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Subject: RE: A CGM Question: handling transparency

At 09:46 AM 8/29/2003 +0200, DULUC Franck wrote:
Hi/bonjour, Lofton, Benoît,
    Thanks for having taken time to discuss it while I was sleeping :-).

No problem!

    I have two questions:
        - Lofton, you give me the way to do it with WebCGM, what about ATA Profile ?

Hmmm... I was about to say "same".  ATA has adopted ESCAPE 46 (alpha transparency) from WebCGM.  But I just noticed that it did NOT adopt the registered COLOUR MODEL RGB-alpha.  This doesn't make sense to me (allow alpha transparency as a stand-alone modal attribute applied to subsequent primitives, but not attached to modal colour attributes?).

This looks like an oversight to me.

Let's ask Dave (Cruikshank) -- ATA GWG chair... Dave, do you see any logic to allowing alpha transparency in ESCAPE 46 but not in colour definitions?


        - Benoît, the way you use defs/use SVG with rect and circle is a kind of workaround, but the question is how to have the canvas transparent. Then you said that canvas in SVG are initialized to transparent black. As I am a user and more a computer scientist than a graphical art specialist, what is transparent black? This is said many times in SVG but I did not manage to find a definition.
Regards and/et Cordialement,
Franck DULUC
SDND - Digital Data Definition and Research
B.P. D0611
316, route de Bayonne
Phone: (33)
Fax: (33)
-----Message d'origine-----
De : Lofton Henderson [mailto:lofton@rockynet.com]
Envoyé : jeudi 28 août 2003 18:25
À : Benoit Bezaire
Cc : cgmopen members mailing list
Objet : RE: A CGM Question: handling transparency

Hi Benoit,
Hi Benoit,

At 12:16 PM 8/28/03 -0400, Benoit Bezaire wrote:
SVG 1.0 ... what is the background?  I.e., if you just have a simple file, <svg>...blah...blah...</svg>, what is the "...blah...blah..." drawn on or over?  You are much more involved with this than I, and I'm drawing a blank on the answer.  Is it well defined in the SVG 1.0 standard, or undefined (i.e., "nothing", transparent), or viewer-dependent?
[Benoit Bezaire] Yes, it is well defined.  A canvas in SVG 1.0/1.0 is always initialized to transparent black.  You can find more info at:

Thanks, that's the bit that I couldn't remember.

The WebCGM solution that I proposed earlier achieves that same effect -- choose the RGB-alpha colour model, and set BACKGROUND COLOUR to (0,0,0,0).


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