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Re: [css-round-display] Decision about if polar-angle turns into an angle or a keyword in the computed value

From: Brad Kemper <brad.kemper@gmail.com>
Date: Mon, 7 Dec 2015 16:17:36 -0800
Cc: www-style list <www-style@w3.org>
Message-Id: <41F14EFA-0213-453D-A58F-C9F0B003E0CF@gmail.com>
To: Jihye Hong <jh.hong@lge.com>

> On Dec 7, 2015, at 12:41 AM, Jihye Hong <jh.hong@lge.com> wrote:
> Recently, the extension of the 2d rotation was added to the CSS Round
> Display [1]. 
> Keyword values, polar-angle and polar-angle-reverse can be the value for the
> 2d rotate function. But it's not clear whether the keyword value turns into
> an angle or remain as a keyword when determining the computed value of
> transform.
> If the keyword value remains as a keyword, you can't animate between it and
> another angle value.
> For example, animating between rotate: polar-angle and rotate: 0 isn't
> possible.
> However, when polar-angle property animates, the changes in it affect to
> the rotation function with the keyword value.
> If the keyword value turns into an angle, you can animate between it and a
> different angle.
> Thus you can animate between rotate: polar-angle and rotate: 0 or between
> rotate: polar-angle and rotate: polar-angle-reverse.
> But if polar-angle property animates, the rotation animation with the
> keyword value will not track the changes in polar-angle property.
> When suggesting polar-angle and polar-angle-reverse as keyword values for 2d
> rotation transform function, the main goal of those value is to rotate the
> element toward the origin point whatever the position of the element is in
> polar coordinates.
> Therefore, the keyword value should remain as a keyword at computed value
> time.
> Maybe there are some needs for animating between polar-angle and a different
> angle, but I think tracking the changes in polar-angle property when
> animating rotation function with polar-angle is more important than that
> case.

I tend to agree. I can imagine a seconds pointer that bounces around the perimeter of a clock, by animating polar length and polar angle every second, where I'd always want it pointed outward. I can also imagine animating a number for the hours and/or minutes and/or seconds as it swept around the clock (you wouldn't then need static numbers displayed on the clock face), which would also be easier if I only had to animate 'polar-angle' and let the rotate angle take care of itself (while using JS to update the text itself every second). 

Animating between rotate(polar-angle) and rotate(0) could be nice too, occasionally, but much less important, in my opinion. It's a shame that we can't just animate the used values to do that, so that we could have our cake and eat it too, but it's the same situation with trying to animate from/to height:auto, I guess. 

> Thanks,
> Jihye Hong
> [1]
> https://drafts.csswg.org/css-round-display/#2d-rotation-transform-function
Received on Tuesday, 8 December 2015 00:18:48 UTC

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