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[css-values] [web-animations] Question about "not additive" for discrete animation #9070
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That seems to make sense to me. I can't recall why we made it Va in the first place. I looked up the SMIL spec to see if it came from there, but even it has:
|
We edited the spec to match (it's now Vb). |
(Since the editors, impls, and WPTs all agree, this is as open-and-shut of an edit as we can really get.) |
Per the definition of discrete animation, it is not additive. The spec says:
Because addition is not commutative, and I expect
Va
is the underlying value, andVb
is the value to combine (i.e. the keyframe effect value), per the-effect-value-of-a-keyframe-animation-effect.So for example:
The expected behavior per the spec is:
100px + 100px
=200px
.100px + auto
=100px
, because discrete is not additive andVresult = Va
.Therefore, this becomes an interpolation from
200px
to100px
. However, this mismatches the wpt and the current behavior of all the browsers. The interpolation is something like from200px
toauto
:And there are other examples:
We use discrete for
<line-names>
, and we use the keyframe value (i.e.Vb
) as the composited<line-names>
values in this test case.I guess I may miss something. However, per these examples and current behaviors of all browsers, should we change the spec words for non-additive in [css-values-4] to use
Vresult = Vb
or effect value? Or perhaps we have similar definition in [web-animations]?cc @birtles
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