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Donner SVG Editor & Engine
SVG-native editor and embeddable SVG2 + CSS3 engine in C++20, with GPU (WebGPU) and compact CPU renderers, built for correctness, security, and performance.
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Donner SVG Editor & Engine
SVG-native editor and embeddable SVG2 + CSS3 engine in C++20, with GPU (WebGPU) and compact CPU renderers, built for correctness, security, and performance.
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Status: Reference (current as of 2026-05-15)
When Donner's rendering of a resvg-test-suite case is correct but the upstream golden is not the right thing to compare against, the test pins Params::WithGoldenOverride("donner/svg/renderer/testdata/golden/resvg-<name>.png") so it compares against a Donner-blessed golden instead. This doc is the catalog of every such override and the reason it exists.
There are two distinct reasons an override is justified:
Custom goldens live in donner/svg/renderer/testdata/golden/resvg-<test-name>.png, named with the new (post-Great-Rename) test stem. The rationale for each is the .withReason("…") argument chained onto the override in resvg_test_suite.cc — grep the test name there to find it inline.
Naming note: these used the old a-* / e-* convention before the suite upgrade (0022). The four originally documented here mapped forward as: a-filter-013/a-filter-015 → drop-shadow-function-mm-values/drop-shadow-function-em-values (now parked, see below); e-marker-045/e-marker-051 (closed-shape / cusp marker direction) were superseded upstream and retired — the surviving marker override is orient=auto-on-M-C-C-4.
| Category | Test | Reason (withReason) |
|---|---|---|
| filters/feSpotLight | complex-transform | resvg bug: SpotLight Y |
| filters/feImage | svg | We render higher quality |
| filters/feSpecularLighting | with-fePointLight | resvg golden |
| painting/context | with-pattern-objectBoundingBox-in-use | resvg golden bakes fractional-tile rounding |
| painting/marker | orient=auto-on-M-C-C-4 | Pre-existing rendering diff (stroke/AA), not cusp-related |
| painting/marker | with-an-image-child | We (correctly) render the image child |
| text/font-size | named-value | Donner uses CSS Fonts Level 4 |
| text/font-size | named-value-without-a-parent | Donner uses CSS Fonts Level 4 |
named-value{,-without-a-parent} reflect CSS Fonts Level 4's revised handling of named font sizes (xx-small … xx-large), which differs from resvg's older table.
with-pattern-objectBoundingBox-in-use runs against a committed Donner render (resvg-with-pattern-objectBoundingBox-in-use.png), shared by both backends (TinyGolden and GeodeGolden pass at the default budget). Evidence that resvg's golden is the artifact: resvg rasterizes pattern tiles at a rounded integer pixel size, and this test's context bounding box yields a fractional 56.57px on-screen tile that resvg draws as 57px, stretching the tile period by ~0.8%. Donner repeats the tile at the exact period. A numeric grid fit confirms it: Donner's render fits an ideal diamond grid anchored at the computed context box (31.82, -116.67), 226.27² with score 1.0, while resvg's golden fits no ideal grid (best score 0.899 — its grid drifts, consistent with per-tile rounding). The integer-tile pattern goldens in the same category (with-pattern-in-use, with-pattern-and-transform-in-use, with-pattern-on-marker, whose tiles land on exact pixel sizes) match Donner exactly, isolating the discrepancy to the fractional-tile case. Revisit if resvg regenerates goldens without the rounding.
These render correctly but differ from resvg because Donner's text stack (and the simple-vs-text-full split) shapes/composes differently. The golden is whichever Donner backend the test runs under.
| Category | Test | Reason |
|---|---|---|
| text/text | complex-graphemes-and-coordinates-list | Simple text can't compose combining marks |
| text/text | compound-emojis-and-coordinates-list | Emoji bitmap scaling differs from the golden |
| text/text | rotate-on-Arabic | Arabic shaping requires text-full |
| text/text | x-and-y-with-multiple-values-and-arabic-text | Arabic shaping; vertical-axis AA diff not the focus |
The text/textPath family carries the bulk of the overrides: sub-pixel character advance and anti-aliasing differences along curved baselines, which differ between the simple and text-full backends. All are .withReason("Minor char") unless noted.
| Category | Test | Reason |
|---|---|---|
| text/textPath | dy-with-tiny-coordinates | AA + minor char advance diffs (text vs text-full) |
| text/textPath | m-L-Z-path | Minor char |
| text/textPath | mixed-children-1 | AA diffs |
| text/textPath | nested | Minor char |
| text/textPath | path-with-ClosePath | Minor char |
| text/textPath | simple-case | Minor char |
| text/textPath | startOffset=-100 | Minor char |
| text/textPath | startOffset=10percent | Minor char |
| text/textPath | startOffset=30 | Minor char |
| text/textPath | startOffset=5mm | Minor char |
| text/textPath | tspan-with-absolute-position | Minor char |
| text/textPath | tspan-with-relative-position | Minor char |
| text/textPath | two-paths | Minor char |
| text/textPath | very-long-text | AA diffs |
| text/textPath | with-baseline-shift | Minor char |
| text/textPath | with-coordinates-on-text | Minor char |
| text/textPath | with-coordinates-on-textPath | Minor char |
| text/textPath | with-rotate | Minor char |
| text/textPath | with-text-anchor | (no reason string) |
| text/textPath | with-transform-on-a-referenced-path | Minor char |
| text/textPath | with-transform-outside-a-referenced-path | Minor char |
| text/textPath | with-underline | Minor char |
| text/text-decoration | indirect | (no reason string) |
Two entries (textPath/with-text-anchor, text-decoration/indirect) carry no withReason. They should either get one or migrate to a per-test threshold; the "Minor char" cluster is the precedent. Tracked in 0021.
resvg-drop-shadow-function-mm-values.png and resvg-drop-shadow-function-em-values.png are the migrated successors of the old a-filter-013 / a-filter-015 drop-shadow blur-halo cases: Donner's three-pass box-blur approximation (correct per CSS Filter Effects L1 §8 / SVG §15.9) produces a different halo shape than resvg's blur, so a Donner golden is required.
They are currently unreferenced because the entire filters/filter-functions INSTANTIATE_TEST_SUITE_P block is commented out — that category throws "Data corrupted" parse errors on CI x86_64 but passes locally on aarch64 (root cause unknown). Keep both files: re-enabling the block (tracked in 0021) will need them. Do not delete as "orphans".
Three goldens added by #515 were never referenced by any override and were removed as dead data (recoverable from git history if a real override need surfaces):
The corresponding text/font-size tests pass against the upstream golden — only named-value{,-without-a-parent} need an override. After this cleanup the golden/ dir holds exactly 37 resvg-*.png: 35 active + the 2 parked drop-shadow goldens above.
1.15.0