<html xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"><head><meta http-equiv=Content-Type content="text/html; charset=utf-8"><meta name=Generator content="Microsoft Word 15 (filtered medium)"><style><!--
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--></style></head><body lang=EN-US link=blue vlink="#954F72"><div class=WordSection1><p class=MsoNormal>Andreas, I think if you want to distinguish USE nodes with picking, you would use a separate node.</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>John</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Sent from <a href="https://go.microsoft.com/fwlink/?LinkId=550986">Mail</a> for Windows 10</p><p class=MsoNormal><o:p> </o:p></p><div style='mso-element:para-border-div;border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal style='border:none;padding:0in'><b>From: </b><a href="mailto:andreasplesch@gmail.com">Andreas Plesch</a><br><b>Sent: </b>Wednesday, December 20, 2017 2:18 PM<br><b>To: </b><a href="mailto:michalis.kambi@gmail.com">Michalis Kamburelis</a><br><b>Cc: </b><a href="mailto:x3d-public@web3d.org">X3D Graphics public mailing list</a><br><b>Subject: </b>Re: [x3d-public] review of various X3D statement implementations forX3DOM</p></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Hi Michalis,</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>yes, that is how DEF/USE should be implemented. The point I am trying</p><p class=MsoNormal>to understand is if there is absolutely no distinction between the</p><p class=MsoNormal>original DEF node and a USE node which references the DEF node, how</p><p class=MsoNormal>can the USE node be identified, for example during picking ? The USE</p><p class=MsoNormal>node still needs to have at least a distinct ID, right ?</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>A conceptual scene graph structure may look like this:</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>group1</p><p class=MsoNormal> node 1: DEF "original"</p><p class=MsoNormal>group2</p><p class=MsoNormal> node 2: USE "original"</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>There are still two nodes. node 2 is not a copy of node 1 but is still</p><p class=MsoNormal>a separate node which happens to reference node 1.</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Or</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>group1</p><p class=MsoNormal> node 1: DEF "orginal"</p><p class=MsoNormal>group2</p><p class=MsoNormal> node 1 (inserted a second time during scene graph construction)</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Closer to spec. but makes it hard (impossible?) to distinguish the two</p><p class=MsoNormal>node 1 instances from each other.</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>So I was thinking something like an additional ID may have to exist:</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>1. group1</p><p class=MsoNormal>2. node 1: DEF "orginal"</p><p class=MsoNormal>3. group2</p><p class=MsoNormal>4. node 1 (inserted during scene graph construction)</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>?</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>-Andreas</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>On Wed, Dec 20, 2017 at 11:03 AM, Michalis Kamburelis</p><p class=MsoNormal><michalis.kambi@gmail.com> wrote:</p><p class=MsoNormal>> 2017-12-20 15:51 GMT+01:00 Andreas Plesch <andreasplesch@gmail.com>:</p><p class=MsoNormal>>> (DEF/USE in x3dom: There are a several x3dom issues about picking a</p><p class=MsoNormal>>> USE Shape. Since x3dom literally places the referenced DEF Shape in</p><p class=MsoNormal>>> the scene graph, the picking actually reports the node of the</p><p class=MsoNormal>>> referenced DEF Shape when the USE Shape is picked. This is because</p><p class=MsoNormal>>> x3dom actually does not keep a distinct representation of the USE node</p><p class=MsoNormal>>> at all. Except for the fact that the DEF node now has two parents.</p><p class=MsoNormal>>> This may be too literal an interpretation of the DEF/USE concept, and</p><p class=MsoNormal>>> I wonder if in the spec. there is a section which explains how the</p><p class=MsoNormal>>> node which has a USE reference is still a distinct node. I suspect</p><p class=MsoNormal>>> that keeping such a distinct node around is how most x3d browsers work</p><p class=MsoNormal>>> ?</p><p class=MsoNormal>><o:p> </o:p></p><p class=MsoNormal>> This DEF / USE (in x3dom) treatment is required by the X3D</p><p class=MsoNormal>> specification, and it (should) be the same in all VRML / X3D browsers.</p><p class=MsoNormal>> I know it is the same in view3dscene and Castle Game Engine. When we</p><p class=MsoNormal>> encounter a "USE Xxx" then internally we *do not* make a copy of the</p><p class=MsoNormal>> "Xxx" node, instead we make an additional link to the "Xxx" node that</p><p class=MsoNormal>> in effect has 2 parents. This implementation is most natural and</p><p class=MsoNormal>> practically required by the X3D specification:</p><p class=MsoNormal>><o:p> </o:p></p><p class=MsoNormal>> http://www.web3d.org/documents/specifications/19775-1/V3.2/Part01/concepts.html#DEFL_USESemantics</p><p class=MsoNormal>><o:p> </o:p></p><p class=MsoNormal>> """</p><p class=MsoNormal>> The USE statement does not create a copy of the node. Instead, the</p><p class=MsoNormal>> same node is inserted into the scene graph a second time, resulting in</p><p class=MsoNormal>> the node having multiple parents (see 4.3.5 Transformation hierarchy,</p><p class=MsoNormal>> for restrictions on self-referential nodes).</p><p class=MsoNormal>> """</p><p class=MsoNormal>><o:p> </o:p></p><p class=MsoNormal>> And that's a very good concept, in my opinion: it allows to use DEF /</p><p class=MsoNormal>> USE mechanism for various optimizations. Since you have only one copy</p><p class=MsoNormal>> of the node, you should also be able to have only one copy of various</p><p class=MsoNormal>> internal things (like OpenGL VBO data) associated e.g. with Shape that</p><p class=MsoNormal>> is USEd multiple times. This is really powerful, you can construct a</p><p class=MsoNormal>> large scene by USEing the same shapes multiple times, and it will</p><p class=MsoNormal>> still render fast and not eat too much memory:)</p><p class=MsoNormal>><o:p> </o:p></p><p class=MsoNormal>> In contrast, expanding the PROTOtypes makes a copy on the contents.</p><p class=MsoNormal>><o:p> </o:p></p><p class=MsoNormal>> Regards,</p><p class=MsoNormal>> Michalis</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>-- </p><p class=MsoNormal>Andreas Plesch</p><p class=MsoNormal>Waltham, MA 02453</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>_______________________________________________</p><p class=MsoNormal>x3d-public mailing list</p><p class=MsoNormal>x3d-public@web3d.org</p><p class=MsoNormal>http://web3d.org/mailman/listinfo/x3d-public_web3d.org</p><p class=MsoNormal><o:p> </o:p></p></div></body></html>