[x3d-public] glTF - HAnim conversion

Leonard Daly Leonard.Daly at realism.com
Tue Dec 11 09:56:56 PST 2018


On 12/11/2018 8:13 AM, Joseph D Williams wrote:
>
> I meant simple standard gltf use of 16 joints per vertex with unused 
> weights set to 0.
>

Joe,

I do not know what you are referring to or where you got your information.

I found a tutorial on the Khronos GitHib 
(https://github.com/KhronosGroup/glTF-Tutorials/blob/master/gltfTutorial/gltfTutorial_020_Skins.md) 
that discusses skinning, rigging, and animation. In "The skinning joints 
and weights" section, it states that (2nd paragraph) the the data 
structure that connects vertices to joints is commonly stored in a 
4-element vector. This limits the number of different joints that can 
affect a vertex to four.


Leonard Daly




> Joe
>
> Sent from Mail <https://go.microsoft.com/fwlink/?LinkId=550986> for 
> Windows 10
>
> *From: *Joseph D Williams <mailto:joedwil at earthlink.net>
> *Sent: *Tuesday, December 11, 2018 8:11 AM
> *To: *Leonard Daly <mailto:Leonard.Daly at realism.com>; 
> x3d-public at web3d.org <mailto:x3d-public at web3d.org>
> *Subject: *Re: [x3d-public] glTF - HAnim conversion
>
> 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.
>
> Joe
>
> *From: *Leonard Daly <mailto:Leonard.Daly at realism.com>
> *Sent: *Tuesday, December 11, 2018 7:38 AM
> *To: *x3d-public at web3d.org <mailto: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
> LA ACM SIGGRAPH Past Chair
> President, Daly Realism - /Creating the Future/
>
>
>
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> x3d-public mailing list
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-- 
*Leonard Daly*
3D Systems & Cloud Consultant
LA ACM SIGGRAPH Past Chair
President, Daly Realism - /Creating the Future/
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