[csswg-drafts] [css-fonts] How does animation work with the extension of `font-size-adjust`? (#6277)

jfkthame has just created a new issue for https://github.com/w3c/csswg-drafts:

== [css-fonts] How does animation work with the extension of `font-size-adjust`? ==
This is a followup to https://github.com/w3c/csswg-drafts/issues/6160, where we resolved to extent `font-size-adjust` to accept the name of a metric (rather than only considering ex-height) in addition to a number.

It occurs to me that this raises a question for animation. Currently, the single value of `font-size-adjust` can be animated as a number; but once we extend the property to take a metric as well, what would it mean to animate between values that are based on different metrics - e.g. between `font-size-adjust: ex 0.4` and `font-size-adjust: cap 0.7`?

In principle it might be nice to compute the resulting used size of each character in the content, and animate this. But the result of `font-size-adjust` may be different on a per-character basis, depending on what fallback fonts actually get chosen, so the cost/complexity of this seems excessive for such an obscure case.

So I suggest that given the potential trickiness of implementation here, we just say that if the metric differs, the animation type falls back to discrete.

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/6277 using your GitHub account


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Received on Saturday, 8 May 2021 10:45:13 UTC