NEW317059
[WPT][backdrop-filter] Add tests for url() reference cases on backdrop-filter 
https://bugs.webkit.org/show_bug.cgi?id=317059
Summary [WPT][backdrop-filter] Add tests for url() reference cases on backdrop-filter
Karl Dubost
Reported 2026-06-12 20:01:23 PDT
The `backdrop-filter` CSS property accepts the same `<filter-value-list>` grammar as `filter`, including `<url>` references to SVG `<filter>` elements (Filter Effects 2 for The 'backdrop-filter' property). WebKit currently silently drops the filter when the chain contains a `url(...)` reference (bug 245510); the existing WPT coverage in `css/filter-effects/` is thin and several spec-prescribed cases have no test at all. This bug tracks adding new WPT tests that cover the reference-filter gaps. It is filed separately from bug 245510 so the test patch can land independently of the implementation work. Specs: * https://drafts.csswg.org/filter-effects-1/ * https://drafts.csswg.org/filter-effects-2/ MISSING TESTS 1. Chained `url()` references aka `backdrop-filter: url(#a) url(#b)` 2. Mixing `<filter-function>` with `<url>` aka `backdrop-filter: invert(1) url(#identity)` 3. `url()` to a non-`<filter>` element. 4. `feDisplacementMap`. 5. `filterUnits="userSpaceOnUse"` with an explicit primitive region.
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Radar WebKit Bug Importer
Comment 1 2026-06-19 20:02:11 PDT
<rdar://problem/180162001>
Iskandar Roslen
Comment 2 2026-07-16 08:22:43 PDT
I've put up https://github.com/WebKit/WebKit/pull/69566 adding WPT ref tests for these cases: chained references, a filter function chained with a reference filter, url() to a non-filter element, and filterUnits=userSpaceOnUse with an explicit primitive subregion. feDisplacementMap coverage (feImage- and feFlood-driven, with computed references) is part of the implementation PR for bug 245510, https://github.com/WebKit/WebKit/pull/68614. The three tests that need bug 245510 are marked as failing so this can land independently of the fix.
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