/*=========================================================================

  Program:   Insight Segmentation & Registration Toolkit
  Module:    $RCSfile: itkLookAtTransformInitializer.txx,v $
  Language:  C++
  Date:      $Date$
  Version:   $Revision$

  Copyright (c) Insight Software Consortium. All rights reserved.
  See ITKCopyright.txt or http://www.itk.org/HTML/Copyright.htm for details.

     This software is distributed WITHOUT ANY WARRANTY; without even 
     the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
     PURPOSE.  See the above copyright notices for more information.

=========================================================================*/

#ifndef __itkLookAtTransformInitializer_txx
#define __itkLookAtTransformInitializer_txx

#include "itkLookAtTransformInitializer.h"

namespace itk
{

template < class TTransform, class TImage >
LookAtTransformInitializer< TTransform, TImage >
::LookAtTransformInitializer()
{
  m_Center.Fill( 0.0 );
  m_Direction.Fill( 0.0 );
  m_Direction[2] = 1.0;
  m_Up.Fill( 0.0 );
  m_Up[1] = 1.0;
}


template < class TTransform, class TImage >
void
LookAtTransformInitializer< TTransform, TImage >
::InitializeTransform()
{
  // Some useful vectors
  VectorType zero; zero.Fill( 0.0 );
  VectorType x; x.Fill( 0.0 ); x[0] = 1.0;
  VectorType y; y.Fill( 0.0 ); y[1] = 1.0;
	
  // Sanity check
  if( !m_Transform )
    {
    itkExceptionMacro( "Transform has not been set" );
    return;
    }
  if( !m_Image )
    {
    itkExceptionMacro( "Image has not been set" );
    return;
    }
  if ( m_Direction == zero )
    {
    itkExceptionMacro( "Direction can not be zero" );
    return;
    }
  if ( m_Up == zero )
    {
    itkExceptionMacro( "Up can not be zero" );
    return;
    }

  // Initialize the transform
  m_Transform->SetIdentity();

  //NOTE: this code is based on the gluLookAt(..) function
  //URL: http://pyopengl.sourceforge.net/documentation/manual/gluLookAt.3G.html
  //URL: http://developer.apple.com/documentation/Darwin/Reference/ManPages/man3/gluLookAt.3.html

  // The plane direction vector corresponds to the "f" vector
  VectorType f( m_Direction );
  f.Normalize();

  // Ensure "up" is not the same direction as "f"
  if (f == m_Up || f == -m_Up)
    {
    itkWarningMacro("The up vector can not be the same as the direction vector. ");
		
	// Redefine "up"
	if ( m_Up != y && m_Up != -y )
	  {
      m_Up = y;
	  }
	else
	  {
      m_Up = x;
	  }
    }

  // Do some cross products to get orthogonal axes
  VectorType s = CrossProduct(f, m_Up);
  s.Normalize();
  VectorType u = CrossProduct(s, f);
  u.Normalize();

  // Set the matrix
  // NOTE: Unlike gluLookAt(..) we DON'T use "-f", which looks down
  //       the negative z-axis. Instead we use "f" because we want
  //       to look down the POSITIVE z-axis.
  TransformType::MatrixType matrix = m_Transform->GetMatrix();
  matrix[0][0]=s[0]; matrix[0][1]=u[0]; matrix[0][2]=f[0];
  matrix[1][0]=s[1]; matrix[1][1]=u[1]; matrix[1][2]=f[1];
  matrix[2][0]=s[2]; matrix[2][1]=u[2]; matrix[2][2]=f[2];
  m_Transform->SetMatrix(matrix);

  // Compute geometric center of the image
  ContinuousIndexType centerIndex;
  PointType centerPoint;
  PointType centerPointAdjusted;
  ImageType::SizeType size = m_Image->GetLargestPossibleRegion().GetSize();
  for( unsigned int dim=0; dim<SpaceDimension; dim++ )
    {
    centerIndex[dim] = 
		static_cast< ContinuousIndexType::ValueType >( size[dim] ) / 2.0;
    }
  m_Image->TransformContinuousIndexToPhysicalPoint( centerIndex, centerPoint );

  // Set the transform center
  m_Transform->SetCenter( centerPoint );

  // Set the transform translation
  VectorType translation;
  for( unsigned int dim=0; dim<SpaceDimension; dim++ )
    {
	translation[dim] = m_Center[dim] - ( centerPoint[dim] * (1.0 - f[dim]) );
    }
  m_Transform->SetTranslation( translation );
}
  

template < class TTransform, class TImage >
void
LookAtTransformInitializer< TTransform, TImage >
::PrintSelf(std::ostream& os, Indent indent) const
{
  Superclass::PrintSelf(os,indent);

  os << indent << "Transform = " << std::endl;
  if (m_Transform)
    { 
    os << indent << m_Transform  << std::endl;
    }
  else
    {
    os << indent << "None" << std::endl;
    }
  os << indent << "Image = " << std::endl;
  if (m_Image)
    { 
    os << indent << m_Image  << std::endl;
    }
  else
    {
    os << indent << "None" << std::endl;
    }

  os << indent << "Center = " << m_Center << std::endl;
  os << indent << "Direction = " << m_Direction << std::endl;
  os << indent << "Up = " << m_Up << std::endl;
}

}  // namespace itk

#endif