pdftract/notes/pdftract-3qz.md

pdftract-3qz: Phase 2.1 Font Type Detection (coordinator)

Summary

Coordinator for sub-phase 2.1: Font Type Detection. All 5 child beads completed successfully, delivering a comprehensive font module that can classify, load, and provide metrics for all PDF font types.

Children Completed

Bead ID	Title	Commit	Verification Note
pdftract-3uq	Font subtype classifier and BaseFont prefix stripper	46c515e	notes/pdftract-3uq.md
pdftract-juc	Standard 14 font registry with hardcoded metrics	7429a67	(included below)
pdftract-6ah	Embedded font program loader (ttf-parser/owned_ttf_parser)	ffaaf69	notes/pdftract-6ah.md
pdftract-cv4	Type 0 composite font + descendant CIDFont loader	5e2390f	notes/pdftract-cv4.md
pdftract-5sh	CIDToGIDMap resolver (Identity and stream forms)	03aa4da	notes/pdftract-5sh.md

Acceptance Criteria Status

Criterion	Status
All children closed	PASS - All 5 child beads closed
Classifier returns one of {Type1, Type1Std14, TrueType, Type0, CIDFontType0, CIDFontType2, Type3, OpenTypeCFF}	PASS
Subset prefix ABCDEF+Times-Roman strips to Times-Roman for Std-14 lookup	PASS
CIDFontType2 with /CIDToGIDMap /Identity: GID == CID	PASS
CIDFontType2 with stream CIDToGIDMap: 2-byte big-endian decode verified	PASS
Module unit tests in crates/pdftract-core/src/font/ pass	PASS - 77 tests
No unwrap/expect on resource dict access	PASS - uses .and_then() and defaults

Module Structure

crates/pdftract-core/src/font/
├── mod.rs        # FontKind enum, classify_font(), strip_subset_prefix()
├── std14.rs      # Standard 14 font metrics registry (build.rs generated)
├── embedded.rs   # EmbeddedFont, FontMetrics, OpenTypeMetrics, EmptyFontMetrics
└── type0.rs      # Type0Font, DescendantCIDFont, CIDToGIDMap, /W array parsing

Test Results

test result: ok. 77 passed; 0 failed; 0 ignored

All font module tests pass, covering:

• Font classification (Type1, Type1Std14, TrueType, Type0, CIDFontType0, CIDFontType2, Type3, OpenTypeCFF)
• Subset prefix stripping (valid, invalid, edge cases)
• Standard 14 font detection
• Type0 composite font loading
• CIDToGIDMap resolution (Identity and stream forms)
• /W array parsing (per-CID and range forms)
• Embedded font program loading (TrueType, OpenType CFF)

Child Bead Summaries

pdftract-3uq: Font subtype classifier and BaseFont prefix stripper

• Implemented FontKind enum with all 8 PDF font types
• strip_subset_prefix() - validates exactly 6 ASCII uppercase + +
• classify_font() - reads /Subtype, /BaseFont, descendant CIDFont, FontDescriptor
• 21 unit tests covering all branches

pdftract-juc: Standard 14 font registry with hardcoded metrics

• build.rs generates compile-time metrics from AFM-derived JSON
• Std14Metrics struct with widths, ascent, descent, italic_angle, font_bbox
• get_std14_metrics() lookup by canonical name (post-prefix-strip)
• Symbol/ZapfDingbats use distinct encodings (SymbolEncoding, ZapfDingbatsEncoding)
• Binary footprint: ~20 KB generated source, ~8 KB data (well under 60 KB limit)

pdftract-6ah: Embedded font program loader

• EmbeddedFont wrapping owned_ttf_parser::OwnedFace
• FontMetrics trait with glyph_id_for(), advance(), bbox()
• EmptyFontMetrics fallback for corrupt/missing font programs
• Graceful handling of subset fonts (unmapped chars return None)
• Diagnostic FONT_PARSE_FAILED for corrupt programs

pdftract-cv4: Type 0 composite font + descendant CIDFont loader

• Type0Font with descendant DescendantCIDFont
• /DW default width parsing (default 1000)
• /W array parsing (per-CID [c [w1 w2 ...]] and range [cfirst clast w])
• Sparse BTreeMap<u32, u16> storage for CID widths
• CIDFontType0 (CFF) vs CIDFontType2 (TrueType) detection

pdftract-5sh: CIDToGIDMap resolver

• CidToGidMap::{Identity, Array(Box<[u16]>)} enum
• Identity short-circuit (zero allocation, GID == CID)
• Stream form: 2-byte big-endian u16 array indexed by CID
• Diagnostic CIDTOGIDMAP_TRUNCATED for odd-byte-count input
• Out-of-range CID returns GID 0 (notdef glyph)

Integration Points

This module delivers the Font value needed by:

• Phase 2.2: Encoding resolution (ToUnicode, differences, AGL fallback)
• Phase 2.3: CJK CMap parsing and CID-to-Unicode mapping
• Phase 2.4: Type3 font content stream execution
• Phase 3: Content stream execution (Tj, TJ, BT/ET operators)

Files Modified/Created

Created:

• crates/pdftract-core/src/font/mod.rs
• crates/pdftract-core/src/font/std14.rs
• crates/pdftract-core/src/font/embedded.rs
• crates/pdftract-core/src/font/type0.rs
• crates/pdftract-core/build.rs
• crates/pdftract-core/build/std14-metrics.json
• crates/pdftract-core/build/generate_std14_metrics.py
• crates/pdftract-core/build/fix_std14_weights.py

Modified:

• crates/pdftract-core/src/lib.rs - added pub mod font;
• crates/pdftract-core/src/diagnostics.rs - added FONT_PARSE_FAILED, CIDTOGIDMAP_TRUNCATED
• .gitignore - added !/crates/pdftract-core/build/ exceptions

Commits Referenced

• 46c515e feat(pdftract-3uq): add font type classifier and subset prefix stripper
• 7429a67 feat(pdftract-juc): implement Standard 14 font metrics registry
• ffaaf69 feat(pdftract-6ah): implement embedded font program loader
• 5e2390f feat(pdftract-cv4): Type 0 composite font + descendant CIDFont loader
• 03aa4da feat(pdftract-5sh): CIDToGIDMap resolver for CIDFontType2
• 075de55 docs(pdftract-cv4): add verification note
• b7392f1 docs(pdftract-6ah): add verification note

Notes

• All child beads have verification notes in notes/ directory
• Type3 font /CharProcs execution deferred to Phase 2.4 (as planned)
• OpenType CFF uses same owned_ttf_parser entrypoint as TrueType (CFF support via opentype-layout feature)
• The classifier handles indirect references gracefully (returns default, does not crash)
• Standard 14 fonts may have embedded font programs; registry serves as fallback

Ready for Next Phase

Phase 2.1 is complete. The font module is ready for:

• Phase 2.2: Encoding resolution (ToUnicode, differences, AGL)
• Phase 2.3: CJK CMap parsing
• Phase 2.4: Type3 content stream execution