RE: Question about setView()

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.