[css-transitions] discrete animations of non-interpolable properties (was Re: renaming "Animatable:" to "Interpolation:" in property definition tables)

On Friday 2015-05-22 22:13 -0700, Garrett Smith wrote:
> It can be better.

Sounds like you're talking about something other than the Subject of
the thread, so changing Subject (as you should have done).

> Switching `display` or `visibility` in the middle of an animation is
> not something I've ever wanted. It's useful to do switch it either at
> the first frame or at the end.

You can choose between these options by choosing between the
'step-start' or 'step-end' timing functions, which are the main ones
that are sensible for discrete animations.

That said, we could probably reduce the compatibility risk by
changing the rules for discrete animations so that the change
happens between a timing function that is less than or equal to 0,
versus a timing function that is greater than 0; this would means
that by default changes would happen at the start.

> When transitioning to computed values
> such as display: "none" or visibility: "hidden" or "collapse", the
> change should occur at the end. But in cases where the computed value
> to transition to is a display other than none, or visibility other
> than "hidden" | "collapse", most of the time, it's best done in the
> beginning, where it's changing the display from "none" and then
> running the adjustable properties (color, font-size, etc) in that new
> display value.

This is why 'visibility' has special animation rules, which remain.

We don't have such rules for 'display', though.

It's not clear to me if the list of things that have a value that's
clearly not for the middle of the animation is just (display:none,
visibility:hidden), or if it's really a substantially longer list.
I think that affects whether we'd want to add a special case for
'display' as well.

That said, there's also substantial Web compatibility risk to any of
these changes (including the one in the spec).

-David

-- 
𝄞   L. David Baron                         http://dbaron.org/   𝄂
𝄢   Mozilla                          https://www.mozilla.org/   𝄂
             Before I built a wall I'd ask to know
             What I was walling in or walling out,
             And to whom I was like to give offense.
               - Robert Frost, Mending Wall (1914)