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Re: [1.2T-LC] inverse and constrained transformations (ISSUE-2073)

From: Cameron McCormack <cam@mcc.id.au>
Date: Sun, 2 Nov 2008 15:39:11 +1100
To: www-svg@w3.org
Message-ID: <20081102043911.GB1656@arc.mcc.id.au>

Hi Olaf.

Dr. Olaf Hoffmann:
> 1)
> Now it is noted:
> "Note that the inverse of the CTM may not always exist. If the CTM is 
> non-invertible, then rendering of the element is disabled. The 'ref(...)' 
> value in this case is not an unsupported value."
> 
> If we consider the main idea of the constrained transformation,
> as far as I understand this, it is, that the element with such a 
> transform value ref(...) is not transformed at all and not that
> the display is disabled.
> I cannot see, that this disabling provides any functionality related
> to a constrained transformation or something useful for authors
> at all.
…
> Therefore I suggest to remove the requirement to disable
> rendering, if the inverse does not exist, as in the previous
> wording, which can be improved maybe, but better not
> with constrains on the functionality or with a requirement
> to change the behaviour of viewers already managing the
> problem without any trouble.

I see that there is merit in allowing transform-ref even when its parent
has a non-invertible CTM, and after discussing it, I have reverted the
text to allow this, but also included a note to point out that the
rootmost svg element’s CTM can be looked up directly in this case.

> 2)
> In '7.6.1 The TransformList value' now appears something
> similar contraproductive. It is noted:
> 
> "If the list of transforms includes a matrix with all values set to zero (that 
> is, 'matrix(0,0,0,0,0,0)'), or any other non-invertible matrix (such 
> as 'matrix(0,0,0,0,50,50)' or 'scale(1,0)'), then rendering of the element is 
> disabled. Such a value is not an unsupported value."
> 
> Previously it was noted:
> "If the list of transforms includes a matrix with all values set to zero (that 
> is, matrix(0,0,0,0,0,0)) then rendering of the element is disabled. Such a 
> value is not an unsupported value."
> 
> 
> Finally with vector-effect non-scaling-stroke it became a simple
> method available to use and to see objects with reduced 
> dimensionality. To get similar effects and functionalities in
> SVG 1.1, this requires clipping, masking, filtering, not available
> at all in SVGT1.2. 
> Therefore it is disappointing that this possibility or functionality
> is now removed in a very late phase of the SVGT1.2 drafts without 
> any reasoning.

I guess I’m not convinced that these are useful use cases, but…

> My suggestion is, that these possibilities are not excluded, 
> that authors can use this in combination with vector-effect 
> non-scaling-stroke to get some tricky functionality (as already
> indicated in previous responses about this issue), else not
> available in SVGT1.2 at all.

…after discussion, I’ve reverted this too.


Hopefully this satisfactorily re-resolves your LC comment.

Thanks,

Cameron

-- 
Cameron McCormack ≝ http://mcc.id.au/
Received on Sunday, 2 November 2008 04:39:50 GMT

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