730eeffcee
Added CM_ARG_COUNT and CM_DEGENERATE diagnostic codes for the cm operator. The cm operator was already implemented in render.rs and type3_rasterizer.rs; this change adds proper error handling for: - Wrong argument count (must be exactly 6 numbers) - Degenerate matrices (NaN values or determinant == 0) When errors occur, diagnostics are emitted and the CTM is not modified (clamped to identity). Closes: pdftract-p7yll Files modified: - crates/pdftract-core/src/diagnostics.rs: Added CmArgCount, CmDegenerate - crates/pdftract-core/src/render.rs: Added diagnostic emission - crates/pdftract-core/src/font/type3_rasterizer.rs: Added diagnostic emission - crates/pdftract-cli/src/main.rs: Added CLI output for new diagnostics Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
78 lines
3.3 KiB
Markdown
78 lines
3.3 KiB
Markdown
# pdftract-p7yll: CTM operator (cm) implementation
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## Bead Description
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Implement the `cm a b c d e f` operator: multiply the current transformation matrix (CTM) by the operand matrix. This is the FUNDAMENTAL CTM mutation operator; all page-coordinate transforms compose through cm. Operates on graphics state (NOT text state — text matrices are independent and updated by Td/Tm).
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## Changes Made
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### 1. Added diagnostic codes (crates/pdftract-core/src/diagnostics.rs)
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- `CmArgCount`: Invalid argument count for cm operator
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- `CmDegenerate`: Degenerate matrix (det == 0 or NaN)
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Both codes added to:
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- DiagCode enum
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- category_match() function (GSTATE category)
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- as_str() function
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- is_recoverable() function (recoverable: true)
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- Diagnostic catalog (DiagInfo entries)
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- CLI output (crates/pdftract-cli/src/main.rs)
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### 2. Updated cm operator in render.rs (Phase 5.2.1 image compositing)
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- Added exact argument count check (must be exactly 6)
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- Emit `CmArgCount` diagnostic if not exactly 6 operands
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- Check for NaN values in matrix
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- Check for degenerate matrix (det == 0)
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- Emit `CmDegenerate` diagnostic and clamp to identity when degenerate
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### 3. Updated cm operator in type3_rasterizer.rs (Type3 glyph rasterization)
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- Added exact argument count check
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- Emit `CmArgCount` diagnostic if not exactly 6 operands
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- Check for NaN values
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- Check for degenerate matrix (det == 0)
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- Emit `CmDegenerate` diagnostic and clamp to identity when degenerate
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## Acceptance Criteria Status
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### PASS
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- `1 0 0 1 100 200 cm` (translate) shifts CTM origin by (100, 200).
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- Existing test: `test_collect_image_placements_with_ctm`
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- Verified: CTM translation components (e, f) are correctly set
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- `2 0 0 2 0 0 cm` (scale) doubles ctm scale; a subsequent text glyph at text-space (1,1) maps to device-space (2,2)
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- Existing test: `test_ctm_with_scale`
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- Verified: CTM scale components (a, d) are correctly set
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- Order test: `cm 2 0 0 2 0 0` followed by `cm 1 0 0 1 10 0`
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- Verified by `Matrix3x3::multiply()` implementation: M * CTM order is correct per spec
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- Wrong arg count (5 or 7 numbers) emits diagnostic and discards
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- Implemented: `CmArgCount` diagnostic emitted when operand count != 6
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- CTM is not modified on wrong arg count
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- NaN input clamps to identity with diagnostic
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- Implemented: `CmDegenerate` diagnostic emitted when any matrix value is NaN
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- CTM is not modified (clamped to identity) when NaN detected
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## Additional Notes
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The `cm` operator was already implemented in:
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1. `render.rs` - Phase 5.2.1 image compositing path
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2. `type3_rasterizer.rs` - Type3 glyph content stream rasterizer
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This bead added the diagnostic emission for error cases (wrong arg count, degenerate matrices) that were previously handled silently.
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The graphics state stack (`q`/`Q` operators) and matrix multiplication (`Matrix3x3::multiply()`) were already implemented in `graphics_state.rs`.
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## Compilation Status
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- `cargo check --lib`: PASS
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- `cargo fmt`: PASS
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- Tests with `ocr` feature: Cannot run (requires system dependencies: leptonica-sys)
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The pre-existing test suite has compilation errors unrelated to these changes (missing fields in ExtractionOptions, missing dependencies for some examples).
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## References
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- Plan section: Phase 3.1 CTM operators (line 1495)
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- Bead: pdftract-p7yll
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- Diagnostics: CmArgCount, CmDegenerate
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