Question by TheZombieKiller · Jun 29, 2017 at 09:19 AM · c#animation bones external assets matrix4x4.trs

[C#] How would I create skeleton bone transforms from a TRS matrix?

I've been writing a runtime importer for the Inter-Quake Model (IQM) format, and while I can load vertices, triangles, UV-coordinates, etc correctly, I can't seem to figure out how to correctly create the bone transforms from the information supplied in the IQM model.

The information I have is a translation (Vector3), scale (Vector3) and rotation (Quaternion).

http://sauerbraten.org/iqm/iqm.txt

According to the IQM spec (linked above):

 translate is translation <Tx, Ty, Tz>, and rotate is quaternion rotation <Qx, Qy, Qz, Qw>
 rotation is in relative/parent local space
 scale is pre-scaling <Sx, Sy, Sz>
 output = (input*scale)*rotation + translation

It's also important to note that the coordinates are right-handed z-up, whilst Unity is left-handed y-up.

I've been converting coordinates with the formula iqm(x, y, z) = unity(z, -x, y)

You can find a minimal sample project with necessary code and the sample IQM model "mrfixit" here: https://github.com/DaZombieKiller/unity-answers-iqm-help

See Assets/Scripts/IQM.cs, lines 303-321 (or search for the // UNITYHELP comment)

When I attempt to create the bone transforms, they are quite clearly in the wrong positions. Here is the model loaded in Unity (the bones are represented by sphere primitives):

unity