- From: Alex Danilo <alex@abbra.com>
- Date: Tue, 29 Jun 2010 22:05:42 +1000
- To: "Dr. Olaf Hoffmann" <Dr.O.Hoffmann@gmx.de>
- Cc: www-svg@w3.org
Hello Olaf & Erik, We included all the Porter-Duff equations in the compositing chapter back around 2002 or so, and the current draft of that is at: http://www.w3.org/TR/SVGCompositing/ I agree it would be good to include the actual equations in the spec. especially since I don't believe the original Porter-Duff paper took alpha into account IIRC. Alex --Original Message--: >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) > > >Olaf > > >
Received on Tuesday, 29 June 2010 12:06:31 UTC