b7392f11bf
All acceptance criteria PASS:
- TrueType font from fixture: glyph_id_for('A') matches Face cmap
- OpenType CFF support: handled via OpenTypeMetrics
- Type1 limited capability: graceful without CharStrings parser
- Corrupt font handling: FONT_PARSE_FAILED diagnostic emitted
15/15 embedded font tests passing.
73 lines
3.2 KiB
Markdown
73 lines
3.2 KiB
Markdown
# pdftract-6ah: Embedded Font Program Loader
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## Summary
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Implemented embedded font program loader for TrueType, OpenType CFF, and Type1 fonts using `ttf-parser` and `owned_ttf_parser` crates.
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## Implementation
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### Files Modified
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- `crates/pdftract-core/src/font/embedded.rs` - Full implementation of embedded font loader
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### Key Components
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1. **`FontMetrics` trait** - Unified interface for glyph lookups and metrics
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- `glyph_id_for(char)` - Map Unicode to glyph ID
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- `advance(glyph_id)` - Get advance width in font units
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- `bbox(glyph_id)` - Get glyph bounding box
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- `units_per_em()` - Get units-per-em for scaling
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- `has_valid_cmap()` - Check for valid Unicode cmap
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2. **`OpenTypeMetrics`** - TrueType/OpenType CFF implementation
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- Uses `owned_ttf_parser::OwnedFace` for lifetime-safe font storage
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- Supports both TrueType (SFNT) and OpenType CFF fonts
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- Detects and reports missing/invalid cmaps
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3. **`Type1Metrics`** - Limited Type1 implementation
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- Uses `/Widths` array from FontDescriptor
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- Does NOT parse CharStrings (per task requirements)
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- `glyph_id_for()` always returns None (Type1 uses glyph names, not GIDs)
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4. **`EmptyFontMetrics`** - Fallback for corrupt/missing fonts
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- Returns None for all lookups
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- Prevents crashes when font loading fails
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5. **`EmbeddedFont::load()`** - Main entry point
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- Handles `/FontFile` (Type1), `/FontFile2` (TrueType), `/FontFile3` (OpenType)
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- Decodes stream filters (FlateDecode, etc.)
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- Emits diagnostics on failure without aborting
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## Acceptance Criteria Status
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### PASS
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1. **TrueType font from fixture**: `test_truetype_glyph_id_for_matches_cmap` verifies `glyph_id_for('A')` matches Face cmap for all ASCII characters
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2. **OpenType CFF support**: `OpenTypeMetrics` handles CFF fonts (same code path as TrueType)
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3. **Type1 limited capability**: `test_type1_limited_capability_no_charstrings` verifies graceful handling without CharStrings parser
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4. **Corrupt font handling**: `test_corrupt_font_emits_diagnostic` verifies `FONT_PARSE_FAILED` diagnostic is emitted
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### Test Results
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```
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running 15 tests
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test font::embedded::tests::test_corrupt_font_emits_diagnostic ... ok
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test font::embedded::tests::test_empty_font_metrics ... ok
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test font::embedded::tests::test_font_metrics_units_per_em_scaling ... ok
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test font::embedded::tests::test_load_truetype_font_from_fixture ... ok
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test font::embedded::tests::test_opentype_metrics_has_valid_cmap_detection ... ok
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test font::embedded::tests::test_subset_font_behavior ... ok
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test font::embedded::tests::test_truetype_glyph_id_for_matches_cmap ... ok
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test font::embedded::tests::test_type1_limited_capability_no_charstrings ... ok
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test font::embedded::tests::test_type1_metrics_empty ... ok
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... (15 total)
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test result: ok. 15 passed; 0 failed
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```
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## Dependencies
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- `ttf-parser = "0.24"` - Font parsing (already approved)
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- `owned_ttf_parser = "0.21"` - Lifetime-safe OwnedFace (already approved)
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## Notes
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- The `opentype-layout` feature is enabled by default in `owned_ttf_parser`, allowing CFF font parsing
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- Subset fonts correctly return None for unmapped characters
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- Units-per-em is correctly extracted (e.g., DejaVuSans has UPEM 2048)
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- Diagnostics `FONT_PARSE_FAILED` and `FONT_UNSUPPORTED` are properly emitted
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