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Subject: RE: [cgmo-webcgm] WebCGM traversal routines


All,

it really doesn't make a difference for screen redraw. If any style change
occurs on foo:two, you will have to redraw the entire area that foo:two
covers, which is the combined area of the bounding boxes before and after
the style change.

Example:

If you first increase the lineweight on that APS you may get away by
redrawing only the APS itself plus everything that is in front of it.
If you then reduce the lineweight you discover parts of anything that lies
behind foo:two, hence you have to redraw everything in that area.

Dieter

-----Original Message-----
From: Cruikshank, David W [mailto:david.w.cruikshank@boeing.com]
Sent: Friday, October 08, 2004 6:42 PM
To: Benoit Bezaire; CGM Open WebCGM TC
Subject: RE: [cgmo-webcgm] WebCGM traversal routines


All,

When I think of the structure of a CGM file with respect to hierarchy, I
think in terms of SGML/XML hierarchy.  That means first child to me means
the first one in the order of the hierarchy, not the last one drawn
graphically.

The question that remains in my mind is the graphical effect.  If you have
three children aps; foo:one, foo:two, and foo:three, and you change the
style of foo:two, do all three have to be re-generated in the graphical
display?  Is there a difference depending on the choice of whether foo:one
or foo:two is first child?

thx...dave

-----Original Message-----
From: Benoit Bezaire [mailto:benoit@itedo.com]
Sent: Thursday, October 07, 2004 8:38 AM
To: CGM Open WebCGM TC
Subject: [cgmo-webcgm] WebCGM traversal routines


Hi all,

  I have a question regarding the WebCGM DOM traversal routines.  I
  have to admit, this one took me by surprise.  Let's take the
  following WebCGM document snippet as an example:

  BEGAPS 'group' ...
  BEGAPSBODY;
    BEGAPS 'one' ...
    ...
    ENDAPS;
    BEGAPS 'two' ...
    ...
    ENDAPS;
    BEGAPS 'three' ...
    ...
    ENDAPS;
    BEGAPS 'four' ...
    ...
    ENDAPS;
  ENDAPS;

  In your opinion; what is the firstChild of 'group'?  Being accustomed
  to the XML world, I was convinced that the answer would be 'one';
  but the existing Isodraw code tells me otherwise, it claims that
  'four' is the firstChild.  Dieter then explained that 'four'
  is the firstChild since it's the foremost object of the group.
  Ok, now it makes sense to me.

  We believe (and please correct us if we are wrong) that other
  private APIs from vendors of this group behave like ours; that a
  firstChild of a group is not the first child based on file order but
  instead, the foremost element (visual tree order).

  So the question is; do we want to adopt the XML/SVG approach (file
  order) or stick with current practices of CGM vendors (visual tree
  order)?

  Note: if we do stick with current practices, I would recommend
  changing the names of these APIs or else they'll be confused with
  XML/SVG APIs.

  I don't know what my preference is on this.  I'm some times in
  favour of the XML/SVG approach (since script writers are used to
  this) but I could be convinced otherwise since WebCGM files are
  binary (so your are left with what you see on screen).  What is
  problematic for me are the XML metadata nodes:

  BEGAPS 'group' ...
  BEGAPSBODY;
    BEGAPS 'foo:simpleData' ...
    ...
    ENDAPS;
    BEGAPS 'foo:complexData' ...
    ...
    ENDAPS;
  ENDAPS;

  Why would the firstChild of 'group' be 'foo:complexData'?

  Obviously looking for your input,

  Regards,

--
 Benoit                 mailto:benoit@itedo.com




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