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pdftract/notes/pdftract-sdx9z.md
jedarden 2cf02c6b2b 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
2026-05-24 02:54:00 -04:00

2.7 KiB
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pdftract-sdx9z: Line struct + baseline computation per span

Summary

Implemented Phase 4.2 line formation infrastructure:

  • Created layout/line.rs module with Line struct and compute_baseline function
  • Added LineDirection enum with serde support (Ltr, Rtl, Mixed)
  • Added helper functions for bbox operations

Files Modified

  • crates/pdftract-core/src/layout/line.rs (new): 247 lines
  • crates/pdftract-core/src/layout/mod.rs: Exported new line module

Acceptance Criteria Status

PASS

  • ✅ compute_baseline([0, 100, 50, 110]) returns 102.0 (height 10, baseline = 100 + 10*0.2)
  • ✅ compute_baseline([0, 100, 50, 100]) returns 100.0 (zero-height case)
  • ✅ union_bboxes correctly computes union of 3 span bboxes
  • ✅ LineDirection serde roundtrips to/from "ltr"/"rtl"/"mixed"
  • ✅ All 11 unit tests pass in layout::line::tests

Implementation Details

Line struct

pub struct Line<S> {
    pub spans: Vec<S>,
    pub bbox: [f32; 4],         // Union of span bboxes
    pub baseline: f32,          // Average of member span baselines
    pub direction: LineDirection,
    pub page_relative_y: f32,   // (page_height - bbox[3]) / page_height
}

compute_baseline function

pub fn compute_baseline(bbox: &[f32; 4]) -> f32 {
    let height = bbox[3] - bbox[1];
    bbox[1] + height * 0.2  // 0.2 = descender approximation
}

LineDirection enum

pub enum LineDirection {
    Ltr,   // Left-to-right
    Rtl,   // Right-to-left
    Mixed, // Bidirectional
}

Plan References

  • Phase 4.2 baseline (lines 1665-1666): y0 + (bbox_height * 0.2) formula
  • RTL detection (line 1686): unicode-bidi crate for future bidi character category lookup

Testing

All tests pass:

running 38 tests
test layout::line::tests::test_compute_baseline_normal_span ... ok
test layout::line::tests::test_compute_baseline_zero_height ... ok
test layout::line::tests::test_compute_baseline_large_height ... ok
test layout::line::tests::test_line_direction_serdes_ltr ... ok
test layout::line::tests::test_line_direction_serdes_rtl ... ok
test layout::line::tests::test_line_direction_serdes_mixed ... ok
test layout::line::tests::test_line_accessors ... ok
test layout::line::tests::test_union_bboxes_single ... ok
test layout::line::tests::test_union_bboxes_multiple ... ok
test layout::line::tests::test_union_bboxes_empty ... ok
test layout::line::tests::test_union_bboxes_nested ... ok
test layout::line::tests::test_union_bboxes_disjoint ... ok

test result: ok. 38 passed; 0 failed

Next Steps

Future beads will implement:

  • Actual line clustering algorithm (baseline proximity grouping)
  • RTL detection using unicode-bidi crate
  • Span-to-line aggregation with reading order sorting