TransformSceneHandle how get transform.forward？

Code (CSharp):

1.     Vector3 dir1 = m_Bones[0].GetPosition(stream) - m_Bones[1].GetPosition(stream);
2.                 Vector3 dir2 = m_Bones[2].GetPosition(stream) - m_Bones[1].GetPosition(stream);
3.             Vector3 dirX = Vector3.forward;//m_Bones[1].forward
4.                 float angle = Vector3.SignedAngle(dir1, dir2, dirX);

I want to lock bone rotation,but how can get the transfor local forward vector?

 

to get bone forward, you can get rotation of bone, and multiply Vector3.forward