1 /*=========================================================================
2
3 Program: Visualization Toolkit
4 Module: vtkUnstructuredGridPartialPreIntegration.h
5
6 Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen
7 All rights reserved.
8 See Copyright.txt or http://www.kitware.com/Copyright.htm for details.
9
10 This software is distributed WITHOUT ANY WARRANTY; without even
11 the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
12 PURPOSE. See the above copyright notice for more information.
13
14 =========================================================================*/
15
16 /*
17 * Copyright 2004 Sandia Corporation.
18 * Under the terms of Contract DE-AC04-94AL85000, there is a non-exclusive
19 * license for use of this work by or on behalf of the
20 * U.S. Government. Redistribution and use in source and binary forms, with
21 * or without modification, are permitted provided that this Notice and any
22 * statement of authorship are reproduced on all copies.
23 */
24
25 /**
26 * @class vtkUnstructuredGridPartialPreIntegration
27 * @brief performs piecewise linear ray integration.
28 *
29 *
30 *
31 * vtkUnstructuredGridPartialPreIntegration performs piecewise linear ray
32 * integration. This will give the same results as
33 * vtkUnstructuredGridLinearRayIntegration (with potentially a error due to
34 * table lookup quantization), but should be notably faster. The algorithm
35 * used is given by Moreland and Angel, "A Fast High Accuracy Volume
36 * Renderer for Unstructured Data."
37 *
38 * This class is thread safe only after the first instance is created.
39 *
40 */
41
42 #ifndef vtkUnstructuredGridPartialPreIntegration_h
43 #define vtkUnstructuredGridPartialPreIntegration_h
44
45 #include "vtkMath.h" // For all the inline methods
46 #include "vtkRenderingVolumeModule.h" // For export macro
47 #include "vtkUnstructuredGridVolumeRayIntegrator.h"
48
49 class vtkPartialPreIntegrationTransferFunction;
50 class vtkVolumeProperty;
51
52 class VTKRENDERINGVOLUME_EXPORT vtkUnstructuredGridPartialPreIntegration
53 : public vtkUnstructuredGridVolumeRayIntegrator
54 {
55 public:
56 vtkTypeMacro(vtkUnstructuredGridPartialPreIntegration, vtkUnstructuredGridVolumeRayIntegrator);
57 static vtkUnstructuredGridPartialPreIntegration* New();
58 void PrintSelf(ostream& os, vtkIndent indent) override;
59
60 void Initialize(vtkVolume* volume, vtkDataArray* scalars) override;
61
62 void Integrate(vtkDoubleArray* intersectionLengths, vtkDataArray* nearIntersections,
63 vtkDataArray* farIntersections, float color[4]) override;
64
65 ///@{
66 /**
67 * Integrates a single ray segment. \c color is blended with the result
68 * (with \c color in front). The result is written back into \c color.
69 */
70 static void IntegrateRay(double length, double intensity_front, double attenuation_front,
71 double intensity_back, double attenuation_back, float color[4]);
72 static void IntegrateRay(double length, const double color_front[3], double attenuation_front,
73 const double color_back[3], double attenuation_back, float color[4]);
74 ///@}
75
76 ///@{
77 /**
78 * Looks up Psi (as defined by Moreland and Angel, "A Fast High Accuracy
79 * Volume Renderer for Unstructured Data") in a table. The table must be
80 * created first, which happens on the first instantiation of this class
81 * or when BuildPsiTable is first called.
82 */
83 static float Psi(float taufD, float taubD);
84 static float* GetPsiTable(int& size);
85 static void BuildPsiTable();
86 ///@}
87
88 protected:
89 vtkUnstructuredGridPartialPreIntegration();
90 ~vtkUnstructuredGridPartialPreIntegration() override;
91
92 vtkVolumeProperty* Property;
93
94 vtkPartialPreIntegrationTransferFunction* TransferFunctions;
95 vtkTimeStamp TransferFunctionsModified;
96 int NumIndependentComponents;
97
98 enum
99 {
100 PSI_TABLE_SIZE = 512
101 };
102
103 static float PsiTable[PSI_TABLE_SIZE * PSI_TABLE_SIZE];
104 static int PsiTableBuilt;
105
106 private:
107 vtkUnstructuredGridPartialPreIntegration(
108 const vtkUnstructuredGridPartialPreIntegration&) = delete;
109 void operator=(const vtkUnstructuredGridPartialPreIntegration&) = delete;
110 };
111
Psi(float taufD,float taubD)112 inline float vtkUnstructuredGridPartialPreIntegration::Psi(float taufD, float taubD)
113 {
114 float gammaf = taufD / (taufD + 1);
115 float gammab = taubD / (taubD + 1);
116 int gammafi = vtkMath::Floor(gammaf * PSI_TABLE_SIZE);
117 int gammabi = vtkMath::Floor(gammab * PSI_TABLE_SIZE);
118 return PsiTable[gammafi * PSI_TABLE_SIZE + gammabi];
119 }
120
GetPsiTable(int & size)121 inline float* vtkUnstructuredGridPartialPreIntegration::GetPsiTable(int& size)
122 {
123 size = PSI_TABLE_SIZE;
124 return PsiTable;
125 }
126
IntegrateRay(double length,double intensity_front,double attenuation_front,double intensity_back,double attenuation_back,float color[4])127 inline void vtkUnstructuredGridPartialPreIntegration::IntegrateRay(double length,
128 double intensity_front, double attenuation_front, double intensity_back, double attenuation_back,
129 float color[4])
130 {
131 float taufD = length * attenuation_front;
132 float taubD = length * attenuation_back;
133 float Psi = vtkUnstructuredGridPartialPreIntegration::Psi(taufD, taubD);
134 float zeta = static_cast<float>(exp(-0.5 * (taufD + taubD)));
135 float alpha = 1 - zeta;
136
137 float newintensity =
138 (1 - color[3]) * (intensity_front * (1 - Psi) + intensity_back * (Psi - zeta));
139 // Is setting the RGB values the same the right thing to do?
140 color[0] += newintensity;
141 color[1] += newintensity;
142 color[2] += newintensity;
143 color[3] += (1 - color[3]) * alpha;
144 }
145
IntegrateRay(double length,const double color_front[3],double attenuation_front,const double color_back[3],double attenuation_back,float color[4])146 inline void vtkUnstructuredGridPartialPreIntegration::IntegrateRay(double length,
147 const double color_front[3], double attenuation_front, const double color_back[3],
148 double attenuation_back, float color[4])
149 {
150 float taufD = length * attenuation_front;
151 float taubD = length * attenuation_back;
152 float Psi = vtkUnstructuredGridPartialPreIntegration::Psi(taufD, taubD);
153 float zeta = static_cast<float>(exp(-0.5 * (taufD + taubD)));
154 float alpha = 1 - zeta;
155
156 color[0] += (1 - color[3]) * (color_front[0] * (1 - Psi) + color_back[0] * (Psi - zeta));
157 color[1] += (1 - color[3]) * (color_front[1] * (1 - Psi) + color_back[1] * (Psi - zeta));
158 color[2] += (1 - color[3]) * (color_front[2] * (1 - Psi) + color_back[2] * (Psi - zeta));
159 color[3] += (1 - color[3]) * alpha;
160 }
161
162 #endif // vtkUnstructuredGridPartialPreIntegration_h
163