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RE: More on getObjectExtent()

From: Bezaire, Benoit <bbezaire@ptc.com>
Date: Tue, 2 Dec 2008 10:58:34 -0500
Message-ID: <B0D4682CF6F84041AC7C42AA6E9E81330C68E101@HQ-MAIL3.ptcnet.ptc.com>
To: "WebCGM WG" <public-webcgm-wg@w3.org>
If company ABC were to hire a computer science new grad (or even a
senior software developer) to implement parts of WebCGM 2.1, he would
read the getObjectExtent wording and say 'what the'? He would read it
again and still say 'what the'? Then he walk to his manager's office and
- what's the extent of a raster?
- what's the extent of a bezier curve? (we've now clarified that one)
- what's the extent of left to right string of text?
- what's the extent of top down string of text?
- how does this work with clipping?
- etc...
Regarding rasters. My point was that 'raster', 'image', 'cell array',
'tile array' is not to be found in the getObjectExtent() wording. You
had to go back to CGM:1999 to find the answer.
Regarding text. What I think is meant is that the font family ascent and
descent define the 'length of the side in the text-up direction'.
Correct? Another question that comes to mind immediately after reading
the wording is how to get the extent for non Restricted Text box.
Another puzzling thing for me is that we say 'bottomline-to-topline
distance of the font', we don't say anything about the used glyphs.
So say the following three strings have the same text attributes:
- "abc" (goes above x-height)
- "wagon" (goes below baseline)
- "were once common" (uses only x-height, no descent, nothing above
x-height or cap height)
According to the wording, they would all have the same 'height'. If
those strings were treated as path, they would yield different heights.


From: public-webcgm-wg-request@w3.org
[mailto:public-webcgm-wg-request@w3.org] On Behalf Of Lofton Henderson
Sent: Monday, December 01, 2008 5:31 PM
Subject: RE: More on getObjectExtent()

At 09:49 AM 12/1/2008 -0500, Bezaire, Benoit wrote:

	Hi Dieter,
	I think most of them (except rasters) have been addressed. 

Please clarify what might be missing here.  Per my previous message, I
did a quick read about Cell Array and Tile Array in CGM:1999.  It seems
clear what is the extent (ignoring transparency/visibility controls for
the moment).  But maybe I'm missing something -- after all, I haven't
tried to implement gOE().

	However, I do not think the group agreed to treat text as path.

Just to be sure I'm understanding -- what exactly does "treat text as
path" mean?  Does it mean the minimal containing box of all the
strokes/areas that are used to actually render the string?

The 2nd paragraph of the gOE description in 5.7.6 seems pretty
definitive, though maybe different from "treat text as path".  It also
seems like a lot cheaper computation.  So two questions:

1.) does the present 5.7.6 gOE approach have some fundamental problem
that makes it unsuitable?
2.) if that present approach is suitable, then:  are there some holes or
defects in the particular details as they are written?



	From: public-webcgm-wg-request@w3.org
[mailto:public-webcgm-wg-request@w3.org] On Behalf Of Weidenbrueck,
	Sent: Sunday, November 30, 2008 12:50 PM
	To: Lofton Henderson; WebCGM WG
	Subject: RE: More on getObjectExtent()
	good start. Do we need to add something about
	- raster images
	- text (should be treated as paths)
	- visibility/transparency (do they have an impact or not)
	- transformations (they do have an impact)

	From: public-webcgm-wg-request@w3.org
[mailto:public-webcgm-wg-request@w3.org] On Behalf Of Lofton Henderson
	Sent: Sonntag, 30. November 2008 17:26
	To: WebCGM WG
	Subject: Re: More on getObjectExtent()
	Since not everyone is satisfied with the simple fix of
"s/abstract locus/locus/" in 5.7.6, I'll make a proposal to close the
"locus" issue:  delete the word "abstract" and link "locus" to a
glossary entry.  
	Here is a first draft proposal:  
	locus -- 
	The Oxford dictionary defines locus as:  "Curve formed by all
points satisfying particular equation of relation between coordinates,
or by point, line, or surface, moving according to mathematically
defined conditions."  In the WebCGM specification, locus refers to the
set of points that comprise the path or shape of a Graphical Primitive
element, or in the appropriate context, the combined shapes or paths
collectively of all of the Graphical Primitive elements in an
Application Structure (APS).  I.e., the locus of an APS comprises the
combined loci of all of the graphical primitives in the APS.  Locus does
not include defining data that are not part of the shape or path of the
graphical primitive, such as control points of Bezier primitives, or the
center point of a Circular Arc Center primitive.
	Question 1:  Are people okay with the solution of adding a
definition to the Glossary?
	Question 2:  Suggestions for improvement of the definition?
	At 09:45 AM 11/19/2008 -0700, Lofton Henderson wrote:

		At 08:32 AM 11/19/2008 -0800, David Cruikshank wrote:

			I would agree with dropping "abstract".  Locus
is a perfectly valid term to define the path of the primitive.
			Probably ought to capture it somewhere to
document the decision.

		Just to clarify that last sentence -- you mean that you
support the issue processing proposal to roll it into Issue3 in the DoC
(see URI below)?

			On Wed, Nov 19, 2008 at 8:04 AM, Lofton
Henderson <lofton@rockynet.com> wrote:

				At 09:26 AM 11/19/2008 -0500, Bezaire,
Benoit wrote:

				I think the wording should be revised. 

				Fair enough.

				Even Google doesn't come up with
anything meaning full for "Abstract locus".

				However, it does give lots of hits for a
search like "definition of mathematical locus".  And we use "locus"
repeatedly, in the proper sense, in the profile (Ch.6) -- i.e., "locus"
is a pretty common term in  and has been used in WebCGM, for example,
since 1999.  So it is my hastily-invented modifier "abstract" that is
				Actually, I think a good solution would
be to drop the word "abstract".  The next sentence after its occurrence
fully explains what "abstract" was meant to convey.  (And we have agreed
to clarify that sentence.)
				(See the getObjectExtent definition in
http://docs.oasis-open.org/webcgm/v2.1/cs01/WebCGM21-DOM.html#L5095 .)
				(Shall I just add this to fix to the
clarification in DoC #3:
e3  ?)


				From: Lofton Henderson
				Sent: Tuesday, November 18, 2008 6:52 PM
				To: Bezaire, Benoit; WebCGM WG
				Subject: Re: More on getObjectExtent()
				At 01:52 PM 11/18/2008 -0500, Bezaire,
Benoit wrote:

				The wording says "[...] The bounding box
calculation is based on the abstract locus of the primitives within the
				What does 'abstract locus' mean?

				The locus is the set of points
comprising the drawn primitive (it's a term I dredged up from my memory
of some old math courses -- I hope I got it right).  "Abstract locus"
means that things like line width are not included, but rather only the
point positions as if the item were drawn with an abstract, infinitely
fine pen.

				I'd like to know if getObjectExtent()
returns a tight bounding box on a given APS. i.e., given a polybezier,
are control points part of the bounding box calculations or not?

				No.  The control points are part of the
defining data, but not part of the drawn primitive.
Received on Tuesday, 2 December 2008 15:59:50 UTC

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