Make rAF and web-animation timestamps relative and coarsened

[noamr]

This fixes a bug in the spec where rAF and web animations were given a shared timestamp (not relative to the time origin).

Closes #7931

• At least two implementers are interested (and none opposed):
  • Alreay implemented at
• Tests are written and can be reviewed and commented upon at:
  • Test that animations receive coarsened timestamps web-platform-tests/wpt#42273
• Implementation bugs are filed:
  • Chromium: https://bugs.chromium.org/p/chromium/issues/detail?id=1422926
  • Gecko: Already works
  • WebKit: Already works
• MDN issue is filed: …
• The top of this comment includes a clear commit message to use.

(See WHATWG Working Mode: Changes for more details.)

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/infrastructure.html ( diff )
/webappapis.html ( diff )

[domenic]

Can we fix IntersectionObserver at the same time? And then we could compute the relativized/coarsened timestamp once, e.g. up around step 5 where now is defined, and then just pass it along three times.

[noamr]

Can we fix IntersectionObserver at the same time? And then we could compute the relativized/coarsened timestamp once, e.g. up around step 5 where now is defined, and then just pass it along three times.

It would need to be computed once per document as each would have a different relative time. So do you mean something like having an associated "current rendering time" for each document?

[domenic]

Good point, that would be unnecessarily messy. Your current structure is good then. Still, should we fix IntersectionObserver at the same time, or just go ahead and merge this as-is? I don't think we can call #7931 closed until we fix all three though, right?

(And maybe we should make Web Animations consistent?? Or maybe that's another can of worms; https://drafts.csswg.org/web-animations-1/#document-timelines looks pretty different from the usual infrastructure.)

[noamr]

Good point, that would be unnecessarily messy. Your current structure is good then. Still, should we fix IntersectionObserver at the same time, or just go ahead and merge this as-is? I don't think we can call #7931 closed until we fix all three though, right?

Also fixed intersection observer.

(And maybe we should make Web Animations consistent?? Or maybe that's another can of worms; https://drafts.csswg.org/web-animations-1/#document-timelines looks pretty different from the usual infrastructure.)

I would fix that as part of web animations. It seems to be worded in a bit of a monkey-patched way there.