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Re: [css3-transitions] Complex easing functions

From: Chris Marrin <cmarrin@apple.com>
Date: Fri, 10 Apr 2009 11:01:46 -0700
Cc: robert@ocallahan.org, Dean Jackson <dino@apple.com>, Jon Rimmer <jon.rimmer@gmail.com>, www-style@w3.org
Message-id: <EC891A62-86C6-4AD2-AE9E-10482312D332@apple.com>
To: Andrew Fedoniouk <news@terrainformatica.com>

On Apr 9, 2009, at 7:19 PM, Andrew Fedoniouk wrote:

>>> ...
>> You'd have to constrain the curve shape to keep the X (input) value  
>> monotonically increasing. Doing that would maintain the 1:1  
>> relationship between input and output.
>
> The question is how exactly "to keep it"?
>
> Cubic-Bezier function is known to exist in parametric form.
> As far as I understand drawing and wording in http://www.w3.org/TR/css3-transitions/
> you propose to use it in non-parametric form as y = B(x).
> In general such equation does not exist for the Cubic-Bezier - is  
> ambiguous in our "space-time" ((C) Dr. O.Hoffmann).
> So in reality you have to use some approximation for the y=B(x)  
> function
> (if yes then which one?) or that part in css3-transitions is  
> misleading.
>
> Why not just to use Cubic-Bezier in parametric form?
> In this case you can use any values for the strong points.


I don't think we have any preference. Whatever is more clear (and  
leads implementors down the right path) is what we should use. I'm  
sure SVG can inform us here. As far as how to maintain the monotonic  
rule, I'm pretty sure we can specify rules for the control points  
which would preclude non-monotonic curve shapes. And if we just  
specify the algorithm to compute the curve values, it will make it  
clear how to deal with ambiguity.

-----
~Chris
cmarrin@apple.com
Received on Friday, 10 April 2009 18:02:55 GMT

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