W3C home > Mailing lists > Public > www-svg@w3.org > October 2009

outstanding filter issues

From: Robert O'Callahan <robert@ocallahan.org>
Date: Tue, 20 Oct 2009 10:37:42 +1300
Message-ID: <11e306600910191437o139d375fg10a2eefbaf205661@mail.gmail.com>
To: www-svg <www-svg@w3.org>
A few issues I discovered in the filter spec don't seem to ever have been
addressed:

http://lists.w3.org/Archives/Public/www-svg/2008May/0013.html
http://lists.w3.org/Archives/Public/www-svg/2008May/0014.html
http://lists.w3.org/Archives/Public/www-svg/2008Jun/0007.html

A general comment: filter primitive subregions and the filter effects region
seem like totally unnecessary complexity. Where clipping is desired, we
could have a simple <feClip> primitive. Not having these regions and
subregions would have made filters much simpler and easier to use and
implement, because as I point out in the messages above, in real-world
content filter primitive regions are sometimes far larger than necessary, so
a real-world implementation needs to calculate optimal temporary surface
sizes based on the filter primitives and the filtered content, so making
authors do it *as well* is just bad.

A while ago I proposed at least relaxing the spec so that filter effects are
not clipped to the filter effects region, suggesting that in most cases
where this clipping has an effect, it happens against the author's wishes.
I've had at least one bug report where an author thought this clipping was a
bug, because their Gaussian blur shadow was being clipped in Firefox but not
in Inkscape. I don't know what came of this proposal, I seem to recall Erik
at least was in favour of it.

Actually now I'd like to propose something slightly more radical. What if we
made the default filter effects region (and therefore the default filter
primitive subregions) be "infinitely" large? This could potentially break
content that relies on the amount of default "overhang" being exactly 10%,
but I doubt there's much of that. This change would mean in most cases
authors could ignore filter effects regions and filter primitive subregions
and get the results they want.

Rob
-- 
"He was pierced for our transgressions, he was crushed for our iniquities;
the punishment that brought us peace was upon him, and by his wounds we are
healed. We all, like sheep, have gone astray, each of us has turned to his
own way; and the LORD has laid on him the iniquity of us all." [Isaiah
53:5-6]
Received on Monday, 19 October 2009 21:38:18 GMT

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