Node.setMatrix() support

How come this is not supported? There’s already a Node.getMatrix.

I’m seeing a bug that I think is related. Using gl-matrix, I have a mat4 and doing this (which I have to do without a setMatrix - bunch of useless calculation and precision loss):

const getTRS = (m: mat4) => {
    return { t: mat4.getTranslation(vec3.create(), m), r: mat4.getRotation(quat.create(), m), s: mat4.getScaling(vec3.create(), m) };
};

const setNodeMatrix = (node: GLTFNode, mat: mat4) => {
    let trs = getTRS(mat);
    node.setTranslation([trs.t[0], trs.t[1], trs.t[2]]);
    // quat.normalize(trs.r, trs.r); // i get asserts either way
    node.setRotation([trs.r[0], trs.r[1], trs.r[2], trs.r[3]]);
    node.setScale([trs.s[0], trs.s[1], trs.s[2]]);

    console.log(mat, node.getMatrix());
    assert(mat4.equals(mat, node.getMatrix()));
}

I get asserts in some cases. Example:

[-0.9307078123092651, 0.36324116587638855, -0.04288084805011749, 0, -0.3623482286930084,  -0.9316428303718567, -0.02730146236717701,  0, -0.044879984110593796, -0.00888469722121954,  0.8988363742828369, 0, 310.8424987792969, -5155.25244140625, -366.21356201171875, 1]
[-0.9307281322940169, 0.3632646333314609,  -0.04257750763746079, 0, -0.36232478384586403, -0.9316375673397288, -0.028303744841263856, 0, -0.04495307531851036,  -0.009824320406136731, 0.8988229395637517, 0, 310.8424987792969, -5155.25244140625, -366.21356201171875, 1]

I can also see that exported meshes are transformed incorrectly compared to my obj exporter that transforms each vertex at export time with the raw matrices, which may be related to this. I don’t know what else it could be. The rest of the code is pretty much the same, and my nodes are placed on the root.

[VelocityRa]

Ok, thanks anyway. Feel free to close this, or leave it open until/if you implement setMatrix.

[donmccurdy]

I’ve had some trouble using gl-matrix to decompose matrices (https://github.com/toji/gl-matrix/issues/408) and so I don’t use those functions internally. There’s a (currently undocumented) MathUtils.decompose(...) function that follows the three.js implementation and this has worked much better for me with, e.g., conversions from other formats:

https://github.com/donmccurdy/glTF-Transform/blob/33a91aff3bfa281ee8fab60fd1d233b41bafd749/packages/core/src/utils/math-utils.ts#L60-L75

Does decomposition work correctly for your model with this approach?

---

As for whether a setMatrix(...) method should be added, I guess it comes down to what that method should do, if it were added? One option is to decompose the matrix within that method, but of course this will give the same result as using MathUtils.decompose by yourself. Another option is store the matrix on the Node, which currently only stores TRS properties. This would create some uncertainty about what happens when setTranslation is called after setMatrix, and what should be put in the exported file, though — TRS properties or a matrix? Other users may prefer that TRS properties be used.