Computes the dot product of two quaternions.
XMVECTOR XM_CALLCONV XMQuaternionDot( FXMVECTOR Q1, FXMVECTOR Q2 );
Returns a vector. The dot product between Q1 and Q2 is replicated into each component.
The DirectXMath quaternion functions use an XMVECTOR 4-vector to represent quaternions, where the X, Y, and Z components are the vector part and the W component is the scalar part.