Silk.NET.Assimp Quaternions are incorrect

[Kermalis]

Summary

Upon parsing Quaternions from NodeAnim*, I was stumbling upon incorrect Quaternions. The aiQuaterniont struct puts W first, but System.Numerics.Quaternion is X first. So it appears Silk.NET is casting those aiQuaternionT* to System.Numerics.Quaternion or something, which results in W being at X which is wrong.

Here's my workaround for parsing them:

NodeAnim* chan = a->MChannels[j];

var positions = new (float, Vector3)[chan->MNumPositionKeys];
for (int k = 0; k < positions.Length; k++)
{
 VectorKey pos = chan->MPositionKeys[k];
 positions[k] = ((float)pos.MTime, pos.MValue);
}
var rotations = new (float, Quaternion)[chan->MNumRotationKeys];
for (int k = 0; k < rotations.Length; k++)
{
 QuatKey rot = chan->MRotationKeys[k];
 rotations[k] = ((float)rot.MTime, new Quaternion(rot.MValue.Y, rot.MValue.Z, rot.MValue.W, rot.MValue.X)); // HERE: Incorrectly casted by library, so order is shifted by one field
}
var scales = new (float, Vector3)[chan->MNumScalingKeys];
for (int k = 0; k < scales.Length; k++)
{
 VectorKey scl = chan->MScalingKeys[k];
 scales[k] = ((float)scl.MTime, scl.MValue);
}

Comments

• Platform: Desktop
• Framework Version: .NET 6.0
• API: OpenGL 3.3 Core

I'm not sure if this is unique to NodeAnim or if it applies all over the library, so it needs some looking into

[HurricanKai]

See https://github.com/dotnet/Silk.NET/blob/main/generator.json#L695
We don't at this time support rewriting types, so we probably just have to remove the mapping and fix this for real in 3.0

[Kermalis]

Well this is also similarly the case with Matrix4x4. The assimp ones are column major, but the System.Numerics ones are row major. Having it be consistent with the rest of .net makes it way easier. At the moment, you have to transpose the matrices you get from Silk.NET.Assimp. If these inconsistencies were addressed it'd be a lot easier to follow tutorials (and make a proper example project with)
Edit: Could also apply to Matrix3x3 although I didn't check any of those