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re: invalid/extreme rectangles in setView()

From: Don <dlarson@cgmlarson.com>
Date: Thu, 4 Dec 2008 13:12:25 -0600
To: Lofton Henderson <lofton@rockynet.com>, WebCGM WG <public-webcgm-wg@w3.org>
Message-ID: <RFBWVTNOQSheOlJGKCpSLTE5NjkxMzQzOTA@foghorn>

Lofton,

 >  All -- 

 >  This is a dangling open piece of Benoit's setView() questions.  We closed
 >  the other piece (about different aspect ratios).  I can't find any thread
 >  discussion about this piece, after Benoit's message below (top), and it
 >  apparently remains open.

 >  Discussion?

I believe we should have very basic checking for Invalid rectangle and 
return boolean as Benoit suggested. A minimal invalidity check would be 
if ymax < ymin or xmax < ymin.  

Don.

 >  -Lofton.

 >  At 09:44 AM 11/19/2008 -0500, Bezaire, Benoit wrote:
 >  I remember this thread. I don't want to reopen old issues.
 >  
 >  However, for this particular API, a script writer can easily loose the
 >  display (zooming on a very small rectangle or zooming our far enough that
 >  nothing is displayed). I think the API should at least return a more
 >  meaningful  value.
 >  
 >  Some options:
 >  i) boolean: TRUE if new view was set; FALSE is rectangle was invalid.
 >  ii) float: returns the scale factor between the old view and the new view.
 >  > 0 is successful, failed otherwise.
 >  iii) WebCGMRect: a rectangle defining the old view.
 >  
 >  Any of those would help the script writer understand what went wrong,
 >  instead of getting in touch with technical support.
 >  
 >  Benoit.

 >  From: Lofton Henderson [mailto:lofton@rockynet.com] 
 >  Sent: Tuesday, November 18, 2008 7:08 PM
 >  To: Bezaire, Benoit; WebCGM WG
 >  Subject: Re: Question about setView()
 >  
 >  At 08:57 AM 11/18/2008 -0500, Bezaire, Benoit wrote:
 >  I'm wondering if the wording of setView() is not a bit short? The draft
 >  doesn't say anything about invalid rectangles being passed in for example.
 >  
 >  Should more feedback be sent to the user? Currently, the function
 >  prototype has a void return type. Should we change that to a boolean or
 >  something else? or throw an exception perhaps.
 >  Dieter raised and we discussed a similar question a few months back.  As a
 >  general rule, CGM and WebCGM say what happens with valid input but have
 >  been relatively silent about error fallbacks, viewer error reactions, etc.
 >  What we have done most recently is say something like "...has no effect".
 >  We generally have not gone to more extensive error reactions.  See for
 >  example the 'grnode' stuff that we added to the interfaces.

 >  My view is that, if we start opening the door to saying what viewers do
 >  for this and that bad input, where do we stop?  Should we go back and
 >  define mandatory error responses for all bad input?

 >  Note that the profile (Ch.6) *does* talk a lot about "degeneracies".  It
 >  says what is the graphical effect of a degenerate primitive, etc., and
 >  this is what is *suggested* in CGM:1999 itself -- WebCGM just makes it
 >  normative.  (But saysnothing more about what the viewer should do when
 >  encountering degeneracies. Silent?  Warning?  Task-bar "abnormality"
 >  icon?)

 >  I guess I favor "...invalid input has no effect, neither graphical nor to
 >  the DOM tree."  Then leave it to the implementor, what else the viewer
 >  might do in the way of error response to the user.

 >  
 >  I also question the possibility of a major scale change, ex: scaling in by
 >  a factor of 100 (and loosing sight of the overall picture). Should the
 >  user be told that such a change occurred?
 >  I guess I view this as another choice for implementors.

 >  I could also live with putting some valid limits on it.  "Valid rectangles
 >  shall not change the scale by more than ...blah..."

 >  -Lofton.
Received on Thursday, 4 December 2008 19:13:24 GMT

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