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Re: [css3-animations][css3-transitions][css3-background] Animating box-shadow

From: Brad Kemper <brad.kemper@gmail.com>
Date: Tue, 1 Nov 2011 17:04:03 -0700
Cc: www-style list <www-style@w3.org>
Message-Id: <477BBE4D-4C17-45BA-A5CC-314B1EC84BEF@gmail.com>
To: Brian Manthos <brianman@microsoft.com>

On Nov 1, 2011, at 4:49 PM, Brian Manthos wrote:

>>> d. Normalizing across fields (offsets, spreads) so that they transition at the same rate is definitely important.
>>> e. WG must decide whether they want "cross-inset" transitions to be evenly split between inset and outset renderings or not.  I suggest "not".  The math is simpler and the rendering is more flexible.  If people want a half-inset, half-outset rendering it's easy to do that with an animation that has an additional middle state of "0 0 0 0 transparent".
>> IMO, if the distance measurements shadows do not go through zero at the same time, then it is not a smooth, believable effect, as there will end up being a jump when a bunch of shadow sticking out of the border box is suddenly found inside the padding box, facing the other way. 
> 
> I must not have phrased this clearly enough.  What I was trying to say was sometimes the transition should spend more time outset than inset (or vice-versa), and that's a good thing.  I was *not* trying to suggest that the fields would transition from inset to outset at different times.
> 
> Let me know if that's not clearer, Brad.  Or if you still are concerned that we mean expect different renderings here.

Ah. I think we are actually in violent agreement here.

>> Also, I had intended that color would just be one transition, independent of when the distance measurements hit zero.
> 
> An example might help:
> from { box-shadow: red 10px 10px; }
> to { box-shadow: blue 40px 40px inset; }
> 
> I think the preferred rendering is 20% outset and 80% inset (relative to time).  Further, I think #ff00ff should be used just before and just after the transition from outset to inset -- rather than at the 25px 25px inset location.

I think I'd like to see it both ways before deciding (Maybe Tab could add it to his visualization tool). But my sense is that if #ff00ff is halfway between red and blue, then it should occur halfway through the animation. It wouldn't seem to hurt the visual illusion as much as not having distances zero out at the same time.

>>> f. Color transitions with rgba.  Premultiplied?  Non-premultiplied?  One or the other depending on another property?
>> Is this question specific to "cross-inset" transitions, or just in general for box-shadow? I don't see any reason for it to be different from other color transitions, do you?
> 
> Fair point.  But I think there may be additional concerns in light of the "non-symmetric inset/outset durations" scenarios.

I'm all ears.
Received on Wednesday, 2 November 2011 00:11:18 GMT

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