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Re: SVG Compositing

From: Alex Danilo <alex@pagefire.com>
Date: Wed, 14 Apr 2010 15:53:57 +1000
Message-Id: <X1RU0L.YSKKVIHE4TPL@pagefire.com>
To: Dirk Schulze <vbs85@gmx.de>
Cc: www-svg@w3.org
Hi,

	There are very good reasons why it is defined the
way it is.
 Many more than I can put into an email.

	Basically the compositing operator is a property
of an object, not 'glue' to join 2 objects together. We
implemented it as you suggest back around 2003 or so and
it doesn't work for the Porter-Duff operators proerly
especially when combined with background-enable='accumulate'.

	Anthony may want to make some more comments.  But the
basic one is that it doesn't work properly if you try to represent
compositing as nodes in the tree - which is effectively what
you suggest.

	Adobe's ASV3 has compositing as a property on objects,
via the adobe-blending-mode property. Illustrator will geberate
that rather than use filters. Compositing can be achieved without
using an intermediate store which I don't think you can expect
when using a filter primitive.

Alex

--Original Message--:
>Hi,
>
>I have a question to SVG Compositing
>(http://www.w3.org/TR/2009/WD-SVGCompositing-20090430). Maybe it's to
>late to make bigger changes on the Spec anyway, but wouldn't it be
>easier to understand compositing by adding a new tag like <composite>?
>
>This tag could have attributes 'source', 'destination', 'operater' and
>other attributes depending on the operator. The handling would be
>simular to feComposite
>(http://www.w3.org/TR/SVG11/filters.html#feComposite).
>
>Short example:
><svg>
><defs>
>  <rect id="rect" width="100" height="100" />
>  <circle id="circle" r="50" cx="120" cy="120" />
></defs>
>
><composite source="url(#rect)" destination="url(#circle)"
>operator="src-in" />
></svg>
>
>Of course it should be possible to cascade the composite effects.
>This is just a design proposal. It's hard to find examples for the use
>of enable-background in the web (beside the wrong test in the test
>suite:
>http://dev.w3.org/SVG/profiles/1.1F2/test/svg/filters-blend-01-b.svg).
>And I don't believe that it will be used more frequently for SVG 2.0 -
>with or without Compositing.
>
>Dirk
>
>
>
Received on Wednesday, 14 April 2010 15:54:28 GMT

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