private void UpdateLightDir()
{
XMMatrix mInvView = m_mView.Inverse();
mInvView.M41 = 0;
mInvView.M42 = 0;
mInvView.M43 = 0;
XMMatrix mLastRotInv = m_mRotSnapshot.Inverse();
XMMatrix mRot = m_ArcBall.GetRotationMatrix();
m_mRotSnapshot = mRot;
// Accumulate the delta of the arcball's rotation in view space.
// Note that per-frame delta rotations could be problematic over long periods of time.
m_mRot *= m_mView * mLastRotInv * mRot * mInvView;
// Since we're accumulating delta rotations, we need to orthonormalize
// the matrix to prevent eventual matrix skew
XMVector pXBasis = XMVector.FromFloat(m_mRot.M11, m_mRot.M12, m_mRot.M13, 0);
XMVector pYBasis = XMVector.FromFloat(m_mRot.M21, m_mRot.M22, m_mRot.M23, 0);
XMVector pZBasis = XMVector.FromFloat(m_mRot.M31, m_mRot.M32, m_mRot.M33, 0);
pXBasis = XMVector3.Normalize(pXBasis);
pYBasis = XMVector3.Cross(pZBasis, pXBasis);
pYBasis = XMVector3.Normalize(pYBasis);
pZBasis = XMVector3.Cross(pXBasis, pYBasis);
pXBasis.W = m_mRot.M14;
pYBasis.W = m_mRot.M24;
pZBasis.W = m_mRot.M34;
XMVector pWBasis = XMVector.FromFloat(m_mRot.M41, m_mRot.M42, m_mRot.M43, m_mRot.M44);
m_mRot = new XMMatrix(pXBasis, pYBasis, pZBasis, pWBasis);
// Transform the default direction vector by the light's rotation matrix
m_vCurrentDir = XMVector3.TransformNormal(m_vDefaultDir, m_mRot);
}
