feat: optimized SVG export writer (fixes #236)#317
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spe-ciellt merged 1 commit intogerbv:developfrom Mar 5, 2026
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SVG export via Cairo's SVG surface produces bloated files because it emits one <path> per Gerber primitive with repeated inline styles and 6-digit coordinate precision. A board with 112k primitives produces a 30MB SVG that SVGO can reduce to 1.8MB. Add a custom SVG writer (export-svg.c) that walks gerbv's data structures directly, producing dramatically smaller output: - CSS class deduplication: unique fill/stroke styles emitted once in <style>, referenced via class="c0". Typical board has <20 unique styles vs 112k inline repetitions. - Reduced precision: 3 decimal places with trailing zero stripping (0.00035mm resolution at 72 DPI, well below visual threshold). - SVG-native elements: <circle>, <rect>, <line>, <polygon> instead of generic <path> where applicable. - <g> grouping with inherited styles for layer/netstate transforms. - All 8 macro primitive types (circle, outline, polygon, moire, thermal, line20/21/22). - Clear polarity workaround using background-color fill, matching the existing vector export fix in draw.c. - Full support for Inkscape layer mode (--svg-layers). The new writer is the default for SVG export. The previous Cairo-based path is available via --svg-cairo CLI flag or the "Use Cairo SVG (legacy)" checkbox in the GUI export dialog. Measured size reduction: 42-69% on test files vs Cairo SVG output. Larger boards with more repeated apertures will see greater reduction. Fixes gerbv#236
This was referenced Mar 1, 2026
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Summary
Adds a custom SVG writer (
export-svg.c) that walks gerbv's data structures directly, bypassing Cairo's SVG surface entirely. This produces dramatically smaller SVG output files.Root cause of #236: Cairo's SVG surface emits one
<path>per Gerber primitive with repeated inline styles and 6-digit coordinate precision. A board with 112,000 primitives = 112,000<path>elements with duplicate style attributes, producing ~30MB files.Key optimizations
<style>, referenced viaclass="c0". A typical board has <20 unique styles vs 112k inline repetitions.<circle>,<rect>,<line>,<polygon>instead of generic<path>where applicable.<g>grouping — Nested groups for layer/netstate transforms carry shared attributes.What's covered
draw.c)--svg-layers)--svg-cairoCLI flag or GUI checkboxMeasured results
Larger boards with many repeated aperture flashes (the #236 scenario) will see the greatest reduction, potentially 85-93% as noted in the issue.
Files changed
src/export-svg.csrc/export-svg.hsrc/export-image.csrc/gerbv.huse_cairo_svgflag togerbv_project_tsrc/main.c--svg-cairoCLI flag for legacy outputsrc/callbacks.csrc/CMakeLists.txtexport-svg.cto library sourcesTest plan
--svg-cairoproduces identical output to the previous code path--svg-layers)Requesting feedback on the approach and testing with real-world files that exercise the edge cases.
Fixes #236