How can I implement my own version of the gluLookAt() function: If I have the desired direction and up vector, how do i calculate the corresponding rotation matrix?
And no, I don’t want to use gluLookAt(). I want to learn how to do it myself
How can I implement my own version of the gluLookAt() function: If I have the desired direction and up vector, how do i calculate the corresponding rotation matrix?
And no, I don’t want to use gluLookAt(). I want to learn how to do it myself
taken from DirectX sdk:
HRESULT D3DUtil_SetViewMatrix( D3DMATRIX& mat, D3DVECTOR& vFrom,
D3DVECTOR& vAt, D3DVECTOR& vWorldUp )
{
// Get the z basis vector, which points straight ahead. This is the
// difference from the eyepoint to the lookat point.
D3DVECTOR vView = vAt - vFrom;
FLOAT fLength = Magnitude( vView );
if( fLength < 1e-6f )
return E_INVALIDARG;
// Normalize the z basis vector
vView /= fLength;
// Get the dot product, and calculate the projection of the z basis
// vector onto the up vector. The projection is the y basis vector.
FLOAT fDotProduct = DotProduct( vWorldUp, vView );
D3DVECTOR vUp = vWorldUp - fDotProduct * vView;
// If this vector has near-zero length because the input specified a
// bogus up vector, let's try a default up vector
if( 1e-6f > ( fLength = Magnitude( vUp ) ) )
{
vUp = D3DVECTOR( 0.0f, 1.0f, 0.0f ) - vView.y * vView;
// If we still have near-zero length, resort to a different axis.
if( 1e-6f > ( fLength = Magnitude( vUp ) ) )
{
vUp = D3DVECTOR( 0.0f, 0.0f, 1.0f ) - vView.z * vView;
if( 1e-6f > ( fLength = Magnitude( vUp ) ) )
return E_INVALIDARG;
}
}
// Normalize the y basis vector
vUp /= fLength;
// The x basis vector is found simply with the cross product of the y
// and z basis vectors
D3DVECTOR vRight = CrossProduct( vUp, vView );
// Start building the matrix. The first three rows contains the basis
// vectors used to rotate the view to point at the lookat point
D3DUtil_SetIdentityMatrix( mat );
mat._11 = vRight.x; mat._12 = vUp.x; mat._13 = vView.x;
mat._21 = vRight.y; mat._22 = vUp.y; mat._23 = vView.y;
mat._31 = vRight.z; mat._32 = vUp.z; mat._33 = vView.z;
// Do the translation values (rotations are still about the eyepoint)
mat._41 = - DotProduct( vFrom, vRight );
mat._42 = - DotProduct( vFrom, vUp );
mat._43 = - DotProduct( vFrom, vView );
return S_OK;
}
they use a right-handed coordinate system, you might have to change some signs
[This message has been edited by Gorg (edited 08-03-2000).]