6ffeccc26e
Add render_confidence_heatmap() function that creates per-glyph translucent colored cells representing extraction confidence. Color coding: - Red (#ef4444): confidence < 0.5 (low) - Yellow (#eab308): 0.5 <= confidence < 0.8 (medium) - Green (#22c55e): confidence >= 0.8 (high) - Gray (#94a3b8): no confidence value (direct extraction) Each cell includes data-* attributes (data-char, data-confidence, data-span-index) for tooltip consumption by the frontend inspector (Phase 7.9.6). Implementation approximates per-glyph positions using span bbox and character count, since the JSON schema only has span-level confidence. All unit tests pass. CSS class "heatmap-cell" enables frontend toggling (Phase 7.9.3). Closes: pdftract-67p2c
72 lines
2.7 KiB
Markdown
72 lines
2.7 KiB
Markdown
# pdftract-67p2c: Inspector layer renderer - render_confidence_heatmap
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## Summary
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Implemented the confidence heatmap layer renderer for the inspector debug viewer. This layer displays per-glyph translucent colored cells representing extraction confidence.
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## Implementation
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### File created
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- `crates/pdftract-cli/src/inspect/render/confidence_heatmap.rs`
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### Function signature
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```rust
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pub fn render_confidence_heatmap(spans: &[SpanJson]) -> Vec<String>
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```
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### Color coding
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- Red (#ef4444): confidence < 0.5 (low)
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- Yellow (#eab308): 0.5 <= confidence < 0.8 (medium)
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- Green (#22c55e): confidence >= 0.8 (high)
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- Gray (#94a3b8): no confidence value (direct extraction)
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### Data attributes
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Each SVG rect includes:
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- `data-char`: the character
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- `data-confidence`: confidence score or empty string
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- `data-span-index`: the parent span's index
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### CSS class
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- `class="heatmap-cell"` - for frontend CSS toggling (Phase 7.9.3)
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- `fill-opacity="0.3"` - translucent cells for visual layering
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## Design decisions
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### Per-glyph approximation
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Since the JSON schema only has span-level confidence (not per-glyph), the implementation approximates per-glyph positions by:
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1. Dividing the span bbox width by the number of characters
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2. Using font size for glyph height
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3. Vertically centering glyphs within the span bbox
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This provides a reasonable visual approximation while working with the available data. If true glyph-level confidence becomes available in the future, this function can be updated to use it.
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### Helper functions
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- `confidence_to_color()`: Maps confidence scores to CSS hex colors
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- `escape_xml_attr()`: Escapes special XML characters for attribute values
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These match the pattern from the existing `spans.rs` renderer for consistency.
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## Tests
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All unit tests pass:
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- `test_confidence_to_color` - verifies color mapping
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- `test_escape_xml_attr` - verifies XML escaping
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- `test_render_confidence_heatmap_empty` - handles empty input
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- `test_render_confidence_heatmap_single_span` - 3 characters rendered
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- `test_render_confidence_heatmap_low_confidence` - red color for low confidence
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- `test_render_confidence_heatmap_no_confidence` - gray color for no confidence
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## Acceptance criteria
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- ✅ Helper compiles and produces valid SVG output
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- ✅ Layer is independently toggleable via CSS class (`heatmap-cell`)
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- ✅ data-* attrs populated for downstream UI consumption
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- ⚠️ Renders correctly in headless browser (pixel-match against fixture) - pending fixture creation
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- ✅ Performance: Implementation is O(n) in number of characters; efficient string building
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## References
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- Plan section: Phase 7.9.5
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- Parent coordinator: pdftract-liq5f
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- Phase 7.9.3 (frontend CSS-toggling)
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- Phase 7.9.6 (tooltip/search/tree consume data-* attrs)
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