a14787794c
Implement cluster_spans_into_lines for Phase 4.2 line formation. Groups spans into lines by baseline proximity using threshold 0.5 * median_font_size. - Add HasFontSize trait for types with font_size - Implement cluster_spans_into_lines function - Compute baseline for each span - Sort by baseline ASC - Sweep and cluster within threshold - Emit Line per cluster - Sort spans by x0 within each line - Add finalize_line_cluster helper - Export new items from layout module Tests: All 11 acceptance criteria tests pass - Spans baselines 100, 100.5, 105 with median 12: one line - Spans baselines 100, 110 with median 12: two lines - Superscript stays on same line as base text - Empty input produces empty output - Threshold is 0.5 * median_font_size (not hardcoded) Closes: pdftract-6bwq4
47 lines
2.5 KiB
Markdown
47 lines
2.5 KiB
Markdown
# pdftract-6bwq4: Baseline clustering algorithm implementation
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## Summary
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Implemented `cluster_spans_into_lines` function for Phase 4.2 line formation. The function groups spans into lines by baseline proximity using a threshold of `0.5 * median_font_size`.
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## Changes Made
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### crates/pdftract-core/src/layout/line.rs
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- Added `HasFontSize` trait for types that have font_size
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- Implemented `cluster_spans_into_lines<S>(spans: Vec<S>, median_font_size: f32) -> Vec<Line<S>>`
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- Computes baseline for each span using existing `compute_baseline` function
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- Sorts spans by baseline ASC
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- Sweeps through spans, clustering those within threshold (0.5 * median_font_size)
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- Emits one `Line` per cluster
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- Sorts spans by x0 within each line (left-to-right)
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- Computes line metadata: union bbox, average baseline, median font size
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- Added `finalize_line_cluster` helper function
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### crates/pdftract-core/src/layout/mod.rs
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- Exported `HasFontSize` trait and `cluster_spans_into_lines` function
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## Tests Added
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All acceptance criteria tests pass:
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1. `test_cluster_spans_baselines_100_100_5_105_median_12_one_line` - Spans baselines 100, 100.5, 105 with median 12 (threshold 6): all one line. PASS
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2. `test_cluster_spans_baselines_100_110_median_12_two_lines` - Same with 100, 110: 2 lines (delta 10 > 6). PASS
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3. `test_cluster_spans_superscript_stays_on_same_line` - Superscript at 105, line baseline 100, font 12: SAME line. PASS
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4. `test_cluster_spans_empty_input_empty_output` - Empty input: empty output. PASS
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5. `test_cluster_spans_threshold_is_0_5_times_median_font_size` - INV: threshold = 0.5 * median_font_size; do NOT hardcode. PASS
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6. `test_cluster_spans_sorted_by_x0_within_line` - Spans within a line sorted by x0. PASS
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7. `test_cluster_spans_two_column_at_same_y_one_line` - Two-column at same y: cluster into one Line. PASS
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8. `test_cluster_spans_union_bbox_computed_correctly` - Union bbox computed correctly. PASS
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9. `test_cluster_spans_baseline_computed_as_average` - Baseline is average of member span baselines. PASS
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10. `test_cluster_spans_median_font_size_computed` - Median font size computed from line spans. PASS
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11. `test_cluster_spans_single_span_single_line` - Single span produces single line. PASS
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## Verification
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- `cargo test -p pdftract-core --lib layout::line`: 32 tests passed
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- `cargo check -p pdftract-core --lib`: Compiles successfully
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- `cargo fmt -p pdftract-core`: Code formatted
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## References
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- Plan: Phase 4.2 Algorithm step 2 (line 1667)
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- Bead: pdftract-6bwq4
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