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Re: [css3-2d-transforms] matrix animation

From: Dean Jackson <dino@apple.com>
Date: Thu, 26 Mar 2009 08:48:21 +1100
Cc: www-style CSS <www-style@w3.org>
Message-Id: <42A58CBC-E90F-4A10-8B8D-A6A6B472500A@apple.com>
To: "Dr. Olaf Hoffmann" <Dr.O.Hoffmann@gmx.de>

On 26/03/2009, at 6:45 AM, Dean Jackson wrote:

> Olaf,
>
> On 26/03/2009, at 12:49 AM, Dr. Olaf Hoffmann wrote:
>
>> I think, it is not a good idea, that a matrix is decomposed in an  
>> (arbitrary)
>> set of other transformations for animation purposes, because:

[snip your points]

>> To resume, I suggest to skip the decomposition idea completely. This
>> avoids mathematical problems and paternalism of authors.
>
> We strongly disagree. We came to this approach for a few reasons:

[snip my reply]

If you wanted more proof here's an example from the apple engineer who  
implemented the decomposition:

Imagine animating from [0.707 -0.707 0.707 0.707 0 0] to [0.707 0.707  
-0.707 0.707 0 0], which is an animation from 45 degrees to -45  
degrees. Without decomposition at 50% you have [0.707 0 0 0.707 0 0],  
which is a rotation of 0 degrees (this is correct) but with a scale of  
0.707 (definitely incorrect)? You'd see a box rotate and shrink, then  
continue rotating and grow again. This would be even worse animating  
from 0 to 180 degrees, where the box would shrink to nothing at the  
50% mark.

Dean
Received on Wednesday, 25 March 2009 21:49:10 GMT

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