LWO Loader incorrect placement of geometry and mesh when used with pivot point placement

[WORMSS]

Description

Hello, I've made a few objects in Lightwave and I use the LWOLoader to load them.

Layer 1, I modeled an object around 0,0,0 and I apply rotation on that mesh, and everything works as expected.

On Layer 2, I modeled another object but I positioned it where it should be relative to Layer 1. But, being a little clever boy, I set the pivot point (Lets just say 2,1,0). In Lightwave when I tell to rotate from the pivot point, it moves as expected.
But when I use THREE to rotate the mesh, it rotates from 0,0,0 and not 2,1,0.

Anyone know how to make LWO respect the layer's Pivot Point?

Reproduction steps

Code

// code goes here

Live example

• jsfiddle-latest-release
• jsfiddle-dev

Screenshots

No response

Version

r156

Device

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Browser

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OS

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[WORMSS]

I've been digging deeper...
I had to learn how the LWO format works, (sadly all the specs on it point to a location on their website that no longer exists)..
Been pulling apart the LWO reader, and came across this little nugget..

pivot: this.reader.getFloat32Array( 3 ), // Note: this seems to be superflous, as the geometry is translated when pivot is present

So, I can see it actually records the pivot points.
but then you inverse translate the geometry instead of translate the mesh.

// TODO: z may need to be reversed to account for coordinate system change
geometry.translate( - layer.pivot[ 0 ], - layer.pivot[ 1 ], - layer.pivot[ 2 ] );

So, now the mesh is in the incorrect place but the geometry has been shifted over to make it "look" like it's in the correct place.
But it doesn't rotate from the correct place.
I don't believe there is a mechanism to move the pivot point of a THREE.Mesh to not rotate from 0,0,0 ? Correct?

[mrdoob]

Is that the best issue title you can come up with? 🤓

[WORMSS]

I suspected I typed it in as a place holder so I could gather all the information and then make a better one..
But I actually went away and came back after several hours and I guess I never went back to fix the title.

[Mugen87]

I don't believe there is a mechanism to move the pivot point of a THREE.Mesh to not rotate from 0,0,0 ? Correct?

Correct. Pivot points like you know them from other engines/projects are not supported, see #15965.

[Mugen87]

As a workaround, instead of transforming the geometry couldn't you add a "dummy" instance of THREE.Object3D or THREE.Group and add the mesh to it? You can then offset the mesh and apply the rotation to the dummy.

[WORMSS]

Yeah, then we would just need to move the mesh so it's 0,0,0 is where the pivot point should be on its parent (or scene)
I have done a kind of proof of concept test with my existing model I am trying to develop but I know I am off on 1 of the axis somewhere.. I am guessing it's the z as apparently something in inverted?? Not tested fully, it was quite late when I was doing it and I am doing it with a model that is oddly shaped..

This is getting it "roughly" into the correct position for rotation, but not quiet yet..

I will set up a proper test environment with some simple boxes in all the orientations so I can be sure it fixes all direction scenarios

[WORMSS]

As a workaround, instead of transforming the geometry couldn't you add a "dummy" instance of THREE.Object3D or THREE.Group and add the mesh to it? You can then offset the mesh and apply the rotation to the dummy.

It's the loader that sets up the hierarchy structure during it's parsing phase..

BUT, I have just seen this on github... I don't remember coming across this when stepping through the code.. but maybe I was just tired..

I will try running this code 'raw' from github and see what happens when I do testing.. maybe it's already fixed but the CDN's don't have the fix...

[WORMSS]

Okay, just as another curiosity...

Green Arrow = Where Z = 0 on the actual Model
Orange Arrow = Where the pivot Point is.
Blue Arrow = Where Three is rotating the model from..

Red wireframe bar

[WORMSS]

const boom_z = objects.boom.userData.pivot[2]; // 2 = z;;
objects.boom.geometry.translate(0, 0, boom_z * 2);
objects.boom.translateZ(-boom_z * 2);

Finally got everything to align..
It seems when I try to correct ALL the axis it would mess everything up..
but because I had something visual I could actually see now I decided to try and maneuver 1 axis at a time.. and noticed actually it's ONLY z that is out.. but it's out by twice as much...

[WORMSS]

Okay, this is how I eventually fixed the pivot points as things got more nested..
This seems to have fixed everything

const { meshes } = await new LWOLoader().loadAsync(urlToLWOFile);
for ( const mesh of meshes ) {
  fixPivots(mesh);
}

function fixPivots(mesh: THREE.Mesh) {
  const [, , z] = mesh.userData.pivot;
  const parentsZ = (mesh.parent?.userData.pivot[2] /* 2 = z */ ?? 0) * 2; // THIS was the killer blow.. 
  mesh.geometry.translate(0, 0, z * 2);
  mesh.translateZ(-z * 2 + parentsZ);
  for (const child of mesh.children) {
    fixPivots(child); // Fix Fix Fix ALL the way down.
  }
}

[Mugen87]

I have fixed a similar issue in another loader by creating a custom 3D object class and implement pivot points there. In this way, you don't have to translate geometries but update the local/world matrices which is probably more what LWO expects. Maybe you can try to enhance LOWLoader like so:

class LWOMesh extends Mesh {

	constructor() {

		super();

		this.pivot = new Vector3();

	}

	updateMatrix() {

		this.matrix.compose( this.position, this.quaternion, this.scale );

		const px = this.pivot.x;
		const py = this.pivot.y;
		const pz = this.pivot.z;

		const te = this.matrix.elements;

		te[ 12 ] += px - te[ 0 ] * px - te[ 4 ] * py - te[ 8 ] * pz;
		te[ 13 ] += py - te[ 1 ] * px - te[ 5 ] * py - te[ 9 ] * pz;
		te[ 14 ] += pz - te[ 2 ] * px - te[ 6 ] * py - te[ 10 ] * pz;

		this.matrixWorldNeedsUpdate = true;

	}

}

Instead of creating instances of Mesh, you use LWOMesh and apply the pivot point from the LWO data. Looking at the code, it seems Points and LineSegments require a similar custom class.

Would be great if you could give this a shot and report back how is it going.

[WORMSS]

Not gonna lie, I totally forgot about coming back here.

I've been using my hack for so long.. I never got around to making a lwo object to test all this..

It was this and another problem I found with using the wrong property for colour with different paint types.
Again, never got around to making a simple test for it..