<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>Wow, I wish I could read specifications better!</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Thanks for an email introduction!</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>Tuesday, July 17, 2018 8:01 PM<br><b>To: </b><a href="mailto:yottzumm@gmail.com">John Carlson</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] HAnim Displacer examples</p></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I found this tutorial the best introduction into how skinning is</p><p class=MsoNormal>performed with glTF:</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>https://github.com/KhronosGroup/glTF-Tutorials/blob/master/gltfTutorial/gltfTutorial_019_SimpleSkin.md</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The spec. itself is short on detail:</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#skins</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The principles at work in both HAnim and glTF are very similar:</p><p class=MsoNormal>joints, weights, transforming from and to joint space, taking into</p><p class=MsoNormal>account the root trafo.</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>There are some important differences. Apparently, the weights in glTF</p><p class=MsoNormal>are direct factors for the joint matrices, and not applied to the</p><p class=MsoNormal>transformed vertex positions like in HAnim. That is how the tutorial</p><p class=MsoNormal>explains it although let's check Three.js implementation to be sure.</p><p class=MsoNormal>The inverse bind matrix needs to be precomputed and provided (although</p><p class=MsoNormal>I think it could be derived from the joint local coordinate system).</p><p class=MsoNormal>The mapping of vertices to be deformed to weighted joints is</p><p class=MsoNormal>different. In glTF each vertex of a skinned mesh is mapped, perhaps</p><p class=MsoNormal>most with 0 weights. In HAnim the joint defines the vertices it</p><p class=MsoNormal>influences.</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I think the shader idea in glTF can be perhaps applied to HAnim: Per</p><p class=MsoNormal>vertex two additional vec4 attributes which are four indices into a</p><p class=MsoNormal>joint matrix array and four weights (as floats).</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>On Tue, Jul 17, 2018 at 4:52 PM John Carlson <yottzumm@gmail.com> wrote:</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>><o:p> </o:p></p><p class=MsoNormal>> GPU assisted HAnim would be best coordinated with glTF skinned</p><p class=MsoNormal>><o:p> </o:p></p><p class=MsoNormal>> deformation support in x3dom. This may require first thinking about</p><p class=MsoNormal>><o:p> </o:p></p><p class=MsoNormal>> how both compare in some detail.</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>> -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>><o:p> </o:p></p><p class=MsoNormal>> Do we have some good glTF examples?</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>> Thanks,</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>> John</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></div></body></html>