hi, guys, how to understand the math used in CDXUTDirectionWidget ::UpdateLightDir
the following code snippet is taken from MS DXTU source code
D3DXMATRIX mInvView;
D3DXMatrixInverse( &mInvView, NULL, &m_mView );
mInvView._41 = mInvView._42 = mInvView._43 = 0;
D3DXMATRIX mLastRotInv;
D3DXMatrixInverse( &mLastRotInv, NULL, &m_mRotSnapshot );
D3DXMATRIX 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
D3DXVECTOR3* pXBasis = ( D3DXVECTOR3* )&m_mRot._11;
D3DXVECTOR3* pYBasis = ( D3DXVECTOR3* )&m_mRot._21;
D3DXVECTOR3* pZBasis = ( D3DXVECTOR3* )&m_mRot._31;
D3DXVec3Normalize( pXBasis, pXBasis );
D3DXVec3Cross( pYBasis, pZBasis, pXBasis );
D3DXVec3Normalize( pYBasis, pYBasis );
D3DXVec3Cross( pZBasis, pXBasis, pYBasis );
https://github.com/Microsoft/DXUT/blob/master/Optional/DXUTcamera.cpp
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