[Ctk-developers] Scenes

Fri Sep 18 21:56:16 UTC 2009

The advantage of a scene graph comes primarily from those nodes which
define attributes rather than drawn objects, because those attributes
can be inherited in lower branches of the scene and represent the state
of the system at any point during scene graph traversal - that is a key
feature, especially when it comes to transform matrices. "Separator"
objects prevent those state changes from propagating, while "Group"
objects don't. It is this mechanism that makes scene graphs ideal for
setting up coordinate systems and controlling parts that move with
respect to each other.
Without that it's not a scene graph, it's a pipeline. Pipelines are
supported in Open Inventor too, but via objects called engines rather
than nodes.

-----Original Message-----
From: ctk-developers-bounces at commontk.org
[mailto:ctk-developers-bounces at commontk.org] On Behalf Of Wolf Ivo
Sent: Friday, September 18, 2009 5:02 PM
To: Stephen Aylward; ctk-developers at commontk.org
Subject: Re: [Ctk-developers] Scenes

Hi Stephen,
As for the MITK team, we traditionally like the type of definition of a
scene that you gave and the mode-view-controller pattern. Both is pretty
close to what is used within MITK (except for some extensions, which
would be great to have) and therefore could nicely be integrated from
CTK. Nevertheless, my feeling is that starting with a scene
implementation is not the easiest way to go.

And caution (correct me, if I am wrong): The Open Inventor definition of
a scene is different from yours (and ours)! Nodes in an Open Inventor
scene graph are not necessarily 'objects' (called shape nodes there),
but can also be lights, materials (e.g. color), transforms (matrices),
switches etc. Thus, the definition "a scene is composed of objects that
fill a portion of space and time" is not compatible with Open Inventor
(a material node does not fill a portion of space). Maybe it is possible
(and desirable) to combine both ideas of defining a scene graph: the
more data-centered approach defined above and the visualization-centered
approach of Open Inventor. But we should be careful that we are talking
about the same things (a topic for the list of questions). 

Regarding a brief presentation, we recently added some semantic
information to our scene description, which might be useful for ctk,
too.

Best regards,

Ivo

________________________________

Von: ctk-developers-bounces at commontk.org im Auftrag von Stephen Aylward
Gesendet: Do 17.09.2009 02:18
An: ctk-developers at commontk.org
Betreff: [Ctk-developers] Scenes

Hi,

ctkScene:  Love it?  Hate it?  Know you can make it better?

Regardless of your current attitude, please send me your ideas and
presentations!!!

I'd like to help organize the discussion on ctkScene that is scheduled
for next Friday.

1) If you are interested in making a brief presentation (less than 10
minutes), then please send me an email with the title.   I will add it
into our agenda.

2) If you have revisions to the Wiki page on ctkScene - please make
those revisions by 5pm EST (22:00 GMT) on Friday.   I am going to
summarize those wiki pages as a set of slides at the start of the
meeting.
      http://my-trac.assembla.com/protoctk/wiki/ctkScene

3) If you have questions, concerns, needs, wants, or rants regarding the
ctkScene, please send them to me and I will create a set of slides
that list "open-issues" to help focus our discussions.   We only have
one-hour, so I'd like to focus on high-level issues that remain, prior
to getting into implementation details.   For example, should a
ctkScene be only a file format or should it also be implemented as a
set of C++ classes?   Should a ctkScene be specific to or independent
of the visualization library?   Should a ctkScene be our primary data
structure, or should our primary data structure simply be an image?
...please add to this list of questions...

Thanks!
Stephen

--
Stephen R. Aylward, Ph.D.
Director of Medical Imaging
Kitware, Inc. - North Carolina Office
http://www.kitware.com <http://www.kitware.com/> stephen.aylward (Skype)
(919) 969-6990 x300
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