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Re: [css3-transitions] Back-tracking transition-timing-function

From: Chris Marrin <cmarrin@apple.com>
Date: Thu, 6 May 2010 09:29:19 -0700
Message-Id: <48FE2B49-E608-4588-A700-3300E96C95B1@apple.com>
To: www-style list <www-style@w3.org>

On May 5, 2010, at 11:46 PM, Simon Fraser wrote:

> We modeled transition/animation timing functions after SVG keySplines:
> http://www.w3.org/TR/2001/REC-smil-animation-20010904/#KeySplinesAttribute
> 
> which limit the values between 0 and 1.
> 
> We'd be OK lifting this restriction for CSS (assuming people are happy with the divergence from SVG), but we'd have to make some rules about how properties like color get clamped when you go outside the 0->1 range.

We discussed it internally a while back. I believe our reasoning for not lifting the restriction was that it adds complexity. You'd have to allow only y to go outside the range (allowing X could cause the curve to become non-monotonic) and it would require extra rules for how to clamp color as Simon mentioned, as well as opacity and others. And it would not give you a true bounce effect, where you wiggle back and forth around the end point until you settle on it. It would only provide a single overshoot past the end value. And even then you get very little control over how the overshoot looks. You can't adjust the slope of the return path independently of the overshoot path. 

So we didn't feel the complexity justified the benefit. I still agree with that point. 

-----
~Chris
cmarrin@apple.com
Received on Thursday, 6 May 2010 16:29:51 GMT

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