Re: [cgmo-webcgm] Two CGM/profile questions

[Lofton Henderson <lofton@rockynet.com>]

At 01:26 PM 6/28/2004 +0200, DULUC Franck wrote:

> Dear all,
>
>         Here are two little questions coming from a person working for me in Airbus (in C/C of this email). 
>
>         Your feedback will be appreciated: 
>
>                 - does Metafile Description element content has to be ordered? (ProfileId then ProfileEd...) 

ISO CGM:1999 requires that valid profiles identify themselves unambiguosly with ProfileId and ProfileEd.  It does not place any constraint on the order.  WebCGM does not constrain the order.  Therefore, IMO, the two pieces (substrings) can be in any order.

References:  CGM:1999 clause 9.5.2.1 and PPF row T.16.2;  WebCGM PPF row T.16.2.

>                 
>                 - in CGM specification (part1), for background colour and table colour default value (p.216) we have 'device-dependent', what does it mean?

It means, if a CGM instance (metafile) does not contain elements that explicitly set the background colour or colour table entries, before elements are encountered that must be drawn,  then the CGM viewer is free to chose the initial colours for background and foreground (i.e., drawn primitives).

Example.  A bitonal drawing (background and only 1 foreground colour used) can be drawn black-on-white for paper/print, or white-on-black for video screen, if there are no BACKGROUND COLOUR and COLOUR TABLE elements in the file.

Note.  All valid profiles contain an "all or none" colour rule.  Metafiles must either defined all colours used (incl. background) or none of them.  I.e., define them all, or default them all, but do NOT define some explicitly and let the others default.

Cheers,
-Lofton.