8bc63ac8b3
- 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
41 lines
1.9 KiB
Markdown
41 lines
1.9 KiB
Markdown
# pdftract-56vwd: x0 histogram builder
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## Summary
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Implemented `build_x0_histogram(spans: &[S], page_width: f32) -> Vec<u32>` function for column detection (Phase 4.3).
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## Changes Made
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### crates/pdftract-core/src/layout/columns.rs
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- Added `build_x0_histogram()` function that builds a 1pt-resolution histogram of span x0 coordinates
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- Added `HasBBox` trait for generic bbox access (returns `[f32; 4]`)
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- Implemented `HasBBox` for `[f32; 4]` and `[f64; 4]` array types
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- Function clamps x0 values to valid histogram range and logs diagnostics for out-of-bounds values
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### crates/pdftract-core/src/layout/mod.rs
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- Exported `build_x0_histogram` function
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## Acceptance Criteria Status
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| Criterion | Status |
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|-----------|--------|
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| 1 span at x0=100, page_width=612: hist[100] == 1 | PASS |
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| 5 spans at x0=100,100,200,200,300: hist[100]==2, hist[200]==2, hist[300]==1 | PASS |
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| Span at x0=-5: clamped to hist[0], diagnostic | PASS |
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| Empty spans: returns Vec of zeros | PASS |
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## Test Results
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All 20 tests in `layout::columns` module pass, including 7 new tests for `build_x0_histogram`:
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- `test_build_x0_histogram_single_span` - Single span histogram
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- `test_build_x0_histogram_multiple_spans` - Multiple spans at different x0 positions
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- `test_build_x0_histogram_clamp_negative_x0` - Negative x0 clamping with diagnostic
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- `test_build_x0_histogram_clamp_overflow_x0` - Overflow x0 clamping with diagnostic
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- `test_build_x0_histogram_empty_spans` - Empty span handling
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- `test_build_x0_histogram_rounding` - Rounding behavior (x0.4 -> x0, x0.6 -> x0+1)
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- `test_build_x0_histogram_a4_page` - A4 page width (595pt)
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## Notes
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- Function signature uses generic `S: HasBBox` trait for flexibility with different span representations
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- 1pt resolution per plan: for 612pt letter page, 612 buckets; for 595pt A4, 595 buckets
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- Only x0 (LEFT edge) is histogrammed; x1 is not used
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- Each span contributes exactly one bucket increment
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- Diagnostics use `tracing::warn!` for out-of-bounds x0 values
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