Method UpdateSliceToWorldMatrix

Rendering/Image/vtkImageResliceMapper.cxx:497–571

------------------------------------------------------------------------------ Update the SliceToWorld transformation matrix

//------------------------------------------------------------------------------
// Update the SliceToWorld transformation matrix
void vtkImageResliceMapper::UpdateSliceToWorldMatrix(vtkCamera* camera)
{
  // Get slice plane in world coords by passing null as the prop matrix
  double plane[4];
  this->GetSlicePlaneInDataCoords(nullptr, plane);

  // Make sure normal is facing towards camera
  vtkMatrix4x4* viewMatrix = camera->GetViewTransformMatrix();
  double* ndop = viewMatrix->Element[2];
  if (vtkMath::Dot(ndop, plane) < 0)
  {
    plane[0] = -plane[0];
    plane[1] = -plane[1];
    plane[2] = -plane[2];
    plane[3] = -plane[3];
  }

  // The normal is the first three elements
  double* normal = plane;

  // The last element is -dot(normal, origin)
  double dp = -plane[3];

  // Compute rotation angle between camera axis and slice normal
  double vec[3];
  vtkMath::Cross(ndop, normal, vec);
  double costheta = vtkMath::Dot(ndop, normal);
  double sintheta = vtkMath::Norm(vec);
  double theta = atan2(sintheta, costheta);
  if (sintheta != 0)
  {
    vec[0] /= sintheta;
    vec[1] /= sintheta;
    vec[2] /= sintheta;
  }
  // convert to quaternion
  costheta = cos(0.5 * theta);
  sintheta = sin(0.5 * theta);
  double quat[4];
  quat[0] = costheta;
  quat[1] = vec[0] * sintheta;
  quat[2] = vec[1] * sintheta;
  quat[3] = vec[2] * sintheta;
  // convert to matrix
  double mat[3][3];
  vtkMath::QuaternionToMatrix3x3(quat, mat);

  // Create a slice-to-world transform matrix
  // The columns are v1, v2, normal
  vtkMatrix4x4* sliceToWorld = this->SliceToWorldMatrix;

  double v1[3], v2[3];
  vtkMath::Multiply3x3(mat, viewMatrix->Element[0], v1);
  vtkMath::Multiply3x3(mat, viewMatrix->Element[1], v2);

  sliceToWorld->Element[0][0] = v1[0];
  sliceToWorld->Element[1][0] = v1[1];
  sliceToWorld->Element[2][0] = v1[2];