RE: [cgmo-webcgm] Why edge-visibility?

[Lofton Henderson <lofton@rockynet.com>]

Summarizing:

CGM:1999 -- allows 0 for LINE WIDTH and EDGE WIDTH.  The effect is
not normatively defined, but annex D.4.6.3 and D.4.6.18 recommend
"minimum available line/edge width."

WebCGM -- allows 0 for LINE WIDTH and EDGE WIDTH.  T.20.3 and
T.20.28 make it normative -- Minimum available line/edge width.

WebCGM -- 5.7.5 defines stroke-weight as overriding both LINE WIDTH and
EDGE WIDTH; 0 is illegal.  (For historical reasons, I think -- see
below.)

Therefore EDGE VISIBILITY is the *only* way to turn off the edges in
CGM:1999, and edge-visibility is the only way to turn them off via the
DOM.

History:

IIRC, we had a lengthy discussion about this sometime ago -- whether
CGM:1999 got it right (0 = minimal, instead of nothing) for LINE/EDGE
WIDTH.  Whether WebCGM 1.0 should have followed D.4.6.3. 
Whether we could change the 1.0 specification retroactively. 
Whether stroke-weight SP should behave the same.  As I recall, we
agreed that we wouldn't design the whole mess the same way if starting
from scratch, but didn't want to contradict CGM:1999 or change the WebCGM
1.0 spec.

-Lofton.

At 02:24 PM 1/7/2009 -0700, Robert Orosz wrote:

Dieter is right, WebCGM doesn't allow a value of zero for the stroke-weight style property. So, the edge-visibility style property would be the only way to override the edge visibility attribute in a given WebCGM instance.
 
Rob

-----Original Message-----

From: Weidenbrueck, Dieter [mailto:dweidenbrueck@ptc.com]

Sent: Wednesday, January 07, 2009 1:57 PM

To: Robert Orosz; Bezaire, Benoit; WebCGM

Subject: RE: [cgmo-webcgm] Why edge-visibility?

What happens if one sets a stroke-weight of zero on an edge? This is not allowed in CGM AFAIK. Do we imply using edge-visibility in these cases?

 

From: Robert Orosz [mailto:roboro@auto-trol.com]

Sent: Mittwoch, 7. Januar 2009 21:54

To: Bezaire, Benoit; WebCGM

Subject: RE: [cgmo-webcgm] Why edge-visibility?

 

The stroke-weight style property applies to both lines and edges. So, if you wanted to turn off edge display without affecting the other lines in the drawing, you need the edge-visibility.

 

Rob

-----Original Message-----

From: Bezaire, Benoit [mailto:bbezaire@ptc.com]

Sent: Wednesday, January 07, 2009 1:42 PM

To: WebCGM

Subject: [cgmo-webcgm] Why edge-visibility?

Hi All,

 

I'm wondering what is the need of edge-visibility? Wouldn't a stroke-weight of zero have the same effect?

 

Thanks,

Benoit.