Known cases where resvg's golden images differ from the correct rendering per the SVG/CSS spec. When a resvg golden is incorrect, we generate Donner's own golden and use Params::WithGoldenOverride() to compare against it instead.

Custom goldens are stored in donner/svg/renderer/testdata/golden/resvg-<test-name>.png.

a-filter-013: Drop-shadow blur on circle (mm units)

SVG: Circle with filter: drop-shadow(5mm 5mm 1mm).

Symptom: ~9100 pixel diff between Donner and resvg golden at default threshold.

Root cause: Blur algorithm difference. Donner uses a three-pass box blur approximation of Gaussian blur (per SVG spec recommendation). Resvg uses a different blur implementation that produces a visually different halo shape around the shadow. The difference is concentrated at the edges of the blur radius where the two approximation methods diverge.

Ruled out: Color space (sRGB vs linearRGB) was tested and made no difference to this test — switching to linearRGB changed the diff by <30 pixels.

Resolution: Custom golden generated from Donner's output. Donner's rendering is correct per CSS Filter Effects Level 1 §8 (sRGB color space) and SVG §15.9 (Gaussian blur approximation via three-pass box filter).

a-filter-015: Drop-shadow blur on circle (em units)

SVG: Circle with filter: drop-shadow(1em 1em 0.2em).

Symptom: ~14600 pixel diff between Donner and resvg golden at default threshold.

Root cause: Same blur algorithm difference as a-filter-013. The larger blur radius (0.2em at the test's font size) amplifies the halo shape difference between the two blur implementations.

Ruled out: Unit resolution was verified correct — em units resolve against the element's computed font-size, and Lengthd::toPixels() produces the same pixel values as manual calculation. Color space switching had no effect.

Resolution: Custom golden generated from Donner's output.

e-marker-045: Marker direction at beginning/end of closed shapes

Symptom: Disagreement about direction to place markers at the beginning/end of closed paths.

Resolution: Custom golden generated from Donner's output.

e-marker-051: Marker direction on cusp

Symptom: Disagreement about marker direction on cusp points.

Resolution: Custom golden generated from Donner's output.