751dae606c
The /Differences overlay handler was already fully implemented. All 28 encoding tests pass. Acceptance criteria: - [PASS] [ 39 /quotesingle 96 /grave ] parses correctly - [PASS] [ 39 /a /b /c ] consecutive assignment works - [PASS] Overlay precedence over base encoding - [PASS] Unknown glyph names returned for L3/L4 fallback
74 lines
2.5 KiB
Markdown
74 lines
2.5 KiB
Markdown
# pdftract-5nbp: /Differences overlay handler verification
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## Summary
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The `/Differences` overlay handler for font encodings was already fully implemented in `crates/pdftract-core/src/font/encoding.rs`. No code changes were required.
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## Implementation details
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### `DifferencesOverlay` struct (lines 128-234)
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- `entries: Vec<(u8, Arc<str>)>` - sparse list of (code, glyph_name) overrides
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- `parse()` method walks the array linearly, maintaining a cursor that resets on each integer
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- `get()` method performs linear search (fine for <32 entries)
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### `FontEncoding` struct (lines 236-364)
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- Combines base encoding with differences overlay
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- `parse_from_font()` handles all encoding indirection patterns
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- `glyph_name_for()` lookup order: differences first, base second
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## Acceptance criteria verification
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### PASS: `[ 39 /quotesingle 96 /grave ]` parsing
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Test: `test_differences_overlay_parse_simple`
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- Code 39 → "quotesingle"
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- Code 96 → "grave"
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### PASS: `[ 39 /a /b /c ]` consecutive assignment
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Test: `test_differences_overlay_parse_consecutive`
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- Code 39 → "a"
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- Code 40 → "b"
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- Code 41 → "c"
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### PASS: Overlay precedence over base encoding
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Tests: `test_font_encoding_glyph_name_with_differences`, `test_font_encoding_lookup_order`
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- Overlaid codes return the override
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- Non-overlaid codes return the base encoding entry
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### PASS: Unknown glyph names returned as-is
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Test: `test_font_encoding_unknown_glyph_name`
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- Arbitrary glyph names not in AGL are returned (not None)
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- Resolver can attempt L3/L4 fallback with the name
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## Critical considerations
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### PASS: Multiple Differences blocks
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Test: `test_differences_overlay_parse_multiple_blocks`
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- Handles `[ 39 /a /b 100 /x /y ]` correctly
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### PASS: Out-of-range code clamping with diagnostics
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Tests: `test_differences_overlay_out_of_range_positive`, `test_differences_overlay_out_of_range_negative`
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- Codes < 0 clamped to 0
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- Codes > 255 clamped to 255
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- Emits `DiagCode::FontEncodingDifferenceOutOfRange` diagnostic
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### PASS: Implicit base encoding
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- `FontEncoding::parse_from_font()` handles `/Differences` without `/BaseEncoding`
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- Falls back to `default_base` parameter (Standard for Type1, built-in for TrueType)
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## Test results
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```
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running 28 tests
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test result: ok. 28 passed; 0 failed; 0 ignored
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```
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## Files
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- `crates/pdftract-core/src/font/encoding.rs` - Full implementation
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- `crates/pdftract-core/src/font/mod.rs` - Re-exports `FontEncoding`, `DifferencesOverlay`, `NamedEncoding`
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## No code changes required
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The implementation was already complete and tested. This bead verified existing functionality.
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