RE: A CGM Question: handling transparency

[Lofton Henderson <lofton@rockynet.com>]

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?

-Lofton.

        - 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
AIRBUS FRANCE
SDND - Digital Data Definition and Research
B.P. D0611
316, route de Bayonne
31060 TOULOUSE Cedex FRANCE
Phone: (33)5.61.18.19.16
Fax: (33)5.61.93.59.44
mailto:franck.duluc@airbus.com

-----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:

http://www.w3.org/TR/SVG11/render.html#Grouping

http://www.w3.org/TR/SVG11/render.html#Elements

 

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).

Cheers,
-Lofton. 

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