<'a> TextBuilder<'a> {
             self.push_separator()?;
         }
         let size = object.font_size();
-        // One font-resolved advance per scalar of the whole object, in run order;
-        // absent when the provider has no font for it. Explicit deltas stay
-        // authoritative and are never replaced, and they are the only thing this
-        // geometry takes from the provider, so an object whose runs all declare their
-        // own deltas never asks it for a font at all.
-        let needs_advances = object.runs().iter().any(|run| !run.has_explicit_delta_x());
-        let resolved = if needs_advances {
-            self.advances
-                .and_then(|advances| advances.advances_mm(self.page, object, size))
-        } else {
-            None
-        };
+        // One metrics entry per scalar of the whole object, in run order; absent
+        // when the provider has no font for it. Explicit deltas stay authoritative
+        // and are never replaced, but a scalar takes its vertical extents from the
+        // resolved font whatever it declares, so the provider is asked for every
+        // object.
+        let resolved = self
+            .metrics
+            .and_then(|metrics| metrics.metrics_mm(self.page, object, size));
         let mut scalar = 0usize;
         for run in object.runs() {
             let (mut x, mut y) = (run.x(), run.y());
             for (index, character) in run.text().chars().enumerate() {
-                let font_advance = resolved
+                let metrics = resolved
                     .as_ref()
                     .and_then(|values| values.get(scalar))
-                    .copied()
+                    .copied();
+                let font_advance = metrics
+                    .map(|metrics| metrics.advance_mm)
                     .filter(|value| value.is_finite() && *value > 0.0);
+                // A glyph that paints nothing (a space) or that no face owns keeps
+                // the conservative font-size footprint above the baseline.
+                let ascent = metrics
+                    .map(|metrics| metrics.ascent_mm)
+                    .filter(|value| value.is_finite() && *value > 0.0)
+                    .unwrap_or(size);
+                let descent = metrics
+                    .map(|metrics| metrics.descent_mm)
+                    .filter(|value| value.is_finite() && *value >= 0.0)
+                    .unwrap_or(0.0);
                 let dx = if run.has_explicit_delta_x() {
                     run.delta_x()[index]
                 } else {
@@ -587,7 +619,9 @@ impl<'a> TextBuilder<'a> {
                 let next_x = finite_add(x, dx)?;
                 let next_y = finite_add(y, dy)?;
                 // A resolved glyph advance is the box width, so the boxes of a run
-                // tile it and a match rectangle hugs the matched text. Without one,
+                // tile it and a match rectangle hugs the matched text. Its ascent and
+                // descent are the vertical extents, so the box covers the painted
+                // glyph instead of stopping at the baseline. Without resolved metrics,
                 // bound the horizontal baseline sweep with a direction-independent
                 // font-size footprint instead; explicit zero advances still receive
                 // nonempty conservative geometry.
@@ -596,8 +630,8 @@ impl<'a> TextBuilder<'a> {
                     left,
                     font_advance.map_or_else(|| dx.abs().max(size), f64::abs),
                 )?;
-                let top = finite_add(y.min(next_y), -size)?;
-                let bottom = y.max(next_y);
+                let top = finite_add(y.min(next_y), -ascent)?;
+                let bottom = finite_add(y.max(next_y), descent)?;
                 let rect = transformed_box(left, top, right, bottom, transform)?;
                 let flags = if character.is_whitespace() {
                     TextCharFlags::WHITESPACE
diff --git a/crates/rofd-core/tests/semantic_text.rs b/crates/rofd-core/tests/semantic_text.rs
index ee3f300d..6df6b6e0 100644
--- a/crates/rofd-core/tests/semantic_text.rs
+++ b/crates/rofd-core/tests/semantic_text.rs
@@ -3,8 +3,8 @@ mod support;
 use std::sync::Arc;
 
 use rofd_core::{
-    Document, Error, FindOptions, LoadOptions, Rect, ResourceLimits, SelectionStyle, TextCharFlags,
-    TextGeometryPrecision, TextObject, TextSelection,
+    Document, Error, FindOptions, LoadOptions, Rect, ResourceLimits, SelectionStyle, TextChar,
+    TextCharFlags, TextGeometryPrecision, TextObject, TextSelection,
 };
 
 fn rect(x: f64, y: f64, width: f64, height: f64) -> Rect {
@@ -289,6 +289,45 @@ fn selection_preserves_canonical_order_when_geometry_runs_backwards() {
     assert_eq!(selection.regions(), &[rect(1.0, 1.0, 12.0, 4.0)]);
 }
 
+/// The band of one face is what a selection region spans: it clears the glyphs the way
+/// a PDF text box does. The band itself comes from the metrics of one face, so its top
+/// and bottom do not depend on which scalars happen to have the tallest ink.
+#[test]
+fn selection_regions_span_the_aligned_band_of_one_face() {
+    let page = page_with_text(
+        r#"<ofd:TextObject ID="2" Boundary="0 0 100 8" Font="10" Size="4"><ofd:TextCode X="1" Y="5">A中, 。</ofd:TextCode></ofd:TextObject>"#,
+    );
+    let text = page.text().unwrap();
+    let boxes: Vec<_> = text
+        .characters()
+        .iter()
+        .filter_map(TextChar::rect_mm)
+        .collect();
+    assert!(boxes.len() > 3, "{boxes:?}");
+    let top = boxes
+        .iter()
+        .map(|rect| rect.y)
+        .fold(f64::INFINITY, f64::min);
+    let bottom = boxes
+        .iter()
+        .map(|rect| rect.y + rect.height)
+        .fold(f64::NEG_INFINITY, f64::max);
+    for rect in &boxes {
+        assert!(
+            (rect.y - top).abs() < 1e-9 && (rect.y + rect.height - bottom).abs() < 1e-9,
+            "aligned band expected, got {rect:?} against {top}..{bottom}"
+        );
+    }
+
+    let selection = text
+        .select(rect(1.0, 1.0, 20.0, 4.0), SelectionStyle::Line)
+        .unwrap();
+    assert_eq!(selection.text(), "A中, 。");
+    let region = selection.regions()[0];
+    assert!((region.y - top).abs() < 1e-9, "{region:?}");
+    assert!((region.height - (bottom - top)).abs() < 1e-9);
+}
+
 #[test]
 fn invalid_rectangles_error_while_empty_or_missed_rectangles_return_empty_results() {
     let page = selection_page();
@@ -398,50 +437,59 @@ fn page_with_text(content: &str) -> rofd_core::Page {
     document_with_page(&page_xml, "", "", &[]).page(0).unwrap()
 }
 
-/// A provider that advances every scalar by half the font size, so the geometry it
-/// produces is distinguishable from both the font-size footprint and explicit deltas.
-struct HalfSizeAdvances {
+/// A provider that advances every scalar by half the font size and paints it between
+/// a quarter and three quarters of the font size around the baseline, so the geometry
+/// it produces is distinguishable from both the font-size footprint and explicit
+/// deltas.
+struct HalfSizeMetrics {
     resolution_failure: bool,
+    empty_ink: bool,
 }
 
-impl rofd_core::TextAdvanceProvider for HalfSizeAdvances {
-    fn advances_mm(
+impl rofd_core::TextMetricsProvider for HalfSizeMetrics {
+    fn metrics_mm(
         &self,
         _page: &rofd_core::Page,
         text: &TextObject,
         size_mm: f64,
-    ) -> Option<Vec<f64>> {
+    ) -> Option<Vec<rofd_core::TextScalarMetrics>> {
         if self.resolution_failure {
             return None;
         }
         Some(
             text.runs()
                 .iter()
-                .flat_map(|run| run.text().chars().map(|_| size_mm / 2.0))
+                .flat_map(|run| {
+                    run.text().chars().map(|_| rofd_core::TextScalarMetrics {
+                        advance_mm: size_mm / 2.0,
+                        ascent_mm: size_mm / 2.0,
+                        descent_mm: if self.empty_ink { 0.0 } else { size_mm / 4.0 },
+                    })
+                })
                 .collect(),
         )
     }
 }
 
-fn document_with_page_and_advances(
+fn document_with_page_and_metrics(
     page_xml: &str,
-    advances: Option<Arc<dyn rofd_core::TextAdvanceProvider>>,
+    metrics: Option<Arc<dyn rofd_core::TextMetricsProvider>>,
 ) -> Document {
     let document_xml = r#"<ofd:Document xmlns:ofd="http://www.ofdspec.org/2016"><ofd:CommonData>
 <ofd:PageArea><ofd:PhysicalBox>0 0 210 297</ofd:PhysicalBox></ofd:PageArea>
 <ofd:PublicRes>Res.xml</ofd:PublicRes></ofd:CommonData>
 <ofd:Pages><ofd:Page ID="900" BaseLoc="Pages/Page_0/Content.xml"/></ofd:Pages></ofd:Document>"#;
     let entries = [("Doc_0/Res.xml", FONT_CATALOG.as_bytes())];
-    Document::from_bytes_with_advances(
+    Document::from_bytes_with_metrics(
         support::ofd_with_document_page_and_entries(document_xml, page_xml, &entries),
         LoadOptions::default(),
-        advances,
+        metrics,
     )
     .unwrap()
 }
 
 #[test]
-fn advance_provider_supplies_scalar_steps_where_deltas_are_absent() {
+fn metrics_provider_supplies_scalar_geometry_where_deltas_are_absent() {
     let page_xml = format!(
         r#"<?xml version="1.0" encoding="UTF-8"?>
 <ofd:Page xmlns:ofd="http://www.ofdspec.org/2016">
@@ -450,17 +498,18 @@ fn advance_provider_supplies_scalar_steps_where_deltas_are_absent() {
         text_object(2, "ABCD")
     );
 
-    let without = document_with_page_and_advances(&page_xml, None)
+    let without = document_with_page_and_metrics(&page_xml, None)
         .page(0)
         .unwrap()
         .text()
         .unwrap()
         .characters()
         .to_vec();
-    let with = document_with_page_and_advances(
+    let with = document_with_page_and_metrics(
         &page_xml,
-        Some(Arc::new(HalfSizeAdvances {
+        Some(Arc::new(HalfSizeMetrics {
             resolution_failure: false,
+            empty_ink: false,
         })),
     )
     .page(0)
@@ -483,11 +532,37 @@ fn advance_provider_supplies_scalar_steps_where_deltas_are_absent() {
     let first_end = with[0].rect_mm().unwrap().x + with[0].rect_mm().unwrap().width;
     assert!((first_end - with[1].rect_mm().unwrap().x).abs() < 1e-9);
 
+    // The vertical box spans the resolved extents around the baseline: the fixture
+    // places it at Y=5, so the box starts half a font size above it and ends a
+    // quarter below.
+    let box_ = with[0].rect_mm().unwrap();
+    assert!((box_.y - (5.0 - 2.0)).abs() < 1e-9, "{box_:?}");
+    assert!((box_.height - 3.0).abs() < 1e-9, "{box_:?}");
+
+    // A glyph that does not paint below its baseline keeps the box bottom there.
+    let flat = document_with_page_and_metrics(
+        &page_xml,
+        Some(Arc::new(HalfSizeMetrics {
+            resolution_failure: false,
+            empty_ink: true,
+        })),
+    )
+    .page(0)
+    .unwrap()
+    .text()
+    .unwrap()
+    .characters()
+    .to_vec();
+    let flat_box = flat[0].rect_mm().unwrap();
+    assert!((flat_box.y - (5.0 - 2.0)).abs() < 1e-9, "{flat_box:?}");
+    assert!((flat_box.height - 2.0).abs() < 1e-9, "{flat_box:?}");
+
     // A provider that cannot resolve a font leaves the font-size footprint alone.
-    let failed = document_with_page_and_advances(
+    let failed = document_with_page_and_metrics(
         &page_xml,
-        Some(Arc::new(HalfSizeAdvances {
+        Some(Arc::new(HalfSizeMetrics {
             resolution_failure: true,
+            empty_ink: false,
         })),
     )
     .page(0)
@@ -508,10 +583,11 @@ fn explicit_deltas_stay_authoritative_with_a_provider() {
 </ofd:Page>"#,
         r#"<ofd:TextObject ID="2" Boundary="0 0 20 8" Font="10" Size="4"><ofd:TextCode X="1" Y="5" DeltaX="9 9 9 9">ABCD</ofd:TextCode></ofd:TextObject>"#
     );
-    let text = document_with_page_and_advances(
+    let text = document_with_page_and_metrics(
         &page_xml,
-        Some(Arc::new(HalfSizeAdvances {
+        Some(Arc::new(HalfSizeMetrics {
             resolution_failure: false,
+            empty_ink: false,
         })),
     )
     .page(0)
diff --git a/crates/rofd-ffi/include/rofd.h b/crates/rofd-ffi/include/rofd.h
index 1232beb1..47d852f2 100644
--- a/crates/rofd-ffi/include/rofd.h
+++ b/crates/rofd-ffi/include/rofd.h
@@ -585,10 +585,11 @@ void rofd_string_free(rofd_string_t *text);
  * scalar in canonical page text, including synthesized separators. Free with
  * rofd_text_layout_free. The snapshot survives page and document destruction.
  * A scalar whose run declares no explicit delta is placed by its font's advance,
- * resolved through the default font stack (the one a renderer created with NULL
- * options uses); a renderer configured with other fallback families may draw
- * slightly different advances. Scalars that cannot be resolved fall back to a
- * conservative font-size box.
+ * and its box spans that font's painted extents around the baseline, both resolved
+ * through the default font stack (the one a renderer created with NULL options
+ * uses); a renderer configured with other fallback families may draw slightly
+ * different glyphs. Scalars that cannot be resolved fall back to a conservative
+ * font-size box.
  * page and layout are required; error is optional. All outputs must be aligned,
  * writable, mutually disjoint and disjoint from live page storage. */
 rofd_status_t rofd_page_get_text_layout(const rofd_page_t *page,
diff --git a/crates/rofd-ffi/src/document.rs b/crates/rofd-ffi/src/document.rs
index 64ea3cec..021d6c97 100644
--- a/crates/rofd-ffi/src/document.rs
+++ b/crates/rofd-ffi/src/document.rs
@@ -104,12 +104,12 @@ pub unsafe extern "C" fn rofd_document_open(
                 return Err(FfiError::invalid_argument("path is empty"));
             }
             let options = LoadOptionsInput::from_ffi(options)?;
-            // Semantic text geometry resolves font advances through the default font
+            // Semantic text geometry resolves font metrics through the default font
             // stack, so search/selection rectangles match the rendered glyphs (see
-            // `text_advance_provider`).
-            let advances: std::sync::Arc<dyn rofd_core::TextAdvanceProvider> =
-                std::sync::Arc::new(crate::renderer::text_advance_provider());
-            let inner = rofd_core::Document::open_with_advances(path, options, Some(advances))
+            // `text_metrics_provider`).
+            let metrics: std::sync::Arc<dyn rofd_core::TextMetricsProvider> =
+                std::sync::Arc::new(crate::renderer::text_metrics_provider());
+            let inner = rofd_core::Document::open_with_metrics(path, options, Some(metrics))
                 .map_err(FfiError::from)?;
             Ok(Box::new(DocumentHandle { inner }))
         })
diff --git a/crates/rofd-ffi/src/renderer.rs b/crates/rofd-ffi/src/renderer.rs
index 44397a7e..5bacc240 100644
--- a/crates/rofd-ffi/src/renderer.rs
+++ b/crates/rofd-ffi/src/renderer.rs
@@ -16,7 +16,7 @@ use rofd_render::{
 use std::ffi::CStr;
 use std::panic::{catch_unwind, AssertUnwindSafe};
 use std::slice;
-use std::sync::OnceLock;
+use std::sync::{Arc, LazyLock};
 
 const MAX_FALLBACK_FAMILIES: usize = 1024;
 const DEFAULT_FALLBACK_FAMILIES: [&str; 3] = ["Noto Sans CJK SC", "Noto Sans", "DejaVu Sans"];
@@ -131,23 +131,24 @@ fn default_fallback_families() -> Vec<String> {
         .collect()
 }
 
-/// Font advances for text runs that carry no explicit `DeltaX`.
+/// Font metrics for the semantic page text index.
 ///
-/// Semantic page geometry is resolved with the same font stack a default renderer
-/// uses (`rofd_renderer_new` with NULL options), so the page text layout, search
-/// rectangles and selection regions land on the glyphs that get drawn. The resolver
-/// is created once per process and kept for the life of the library, because the
-/// system font database scan is the expensive part. A renderer created with other
-/// fallback families still chooses its own faces for drawing.
-pub(crate) fn text_advance_provider() -> rofd_render::FontTextAdvances<'static> {
-    static RESOLVER: OnceLock<&'static SystemFontResolver> = OnceLock::new();
-    let resolver = RESOLVER.get_or_init(|| {
-        Box::leak(Box::new(SystemFontResolver::with_system_fonts(
+/// Page text geometry is resolved with the same font stack a default renderer uses
+/// (`rofd_renderer_new` with NULL options), so the page text layout, search
+/// rectangles and selection regions land on the glyphs that get drawn - including the
+/// vertical extent of each glyph, so a highlight covers the text it belongs to. The
+/// resolver is created once per process and shared with every document that resolves
+/// metrics, because the system font database scan is the expensive part. A renderer
+/// created with other fallback families still chooses its own faces for drawing.
+pub(crate) fn text_metrics_provider() -> rofd_render::FontTextMetrics {
+    static RESOLVER: LazyLock<Arc<SystemFontResolver>> = LazyLock::new(|| {
+        Arc::new(SystemFontResolver::with_system_fonts(
             default_fallback_families(),
             64 * 1024 * 1024,
-        )))
+        ))
     });
-    rofd_render::FontTextAdvances::new(*resolver)
+    let resolver: Arc<SystemFontResolver> = Arc::clone(&RESOLVER);
+    rofd_render::FontTextMetrics::new(resolver)
 }
 
 pub(crate) struct RenderOptionsInput;
diff --git a/crates/rofd-ffi/tests/semantic.rs b/crates/rofd-ffi/tests/semantic.rs
index 086a2543..c7828bdd 100644
--- a/crates/rofd-ffi/tests/semantic.rs
+++ b/crates/rofd-ffi/tests/semantic.rs
@@ -1,6 +1,7 @@
 #[path = "../../rofd-core/tests/support/mod.rs"]
 mod support;
 
+use cairo::{Context, Format, ImageSurface};
 use rofd_ffi::*;
 use std::ffi::{CStr, CString};
 use std::mem::{size_of, MaybeUninit};
@@ -162,6 +163,18 @@ unsafe fn selection_bytes(selection: *const rofd_text_selection_t) -> Vec<u8> {
     }
 }
 
+unsafe fn selection_region_count(selection: *const rofd_text_selection_t) -> usize {
+    let mut count = usize::MAX;
+    // SAFETY: The output is valid and distinct from the live immutable selection handle.
+    unsafe {
+        assert_eq!(
+            rofd_text_selection_get_region_count(selection, &mut count, ptr::null_mut()),
+            ROFD_STATUS_OK
+        );
+    }
+    count
+}
+
 unsafe fn selection_region(selection: *const rofd_text_selection_t, index: usize) -> rofd_rect_t {
     let mut region = rofd_rect_t {
         x_mm: f64::NAN,
@@ -1021,3 +1034,187 @@ fn text_geometry_and_search_rectangles_use_font_advances() {
         rofd_page_free(page);
     }
 }
+
+/// A character box covers the glyph a renderer paints, including the part below the
+/// baseline: the font-size footprint ended exactly at the baseline, so a selection or
+/// search highlight built from the ABI's rectangles was clipped at the bottom of the
+/// text (CJK overshoot and Latin descenders alike).
+#[test]
+fn text_layout_rectangles_cover_the_rendered_ink_below_the_baseline() {
+    const FONT: &[u8] = include_bytes!("../../rofd-render/tests/fixtures/fonts/phase3-subset.ttf");
+    // A stays above the baseline, 中 reaches 0.079 em below it in this subset (Noto
+    // Sans CJK SC): the two boxes still have to span one band.
+    let xml = r#"<ofd:Page xmlns:ofd="http://www.ofdspec.org/2016"><ofd:Content><ofd:Layer ID="1"><ofd:TextObject ID="2" Boundary="0 0 30 10" Font="10" Size="4"><ofd:TextCode X="1" Y="4">A中</ofd:TextCode></ofd:TextObject></ofd:Layer></ofd:Content></ofd:Page>"#;
+    let document = r#"<ofd:Document xmlns:ofd="http://www.ofdspec.org/2016"><ofd:CommonData><ofd:PageArea><ofd:PhysicalBox>0 0 30 10</ofd:PhysicalBox></ofd:PageArea><ofd:DocumentRes>Res.xml</ofd:DocumentRes></ofd:CommonData><ofd:Pages><ofd:Page ID="900" BaseLoc="Pages/Page_0/Content.xml"/></ofd:Pages></ofd:Document>"#;
+    let font = br#"<ofd:Res xmlns:ofd="http://www.ofdspec.org/2016"><ofd:Fonts><ofd:Font ID="10" FontName="Fixture"><ofd:FontFile>Fonts/subset.ttf</ofd:FontFile></ofd:Font></ofd:Fonts></ofd:Res>"#;
+    let bytes = support::ofd_with_document_page_and_entries(
+        document,
+        xml,
+        &[("Doc_0/Res.xml", font), ("Doc_0/Fonts/subset.ttf", FONT)],
+    );
+    static NEXT: AtomicUsize = AtomicUsize::new(0);
+    let path = std::env::temp_dir().join(format!(
+        "rofd-ffi-semantic-ink-{}-{}.ofd",
+        std::process::id(),
+        NEXT.fetch_add(1, Ordering::Relaxed)
+    ));
+    std::fs::write(&path, bytes).unwrap();
+    let cpath = CString::new(path.to_str().unwrap()).unwrap();
+
+    let mut document_handle = ptr::null_mut();
+    let mut page = ptr::null_mut();
+    let mut renderer = ptr::null_mut();
+    let mut layout = ptr::null_mut();
+    let mut report = ptr::null_mut();
+    // SAFETY: Live handles, initialized records and disjoint outputs; every handle is
+    // freed once after its last borrow.
+    unsafe {
+        assert_eq!(
+            rofd_document_open(
+                cpath.as_ptr(),
+                ptr::null(),
+                &mut document_handle,
+                ptr::null_mut()
+            ),
+            ROFD_STATUS_OK
+        );
+        std::fs::remove_file(&path).unwrap();
+        assert_eq!(
+            rofd_document_get_page(document_handle, 0, &mut page, ptr::null_mut()),
+            ROFD_STATUS_OK
+        );
+
+        // 254 dpi renders exactly ten pixels per millimetre.
+        let options = rofd_render_options_t {
+            dpi: 254.0,
+            ..Default::default()
+        };
+        assert_eq!(
+            rofd_renderer_new(ptr::null(), &mut renderer, ptr::null_mut()),
+            ROFD_STATUS_OK
+        );
+        let (mut width, mut height) = (0, 0);
+        assert_eq!(
+            rofd_renderer_get_pixel_canvas_size(
+                renderer,
+                page,
+                &options,
+                &mut width,
+                &mut height,
+                ptr::null_mut()
+            ),
+            ROFD_STATUS_OK
+        );
+        let surface = ImageSurface::create(Format::ARgb32, width, height).unwrap();
+        let context = Context::new(&surface).unwrap();
+        assert_eq!(
+            rofd_renderer_render_page_cairo(
+                renderer,
+                page,
+                context.to_raw_none(),
+                &options,
+                &mut report,
+                ptr::null_mut()
+            ),
+            ROFD_STATUS_OK
+        );
+        drop(context);
+
+        assert_eq!(
+            rofd_page_get_text_layout(page, &mut layout, ptr::null_mut()),
+            ROFD_STATUS_OK
+        );
+        let mut count = 0;
+        assert_eq!(
+            rofd_text_layout_get_count(layout, &mut count, ptr::null_mut()),
+            ROFD_STATUS_OK
+        );
+        assert_eq!(count, 2);
+
+        surface.flush();
+        let (mut ink_left, mut ink_top) = (i32::MAX, i32::MAX);
+        let (mut ink_right, mut ink_bottom) = (i32::MIN, i32::MIN);
+        let stride = surface.stride() as usize;
+        surface
+            .with_data(|data| {
+                for y in 0..height {
+                    for x in 0..width {
+                        let offset = y as usize * stride + x as usize * 4;
+                        if data[offset..offset + 3] == [255, 255, 255] {
+                            continue;
+                        }
+                        ink_left = ink_left.min(x);
+                        ink_top = ink_top.min(y);
+                        ink_right = ink_right.max(x);
+                        ink_bottom = ink_bottom.max(y);
+                    }
+                }
+            })
+            .unwrap();
+        assert!(ink_bottom > ink_top, "the embedded glyphs must paint");
+
+        // Both scalars span one band, taken from the face's metrics rather than from
+        // each glyph's own ink, so Latin, CJK and punctuation line up.
+        let a = character(layout, 0).rect_mm;
+        let cjk = character(layout, 1).rect_mm;
+        assert_eq!(a.y_mm, cjk.y_mm);
+        assert_eq!(a.height_mm, cjk.height_mm);
+        let slack = 1.0;
+        let (box_left, box_top) = (a.x_mm * 10.0, a.y_mm * 10.0);
+        let (box_right, box_bottom) = (
+            (cjk.x_mm + cjk.width_mm) * 10.0,
+            (a.y_mm + a.height_mm) * 10.0,
+        );
+
+        // The band is the face's ascent and descent (hhea 1160/-288 over the subset's
+        // 1000-unit em), so it sticks out above and below the ink instead of hugging
+        // it, and its bottom clears the baseline (40 px at ten pixels per millimetre).
+        assert!(box_top < f64::from(ink_top), "top {box_top} vs {ink_top}");
+        assert!(box_bottom > 40.0, "bottom {box_bottom} vs the baseline");
+        assert!(
+            box_bottom > f64::from(ink_bottom),
+            "bottom {box_bottom} vs {ink_bottom}"
+        );
+        assert!(
+            box_left <= f64::from(ink_left) + slack,
+            "left {box_left} vs {ink_left}"
+        );
+        assert!(
+            box_right >= f64::from(ink_right) - slack,
+            "right {box_right} vs {ink_right}"
+        );
+
+        // A line selection over the same text spans that band.
+        let area = rofd_rect_t {
+            x_mm: 0.0,
+            y_mm: 0.0,
+            width_mm: 30.0,
+            height_mm: 10.0,
+        };
+        let mut selection = ptr::null_mut();
+        assert_eq!(
+            rofd_page_get_selected_text(
+                page,
+                ROFD_SELECTION_LINE,
+                &area,
+                &mut selection,
+                ptr::null_mut()
+            ),
+            ROFD_STATUS_OK
+        );
+        assert_eq!(selection_region_count(selection), 1);
+        let region = selection_region(selection, 0);
+        assert!(
+            (region.y_mm - a.y_mm).abs() < 1e-3,
+            "region {region:?} vs band {a:?}"
+        );
+        assert!((region.height_mm - a.height_mm).abs() < 1e-3);
+        rofd_text_selection_free(selection);
+
+        rofd_render_report_free(report);
+        rofd_text_layout_free(layout);
+        rofd_renderer_free(renderer);
+        rofd_page_free(page);
+        rofd_document_free(document_handle);
+    }
+}
diff --git a/crates/rofd-render/src/fonts.rs b/crates/rofd-render/src/fonts.rs
index 2ce8f211..cbe2d636 100644
--- a/crates/rofd-render/src/fonts.rs
+++ b/crates/rofd-render/src/fonts.rs
@@ -5,8 +5,8 @@ use std::sync::{Arc, Condvar, Mutex};
 use fontdb::{Database, Family, Query, Source, ID};
 use freetype::face::LoadFlag;
 use rofd_core::{
-    FontResource, Page, ResourceIdentity, ResourceLimits, TextAdvanceProvider, TextObject,
-    Transform,
+    FontResource, Page, ResourceIdentity, ResourceLimits, TextMetricsProvider, TextObject,
+    TextScalarMetrics, Transform,
 };
 
 use crate::{Error, Result};
@@ -100,6 +100,11 @@ pub struct ResolvedFont {
     family_name: Option<Arc<str>>,
     glyph_count: u32,
     units_per_em: u16,
+    /// Typographic ascender in font units, or zero when the face declares none.
+    ascender: i64,
+    /// Typographic descender in font units (negative below the baseline), or zero
+    /// when the face declares none.
+    descender: i64,
     metrics: Arc<Mutex<FontMetricsCache>>,
 }
 
@@ -243,6 +248,10 @@ impl ResolvedFont {
             });
         }
         let family_name = face.family_name().map(Arc::<str>::from);
+        // The face's own typographic extents, in font units. Everything painted from
+        // this face sits inside them (see `typographic_extents_mm`).
+        let ascender = i64::from(face.ascender());
+        let descender = i64::from(face.descender());
         Ok(Self {
             bytes,
             face_index,
@@ -251,6 +260,8 @@ impl ResolvedFont {
             family_name,
             glyph_count,
             units_per_em,
+            ascender,
+            descender,
             metrics: Arc::new(Mutex::new(FontMetricsCache::default())),
         })
     }
@@ -298,13 +309,8 @@ impl ResolvedFont {
     /// Returns the unshaped horizontal-layout advance at `size_mm`.
     pub fn glyph_advance_mm(&self, glyph_id: u32, size_mm: f64) -> Result<(f64, f64)> {
         validate_glyph(self, glyph_id)?;
-        if !size_mm.is_finite() || size_mm <= 0.0 {
-            return Err(Error::InvalidFont {
-                identity: self.identity().to_owned(),
-                message: "glyph advance size must be finite and positive".to_owned(),
-            });
-        }
-        self.advance_mm(glyph_id, size_mm)
+        self.scaled_metrics(glyph_id, size_mm)
+            .map(|metrics| metrics.advance)
     }
 
     fn glyph_for(&self, character: char) -> Result<Option<u32>> {
@@ -319,35 +325,77 @@ impl ResolvedFont {
         Ok(glyph_id)
     }
 
-    fn advance_mm(&self, glyph_id: u32, size_mm: f64) -> Result<(f64, f64)> {
-        let mut metrics = self.metrics.lock().map_err(|_| Error::FontCache {
-            message: "face metadata lock is poisoned".to_owned(),
-        })?;
-        let advance = if let Some(advance) = metrics.advances.get(&glyph_id) {
-            *advance
-        } else {
-            let advance = self.with_face(|face| {
-                face.load_glyph(glyph_id, LoadFlag::NO_SCALE | LoadFlag::NO_HINTING)
-                    .map_err(|error| Error::InvalidFont {
-                        identity: self.identity().to_owned(),
-                        message: error.to_string(),
-                    })?;
-                let advance = face.glyph().advance();
-                Ok((advance.x, advance.y))
-            })?;
-            metrics.advances.insert(glyph_id, advance);
-            advance
-        };
+    /// Returns the advance and the vertical extents of `glyph_id` at `size_mm`.
+    ///
+    /// The extents are the face's own typographic ascent and descent, so every glyph
+    /// of one face at one size reports the same pair: a character box built from them
+    /// covers the glyph (the extents span everything the face can paint around the
+    /// baseline) and lines up with the boxes of the other glyphs, exactly like the
+    /// font metrics a PDF text box uses. A face that declares no usable metrics keeps
+    /// the font-size footprint above the baseline.
+    fn scaled_metrics(&self, glyph_id: u32, size_mm: f64) -> Result<GlyphMetrics> {
+        if !size_mm.is_finite() || size_mm <= 0.0 {
+            return Err(Error::InvalidFont {
+                identity: self.identity().to_owned(),
+                message: "glyph advance size must be finite and positive".to_owned(),
+            });
+        }
+        let unscaled = self.advance_units(glyph_id)?;
         let scale = size_mm / f64::from(self.units_per_em);
-        let x = advance.0 as f64 * scale;
-        let y = advance.1 as f64 * scale;
-        if !x.is_finite() || !y.is_finite() {
+        let advance = (unscaled.0 as f64 * scale, unscaled.1 as f64 * scale);
+        if !advance.0.is_finite() || !advance.1.is_finite() {
             return Err(Error::InvalidFont {
                 identity: self.identity().to_owned(),
                 message: "glyph advance is non-finite".to_owned(),
             });
         }
-        Ok((x, y))
+        let (ascent, descent) = self.typographic_extents_mm(size_mm);
+        Ok(GlyphMetrics {
+            advance,
+            ascent,
+            descent,
+        })
+    }
+
+    /// Returns the face's typographic extent above and below the baseline at
+    /// `size_mm`, or the font-size footprint when the face declares none.
+    ///
+    /// The pair is identical for every glyph of the face at one size, which is what
+    /// keeps character boxes of different scripts and of punctuation aligned. It is
+    /// the same font metric poppler uses for a PDF text box
+    /// (`TextWord::setInitialBounds`: `yMin = y - ascent`, `yMax = y - descent`).
+    fn typographic_extents_mm(&self, size_mm: f64) -> (f64, f64) {
+        if self.ascender <= 0 || self.descender >= 0 {
+            return (size_mm, 0.0);
+        }
+        let scale = size_mm / f64::from(self.units_per_em);
+        let ascent = self.ascender as f64 * scale;
+        let descent = -(self.descender as f64) * scale;
+        if !ascent.is_finite() || !descent.is_finite() || ascent <= 0.0 || descent < 0.0 {
+            return (size_mm, 0.0);
+        }
+        (ascent, descent)
+    }
+
+    /// Returns the cached unscaled advance of `glyph_id`, loading it on first use.
+    fn advance_units(&self, glyph_id: u32) -> Result<(i64, i64)> {
+        let mut metrics = self.metrics.lock().map_err(|_| Error::FontCache {
+            message: "face metadata lock is poisoned".to_owned(),
+        })?;
+        if let Some(advance) = metrics.advances.get(&glyph_id) {
+            return Ok(*advance);
+        }
+        let advance = self.with_face(|face| {
+            face.load_glyph(glyph_id, LoadFlag::NO_SCALE | LoadFlag::NO_HINTING)
+                .map_err(|error| Error::InvalidFont {
+                    identity: self.identity().to_owned(),
+                    message: error.to_string(),
+                })?;
+            let advance = face.glyph().advance();
+            Ok((advance.x, advance.y))
+        })?;
+        metrics.advances.insert(glyph_id, advance);
+        Ok(advance)
     }
 
     fn with_face<T>(
@@ -410,13 +458,43 @@ pub enum FontDiagnostic {
     },
 }
 
+/// Advance and vertical extents of one positioned glyph, in millimetres.
+///
+/// Every value is relative to the glyph's own pen position, which is the baseline
+/// origin the renderer paints it from. The advance is the glyph's; the extents are
+/// the selected face's typographic ascent and descent, so they are the same for every
+/// glyph the face owns and a box built from them stays aligned across scripts.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct GlyphMetrics {
+    advance: (f64, f64),
+    ascent: f64,
+    descent: f64,
+}
+
+impl GlyphMetrics {
+    /// Returns the advance this glyph contributes on each axis, in millimetres.
+    pub fn advance(&self) -> (f64, f64) {
+        self.advance
+    }
+    /// Returns the selected face's typographic ascent above the baseline, in
+    /// millimetres.
+    pub fn ascent(&self) -> f64 {
+        self.ascent
+    }
+    /// Returns the selected face's typographic descent below the baseline, in
+    /// millimetres.
+    pub fn descent(&self) -> f64 {
+        self.descent
+    }
+}
+
 /// One exact glyph placement in OFD object-space millimetres.
 #[derive(Clone, Debug, PartialEq)]
 pub struct PositionedGlyph {
     glyph_id: u32,
     x: f64,
     y: f64,
-    advance: (f64, f64),
+    metrics: GlyphMetrics,
     character: Option<char>,
     source_range: Range<usize>,
     scalar_index: usize,
@@ -439,14 +517,15 @@ impl PositionedGlyph {
     pub fn y(&self) -> f64 {
         self.y
     }
-    /// Returns the advance this glyph contributes on each axis, in millimetres.
+    /// Returns the advance and vertical extents of this glyph in millimetres.
     ///
-    /// This is the selected face advance, or the font size when no face was
-    /// available. It is what positions the next glyph, so a caller that needs the
-    /// per-scalar geometry of a run without explicit deltas can sum it instead of
-    /// resolving fonts again.
-    pub fn advance(&self) -> (f64, f64) {
-        self.advance
+    /// The advance is the selected face advance, or the font size when no face was
+    /// available; it is what positions the next glyph, so a caller that needs the
+    /// per-scalar geometry of a run can sum it instead of resolving fonts again. The
+    /// extents are the selected face's typographic metrics, so a caller can size a
+    /// character box that covers the glyph and matches its neighbours.
+    pub fn metrics(&self) -> GlyphMetrics {
+        self.metrics
     }
     /// Returns the associated source scalar, or `None` for an extra mapped glyph.
     pub fn character(&self) -> Option<char> {
@@ -1124,12 +1203,12 @@ pub fn position_glyph_runs(
                         let (offset_x, offset_y) = glyph_transform
                             .map(|t| (t.x(), t.y()))
                             .unwrap_or((0.0, 0.0));
-                        let advance = selected.advance_mm(glyph_id, text.font_size())?;
+                        let metrics = selected.scaled_metrics(glyph_id, text.font_size())?;
                         glyphs.push(PositionedGlyph {
                             glyph_id,
                             x: finite_coordinate(text, "glyph x", x + inferred_x + offset_x)?,
                             y: finite_coordinate(text, "glyph y", y + inferred_y + offset_y)?,
-                            advance,
+                            metrics,
                             character,
                             source_range: start_byte..end_byte,
                             scalar_index,
@@ -1138,8 +1217,10 @@ pub fn position_glyph_runs(
                             font_source: selected.source().clone(),
                             transform: glyph_transform.and_then(|t| t.matrix()),
                         });
-                        inferred_x = finite_coordinate(text, "advance x", inferred_x + advance.0)?;
-                        inferred_y = finite_coordinate(text, "advance y", inferred_y + advance.1)?;
+                        inferred_x =
+                            finite_coordinate(text, "advance x", inferred_x + metrics.advance.0)?;
+                        inferred_y =
+                            finite_coordinate(text, "advance y", inferred_y + metrics.advance.1)?;
                     }
                     let delta_x = if run.has_explicit_delta_x() {
                         run.delta_x()[local..end_local].iter().sum()
@@ -1197,17 +1278,21 @@ pub fn position_glyph_runs(
                 &requested,
                 &mut diagnostics,
             )?;
-            let advance = selection
+            let metrics = selection
                 .font
                 .as_ref()
-                .map(|font| font.advance_mm(selection.glyph_id, text.font_size()))
+                .map(|font| font.scaled_metrics(selection.glyph_id, text.font_size()))
                 .transpose()?
-                .unwrap_or((text.font_size(), 0.0));
+                .unwrap_or(GlyphMetrics {
+                    advance: (text.font_size(), 0.0),
+                    ascent: text.font_size(),
+                    descent: 0.0,
+                });
             glyphs.push(PositionedGlyph {
                 glyph_id: selection.glyph_id,
                 x: finite_coordinate(text, "glyph x", x)?,
                 y: finite_coordinate(text, "glyph y", y)?,
-                advance,
+                metrics,
                 character: Some(character),
                 source_range: byte_start..byte_end,
                 scalar_index,
@@ -1219,12 +1304,12 @@ pub fn position_glyph_runs(
             let delta_x = if run.has_explicit_delta_x() {
                 run.delta_x()[local]
             } else {
-                advance.0
+                metrics.advance.0
             };
             let delta_y = if run.has_explicit_delta_y() {
                 run.delta_y()[local]
             } else {
-                advance.1
+                metrics.advance.1
             };
             x = finite_coordinate(text, "glyph x", x + delta_x)?;
             y = finite_coordinate(text, "glyph y", y + delta_y)?;
@@ -1244,49 +1329,76 @@ pub fn position_glyph_runs(
     Ok(runs)
 }
 
-/// Per-scalar advances from the same font resolution the renderer positions text with.
+/// Per-scalar metrics from the same font resolution the renderer positions text with.
 ///
-/// This is the [`TextAdvanceProvider`] rofd-core asks for when a text run carries no
-/// explicit `DeltaX`: the answer is the advance of the glyph the positioner selected,
-/// summed per scalar for structured `Glyphs` mappings, so page geometry matches the
-/// rendered glyphs. Resolution failures answer `None`, which keeps rofd-core's
-/// font-size footprint.
-#[derive(Clone, Copy)]
-pub struct FontTextAdvances<'a> {
-    resolver: &'a dyn FontResolver,
+/// This is the [`TextMetricsProvider`] rofd-core asks for: the answer is the advance
+/// of the glyph the positioner selected, summed per scalar for structured `Glyphs`
+/// mappings, and that glyph's painted extents around the baseline, so a character box
+/// covers the glyph a renderer draws. Resolution failures answer `None`, which keeps
+/// rofd-core's font-size footprint.
+#[derive(Clone)]
+pub struct FontTextMetrics {
+    resolver: Arc<dyn FontResolver>,
 }
 
-impl<'a> FontTextAdvances<'a> {
+impl FontTextMetrics {
     /// Wraps the resolver a renderer would use for the same page.
-    pub fn new(resolver: &'a dyn FontResolver) -> Self {
+    ///
+    /// The provider owns the shared resolver, because a document holds it for its
+    /// whole life and page text is built lazily on later queries.
+    pub fn new(resolver: Arc<dyn FontResolver>) -> Self {
         Self { resolver }
     }
 }
 
-impl TextAdvanceProvider for FontTextAdvances<'_> {
-    fn advances_mm(&self, page: &Page, text: &TextObject, size_mm: f64) -> Option<Vec<f64>> {
+impl TextMetricsProvider for FontTextMetrics {
+    fn metrics_mm(
+        &self,
+        page: &Page,
+        text: &TextObject,
+        size_mm: f64,
+    ) -> Option<Vec<TextScalarMetrics>> {
         let resource = page.font_resource(text.font_id()).ok()?;
-        let runs =
-            position_glyph_runs(self.resolver, &resource, text, page.resource_limits()).ok()?;
+        let runs = position_glyph_runs(
+            self.resolver.as_ref(),
+            &resource,
+            text,
+            page.resource_limits(),
+        )
+        .ok()?;
         let total = text.runs().iter().try_fold(0usize, |total, run| {
             total.checked_add(run.text().chars().count())
         })?;
         // Glyphs of one structured mapping share the scalar index of the mapped
         // range, so their advances sum there, exactly as the positioner advances the
-        // mapped run. A scalar without a glyph keeps the size footprint the builder
-        // uses on its own.
-        let mut advances: Vec<Option<f64>> = vec![None; total];
+        // mapped run, and their extents widen it, because the box has to cover every
+        // glyph painted for that scalar. A scalar without a glyph keeps the size
+        // footprint the builder uses on its own.
+        let mut resolved: Vec<Option<TextScalarMetrics>> = vec![None; total];
         for run in &runs {
             for glyph in run.glyphs() {
-                let slot = advances.get_mut(glyph.scalar_index())?;
-                let (x, _) = glyph.advance();
-                *slot = Some(slot.unwrap_or(0.0) + x);
+                let metrics = glyph.metrics();
+                let slot = resolved.get_mut(glyph.scalar_index())?;
+                let entry = slot.get_or_insert(TextScalarMetrics {
+                    advance_mm: 0.0,
+                    ascent_mm: 0.0,
+                    descent_mm: 0.0,
+                });
+                entry.advance_mm += metrics.advance().0;
+                entry.ascent_mm = entry.ascent_mm.max(metrics.ascent());
+                entry.descent_mm = entry.descent_mm.max(metrics.descent());
             }
         }
         Some(
-            advances
+            resolved
                 .into_iter()
-                .map(|advance| advance.unwrap_or(size_mm))
+                .map(|entry| {
+                    entry.unwrap_or(TextScalarMetrics {
+                        advance_mm: size_mm,
+                        ascent_mm: size_mm,
+                        descent_mm: 0.0,
+                    })
+                })
                 .collect(),
         )
     }
diff --git a/crates/rofd-render/src/lib.rs b/crates/rofd-render/src/lib.rs
index 02a25101..2340547c 100644
--- a/crates/rofd-render/src/lib.rs
+++ b/crates/rofd-render/src/lib.rs
@@ -19,8 +19,8 @@ pub use display_list::{
     ClipPath, Command, DisplayList, DisplayListBuilder, RenderDiagnostic, RenderDiagnosticKind,
 };
 pub use fonts::{
-    position_glyph_runs, FontDiagnostic, FontIdentity, FontResolver, FontSource, FontTextAdvances,
-    GlyphRun, PositionedGlyph, ResolvedFont, SystemFontResolver,
+    position_glyph_runs, FontDiagnostic, FontIdentity, FontResolver, FontSource, FontTextMetrics,
+    GlyphMetrics, GlyphRun, PositionedGlyph, ResolvedFont, SystemFontResolver,
 };
 pub use images::{DecodedImage, ImageDecoder};
 
diff --git a/crates/rofd-render/tests/cairo_text.rs b/crates/rofd-render/tests/cairo_text.rs
index 65cb6785..84f2ed54 100644
--- a/crates/rofd-render/tests/cairo_text.rs
+++ b/crates/rofd-render/tests/cairo_text.rs
@@ -1,11 +1,16 @@
 use std::io::{Cursor, Write};
+use std::sync::Arc;
+
+use fontdb::Database;
 
 use cairo::{
     Antialias, Context, FillRule, FontOptions, Format, HintMetrics, HintStyle, ImageSurface,
     Matrix, Operator, PathSegment, SubpixelOrder,
 };
 use rofd_core::{Document, LoadOptions};
-use rofd_render::{CairoRenderer, Error, PixelRect, RenderOptions};
+use rofd_render::{
+    CairoRenderer, Error, FontTextMetrics, PixelRect, RenderOptions, SystemFontResolver,
+};
 use zip::{write::SimpleFileOptions, ZipWriter};
 
 const FONT: &[u8] = include_bytes!("fixtures/fonts/phase3-subset.ttf");
@@ -152,6 +157,83 @@ fn embedded_latin_and_cjk_glyphs_render_at_positioned_baselines() {
     assert_eq!(bounds, (30, 46, 136, 83));
 }
 
+#[test]
+fn semantic_character_boxes_cover_the_rendered_ink() {
+    let content = r#"<ofd:TextObject ID="2" Boundary="2 3 24 12" Font="10" Size="4" Fill="true" Stroke="false"><ofd:FillColor Value="0 0 0"/><ofd:TextCode X="1" Y="5">A中</ofd:TextCode></ofd:TextObject>"#;
+    let mut database = Database::new();
+    database.load_font_data(FONT.to_vec());
+    let resolver: Arc<dyn rofd_render::FontResolver> = Arc::new(SystemFontResolver::from_database(
+        database,
+        Vec::new(),
+        1 << 20,
+    ));
+    let metrics: Arc<dyn rofd_core::TextMetricsProvider> = Arc::new(FontTextMetrics::new(resolver));
+    let page =
+        Document::from_bytes_with_metrics(package(content), LoadOptions::default(), Some(metrics))
+            .unwrap()
+            .page(0)
+            .unwrap();
+
+    let mut surface = render(&page, 0);
+    let (left, top, right, bottom) =
+        ink_bounds(&mut surface).expect("controlled glyphs must paint");
+
+    // 254 dpi renders exactly ten pixels per millimetre.
+    let boxes: Vec<(f64, f64, f64, f64)> = page
+        .text()
+        .unwrap()
+        .characters()
+        .iter()
+        .map(|character| {
+            let rect = character.rect_mm().expect("both glyphs carry geometry");
+            (
+                rect.x * 10.0,
+                rect.y * 10.0,
+                (rect.x + rect.width) * 10.0,
+                (rect.y + rect.height) * 10.0,
+            )
+        })
+        .collect();
+    assert_eq!(boxes.len(), 2);
+    // One band for the whole text object: the boxes of A and 中 share their top and
+    // bottom, because both come from the face's metrics rather than from each glyph's
+    // ink.
+    for index in 1..boxes.len() {
+        assert_eq!(boxes[index].1, boxes[0].1, "tops differ: {boxes:?}");
+        assert_eq!(boxes[index].3, boxes[0].3, "bottoms differ: {boxes:?}");
+    }
+    let box_left = boxes
+        .iter()
+        .map(|box_| box_.0)
+        .fold(f64::INFINITY, f64::min);
+    let box_top = boxes
+        .iter()
+        .map(|box_| box_.1)
+        .fold(f64::INFINITY, f64::min);
+    let box_right = boxes
+        .iter()
+        .map(|box_| box_.2)
+        .fold(f64::NEG_INFINITY, f64::max);
+    let box_bottom = boxes
+        .iter()
+        .map(|box_| box_.3)
+        .fold(f64::NEG_INFINITY, f64::max);
+
+    // The band contains the painted ink and sticks out above and below it, the way a
+    // PDF text box built from the same font metrics does.
+    let slack = 1.0;
+    assert!(f64::from(left) >= box_left - slack, "{left} vs {box_left}");
+    assert!(
+        f64::from(right) <= box_right + slack,
+        "{right} vs {box_right}"
+    );
+    assert!(box_top < f64::from(top), "{box_top} vs {top}");
+    assert!(box_bottom > f64::from(bottom), "{box_bottom} vs {bottom}");
+    // 中 paints below the baseline, which is where the font-size footprint stopped:
+    // the band's bottom is below the baseline even without the ink.
+    assert!(box_bottom > 80.0, "{box_bottom} vs the baseline");
+}
+
 #[test]
 fn embedded_text_regions_preserve_fractional_glyph_positions_at_every_rotation() {
     let page = page(
diff --git a/crates/rofd-render/tests/fonts.rs b/crates/rofd-render/tests/fonts.rs
index d95e8ce1..0eb85306 100644
--- a/crates/rofd-render/tests/fonts.rs
+++ b/crates/rofd-render/tests/fonts.rs
@@ -4,7 +4,7 @@ use std::sync::Arc;
 use std::thread;
 
 use fontdb::Database;
-use rofd_core::{Document, LoadOptions, PageObject, ResourceLimits, TextAdvanceProvider};
+use rofd_core::{Document, LoadOptions, PageObject, ResourceLimits, TextMetricsProvider};
 use rofd_render::{
     position_glyph_runs, Error, FontDiagnostic, FontIdentity, FontResolver, FontSource,
     ResolvedFont, SystemFontResolver,
@@ -854,16 +854,18 @@ fn equal_resource_ids_from_distinct_documents_do_not_share_cache_entries() {
     );
 }
 
-/// The provider rofd-core asks for must answer exactly the advances the positioner
-/// used, so page geometry lands on the glyphs a renderer draws.
+/// The provider rofd-core asks for must answer exactly the geometry the positioner
+/// used, so page character boxes land on the glyphs a renderer draws - horizontally
+/// on their advance and vertically on their painted extents.
 #[test]
-fn font_text_advances_match_the_positioner_and_follow_font_metrics() {
+fn font_text_metrics_match_the_positioner_and_follow_font_metrics() {
     // A, B and Z carry proportional advances in the fixture subset; most other
     // Latin scalars map to a full-width face advance equal to the font size, which
-    // would not distinguish metrics from the size-based fallback.
+    // would not distinguish metrics from the size-based fallback. 中 adds a CJK glyph
+    // whose ink reaches below the baseline.
     let document = package_named(
-        Some(LATIN_FONT),
-        r#"<ofd:TextCode X="0" Y="4">ABZ</ofd:TextCode>"#,
+        Some(FONT),
+        r#"<ofd:TextCode X="0" Y="4">ABZ中</ofd:TextCode>"#,
         "",
         "Fixture",
     );
@@ -871,13 +873,13 @@ fn font_text_advances_match_the_positioner_and_follow_font_metrics() {
     let page = document.page(0).unwrap();
     let resource = document.font_resource(text.font_id()).unwrap();
     let mut database = Database::new();
-    database.load_font_data(LATIN_FONT.to_vec());
+    database.load_font_data(FONT.to_vec());
     let resolver = SystemFontResolver::from_database(database, Vec::new(), 1 << 20);
 
     let runs = position_glyph_runs(&resolver, &resource, &text, page.resource_limits()).unwrap();
-    let provider = rofd_render::FontTextAdvances::new(&resolver);
-    let advances = provider
-        .advances_mm(&page, &text, text.font_size())
+    let provider = rofd_render::FontTextMetrics::new(Arc::new(resolver));
+    let metrics = provider
+        .metrics_mm(&page, &text, text.font_size())
         .expect("embedded font resolves");
 
     assert!(
@@ -886,29 +888,58 @@ fn font_text_advances_match_the_positioner_and_follow_font_metrics() {
         runs[0].diagnostics()
     );
 
-    // One advance per scalar, equal to the advance of the glyph that owns it.
-    let positioned: Vec<f64> = runs
+    // One entry per scalar, equal to the metrics of the glyph that owns it.
+    let positioned: Vec<rofd_render::GlyphMetrics> = runs
         .iter()
         .flat_map(|run| run.glyphs())
-        .map(|glyph| glyph.advance().0)
+        .map(|glyph| glyph.metrics())
         .collect();
-    assert_eq!(advances.len(), positioned.len());
-    assert_eq!(advances.len(), 3);
-    for (index, advance) in advances.iter().enumerate() {
+    let advances: Vec<f64> = metrics.iter().map(|metrics| metrics.advance_mm).collect();
+    assert_eq!(metrics.len(), positioned.len());
+    assert_eq!(metrics.len(), 4);
+    for (index, entry) in metrics.iter().enumerate() {
         assert!(
-            (advance - positioned[index]).abs() < 1e-9,
-            "scalar {index}: provider {advance} vs positioner {}",
-            positioned[index]
+            (entry.advance_mm - positioned[index].advance().0).abs() < 1e-9,
+            "scalar {index}: provider {} vs positioner {}",
+            entry.advance_mm,
+            positioned[index].advance().0
         );
+        assert_eq!(entry.ascent_mm, positioned[index].ascent(), "{index}");
+        assert_eq!(entry.descent_mm, positioned[index].descent(), "{index}");
     }
 
-    // Font metrics, not a uniform font-size footprint.
+    // Font metrics, not a uniform font-size footprint: the Latin scalars are narrower
+    // than the size, while the full-width 中 fills its em.
     assert!(advances[0] < advances[1], "{advances:?}");
-    assert!(advances.iter().all(|advance| *advance < text.font_size()));
+    assert!(
+        (advances[3] - text.font_size()).abs() < 1e-9,
+        "{advances:?}"
+    );
+    assert!(advances[..3]
+        .iter()
+        .all(|advance| *advance < text.font_size()));
     assert!(advances.iter().all(|advance| *advance > 0.0));
 
+    // The vertical extents come from the face's own metrics (hhea 1160/-288 over the
+    // subset's 1000-unit em), scaled to Size: every glyph reports the same pair, which
+    // is what keeps the boxes of Latin, CJK and punctuation aligned.
+    let size = text.font_size();
+    let per_em = |units: f64| units / 1000.0 * size;
+    for entry in &metrics {
+        assert!(
+            (entry.ascent_mm - per_em(1160.0)).abs() < 1e-6,
+            "{metrics:?}"
+        );
+        assert!(
+            (entry.descent_mm - per_em(288.0)).abs() < 1e-6,
+            "{metrics:?}"
+        );
+    }
+    // 中 paints below the baseline and A does not, yet both boxes span the same band.
+    assert!(metrics[3].descent_mm > 0.0);
+
     // Both layers agree on where the run ends.
     let semantic_end: f64 = advances.iter().sum();
-    let positioned_end: f64 = positioned.iter().sum();
+    let positioned_end: f64 = positioned.iter().map(|metrics| metrics.advance().0).sum();
     assert!((semantic_end - positioned_end).abs() < 1e-9);
 }
diff --git a/docs/superpowers/specs/2026-09-09-poppler-style-c-semantic-api-design.md b/docs/superpowers/specs/2026-09-09-poppler-style-c-semantic-api-design.md
index 3448607c..6b051ce6 100644
--- a/docs/superpowers/specs/2026-09-09-poppler-style-c-semantic-api-design.md
+++ b/docs/superpowers/specs/2026-09-09-poppler-style-c-semantic-api-design.md
@@ -90,12 +90,14 @@ Where OFD data cannot yield an exact glyph box, the API returns a conservative
 finite character box and records its precision in flags instead of pretending
 font-derived accuracy.
 
-A run that declares no delta for a scalar is positioned by its font's advance, so
-the core builder accepts an optional `TextAdvanceProvider` that answers those
-advances without pulling fonts into the core crate: `rofd-render` implements it
-over the same font resolution the renderer positions text with, and `rofd-ffi`
-loads documents with the default font stack so the ABI's rectangles land on the
-glyphs a default renderer draws. Without a provider the builder keeps the
+A run that declares no delta for a scalar is positioned by its font's advance, and
+the glyph is painted at that font's extent around the baseline, so the core builder
+accepts an optional `TextMetricsProvider` that answers both without pulling fonts
+into the core crate: `rofd-render` implements it over the same font resolution the
+renderer positions text with, and `rofd-ffi` loads documents with the default font
+stack so the ABI's rectangles land on the glyphs a default renderer draws - covered
+horizontally by the advance and vertically by the painted ascent and descent, which
+is what a highlight or caret needs. Without a provider the builder keeps the
 font-size footprint, and scalars it cannot resolve stay flagged as conservative.
 
 Reading order is deterministic. It starts with effective paint/source order,

From 3d2446cf7b4ead1282e204395f4506e6a038add1 Mon Sep 17 00:00:00 2001
From: Yangtse Su <yangtsesu@gmail.com>
Date: Mon, 19 Oct 2026 16:24:06 +0800
Subject: [PATCH 2/2] feat(core): grow a selection region by the margin a PDF
 selection has

A PDF reader grows a selected line's band by an eighth of its height above and below
(poppler's `TextSelectionSizer::visitLine`: `margin = (yMax - yMin) / 8`). That is what
makes a selected line read as one band that clears the glyphs instead of ending on
them. `TextSelection::regions` now grows each line union the same way, so a selection
region has the shape a PDF selection has in the same viewer. Character boxes and match
rectangles keep the plain band, the way poppler keeps them.

Verified: cargo fmt --all -- --check; cargo clippy -p rofd-core -p rofd-render
-p rofd-ffi --all-targets -- -D warnings; cargo test for the three crates (core: the
three selection tests' regions and
`crates/rofd-core/tests/semantic_text.rs::selection_regions_carry_the_pdf_highlight_margin_on_an_aligned_band`;
FFI: `crates/rofd-ffi/tests/semantic.rs::text_layout_rectangles_cover_the_rendered_ink_below_the_baseline`
asserts the region equals the band plus the margin), and
`crates/rofd-ffi/tests/run_c_tests.sh` (the export set is unchanged).
---
 crates/rofd-core/src/semantic.rs        | 28 +++++++++++++++++++++----
 crates/rofd-core/tests/semantic_text.rs | 26 +++++++++++++----------
 crates/rofd-ffi/tests/semantic.rs       | 11 ++++++----
 3 files changed, 46 insertions(+), 19 deletions(-)

diff --git a/crates/rofd-core/src/semantic.rs b/crates/rofd-core/src/semantic.rs
index 8de2e11f..98d1e3a7 100644
--- a/crates/rofd-core/src/semantic.rs
+++ b/crates/rofd-core/src/semantic.rs
@@ -109,7 +109,8 @@ impl TextSelection {
         &self.text
     }
 
-    /// Returns one union of selected visible boxes per participating logical line.
+    /// Returns one union of selected visible boxes per participating logical line,
+    /// each grown by the highlight margin a PDF selection region has.
     pub fn regions(&self) -> &[Rect] {
         &self.regions
     }
@@ -358,7 +359,9 @@ impl PageText {
     /// Glyph and word selections emit selected source scalars without synthesized
     /// separators. Line selections retain a synthesized newline only when both
     /// adjacent lines are selected. Regions are ordered by canonical text, with
-    /// one union per selected logical line, never across synthesized separators.
+    /// one union per selected logical line, never across synthesized separators. Each
+    /// union carries the highlight margin a PDF reader's selection region has: it is
+    /// grown by an eighth of its height above and below.
     pub fn select(&self, area: Rect, style: SelectionStyle) -> Result<TextSelection> {
         validate_area(area)?;
         let mut selected = self
@@ -388,7 +391,7 @@ impl PageText {
         for (index, character) in self.characters.iter().enumerate() {
             if self.is_separator(index) {
                 if let Some(rect) = region.take() {
-                    selection.regions.push(rect);
+                    selection.regions.push(selection_region(rect)?);
                 }
                 if style == SelectionStyle::Line
                     && index.checked_sub(1).is_some_and(|before| selected[before])
@@ -409,7 +412,7 @@ impl PageText {
             }
         }
         if let Some(rect) = region {
-            selection.regions.push(rect);
+            selection.regions.push(selection_region(rect)?);
         }
         Ok(selection)
     }
@@ -429,6 +432,23 @@ impl PageText {
     }
 }
 
+/// Returns the rectangle a selection highlight paints for one selected line.
+///
+/// A PDF reader grows the line band by an eighth of its height above and below
+/// (poppler's `TextSelectionSizer::visitLine`: `margin = (yMax - yMin) / 8`), which is
+/// what makes a selected line read as one band that clears the glyphs instead of
+/// ending on them. Selection regions mirror that growth; character boxes and match
+/// rectangles stay the plain band.
+fn selection_region(rect: Rect) -> Result<Rect> {
+    let margin = rect.height / 8.0;
+    Ok(Rect {
+        x: rect.x,
+        y: finite_add(rect.y, -margin)?,
+        width: rect.width,
+        height: finite_add(rect.height, 2.0 * margin)?,
+    })
+}
+
 fn expand_selected_group(selected: &mut [bool]) {
     if selected.iter().any(|hit| *hit) {
         selected.fill(true);
diff --git a/crates/rofd-core/tests/semantic_text.rs b/crates/rofd-core/tests/semantic_text.rs
index 6df6b6e0..c2d2b6f7 100644
--- a/crates/rofd-core/tests/semantic_text.rs
+++ b/crates/rofd-core/tests/semantic_text.rs
@@ -220,9 +220,11 @@ fn area_extraction_and_glyph_selection_require_positive_intersection() {
     assert_eq!(text.text_for_area(area).unwrap(), "bf");
     let selection = text.select(area, SelectionStyle::Glyph).unwrap();
     assert_eq!(selection.text(), "bf");
+    // Each region is the line band grown by an eighth of its height on both sides,
+    // the margin a PDF selection region has.
     assert_eq!(
         selection.regions(),
-        &[rect(5.0, 1.0, 4.0, 4.0), rect(5.0, 11.0, 4.0, 4.0)]
+        &[rect(5.0, 0.5, 4.0, 5.0), rect(5.0, 10.5, 4.0, 5.0)]
     );
     assert_eq!(text.text_for_area(rect(8.9, 2.0, 0.2, 1.0)).unwrap(), "b_");
     assert_eq!(text.text_for_area(rect(1.0, 5.0, 4.0, 1.0)).unwrap(), "");
@@ -236,7 +238,7 @@ fn word_selection_expands_unicode_words_without_crossing_punctuation_or_space()
         .select(rect(6.0, 2.0, 8.0, 1.0), SelectionStyle::Word)
         .unwrap();
     assert_eq!(selection.text(), "ab_中");
-    assert_eq!(selection.regions(), &[rect(1.0, 1.0, 16.0, 4.0)]);
+    assert_eq!(selection.regions(), &[rect(1.0, 0.5, 16.0, 5.0)]);
     assert_eq!(
         text.select(rect(18.0, 2.0, 1.0, 1.0), SelectionStyle::Word)
             .unwrap()
@@ -265,14 +267,14 @@ fn line_selection_preserves_internal_synthesized_newlines_and_region_order() {
         .select(rect(6.0, 2.0, 1.0, 1.0), SelectionStyle::Line)
         .unwrap();
     assert_eq!(one.text(), "ab_中, cd");
-    assert_eq!(one.regions(), &[rect(1.0, 1.0, 32.0, 4.0)]);
+    assert_eq!(one.regions(), &[rect(1.0, 0.5, 32.0, 5.0)]);
     let both = text
         .select(rect(6.0, 2.0, 1.0, 12.0), SelectionStyle::Line)
         .unwrap();
     assert_eq!(both.text(), "ab_中, cd\nef gh");
     assert_eq!(
         both.regions(),
-        &[rect(1.0, 1.0, 32.0, 4.0), rect(1.0, 11.0, 20.0, 4.0)]
+        &[rect(1.0, 0.5, 32.0, 5.0), rect(1.0, 10.5, 20.0, 5.0)]
     );
 }
 
@@ -286,14 +288,15 @@ fn selection_preserves_canonical_order_when_geometry_runs_backwards() {
     assert_eq!(text.text_for_area(area).unwrap(), "abc");
     let selection = text.select(area, SelectionStyle::Glyph).unwrap();
     assert_eq!(selection.text(), "abc");
-    assert_eq!(selection.regions(), &[rect(1.0, 1.0, 12.0, 4.0)]);
+    assert_eq!(selection.regions(), &[rect(1.0, 0.5, 12.0, 5.0)]);
 }
 
-/// The band of one face is what a selection region spans: it clears the glyphs the way
-/// a PDF text box does. The band itself comes from the metrics of one face, so its top
-/// and bottom do not depend on which scalars happen to have the tallest ink.
+/// A selection region is the line band grown by an eighth of its height on both sides:
+/// the highlight clears the glyphs the way a PDF reader's does. The band itself comes
+/// from the metrics of one face, so its top and bottom do not depend on which scalars
+/// happen to have the tallest ink.
 #[test]
-fn selection_regions_span_the_aligned_band_of_one_face() {
+fn selection_regions_carry_the_pdf_highlight_margin_on_an_aligned_band() {
     let page = page_with_text(
         r#"<ofd:TextObject ID="2" Boundary="0 0 100 8" Font="10" Size="4"><ofd:TextCode X="1" Y="5">A中, 。</ofd:TextCode></ofd:TextObject>"#,
     );
@@ -324,8 +327,9 @@ fn selection_regions_span_the_aligned_band_of_one_face() {
         .unwrap();
     assert_eq!(selection.text(), "A中, 。");
     let region = selection.regions()[0];
-    assert!((region.y - top).abs() < 1e-9, "{region:?}");
-    assert!((region.height - (bottom - top)).abs() < 1e-9);
+    let margin = (bottom - top) / 8.0;
+    assert!((region.y - (top - margin)).abs() < 1e-9, "{region:?}");
+    assert!((region.height - (bottom - top + 2.0 * margin)).abs() < 1e-9);
 }
 
 #[test]
diff --git a/crates/rofd-ffi/tests/semantic.rs b/crates/rofd-ffi/tests/semantic.rs
index c7828bdd..311a1770 100644
--- a/crates/rofd-ffi/tests/semantic.rs
+++ b/crates/rofd-ffi/tests/semantic.rs
@@ -1184,7 +1184,8 @@ fn text_layout_rectangles_cover_the_rendered_ink_below_the_baseline() {
             "right {box_right} vs {ink_right}"
         );
 
-        // A line selection over the same text spans that band.
+        // A line selection over the same text is that band grown by an eighth of its
+        // height on both sides, the margin a PDF selection region has.
         let area = rofd_rect_t {
             x_mm: 0.0,
             y_mm: 0.0,
@@ -1204,11 +1205,13 @@ fn text_layout_rectangles_cover_the_rendered_ink_below_the_baseline() {
         );
         assert_eq!(selection_region_count(selection), 1);
         let region = selection_region(selection, 0);
+        let margin = a.height_mm / 8.0;
         assert!(
-            (region.y_mm - a.y_mm).abs() < 1e-3,
-            "region {region:?} vs band {a:?}"
+            (region.y_mm - (a.y_mm - margin)).abs() < 1e-3,
+            "region {region:?} vs band {:?} + margin {margin}",
+            a
         );
-        assert!((region.height_mm - a.height_mm).abs() < 1e-3);
+        assert!((region.height_mm - (a.height_mm + 2.0 * margin)).abs() < 1e-3);
         rofd_text_selection_free(selection);
 
         rofd_render_report_free(report);