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pdftract/notes/pdftract-53liu.md
jedarden 9f377d1609 docs(pdftract-53liu): verify Phase 4.2 Line Formation coordinator 
All 4 children beads closed with verification:
- Line struct + baseline computation (pdftract-sdx9z)
- Baseline clustering algorithm (pdftract-6bwq4)
- Within-line span sorting (pdftract-1jkme)
- RTL direction detection (pdftract-1ofnz)

Acceptance criteria:
- ✅ All 4 children closed
- ✅ Two-column layout: columns NOT merged into one line (test_two_column_separate_blocks)
- ✅ Superscript span at higher y: clustered with baseline text
- ✅ Arabic text: bidi R characters detected, spans sorted right-to-left
- ✅ Mixed Latin+Arabic line: detected as "mixed" direction

44/44 tests pass in layout::line module.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
2026-05-28 01:15:31 -04:00

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pdftract-53liu: Phase 4.2 Line Formation (coordinator)

Summary

Coordinator bead for Phase 4.2 Line Formation. All 4 children beads completed successfully:

  • pdftract-sdx9z: Line struct + baseline computation
  • pdftract-6bwq4: Baseline clustering algorithm (0.5 * median_font_size)
  • pdftract-1jkme: Within-line span sorting (LTR/RTL)
  • pdftract-1ofnz: RTL direction detection (unicode-bidi)

Acceptance Criteria Status

Criterion Status Evidence
All 4 children closed PASS All 4 children verified closed
Two-column layout: columns NOT merged into one line PASS test_two_column_separate_blocks (Phase 4.4)
Superscript span at higher y: clustered with baseline text PASS test_cluster_spans_superscript_stays_on_same_line
Arabic text: bidi R characters detected, spans sorted right-to-left PASS test_detect_line_direction_arabic_text
Mixed Latin+Arabic line: detected as "mixed" direction PASS test_detect_line_direction_mixed_latin_arabic

Implementation Summary

Line struct (layout/line.rs)

  • Line<S> generic struct with spans, bbox, baseline, direction, page_relative_y
  • LineDirection enum (Ltr, Rtl, Mixed) with serde support
  • compute_baseline(bbox) = y0 + (bbox_height * 0.2) per plan formula

Baseline clustering

  • cluster_spans_into_lines(spans, median_font_size) groups spans by baseline proximity
  • Threshold: 0.5 * median_font_size (not hardcoded)
  • Handles superscripts correctly (small font, slightly higher baseline stays with main line)
  • Sorts spans by x0 within each line (LTR default)

RTL detection

  • detect_line_direction(text) using unicode-bidi crate
  • Counts L vs R/AL bidi classes
  • Returns Ltr if ltr > rtl OR both zero (empty/neutral)
  • Returns Rtl if rtl > ltr
  • Returns Mixed if tied (both > 0)

Within-line sorting

  • sort_spans_in_line(line) handles LTR (x0 asc), RTL (x1 desc), Mixed (fallback to x0 asc)
  • Stable sort preserves insertion order on ties
  • NaN bbox handled as Ordering::Equal

Test Results

Summary [   0.040s] 44 tests run: 44 passed, 2409 skipped

All line module tests pass including:

  • 11 baseline computation tests
  • 11 clustering algorithm tests
  • 12 RTL direction detection tests
  • 7 span sorting tests
  • 3 block formation tests (including two-column)

References

  • Plan: Phase 4.2 Line Formation (lines 1660-1675)
  • Children verification notes: notes/pdftract-{sdx9z,6bwq4,1jkme,1ofnz}.md