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pdftract/notes/pdftract-56vwd.md
jedarden 8bc63ac8b3 feat(pdftract-56vwd): implement build_x0_histogram for column detection 
- Add build_x0_histogram() function for 1pt-resolution x0 histogram
- Add HasBBox trait for generic bbox access
- Implement for [f32; 4] and [f64; 4] types
- Clamp out-of-bounds x0 values with diagnostics
- Add 7 tests covering single/multiple spans, clamping, rounding, A4 pages

Acceptance criteria PASS:
- Single span at x0=100: hist[100] == 1
- Multiple spans: hist[100]==2, hist[200]==2, hist[300]==1
- Negative x0 clamped to hist[0] with diagnostic
- Empty spans returns zero Vec

Closes: pdftract-56vwd
2026-05-25 11:59:27 -04:00

1.9 KiB
Raw Blame History

pdftract-56vwd: x0 histogram builder

Summary

Implemented build_x0_histogram(spans: &[S], page_width: f32) -> Vec<u32> function for column detection (Phase 4.3).

Changes Made

crates/pdftract-core/src/layout/columns.rs

  • Added build_x0_histogram() function that builds a 1pt-resolution histogram of span x0 coordinates
  • Added HasBBox trait for generic bbox access (returns [f32; 4])
  • Implemented HasBBox for [f32; 4] and [f64; 4] array types
  • Function clamps x0 values to valid histogram range and logs diagnostics for out-of-bounds values

crates/pdftract-core/src/layout/mod.rs

  • Exported build_x0_histogram function

Acceptance Criteria Status

Criterion Status
1 span at x0=100, page_width=612: hist[100] == 1 PASS
5 spans at x0=100,100,200,200,300: hist[100]==2, hist[200]==2, hist[300]==1 PASS
Span at x0=-5: clamped to hist[0], diagnostic PASS
Empty spans: returns Vec of zeros PASS

Test Results

All 20 tests in layout::columns module pass, including 7 new tests for build_x0_histogram:

  • test_build_x0_histogram_single_span - Single span histogram
  • test_build_x0_histogram_multiple_spans - Multiple spans at different x0 positions
  • test_build_x0_histogram_clamp_negative_x0 - Negative x0 clamping with diagnostic
  • test_build_x0_histogram_clamp_overflow_x0 - Overflow x0 clamping with diagnostic
  • test_build_x0_histogram_empty_spans - Empty span handling
  • test_build_x0_histogram_rounding - Rounding behavior (x0.4 -> x0, x0.6 -> x0+1)
  • test_build_x0_histogram_a4_page - A4 page width (595pt)

Notes

  • Function signature uses generic S: HasBBox trait for flexibility with different span representations
  • 1pt resolution per plan: for 612pt letter page, 612 buckets; for 595pt A4, 595 buckets
  • Only x0 (LEFT edge) is histogrammed; x1 is not used
  • Each span contributes exactly one bucket increment
  • Diagnostics use tracing::warn! for out-of-bounds x0 values