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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>

Benjamin,

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    
multiplication).

Dean

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 GMT

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