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RE: re[2]: invalid/extreme rectangles in setView()

From: Lofton Henderson <lofton@rockynet.com>
Date: Thu, 04 Dec 2008 14:46:12 -0700
Message-Id: <5.1.0.14.2.20081204143405.01618930@localhost>
To: "WebCGM WG" <public-webcgm-wg@w3.org>

Okay, we have:

1 vote for "as is" in 2.1 LCWD -- lower-left and upper-right corners.  And 
addressing the implied error condition (in setView -- invalid rectangle) 
if, for example, the input points were upper-left and lower-right.

1 vote for changing to "two diagonal corner points", consistent with all 
other rectangles in WebCGM.

Other thoughts?

Unless there is a clear majority for changing, "as is" wins.

Just to clarify...

Btw, as I understand, no one is proposing error conditions in WebCGMRect, 
are they?  I thought Ben was asking for some return indication or exception 
from setView().  So it would be possible to create a WebCGMRect with the 4 
numbers leading to a "bad" rect.
E.g., myRect.xll>myRect.xur  and yRect.yll>myRect.yur

(Although Ben asked about setView(), what would unionRect() do about bad 
input?)

-Lofton.

At 03:57 PM 12/4/2008 -0500, Bezaire, Benoit wrote:

>Let's try an make is easy for script writers, ok? Else these new DOM
>calls will never get used.
>
>Two opposite corner points just complicates the code for script writers,
>they have to add 'checks' to determine which point is which. I didn't
>oppose the decision for viewcontext back in WebCGM 2.0 since script
>writers were unlikely to change the viewcontext. I think it's different
>for WebCGMRect() though.
>
>Benoit.
>
>-----Original Message-----
>From: public-webcgm-wg-request@w3.org
>[mailto:public-webcgm-wg-request@w3.org] On Behalf Of Don
>Sent: Thursday, December 04, 2008 3:30 PM
>To: Lofton Henderson; WebCGM WG
>Subject: re[2]: invalid/extreme rectangles in setView()
>
>
>Lofton,
>
>  >  At 01:12 PM 12/4/2008 -0600, Don wrote:
>
>  >  >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.
>
>  >  Side question:  I just looked at WebCGMRect.  Does anyone recall why
>we  >  parameterized it in terms of "lower left corner" and "upper right
> >  corner"?  Why not just "two diagonally opposite corner points P1 and
>P2  >  [(x1,y1) and (x2,y2)]"?
>
>I not sure why but I think it would be nice to be consistent with
>viewcontext where we define viewcontext as "defining two corner points
>of a rectangle".
>
>http://www.w3.org/TR/2008/WD-webcgm21-20080917/WebCGM21-IC.html#webcgm_3
>_2_2_2
>
>  >  For the former, it sets up an error condition (or is "error prone").
>Do we  >  need that error condition?  For the latter, the only error
>condition is a  >  degenerate rectangle, i.e., zero area, i.e.,
>xmin=xmax and/or ymin=ymax.
>
>I don't think we need any error checking at all on WebCGMRect. A
>programmer may want to set a WebCGMRect = 0,0,0,0 for example as some
>kind of indication.
>
>Don.
>  >  There may be a reason we did it this way (more error prone, or
>allows  >  setting an error), but I don't recall it.  I do recall the
>stuff about  >  getObjExt() on an APS with no primitives, but we now
>return 'null' for  >  that, so we don't need the somewhat hokey mirrored
>rectangle.
>
>  >
>http://www.w3.org/TR/2008/WD-webcgm21-20080917/WebCGM21-DOM.html#webcgmr
>ect
>
>  >  -Lofton.
>
>
>  >  >  >  -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 21:47:04 GMT

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