VTK – Rotate Vector To Special Direction

I take notes about how to rotate vector to a special direction.

#include "./tool.h"

#include <vtkTransform.h>
#include <vtkSmartPointer.h>

#define vtkSPtr vtkSmartPointer
#define vtkSPtrNew(Var, Type) vtkSPtr<Type> Var = vtkSPtr<Type>::New();

vtkSPtr<vtkTransform> RotateVecToSpecialDir(Point vec0, Point vec1)
{
    vtkSPtrNew(trans, vtkTransform);
    
    vec0.Unit();
    vec1.Unit();
    
    double radian = vtkMath::AngleBetweenVectors(vec0.point, vec1.point);
    double degree = vtkMath::DegreesFromRadians(radian);
    
    if (fabs(degree) < 0.0001)
    {
        return trans;
    }
    
    if (fabs(degree - 180.0) < 0.0001)
    {
        Point rotationAxis;
        if (fabs(vec0[0]) < fabs(vec0[1]) - 1e-6)
        {
            rotationAxis = Point(1, 0, 0) ^ vec0;
        }
        else
        {
            rotationAxis = Point(0, 1, 0) ^ vec0;
        }
        rotationAxis.Unit();
        trans->RotateWXYZ(180.0, rotationAxis[0], rotationAxis[1], rotationAxis[2]);
    }
    else
    {
        Point rotationAxis = vec0 ^ vec1;
        rotationAxis.Unit();
        trans->RotateWXYZ(degree, rotationAxis[0], rotationAxis[1], rotationAxis[2]);
    }
    
    trans->Update();
    return trans;
}

int main(int, char *[])
{
    PointStruct vec0( 1, 1, 0 );
    PointStruct vec1( -1, 1, 0 );
    PointStruct vecZ( 0, 0, 1 );
    auto trans = RotateVecToSpecialDir( vec0, vec1 );

    PointStruct tester = vec0;
    trans->TransformVector( tester.point, tester.point );
    cout << tester << endl;
    return EXIT_SUCCESS;
}