2cf02c6b2b
- 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
85 lines
2.7 KiB
Markdown
85 lines
2.7 KiB
Markdown
# pdftract-sdx9z: Line struct + baseline computation per span
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## Summary
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Implemented Phase 4.2 line formation infrastructure:
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- Created `layout/line.rs` module with `Line` struct and `compute_baseline` function
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- Added `LineDirection` enum with serde support (Ltr, Rtl, Mixed)
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- Added helper functions for bbox operations
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## Files Modified
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- `crates/pdftract-core/src/layout/line.rs` (new): 247 lines
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- `crates/pdftract-core/src/layout/mod.rs`: Exported new line module
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## Acceptance Criteria Status
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### PASS
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- ✅ `compute_baseline([0, 100, 50, 110])` returns `102.0` (height 10, baseline = 100 + 10*0.2)
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- ✅ `compute_baseline([0, 100, 50, 100])` returns `100.0` (zero-height case)
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- ✅ `union_bboxes` correctly computes union of 3 span bboxes
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- ✅ `LineDirection` serde roundtrips to/from "ltr"/"rtl"/"mixed"
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- ✅ All 11 unit tests pass in `layout::line::tests`
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## Implementation Details
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### `Line` struct
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```rust
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pub struct Line<S> {
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pub spans: Vec<S>,
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pub bbox: [f32; 4], // Union of span bboxes
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pub baseline: f32, // Average of member span baselines
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pub direction: LineDirection,
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pub page_relative_y: f32, // (page_height - bbox[3]) / page_height
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}
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```
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### `compute_baseline` function
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```rust
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pub fn compute_baseline(bbox: &[f32; 4]) -> f32 {
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let height = bbox[3] - bbox[1];
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bbox[1] + height * 0.2 // 0.2 = descender approximation
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}
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```
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### `LineDirection` enum
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```rust
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pub enum LineDirection {
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Ltr, // Left-to-right
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Rtl, // Right-to-left
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Mixed, // Bidirectional
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}
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```
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## Plan References
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- Phase 4.2 baseline (lines 1665-1666): `y0 + (bbox_height * 0.2)` formula
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- RTL detection (line 1686): `unicode-bidi` crate for future bidi character category lookup
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## Testing
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All tests pass:
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```
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running 38 tests
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test layout::line::tests::test_compute_baseline_normal_span ... ok
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test layout::line::tests::test_compute_baseline_zero_height ... ok
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test layout::line::tests::test_compute_baseline_large_height ... ok
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test layout::line::tests::test_line_direction_serdes_ltr ... ok
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test layout::line::tests::test_line_direction_serdes_rtl ... ok
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test layout::line::tests::test_line_direction_serdes_mixed ... ok
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test layout::line::tests::test_line_accessors ... ok
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test layout::line::tests::test_union_bboxes_single ... ok
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test layout::line::tests::test_union_bboxes_multiple ... ok
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test layout::line::tests::test_union_bboxes_empty ... ok
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test layout::line::tests::test_union_bboxes_nested ... ok
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test layout::line::tests::test_union_bboxes_disjoint ... ok
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test result: ok. 38 passed; 0 failed
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```
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## Next Steps
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Future beads will implement:
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- Actual line clustering algorithm (baseline proximity grouping)
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- RTL detection using `unicode-bidi` crate
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- Span-to-line aggregation with reading order sorting
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