pdftract/notes/pdftract-1uj5.md

Verification Note: pdftract-1uj5

Summary

Implemented resolve_type3() function for Type 3 font encoding resolution using the Type 3-specific fallback chain (L1: ToUnicode, L2: AGL, skip L3, L4: shape recognition).

Implementation

Files Modified

1. crates/pdftract-core/src/font/shape.rs

   • Added ShapeEntry struct for pHash + char pairs
   • Added ShapeMatch struct for lookup results with Hamming distance
   • Added lookup_shape() function for shape database lookup (stub returning empty DB)
   • Added ShapeMatch::is_acceptable() method for threshold check (≤8 bits)

2. crates/pdftract-core/src/font/resolver.rs

   • Added imports: lookup_shape, phash_glyph, Type3Font, rasterize_type3_glyph
   • Added resolve_type3() function implementing Type 3-specific chain:
     • L1: ToUnicode CMap lookup (reuses resolve_level1)
     • L2: Encoding + AGL lookup (reuses resolve_level2)
     • L3: SKIPPED with comment for Type 3 fonts
     • L4: Shape recognition via resolve_type3_level4
   • Added resolve_type3_level4() function:
     • Gets glyph name from encoding
     • Rasterizes glyph via rasterize_type3_glyph
     • Computes pHash via phash_glyph
     • Looks up in shape DB via lookup_shape
     • Returns ResolvedGlyph with UnicodeSource::ShapeMatch and confidence 0.7
   • Added 3 tests for Type 3 resolution

3. crates/pdftract-core/src/font/mod.rs

   • Updated exports to include resolve_type3, lookup_shape, ShapeEntry, ShapeMatch

4. crates/pdftract-core/src/font/type3.rs

   • Fixed overflow bug in load_widths(): cast to usize before arithmetic to avoid overflow when last_char=255, first_char=0

Acceptance Criteria Status

Criteria	Status	Notes
Type 3 with ToUnicode 0x41 -> 'A' (1.0)	PASS	Test: test_resolve_type3_with_tounicode
Type 3 with glyph name 'A' via Encoding (0.9)	PASS	Test: test_resolve_type3_with_agl
Type 3 with arbitrary name + shape match (0.7)	WARN	Shape DB is stub (empty) - infrastructure ready, awaits build/glyph-shapes.json
Type 3 with arbitrary name + no match (0.0) + diag	PASS	Test: test_resolve_type3_fallback_to_fffd

Test Results

cargo test --lib -p pdftract-core -- resolver::tests::test_resolve_type3
# All 3 tests passed

cargo test --lib -p pdftract-core -- font::shape::
# 16 tests passed

Technical Notes

1. Shape DB Stub: The lookup_shape() function returns an empty database slice. The actual shape database generation from build/glyph-shapes.json is a separate bead (Phase 2.5).

2. L3 Skip: Explicit comment added: // Type 3 fonts have no embedded program; L3 fingerprinting not applicable

3. Diagnostic Codes: Uses existing DiagCode::FontGlyphUnmapped for Type 3 failures. The bead description mentioned TYPE3_GLYPH_UNMAPPED but the existing code is sufficient.

4. Caching: Per bead guidance, caching is shared with the Phase 2.2 resolver via the polymorphic ResolverCache key. No parallel Type 3 cache was created.

5. Branching on Font Kind: The bead description mentions Branch on font.kind() but the current architecture has Type3Font as a separate struct with its own encoding field. Callers check font kind and dispatch to resolve_type3() directly for Type 3 fonts.

Commits

• fix(pdftract-1uj5): fix overflow in Type3Font::load_widths
• feat(pdftract-1uj5): implement resolve_type3 for Type 3 font encoding resolution
• feat(pdftract-1uj5): add shape lookup stub and ShapeMatch types

Next Steps

The shape database population (Phase 2.5) will need to:

1. Generate build/glyph-shapes.json from offline glyph rendering
2. Update shape_database() in shape.rs to return the generated data
3. Re-test acceptance criterion #3 with actual shape matches