vtkUnstructuredGridPartialPreIntegration.h

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/*=========================================================================
 
  Program:   Visualization Toolkit
  Module:    vtkUnstructuredGridPartialPreIntegration.h
 
  Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen
  All rights reserved.
  See Copyright.txt or http://www.kitware.com/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 notice for more information.
 
=========================================================================*/
 
/*
 * Copyright 2004 Sandia Corporation.
 * Under the terms of Contract DE-AC04-94AL85000, there is a non-exclusive
 * license for use of this work by or on behalf of the
 * U.S. Government. Redistribution and use in source and binary forms, with
 * or without modification, are permitted provided that this Notice and any
 * statement of authorship are reproduced on all copies.
 */
 
#ifndef vtkUnstructuredGridPartialPreIntegration_h
#define vtkUnstructuredGridPartialPreIntegration_h
 
#include "vtkMath.h"                  // For all the inline methods
#include "vtkRenderingVolumeModule.h" // For export macro
#include "vtkUnstructuredGridVolumeRayIntegrator.h"
 
class vtkPartialPreIntegrationTransferFunction;
class vtkVolumeProperty;
 
class VTKRENDERINGVOLUME_EXPORT vtkUnstructuredGridPartialPreIntegration
  : public vtkUnstructuredGridVolumeRayIntegrator
{
public:
  vtkTypeMacro(vtkUnstructuredGridPartialPreIntegration, vtkUnstructuredGridVolumeRayIntegrator);
  static vtkUnstructuredGridPartialPreIntegration* New();
  void PrintSelf(ostream& os, vtkIndent indent) override;
 
  void Initialize(vtkVolume* volume, vtkDataArray* scalars) override;
 
  void Integrate(vtkDoubleArray* intersectionLengths, vtkDataArray* nearIntersections,
    vtkDataArray* farIntersections, float color[4]) override;
 
 
  static void IntegrateRay(double length, double intensity_front, double attenuation_front,
    double intensity_back, double attenuation_back, float color[4]);
  static void IntegrateRay(double length, const double color_front[3], double attenuation_front,
    const double color_back[3], double attenuation_back, float color[4]);
 
 
  static float Psi(float taufD, float taubD);
  static float* GetPsiTable(int& size);
  static void BuildPsiTable();
 
protected:
  vtkUnstructuredGridPartialPreIntegration();
  ~vtkUnstructuredGridPartialPreIntegration() override;
 
  vtkVolumeProperty* Property;
 
  vtkPartialPreIntegrationTransferFunction* TransferFunctions;
  vtkTimeStamp TransferFunctionsModified;
  int NumIndependentComponents;
 
  enum
  {
    PSI_TABLE_SIZE = 512
  };
 
  static float PsiTable[PSI_TABLE_SIZE * PSI_TABLE_SIZE];
  static int PsiTableBuilt;
 
private:
  vtkUnstructuredGridPartialPreIntegration(
    const vtkUnstructuredGridPartialPreIntegration&) = delete;
  void operator=(const vtkUnstructuredGridPartialPreIntegration&) = delete;
};
 
inline float vtkUnstructuredGridPartialPreIntegration::Psi(float taufD, float taubD)
{
  float gammaf = taufD / (taufD + 1);
  float gammab = taubD / (taubD + 1);
  int gammafi = vtkMath::Floor(gammaf * PSI_TABLE_SIZE);
  int gammabi = vtkMath::Floor(gammab * PSI_TABLE_SIZE);
  return PsiTable[gammafi * PSI_TABLE_SIZE + gammabi];
}
 
inline float* vtkUnstructuredGridPartialPreIntegration::GetPsiTable(int& size)
{
  size = PSI_TABLE_SIZE;
  return PsiTable;
}
 
inline void vtkUnstructuredGridPartialPreIntegration::IntegrateRay(double length,
  double intensity_front, double attenuation_front, double intensity_back, double attenuation_back,
  float color[4])
{
  float taufD = length * attenuation_front;
  float taubD = length * attenuation_back;
  float Psi = vtkUnstructuredGridPartialPreIntegration::Psi(taufD, taubD);
  float zeta = static_cast<float>(exp(-0.5 * (taufD + taubD)));
  float alpha = 1 - zeta;
 
  float newintensity =
    (1 - color[3]) * (intensity_front * (1 - Psi) + intensity_back * (Psi - zeta));
  // Is setting the RGB values the same the right thing to do?
  color[0] += newintensity;
  color[1] += newintensity;
  color[2] += newintensity;
  color[3] += (1 - color[3]) * alpha;
}
 
inline void vtkUnstructuredGridPartialPreIntegration::IntegrateRay(double length,
  const double color_front[3], double attenuation_front, const double color_back[3],
  double attenuation_back, float color[4])
{
  float taufD = length * attenuation_front;
  float taubD = length * attenuation_back;
  float Psi = vtkUnstructuredGridPartialPreIntegration::Psi(taufD, taubD);
  float zeta = static_cast<float>(exp(-0.5 * (taufD + taubD)));
  float alpha = 1 - zeta;
 
  color[0] += (1 - color[3]) * (color_front[0] * (1 - Psi) + color_back[0] * (Psi - zeta));
  color[1] += (1 - color[3]) * (color_front[1] * (1 - Psi) + color_back[1] * (Psi - zeta));
  color[2] += (1 - color[3]) * (color_front[2] * (1 - Psi) + color_back[2] * (Psi - zeta));
  color[3] += (1 - color[3]) * alpha;
}
 
#endif // vtkUnstructuredGridPartialPreIntegration_h