Trouble creating programmatic skeleton and bones

Questions
1

Hello, I am trying to create a simple skeleton that consists of individual meshes that are attached to each bone, no weights. I’ve created a basic skeleton with pelvis, thigh and shin bones, but I’m not getting the result that I expect.

  1. The skeletal viewer shows a strange visualization of bones, where they are all just pointing straight up. And, only the LINES visualization seems to display anything, the SPHERES and SPHERE_AND_SPURS style displays nothing.

  2. I was expecting the lines between bones to be connected, and I thought setting the rest pose translations was all that’s necessary to achieve this.

The code for my example is available here:
https://playground.babylonjs.com/#AT1ZNB

2

Welcome aboard!

Have a look at this thread for a PG that creates a skeleton manually: Bones - Freeze transformations - #7 by reimund

Other threads related to bones and skeletons that may help:

1 Like
3

Thanks for the links, especially the playground by reimund.

Using the example, I was able to deduce that the problem for why the bones were all pointing up was:

  • bone.length = ...

Afterwards, I tried changing the visualizer to use SPHERE_AND_SPURS, but that resulted in no visualization at all. Making the following changes fixed this:

  • Remove setRestPose()
  • Put the default transformation directly into the Bone constructor

Final code adjustments:

function make_bone(skeleton, parent, name, rest_pose, length) {
    const bone = new BABYLON.Bone(name, skeleton, parent, rest_pose);
    //const bone = new BABYLON.Bone(name, skeleton, parent);
    //bone.setRestPose(rest_pose);
    //bone.length = length;
    return bone;
}

I’m not sure why these changes were necessary, would greatly appreciate an explanation.

Updated my playground: https://playground.babylonjs.com/#AT1ZNB#1

4

All I can tell is that when you pass your initial matrix (rest_pose) as the 4th parameter of the constructor, this matrix is used to generate an internal _invertedAbsoluteTransform matrix which seems needed for the skeleton to generate the correct bone matrices used by the vertex shader.

5

Thanks anyway, at least I’ve solved my initial problem :slight_smile: