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

  Program:   Visualization Toolkit
  Module:    vtkViewRays.h
  Language:  C++
  Date:      $Date$
  Version:   $Revision$


Copyright (c) 1993-1998 Ken Martin, Will Schroeder, Bill Lorensen.

This software is copyrighted by Ken Martin, Will Schroeder and Bill Lorensen.
The following terms apply to all files associated with the software unless
explicitly disclaimed in individual files. This copyright specifically does
not apply to the related textbook "The Visualization Toolkit" ISBN
013199837-4 published by Prentice Hall which is covered by its own copyright.

The authors hereby grant permission to use, copy, and distribute this
software and its documentation for any purpose, provided that existing
copyright notices are retained in all copies and that this notice is included
verbatim in any distributions. Additionally, the authors grant permission to
modify this software and its documentation for any purpose, provided that
such modifications are not distributed without the explicit consent of the
authors and that existing copyright notices are retained in all copies. Some
of the algorithms implemented by this software are patented, observe all
applicable patent law.

IN NO EVENT SHALL THE AUTHORS OR DISTRIBUTORS BE LIABLE TO ANY PARTY FOR
DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT
OF THE USE OF THIS SOFTWARE, ITS DOCUMENTATION, OR ANY DERIVATIVES THEREOF,
EVEN IF THE AUTHORS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

THE AUTHORS AND DISTRIBUTORS SPECIFICALLY DISCLAIM ANY WARRANTIES, INCLUDING,
BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
PARTICULAR PURPOSE, AND NON-INFRINGEMENT.  THIS SOFTWARE IS PROVIDED ON AN
"AS IS" BASIS, AND THE AUTHORS AND DISTRIBUTORS HAVE NO OBLIGATION TO PROVIDE
MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.


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

// .NAME vtkViewRays - provides view ray information for efficiently casting rays
// .SECTION Description
// The vtkViewRays class calculates and stores the relevant information 
// necessary to efficiently render perspective or parallel viewing rays. 
// View rays are typically used by a ray caster where a view ray is
// cast per pixel in the requested image. 
//
// The number of view rays requested in both X and Y is specified by
// the SetSize() method. The camera model used to create the view ray 
// information is specified by the SetRenderer() method. Both the SetSize()
// and SetRenderer() method must be called before viewing ray information 
// can be requested. vtkViewRays will recompute view ray information should
// the critical information in the camera, the renderer or number of rays 
// change.
//
// vtkViewRays contains view ray information in view coordinates for either 
// parallel or perspective viewing transformations. This reduces the
// computational burden on a ray caster since the computation of perspective,
// normalized viewing ray vectors is pre-computed once rather than during each
// rendering.
// 
// When the camera viewing transform is perspective the start of each 
// viewing vector (eye point) is fixed, but the direction of each ray varies. 
// Therefore, vtkViewRays contains a 2D array of 3D unit vectors each 
// representing the direction of a view ray with respect to the viewing 
// coordinate system. A pointer to this 2D array of vectors is obtained by 
// calling the GetPerspectiveViewRays() method.
//
// When the camera viewing transform is parallel the start of each viewing 
// vector varies across the viewing plane but the direction remains constant. 
// Since the starting point of each view ray can be captured by regularly 
// sampling the parallel viewing plane, a 2D array of starting view ray 
// positions is NOT used. Instead, the first view ray position (bottom left
// corner of view) is returned by the GetParallelStartPosition() method and
// the X and Y distance increments to the next view ray starting position 
// are returned by the GetParallelIncrements() method.

#ifndef __vtkViewRays_h
#define __vtkViewRays_h
#include "vtkObject.h"
#include "vtkMatrix4x4.h"
class vtkRenderer;

class VTK_EXPORT vtkViewRays :public vtkObject
  {
  public:
  vtkViewRays(void);
  ~vtkViewRays(void);
  static vtkViewRays *New() {return new vtkViewRays;};
  const char *GetClassName() {return "vtkViewRays";};
  void PrintSelf(ostream& os,vtkIndent indent);

  // Description:
  // Specify the vtkRenderer whose camera will be used to to calculate 
  // the view rays. The type of camera (parallel, perspective) will
  // determine which type of view ray information is calculated.
  vtkGetObjectMacro(Renderer,vtkRenderer);
  vtkSetObjectMacro(Renderer,vtkRenderer);

  // Description:
  // Set the image size for the view rays.
  vtkSetVector2Macro(Size,int);
  vtkGetVector2Macro(Size,int);

  // Description:
  // Retrieve the 2D array of normalized view ray vectors formatted as
  // 3 floats per vector (dx,dy,dz).  This method is only valid after the 
  // SetSize() and SetRenderer() methods have been called.
  float *GetPerspectiveViewRays(void);

  // Description:
  // Retrieve the position of the bottom left ray
  float *GetParallelStartPosition(void);

  // Description:
  // Retrieve the distance to the next ray starting point along the X and
  // Y direction.
  float *GetParallelIncrements(void);

protected:
  vtkRenderer     *Renderer;		// Renderer contains a camera
  int             Size[2];		// Number of view rays
  unsigned long   ViewRaysCamMtime;	// Camera modified time
  unsigned long   ViewRaysMTime;	// View rays modified time

  // Parallel camera information
  void            ComputeParallelInfo( int size[2] );
  float           StartPosition[3];	// Position of lower left ray
  float           Increments[2];	// Distance to move 1 ray over in X,Y

  // Perspective camera information
  void            ComputePerspectiveInfo(float *vr_ptr,int size[2]);
  float           *ViewRays;
  };
#endif



