RE: Question about setView()

I have put this on tomorrow's agenda...

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 says nothing 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.