pdftract/notes/pdftract-cv4.md

Verification Note: pdftract-cv4

Task: Type 0 composite font + descendant CIDFont loader

Date: 2026-05-23

Summary

Implemented Type0Font::load() following /DescendantFonts to the CIDFont dictionary, classifying the descendant as CIDFontType0 or CIDFontType2, reading /DW (default width), parsing /W array (two formats), and producing Type0Font containing both parent and descendant.

Acceptance Criteria Results

PASS

1. Type0 font with CIDFontType2 descendant loads; widths from [10 [500 600]] resolve as CID 10 -> 500, CID 11 -> 600

   • Test: test_acceptance_type0_with_cidfonttype2 passes
   • Implementation: parse_w_array() handles per-CID form [c [w1 w2 ...]]

2. Range form [100 200 800] resolves: CIDs 100..=200 all -> 800

   • Test: test_acceptance_range_form passes
   • Implementation: parse_w_array() handles range form [cfirst clast w]

3. Missing CID falls back to DW (default 1000)

   • Test: test_acceptance_missing_cid_fallback passes
   • Implementation: get_width() returns widths.get(&cid).copied().unwrap_or(default_width)

4. CIDFontType0 (CFF) descendant: ttf-parser CFF entrypoint used

   • Test: test_load_type0_font_cidfonttype0 passes
   • Implementation: load_font_program() delegates to EmbeddedFont::load() which uses OpenTypeMetrics::from_data() - ttf-parser handles both TrueType and CFF

WARN

None

FAIL

None

Files Modified

• crates/pdftract-core/src/font/mod.rs: Added pub mod type0; and re-exports
• crates/pdftract-core/src/font/type0.rs: New file (1035 lines) implementing:
  • Type0Font::load() - main entry point
  • parse_w_array() - parses /W array in both formats
  • load_cid_to_gid_map() - loads CIDToGIDMap for CIDFontType2
  • load_font_program() - loads embedded font from FontDescriptor
  • CIDToGIDMap enum with Identity and Custom variants
  • DescendantCIDFont struct with metrics and font program
  • 23 unit tests (all passing)

Test Results

cargo test -p pdftract-core --lib font::type0
running 23 tests
test result: ok. 23 passed; 0 failed

All 75 font module tests pass.

Implementation Notes

1. /W Array Parsing: Token-by-token scan that switches between per-CID and range formats based on whether the second element is an array or integer
2. Sparse Storage: Uses BTreeMap<u32, u16> for widths to handle arbitrary CID values (e.g., 50000+)
3. CIDToGIDMap: Supports Identity (GID == CID) and Custom (2-byte big-endian stream) variants
4. Font Program: Loaded via EmbeddedFont::load() which handles both CFF and TrueType via ttf-parser
5. Graceful Degradation: Missing FontDescriptor or font program emits diagnostic but doesn't fail the load

Git Commit

commit c12148a
feat(pdftract-cv4): Type 0 composite font + descendant CIDFont loader