fix: improve PDF layout generation for Direct track
Key fixes: - Skip large vector_graphics charts (>50% page coverage) that cover text - Fix font fallback to use NotoSansSC for CJK support instead of Helvetica - Improve translated table rendering with dynamic font sizing - Add merged cell (row_span/col_span) support for reflow tables - Skip text elements inside table bboxes to avoid duplication Archive openspec proposal: fix-pdf-table-rendering 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>
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# Design: Fix PDF Table Rendering
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## Context
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OCR track produces tables with:
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- `cell_boxes`: Accurate pixel coordinates for each cell border
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- `cells`: Content with row/col indices and row_span/col_span
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- `embedded_images`: Images within table cells
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Current implementations fail to use these correctly:
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- **Reflow PDF**: Ignores merged cells, misaligns content
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- **Translated Layout PDF**: Creates new Table object instead of using cell_boxes
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## Goals / Non-Goals
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**Goals:**
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- Translated Layout PDF tables match untranslated Layout PDF quality
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- Reflow PDF tables are readable and correctly structured
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- Embedded images appear in both formats
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**Non-Goals:**
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- Perfect pixel-level replication of original table styling
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- Support for complex nested tables
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## Decisions
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### Decision 1: Translated Layout PDF uses Layered Rendering
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**What**: Draw cell borders using `cell_boxes`, then render translated text in each cell separately
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**Why**: This matches the working approach in `_draw_table_with_cell_boxes()` for untranslated PDFs
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```python
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# Step 1: Draw borders using cell_boxes
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for cell_box in cell_boxes:
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pdf_canvas.rect(x, y, width, height)
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# Step 2: Render text for each cell
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for cell in cells:
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cell_bbox = find_matching_cell_box(cell, cell_boxes)
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draw_text_in_bbox(translated_content, cell_bbox)
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```
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### Decision 2: Reflow PDF uses ReportLab SPAN for merged cells
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**What**: Apply `('SPAN', (col1, row1), (col2, row2))` style for merged cells
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**Why**: ReportLab's Table natively supports merged cells via TableStyle
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```python
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# Build span commands from cell data
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for cell in cells:
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if cell.row_span > 1 or cell.col_span > 1:
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spans.append(('SPAN',
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(cell.col, cell.row),
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(cell.col + cell.col_span - 1, cell.row + cell.row_span - 1)))
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```
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### Decision 3: Column widths from cell_boxes ratio
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**What**: Calculate column widths proportionally from cell_boxes
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**Why**: Preserves original table structure in reflow mode
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## Risks / Trade-offs
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| Risk | Mitigation |
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|------|------------|
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| Text overflow in translated cells | Shrink font (min 8pt) or truncate with ellipsis |
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| cell_boxes not matching cells count | Fall back to equal-width columns |
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| Complex merged cell patterns | Handle simple spans, skip complex patterns |
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## Open Questions
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- Should reflow PDF preserve exact column width ratios or allow ReportLab auto-sizing?
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- How to handle cells with both text and images?
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# Change: Fix PDF Table Rendering Issues
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## Why
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OCR track PDF exports have significant table rendering problems:
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1. **Reflow PDF** (both translated and untranslated): Tables are misaligned due to missing row_span/col_span support
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2. **Translated Layout PDF**: Table borders disappear and text overlaps because it doesn't use the accurate `cell_boxes` positioning
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## What Changes
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- **Translated Layout PDF**: Adopt layered rendering approach (borders + text separately) using `cell_boxes` from metadata
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- **Reflow PDF Tables**: Fix cell extraction and add basic merged cell support
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- Ensure embedded images in tables are rendered correctly in all PDF formats
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## Impact
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- Affected specs: result-export
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- Affected code:
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- `backend/app/services/pdf_generator_service.py`
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- `_draw_translated_table()` - needs complete rewrite
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- `_create_reflow_table()` - needs merged cell support
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## MODIFIED Requirements
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### Requirement: Translated Layout PDF Generation
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The system SHALL generate layout-preserving PDFs with translated content that maintain accurate table structure.
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#### Scenario: Table with accurate borders
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- **GIVEN** an OCR result with tables containing `cell_boxes` metadata
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- **WHEN** generating translated layout PDF
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- **THEN** table cell borders SHALL be drawn at positions matching `cell_boxes`
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- **AND** translated text SHALL be rendered within each cell's bounding box
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#### Scenario: Text overflow handling
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- **GIVEN** translated text longer than original text
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- **WHEN** text exceeds cell bounding box
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- **THEN** the system SHALL reduce font size (minimum 8pt) to fit content
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- **OR** truncate with ellipsis if minimum font size is insufficient
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#### Scenario: Embedded images in tables
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- **GIVEN** a table with `embedded_images` in metadata
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- **WHEN** generating translated layout PDF
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- **THEN** images SHALL be rendered at their original positions within the table
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### Requirement: Reflow PDF Table Rendering
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The system SHALL generate reflow PDFs with properly structured tables including merged cell support.
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#### Scenario: Basic table rendering
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- **GIVEN** an OCR result with table cells containing `row`, `col`, `content`
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- **WHEN** generating reflow PDF
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- **THEN** cells SHALL be grouped by row and column indices
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- **AND** table SHALL render with visible borders
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#### Scenario: Merged cells support
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- **GIVEN** table cells with `row_span` or `col_span` greater than 1
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- **WHEN** generating reflow PDF
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- **THEN** the system SHALL apply appropriate cell spanning
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- **AND** merged cells SHALL display content without duplication
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#### Scenario: Column width calculation
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- **GIVEN** a table with `cell_boxes` metadata
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- **WHEN** generating reflow PDF
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- **THEN** column widths SHOULD be proportional to original cell widths
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# Tasks: Fix PDF Table Rendering
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## 1. Translated Layout PDF - Table Fix (P0)
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- [ ] 1.1 Refactor `_draw_translated_table()` to use layered rendering approach
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- [ ] 1.2 Use `cell_boxes` from metadata for accurate border positioning
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- [ ] 1.3 Render translated text within each cell's bbox using Paragraph with wordWrap
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- [ ] 1.4 Handle text overflow (shrink font to minimum 8pt or truncate)
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- [ ] 1.5 Draw embedded images at correct positions
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## 2. Reflow PDF - Table Fix (P1)
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- [ ] 2.1 Fix `_create_reflow_table()` cell extraction from content dict
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- [ ] 2.2 Add row_span/col_span handling using ReportLab SPAN style
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- [ ] 2.3 Calculate proportional column widths based on cell_boxes
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- [ ] 2.4 Embed images in table cells instead of after table
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## 3. Testing & Validation
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- [ ] 3.1 Test with task 48b9e849-f6e3-462f-83a1-911ded701958 (has merged cells)
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- [ ] 3.2 Verify translated layout PDF has visible borders
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- [ ] 3.3 Verify reflow PDF tables align correctly
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- [ ] 3.4 Verify embedded images appear in both formats
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