Implemented the full SVG page renderer for the inspector debug viewer
(Phase 7.9.4). The renderer generates complete SVG documents with multiple
layers for visual debugging of PDF extraction results.
Changes:
- Implemented render_page_svg() with 10 layers (background, selection, 8 overlays)
- Added selection layer with invisible <text> elements for browser text selection
- Integrated all 8 overlay layer renderers (spans, blocks, columns, reading_order,
confidence_heatmap, ocr, mcid, anchors)
- Added arrowhead marker definition for reading order arrows
- Implemented helper functions: render_selection_layer(), render_ocr_layer(),
extract_columns_from_spans(), escape_xml_text()
- Added comprehensive unit tests for all functions
Acceptance criteria:
- ✅ Per-page SVG structure with proper viewBox and namespace
- ✅ 8 toggleable overlay layers with correct class names
- ✅ Color coding by confidence (spans) and kind (blocks)
- ✅ Coordinate system flip (PDF y-up to SVG y-down)
- ✅ Invisible <text> elements for browser text selection
- ✅ SVG determinism (same input produces identical output)
Deferred:
- Glyph paths via ttf-parser (requires font data not in JSON)
- Performance testing (requires full inspector integration)
- MCID layer (MCID tracking not in schema yet)
Closes: pdftract-4ct3y
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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