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Re: clipPath inconsistencies

From: Erik Dahlstrom <ed@opera.com>
Date: Thu, 15 Jul 2010 12:40:33 +0200
To: www-svg@w3.org
Message-ID: <op.vfvrxsllgeuyw5@localhost>
On Thu, 15 Jul 2010 11:39:24 +0200, Nikolas Zimmermann  
<zimmermann@physik.rwth-aachen.de> wrote:

> Good morning SVG crowd,
>
> I'd like to discuss clipping inconsistencies between Opera/FF and
> WebKit, when it comes to error handling.
> In the screenshot you can see WebKit, Firefox and Opera rendering the
> clip-path-recursive-call-by-child.svg example (attached in this mail).
...
> I've chosen to ignore the clipPath, which is in error state (as it
> contains a cycle), but still render the object, which referenced it.
>
> Firefox seems to detect the cycle and doesn't render the element at
> all (probably because of the note in the error processing document).
> Opera just ignores the cycle and renders both elements.

No, what Opera does is detect the cycle and break it at the time it's  
discovered, and we've chosen to follow the spec for what happens if  
there's an invalid clip-path IRI reference in a child element of a  
clipPath element:
[[  If the IRI reference is not valid (e.g it points to an object that  
doesn't exist or the object is not a ‘clipPath’ element) the ‘clip-path’  
property must be treated as if it hadn't been specified. ]]

Which means that the rect inside the clipPath should be drawn (or in other  
words: it should contribute to the clipping region), but without the  
'clip-path' property applied.

Note that there's nothing in the spec that says that the 'clip-path' IRI  
reference means the element in question is "in error", so the error  
processing rules don't apply in this case.

Cheers
/Erik

-- 
Erik Dahlstrom, Core Technology Developer, Opera Software
Co-Chair, W3C SVG Working Group
Personal blog: http://my.opera.com/macdev_ed
Received on Thursday, 15 July 2010 10:41:13 GMT

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