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Re: [SVG1.1F2 LC] 15.12 Filter primitive ‘feComposite’ formula

From: Dr. Olaf Hoffmann <Dr.O.Hoffmann@gmx.de>
Date: Tue, 29 Jun 2010 13:57:22 +0200
To: www-svg@w3.org
Message-Id: <201006291357.23075.Dr.O.Hoffmann@gmx.de>
Erik Dahlstrom:

>What other operations? Where in the spec?

>Are you suggesting adding all the porter-duff equations for 'over', 'xor'  
>etc to the feComposite section?

Yes, for operator = "over | in | out | atop | xor" of feComposite.
This should be not very difficult, because at least for them the
usual implementations seem to agree on a result.
Interestingly, for the arithmetic operator, where a formula is
provided, I have seen different interpretations, for example
Batik/Squiggle differs sometimes from Opera ;o)
But I think, this is no indication, that providing formuals is
a disadvantage.
Informative additions would be enough, if it is not intended
to risk some relevant change (what is not really likely).

To find out, what the operators mean (including opacity), 
I had to search, read an article at wikipedia, finding a reference 
to the online version of the article from Porter and Duff, reading
and understanding this, deviating the meaning for SVG filters.
I think, this cascade of actions for the reader can be shortened
dramatically by simply providing the formulas.
If we assume, that the online version of the article is not
accessible forever, the necessary action can be even more
time consuming - traveling to a specialised library, booking the
magazine, maybe including interlending, waiting, finally reading,
captured by Star Wars reminiscences... ;o)

Received on Tuesday, 29 June 2010 11:59:32 UTC

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