jedarden 0371815f9b docs(pdftract-1l6wn): verify BMC/BDC/EMC operators already implemented

This bead asked for implementation of BMC/BDC/EMC marked-content
operators and MarkedContentStack, but these were already fully
implemented in the codebase with comprehensive test coverage.

Verification note documents:
- MarkedContentStack in marked_content_stack.rs
- BMC/BDC/EMC parsers in marked_content_operators.rs
- Integration into execute_with_do in content_stream.rs
- All 6 acceptance criteria covered by passing tests
- 57 marked-content tests all passing

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

2026-05-28 01:29:07 -04:00

3.5 KiB

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Verification Note: pdftract-1l6wn - BMC/BDC/EMC Operator Parsers

Bead Description

Implement the 3 marked-content operators: BMC /Tag, BDC /Tag <<props>> or BDC /Tag /PropName, and EMC. Maintain a marked_content_stack: Vec<MarkedContentFrame> on the page executor.

Status: ALREADY IMPLEMENTED ✅

The BMC/BDC/EMC operator parsers and MarkedContentStack are already fully implemented in the codebase.

Implementation Location

1. MarkedContentStack

File: crates/pdftract-core/src/parser/marked_content_stack.rs
Structure: MarkedContentStack with Vec<MarkedContentFrame>
Depth limit: 64 (enforced with MAX_MC_DEPTH constant)
Diagnostics: EmcWithoutBmc, MarkedContentDepthExceeded

2. MarkedContent Operators

File: crates/pdftract-core/src/parser/marked_content_operators.rs
Functions:
- parse_bmc(stack, tag) - BMC operator
- parse_bdc(stack, tag, props, resources, default_off_ocgs, diagnostics) - BDC operator
- parse_emc(stack) - EMC operator

3. Integration into Content Stream

File: crates/pdftract-core/src/content_stream.rs
Function: execute_with_do (lines 875-965)
The marked-content stack is instantiated and BMC/BDC/EMC operators are wired into the main content stream execution loop.

Acceptance Criteria Verification

All acceptance criteria are covered by passing tests:

Criterion	Test Name	Status
BMC /Span EMC: stack push then pop, balanced	`test_push_bmc` + `test_pop_emc`	✅ PASS
BDC /Span <</MCID 42>> EMC: frame with mcid=Some(42)	`test_parse_bdc_with_inline_dict_mcid`	✅ PASS
BDC /P /MyProps EMC with resolved /MCID 7	`test_parse_bdc_with_property_name_found`	✅ PASS
BDC /P /UnknownProps EMC: diagnostic for unknown prop name	`test_parse_bdc_with_property_name_not_found`	✅ PASS
EMC without BMC: EMC_WITHOUT_BMC diagnostic, no panic	`test_pop_emc_underflow`	✅ PASS
64 nested BMC: succeeds; 65th emits depth diagnostic	`test_stack_depth_limit`	✅ PASS

Test Results

cargo test -p pdftract-core --lib 2>&1 | grep -E "test.*marked_content|test.*parse_bmc|test.*parse_bdc|test.*parse_emc"

All 57 marked-content related tests passed:

18 tests in parser::marked_content_stack::tests
30 tests in parser::marked_content_operators::tests
9 tests in other modules using marked-content features

Key Implementation Details

INV: Marked Content Stack Independence

The marked-content stack is independent of the graphics state stack. The q/Q operators do NOT affect it (per PDF spec section 14.5). This is correctly implemented in content_stream.rs where the two stacks are managed separately.

Property Name Resolution

ResourceDict::lookup_properties() is used to resolve property names in BDC operators. The implementation handles both inline dictionaries and property resource names.

MCID Extraction

Supports Integer and Real (whole number) MCID values
Negative MCID values are rejected per spec ("non-negative integer")
Missing /MCID results in mcid=None (valid for BMC or BDC without properties)

OCG Hidden Flag (bead pdftract-1q19p)

The is_hidden flag on MarkedContentFrame tracks content within default-OFF Optional Content Groups. This is integrated into the BDC parser for /OC tags.

Conclusion

No implementation work was required for this bead. The BMC/BDC/EMC operator parsers and MarkedContentStack were already fully implemented with comprehensive test coverage. All acceptance criteria are met.

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