[x3d-public] glTF - HAnim conversion

Joseph D Williams joedwil at earthlink.net
Tue Dec 11 08:10:52 PST 2018

What was the detail that (for the convenience of the hardware) ‘always’ used 19 joints per vertex with unused joints weights set to 0?
I thought I have heard that a few times.

From: Leonard Daly
Sent: Tuesday, December 11, 2018 7:38 AM
To: x3d-public at web3d.org
Subject: Re: [x3d-public] glTF - HAnim conversion

• glTF associates a joint or
multiple joints to each vertex of a mesh 
yes, gltf apparently associates ‘all’ or always at least 16(?) joints (and weights) with each vertex. That means there is feature called a vertex that has a list of joints and weights associated with it. There is one of these for each vertex, all listing all joints and weights.

Yes. For glTF, the minimum a compliant viewer needs to support is 4 joints (out of many) per vertex. A viewer is free to ignore additional joints, with the lowest weights.

Standard practice in the animation industry is to use a maximum of four joints per skin vertex. There is no standard that limits this. Practical experience from rigging (attaching vertices to joints (aka bones)) and performance indicates that (for the most part) four is the most that is needed. In many cases it is only two.

So for practical purposes, the limit in glTF does not impact what can be done.

Leonard Daly
3D Systems & Cloud Consultant
President, Daly Realism - Creating the Future 

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