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feOffset default filter subregion (ACTION-3345)

From: Erik Dahlstrom <ed@opera.com>
Date: Thu, 30 Aug 2012 14:59:43 +0200
To: "www-svg@w3.org" <www-svg@w3.org>
Message-ID: <op.wjuudtn3geuyw5@gnorps>

here's some feedback on the feOffset issue[1] (part of my ACTION-3345).

For feOffset Opera doesn't default the feOffset's subregion to the union  
of its input's subregions[2] because we thought it was non-intuitive.  
Snippet illustrating what this is about:

<filter id="feoffset1" primitiveUnits="objectBoundingBox" x="0%" y="0%"  
width="200%" height="200%">
   <feFlood width="100%" height="100%" flood-color="lime"/>
   <feOffset dx="0.1" dy="0.2"/>

I read the above as:
* the filter region is 200% of the bbox of the element that uses the filter
* floodfill the bbox area with green
* move the filled area (0.1*bbox.x, 0.2*bbox.y)

I think it's not really intuitive to clip the feOffset since it didn't  
actually specify a subregion, I'd rather see it as the feOffset can move  
things around whereever it likes (but inside the filter region). In case  
feOffset specifies a subregion then it should get clipped, e.g <feOffset  
dx="0.1" dy="0.2" width="50%" height="50%"/>.

I'd prefer to make an exception for feOffset (as is done for feTile  
already) and say that the default subregion for feOffset is the filter  

Also see the bug reported here[3] with testcase[4] (draft).

[1] http://www.w3.org/2012/08/16-svg-minutes.html#item04
[2] http://www.w3.org/TR/SVG/filters.html#FilterPrimitiveSubRegion
[3] http://lists.w3.org/Archives/Public/www-svg/2010Oct/0122.html

Erik Dahlstrom, Core Technology Developer, Opera Software
Co-Chair, W3C SVG Working Group
Personal blog: http://my.opera.com/macdev_ed
Received on Thursday, 30 August 2012 13:00:24 UTC

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