[x3d-public] glTF - HAnim conversion

Joseph D Williams joedwil at earthlink.net
Tue Dec 11 10:33:17 PST 2018


I believe in a reasonable limit is four in relatively simple humanoid joint animations, and it makes sense in the days before GPU with specialized scripts. Maybe this advice should be in hanim somewhere, but this is still mainly platform specific, and a 'recommendation’ to maybe limit artists from just depending totally upon joints and also use displacer-like objects for high detail. 

But the idea of the list of 16 joints per vertex was how to handle the packaging and I thought I understood that the hardware likes it best where the field is filled with 16 references including bunches of zeros if not applied in that step.  

Glad you saw that very basic free-form, not-hanim-related at all, tutorial. Andreas is working at just above that level last I saw. 
Can you see and give a read to the skin-no-geometry example I sent a few ago? 

As we progress in learning about this important topic – in fact the entire reason that vrml was created is hanim - with further learning we will find better understanding of the humanoid model, and at some point dismiss (the very primitive) idea of using translation rather than center for describing effective joint locations in the skeleton that exists in the humanoid space.   

Thanks and Best,
Joe




From: Leonard Daly
Sent: Tuesday, December 11, 2018 9:57 AM
To: x3d-public at web3d.org
Subject: Re: [x3d-public] glTF - HAnim conversion

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 for Windows 10
 
From: Joseph D Williams
Sent: Tuesday, December 11, 2018 8:11 AM
To: Leonard Daly; 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
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
LA ACM SIGGRAPH Past Chair
President, Daly Realism - Creating the Future 
 
 



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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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