Microsoft DirectX 8.1 (Visual Basic)

D3DXQuaternionInverse

Conjugates and renormalizes a quaternion.

D3DXQuaternionInverse( _ 
    QOut As D3DQUATERNION, _ 
    Q As D3DQUATERNION)

QOut: D3DQUATERNION type that is the result of the operation, the inverse quaternion of the quaternion.
Q: The source D3DQUATERNION type.

If the function fails, an error is raised and Err.Number can be set to one of the following values.

For information on trapping errors, see the Microsoft® Visual Basic® Error Handling topic.

For a unit quaternion, Q == (cos(theta), sin(theta) * v)
The inverse of Q is, Inv(Q) = Conjugate(Q)/LengthSq(Q)