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Re: animateTransform & matrix

From: Dean Jackson <dean@w3.org>
Date: Tue, 21 Jan 2003 23:47:59 +1100
To: Benjamin Himpel <bhimpel@yahoo.com>
Cc: www-svg@w3.org
Message-ID: <20030121124759.GE26052@grorg.org>


I asked Jon Ferraiolo, the editor of the SVG 1.0 specification
for the answer, since I couldn't remember. Here is his answer:

If you allow animation of an arbitrary matrix to another arbitrary matrix,
there is a chance you can reach a singularity midway through the animation.
To avoid this, we restricted animateTransform to specify a single type of 
transform (i.e., scale vs. rotate vs. translate etc.). A content develop
can still achieve arbitrary matrix transforms via the 'additive' feature    
for animateTransform (where additive in this case actually means matrix    


On Sun, 19 Jan 2003, Benjamin Himpel wrote:

> Hi,
> Why can one not use animateTransform together with
> matrix? Why does the specification not allow
> expressions like the following?
> <animateTransform attributeName="transform"
> attributeType="XML"
> type="matrix" from="1,0,0,1,0,0" to="2,3,1,2,1,1"
> dur="5s"
> additive="sum" fill="freeze"/>
> One could simply define this to be the animation,
> which follows the straight line between the two
> transformation matrices with constant speed.
> I found the following excerpt in some newsgroup, but
> do not remember which:
> "Because of mathematical issues, we couldn't allow
> arbitrary matrics to be part of the animation values.
> You can only animate primitive operations such as
> rotate, scale or translate. But you can define
> additive 'animateTransform' animations on the same
> 'transform' attribute in such a way that you can
> achieve most arbitrary matrix effects.
> Bottom line - you should be able to do just about
> everything you can do with a matrix using some
> combination of 'animateTransform' animations."
> I do not understand, what mathematical issues would
> relevant here. As matter of fact mathematicians would
> not mind to simply specify the path (including its
> parametrization) of transformation matrices instead of
> the complicated and inefficient way of using
> compositions of animations for primitive
> transformations. Also it is much more difficult than
> it seems, to find the _animated_ composition of
> primitive transformation which is equal to a specified
> path (including parametrization) of transformation
> matrices.
> Does anybody have an answer to or comments about any
> of this?
> Thanks,
> Ben
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Received on Tuesday, 21 January 2003 07:48:02 UTC

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