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<div class="moz-cite-prefix">Michalis states the spec correctly wrt
DEF/USE and node reuse. X3DOM is operating in the HTML5
environment. HTML5 prohibits an element with multiple parents, so
the X3D node cannot be inserted into the HTML5 document; however,
it can be multiply-parented in the scene graph as that is not part
of the DOM.<br>
<br>
Leonard Daly<br>
<br>
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cite="mid:CAKzBGZOecDF=0tEhPYkTWZRXGk7A0bi6kmY0pb=bTPv_Sb6fOg@mail.gmail.com">
<pre wrap="">2017-12-20 15:51 GMT+01:00 Andreas Plesch <a class="moz-txt-link-rfc2396E" href="mailto:andreasplesch@gmail.com"><andreasplesch@gmail.com></a>:
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<pre wrap="">(DEF/USE in x3dom: There are a several x3dom issues about picking a
USE Shape. Since x3dom literally places the referenced DEF Shape in
the scene graph, the picking actually reports the node of the
referenced DEF Shape when the USE Shape is picked. This is because
x3dom actually does not keep a distinct representation of the USE node
at all. Except for the fact that the DEF node now has two parents.
This may be too literal an interpretation of the DEF/USE concept, and
I wonder if in the spec. there is a section which explains how the
node which has a USE reference is still a distinct node. I suspect
that keeping such a distinct node around is how most x3d browsers work
?
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<pre wrap="">
This DEF / USE (in x3dom) treatment is required by the X3D
specification, and it (should) be the same in all VRML / X3D browsers.
I know it is the same in view3dscene and Castle Game Engine. When we
encounter a "USE Xxx" then internally we *do not* make a copy of the
"Xxx" node, instead we make an additional link to the "Xxx" node that
in effect has 2 parents. This implementation is most natural and
practically required by the X3D specification:
<a class="moz-txt-link-freetext" href="http://www.web3d.org/documents/specifications/19775-1/V3.2/Part01/concepts.html#DEFL_USESemantics">http://www.web3d.org/documents/specifications/19775-1/V3.2/Part01/concepts.html#DEFL_USESemantics</a>
"""
The USE statement does not create a copy of the node. Instead, the
same node is inserted into the scene graph a second time, resulting in
the node having multiple parents (see 4.3.5 Transformation hierarchy,
for restrictions on self-referential nodes).
"""
And that's a very good concept, in my opinion: it allows to use DEF /
USE mechanism for various optimizations. Since you have only one copy
of the node, you should also be able to have only one copy of various
internal things (like OpenGL VBO data) associated e.g. with Shape that
is USEd multiple times. This is really powerful, you can construct a
large scene by USEing the same shapes multiple times, and it will
still render fast and not eat too much memory:)
In contrast, expanding the PROTOtypes makes a copy on the contents.
Regards,
Michalis
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</pre>
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<div class="moz-signature">-- <br>
<font class="tahoma,arial,helvetica san serif" color="#333366">
<font size="+1"><b>Leonard Daly</b></font><br>
3D Systems & Cloud Consultant<br>
LA ACM SIGGRAPH Past Chair<br>
President, Daly Realism - <i>Creating the Future</i>
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