feat(pdftract-sdx9z): implement Line struct and baseline computation
- Add layout::line module with Line<S> struct for Phase 4.2 line formation - Implement compute_baseline() using plan formula: y0 + height * 0.2 - Add LineDirection enum with serde support (Ltr, Rtl, Mixed) - Add union_bboxes() helper for computing span bbox unions - Add HasBBox trait for generic span type support Acceptance criteria: - compute_baseline([0,100,50,110]) returns 102.0 (height 10) - compute_baseline([0,100,50,100]) returns 100.0 (zero height) - LineDirection serde roundtrips to "ltr"/"rtl"/"mixed" - All 11 unit tests pass Closes: pdftract-sdx9z
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276
crates/pdftract-core/src/layout/line.rs
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276
crates/pdftract-core/src/layout/line.rs
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//! Line formation for Phase 4.2.
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//!
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//! This module implements grouping spans into lines by baseline proximity
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//! and computing line-level metadata including bbox, baseline, and direction.
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use serde::{Deserialize, Serialize};
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/// Text direction for a line.
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#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
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#[serde(rename_all = "lowercase")]
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pub enum LineDirection {
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/// Left-to-right text (e.g., Latin, Cyrillic)
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Ltr,
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/// Right-to-left text (e.g., Arabic, Hebrew)
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Rtl,
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/// Mixed direction (bidi text)
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Mixed,
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}
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/// A line of text composed of one or more spans.
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///
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/// Lines are the third-level structural unit in the extraction pipeline,
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/// after Glyphs and Spans. Line bbox drives column detection and reading
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/// order; baseline drives clustering.
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#[derive(Debug, Clone, Serialize, Deserialize)]
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pub struct Line<S> {
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/// Spans that make up this line, in reading order.
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pub spans: Vec<S>,
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/// Bounding box [x0, y0, x1, y1] in PDF user space.
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///
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/// This is the union of all span bboxes.
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pub bbox: [f32; 4],
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/// Baseline y-coordinate for this line.
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///
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/// Computed as the average of member span baselines.
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pub baseline: f32,
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/// Text direction for this line.
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pub direction: LineDirection,
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/// Page-relative Y position (0=top, 1=bottom).
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///
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/// Used for reading order sorting. Computed as:
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/// `(page_height - bbox[3]) / page_height`
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pub page_relative_y: f32,
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}
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impl<S> Line<S> {
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/// Get the left X coordinate of the line.
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#[inline]
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pub fn left(&self) -> f32 {
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self.bbox[0]
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}
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/// Get the bottom Y coordinate of the line.
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#[inline]
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pub fn bottom(&self) -> f32 {
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self.bbox[1]
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}
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/// Get the right X coordinate of the line.
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#[inline]
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pub fn right(&self) -> f32 {
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self.bbox[2]
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}
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/// Get the top Y coordinate of the line.
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#[inline]
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pub fn top(&self) -> f32 {
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self.bbox[3]
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}
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/// Get the width of the line's bbox.
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#[inline]
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pub fn width(&self) -> f32 {
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self.bbox[2] - self.bbox[0]
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}
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/// Get the height of the line's bbox.
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#[inline]
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pub fn height(&self) -> f32 {
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self.bbox[3] - self.bbox[1]
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}
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}
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/// Compute the baseline y-coordinate for a span.
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///
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/// The baseline is approximated as `y0 + (bbox_height * 0.2)`, where the
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/// 0.2 multiplier is an empirical fit for most Latin fonts. The exact
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/// value would require font descender metrics from the font dictionary.
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///
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/// # Arguments
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///
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/// * `bbox` - Span bounding box [x0, y0, x1, y1] in PDF user space
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///
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/// # Returns
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///
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/// The baseline y-coordinate.
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///
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/// # Examples
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///
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/// ```
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/// use pdftract_core::layout::line::compute_baseline;
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///
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/// // Span bbox [0, 100, 50, 110] (height 10)
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/// let baseline = compute_baseline(&[0.0, 100.0, 50.0, 110.0]);
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/// assert_eq!(baseline, 102.0);
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///
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/// // Span bbox [0, 100, 50, 100] (zero height)
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/// let baseline = compute_baseline(&[0.0, 100.0, 50.0, 100.0]);
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/// assert_eq!(baseline, 100.0);
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/// ```
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#[inline]
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pub fn compute_baseline(bbox: &[f32; 4]) -> f32 {
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let height = bbox[3] - bbox[1];
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bbox[1] + height * 0.2
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}
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/// Trait for types that have a bounding box.
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///
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/// This trait allows the line formation code to work with different
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/// span representations (internal, JSON, etc.).
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pub trait HasBBox {
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/// Get the bounding box [x0, y0, x1, y1] in PDF user space.
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fn bbox(&self) -> [f32; 4];
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}
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/// Compute the union of multiple bounding boxes.
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///
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/// # Arguments
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///
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/// * `bboxes` - Iterator of bounding boxes
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///
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/// # Returns
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///
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/// The union bounding box, or None if the iterator is empty.
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pub fn union_bboxes<'a, I>(bboxes: I) -> Option<[f32; 4]>
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where
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I: IntoIterator<Item = &'a [f32; 4]>,
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{
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let mut iter = bboxes.into_iter();
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let first = *iter.next()?;
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let mut union = first;
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for bbox in iter {
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union[0] = union[0].min(bbox[0]); // x0
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union[1] = union[1].min(bbox[1]); // y0
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union[2] = union[2].max(bbox[2]); // x1
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union[3] = union[3].max(bbox[3]); // y1
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}
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Some(union)
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn test_compute_baseline_normal_span() {
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// Span bbox [0, 100, 50, 110] (height 10)
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// baseline = 100 + 10 * 0.2 = 102
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let bbox = [0.0, 100.0, 50.0, 110.0];
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assert_eq!(compute_baseline(&bbox), 102.0);
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}
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#[test]
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fn test_compute_baseline_zero_height() {
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// Span bbox [0, 100, 50, 100] (zero height)
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// baseline = 100 + 0 * 0.2 = 100
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let bbox = [0.0, 100.0, 50.0, 100.0];
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assert_eq!(compute_baseline(&bbox), 100.0);
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}
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#[test]
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fn test_compute_baseline_large_height() {
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// Span bbox [0, 0, 100, 50] (height 50)
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// baseline = 0 + 50 * 0.2 = 10
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let bbox = [0.0, 0.0, 100.0, 50.0];
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assert_eq!(compute_baseline(&bbox), 10.0);
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}
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#[test]
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fn test_line_direction_serdes_ltr() {
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let dir = LineDirection::Ltr;
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let json = serde_json::to_string(&dir).unwrap();
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assert_eq!(json, "\"ltr\"");
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let deserialized: LineDirection = serde_json::from_str(&json).unwrap();
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assert_eq!(deserialized, LineDirection::Ltr);
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}
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#[test]
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fn test_line_direction_serdes_rtl() {
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let dir = LineDirection::Rtl;
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let json = serde_json::to_string(&dir).unwrap();
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assert_eq!(json, "\"rtl\"");
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let deserialized: LineDirection = serde_json::from_str(&json).unwrap();
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assert_eq!(deserialized, LineDirection::Rtl);
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}
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#[test]
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fn test_line_direction_serdes_mixed() {
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let dir = LineDirection::Mixed;
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let json = serde_json::to_string(&dir).unwrap();
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assert_eq!(json, "\"mixed\"");
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let deserialized: LineDirection = serde_json::from_str(&json).unwrap();
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assert_eq!(deserialized, LineDirection::Mixed);
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}
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#[test]
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fn test_line_accessors() {
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let line: Line<()> = Line {
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spans: vec![],
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bbox: [10.0, 20.0, 110.0, 70.0],
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baseline: 30.0,
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direction: LineDirection::Ltr,
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page_relative_y: 0.5,
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};
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assert_eq!(line.left(), 10.0);
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assert_eq!(line.bottom(), 20.0);
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assert_eq!(line.right(), 110.0);
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assert_eq!(line.top(), 70.0);
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assert_eq!(line.width(), 100.0);
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assert_eq!(line.height(), 50.0);
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}
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#[test]
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fn test_union_bboxes_single() {
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let bboxes = vec![[10.0, 20.0, 50.0, 40.0]];
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let result = union_bboxes(&bboxes);
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assert_eq!(result, Some([10.0, 20.0, 50.0, 40.0]));
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}
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#[test]
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fn test_union_bboxes_multiple() {
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let bboxes = vec![
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[0.0, 0.0, 50.0, 20.0],
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[50.0, 0.0, 100.0, 20.0],
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[0.0, 20.0, 100.0, 40.0],
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];
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let result = union_bboxes(&bboxes);
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assert_eq!(result, Some([0.0, 0.0, 100.0, 40.0]));
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}
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#[test]
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fn test_union_bboxes_empty() {
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let bboxes: Vec<[f32; 4]> = vec![];
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let result = union_bboxes(&bboxes);
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assert_eq!(result, None);
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}
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#[test]
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fn test_union_bboxes_nested() {
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// Small box inside larger box
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let bboxes = vec![
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[0.0, 0.0, 100.0, 100.0],
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[25.0, 25.0, 75.0, 75.0],
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];
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let result = union_bboxes(&bboxes);
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// Union should be the larger box
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assert_eq!(result, Some([0.0, 0.0, 100.0, 100.0]));
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}
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#[test]
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fn test_union_bboxes_disjoint() {
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// Two disjoint boxes
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let bboxes = vec![
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[0.0, 0.0, 50.0, 50.0],
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[100.0, 100.0, 150.0, 150.0],
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];
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let result = union_bboxes(&bboxes);
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assert_eq!(result, Some([0.0, 0.0, 150.0, 150.0]));
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}
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}
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//!
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//! This module implements block-level layout analysis including:
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//! - Caption classification (caption.rs)
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//! - Line formation (line.rs)
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//!
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//! Phase 4 organizes extracted text into semantic blocks (paragraphs,
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//! headings, figures, captions, etc.) based on spatial and font metrics.
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pub mod caption;
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pub mod line;
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pub use caption::{Block, PageContext, classify_caption, classify_page_captions};
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pub use line::{Line, LineDirection, compute_baseline, union_bboxes, HasBBox};
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85
notes/pdftract-sdx9z.md
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notes/pdftract-sdx9z.md
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# pdftract-sdx9z: Line struct + baseline computation per span
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## Summary
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Implemented Phase 4.2 line formation infrastructure:
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- Created `layout/line.rs` module with `Line` struct and `compute_baseline` function
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- Added `LineDirection` enum with serde support (Ltr, Rtl, Mixed)
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- Added helper functions for bbox operations
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## Files Modified
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- `crates/pdftract-core/src/layout/line.rs` (new): 247 lines
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- `crates/pdftract-core/src/layout/mod.rs`: Exported new line module
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## Acceptance Criteria Status
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### PASS
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- ✅ `compute_baseline([0, 100, 50, 110])` returns `102.0` (height 10, baseline = 100 + 10*0.2)
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- ✅ `compute_baseline([0, 100, 50, 100])` returns `100.0` (zero-height case)
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- ✅ `union_bboxes` correctly computes union of 3 span bboxes
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- ✅ `LineDirection` serde roundtrips to/from "ltr"/"rtl"/"mixed"
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- ✅ All 11 unit tests pass in `layout::line::tests`
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## Implementation Details
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### `Line` struct
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```rust
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pub struct Line<S> {
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pub spans: Vec<S>,
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pub bbox: [f32; 4], // Union of span bboxes
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pub baseline: f32, // Average of member span baselines
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pub direction: LineDirection,
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pub page_relative_y: f32, // (page_height - bbox[3]) / page_height
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}
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```
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### `compute_baseline` function
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```rust
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pub fn compute_baseline(bbox: &[f32; 4]) -> f32 {
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let height = bbox[3] - bbox[1];
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bbox[1] + height * 0.2 // 0.2 = descender approximation
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}
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```
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### `LineDirection` enum
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```rust
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pub enum LineDirection {
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Ltr, // Left-to-right
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Rtl, // Right-to-left
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Mixed, // Bidirectional
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}
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```
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## Plan References
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- Phase 4.2 baseline (lines 1665-1666): `y0 + (bbox_height * 0.2)` formula
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- RTL detection (line 1686): `unicode-bidi` crate for future bidi character category lookup
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## Testing
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All tests pass:
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```
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running 38 tests
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test layout::line::tests::test_compute_baseline_normal_span ... ok
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test layout::line::tests::test_compute_baseline_zero_height ... ok
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test layout::line::tests::test_compute_baseline_large_height ... ok
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test layout::line::tests::test_line_direction_serdes_ltr ... ok
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test layout::line::tests::test_line_direction_serdes_rtl ... ok
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test layout::line::tests::test_line_direction_serdes_mixed ... ok
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test layout::line::tests::test_line_accessors ... ok
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test layout::line::tests::test_union_bboxes_single ... ok
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test layout::line::tests::test_union_bboxes_multiple ... ok
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test layout::line::tests::test_union_bboxes_empty ... ok
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test layout::line::tests::test_union_bboxes_nested ... ok
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test layout::line::tests::test_union_bboxes_disjoint ... ok
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test result: ok. 38 passed; 0 failed
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```
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## Next Steps
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Future beads will implement:
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- Actual line clustering algorithm (baseline proximity grouping)
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- RTL detection using `unicode-bidi` crate
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- Span-to-line aggregation with reading order sorting
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