312606 2026-04-17 15:13:02 -0700 [threaded-animations] additive transform animations use matrix interpolation which does not account for additivity 2026-04-17 23:29:46 -0700 1 1 1 Unclassified WebKit Animations WebKit Nightly Build Unspecified Unspecified RESOLVED FIXED https://github.com/web-platform-tests/wpt/pull/59327 InRadar P2 Normal --- 1 graouts graouts graouts webkit-bug-importer oldest_to_newest 2201670 0 479156 graouts 2026-04-17 15:13:02 -0700 Created attachment 479156 Test Consider this simple animation: @keyframes scale { 0%, 100% { transform: scale(2) } } … and this additional style: div { transform: translateX(100px); animation: scale 1s infinite; animation-composition: add; } This should yield a computed value of `transform: translateX(100px) scale(2)` but we end up instead in `void TransformationMatrix::blend(const TransformationMatrix&, double, CompositeOperation)` which has no idea about how to account for additivity. 2201671 1 webkit-bug-importer 2026-04-17 15:13:19 -0700 <rdar://problem/175039068> 2201683 2 graouts 2026-04-17 15:47:20 -0700 Pull request: https://github.com/WebKit/WebKit/pull/63008 2201684 3 graouts 2026-04-17 15:49:40 -0700 Submitted web-platform-tests pull request: https://github.com/web-platform-tests/wpt/pull/59327 2201798 4 graouts 2026-04-17 23:29:46 -0700 Committed 311516@main (31a9b52): https://commits.webkit.org/311516@main 479156 2026-04-17 15:13:02 -0700 2026-04-17 15:13:02 -0700 Test additive-transform.html text/html 352 graouts PHN0eWxlPgoKQGtleWZyYW1lcyBzY2FsZSB7CiAgICAwJSwgMTAwJSB7IHRyYW5zZm9ybTogc2Nh bGUoMikgfQp9CgpkaXYgewogICAgZGlzcGxheTogYmxvY2s7CiAgICBiYWNrZ3JvdW5kLWNvbG9y OiBibHVlOwogICAgYmFja2dyb3VuZC1yZXBlYXQ6IG5vLXJlcGVhdDsKICAgIGhlaWdodDogMTAw cHg7CiAgICB3aWR0aDogMTAwcHg7CgogICAgdHJhbnNmb3JtLW9yaWdpbjogdG9wIGxlZnQ7CiAg ICB0cmFuc2Zvcm06IHRyYW5zbGF0ZVgoMTAwcHgpOwoKICAgIGFuaW1hdGlvbjogc2NhbGUgMXMg aW5maW5pdGU7CiAgICBhbmltYXRpb24tY29tcG9zaXRpb246IGFkZDsKfQoKPC9zdHlsZT4KCjxk aXY+PC9kaXY+Cg==