上篇文章（VTK----VTK数据结构详解（计算机篇）-CSDN博客）从计算机数据结构（数组、链表等）的角度对数据数组 、数据对象 、数据属性的实现原理进行了说明，下面从代码的层面详细说明它们的使用及相关实现逻辑。
1 数据数组
以vtkFloatArray为例，下面是它的使用及其VTK内部实现的代码：
vtkNew<vtkFloatArray> scalars;
scalars->InsertTuple1(0, 1);
cpp
void vtkDataArray::InsertTuple1(vtkIdType i, double value)
{
int numComp = this->GetNumberOfComponents();
if (numComp != 1)
{
vtkErrorMacro(
"The number of components do not match the number requested: " << numComp << " != 1");
}
this->InsertTuple(i, &value);
}
template <class ValueTypeT>
void vtkAOSDataArrayTemplate<ValueTypeT>::InsertTuple(vtkIdType tupleIdx, const double* tuple)
{
if (this->EnsureAccessToTuple(tupleIdx))
{
// See note in SetTuple about std::copy vs for loops on MSVC.
const vtkIdType valueIdx = tupleIdx * this->NumberOfComponents;
ValueTypeT* data = this->Buffer->GetBuffer() + valueIdx;
for (int i = 0; i < this->NumberOfComponents; ++i)
{
data[i] = static_cast<ValueType>(tuple[i]);
}
this->MaxId = std::max(this->MaxId, valueIdx + this->NumberOfComponents - 1);
}
}
template <class DerivedT, class ValueTypeT>
bool vtkGenericDataArray<DerivedT, ValueTypeT>::EnsureAccessToTuple(vtkIdType tupleIdx)
{
if (tupleIdx < 0)
{
return false;
}
vtkIdType minSize = (1 + tupleIdx) * this->NumberOfComponents;
vtkIdType expectedMaxId = minSize - 1;
if (this->MaxId < expectedMaxId)
{
if (this->Size < minSize)
{
if (!this->Resize(tupleIdx + 1))
{
return false;
}
}
this->MaxId = expectedMaxId;
}
return true;
}从代码可以看出，插入值采用的是数组指针偏移的方式。插入前，通过EnsureAccessToTuple函数先检查是否需要Resize。插入时，指针偏移tupleIdx * NumberOfComponents，tupleIdx是当前准备在元组中插入的索引位置，NumberOfComponents是元组大小（可以理解为子一级的数组，子一级数组大小是固定值），上面的例子调用的是InsertTuple1，对应是一元组，所以NumberOfComponents等于1。在vtkDataArray.h中可以看到其提供了InsertTuple1、InsertTuple2、InsertTuple3、InsertTuple4、InsertTuple6、InsertTuple9这些接口分别用于插入对应大小的元组元素。
2 数据对象
vtkPolyData
上一篇文章提到vtkPolyData通过维护四个单独的列表（顶点（vertices）、线（lines）、多边形（polygons）和三角形带（triangle strips））来间接表示单元的类型，下面通过一个例子来看看它的使用。
cpp
#include <vtkAutoInit.h>
VTK_MODULE_INIT(vtkRenderingOpenGL2);
VTK_MODULE_INIT(vtkInteractionStyle);
VTK_MODULE_INIT(vtkRenderingFreeType);
VTK_MODULE_INIT(vtkRenderingVolumeOpenGL2);
#include <vtkActor.h>
#include <vtkNamedColors.h>
#include <vtkPolyData.h>
#include <vtkPolyDataMapper.h>
#include <vtkProperty.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>
#include <vtkSphereSource.h>
#include <vtkOpenGLRenderer.h>
#include <vtkOpenGLState.h>
int main(int, char*[])
{
vtkNew<vtkNamedColors> colors;
static double pts[25][3] = {
{0.00, 1.00, 0.00 }, {0.00, 0.71, 0.71 }, {0.00, 0.00, 1.00 }, {0.00, -0.71, 0.71 }, {0.00, -1.00, 0.00 },
{0.00, 1.00, 0.00 }, {0.71, 0.71, 0.00 }, {1.00, 0.00, 0.00 }, {0.71, -0.71, 0.00 }, {0.00, -1.00, 0.00 },
{0.00, 1.00, 0.00 }, {0.00, 0.71, -0.71 }, {0.00, 0.00, -1.00 }, {0.00, -0.71, -0.71 }, {0.00, -1.00, 0.00 },
{0.00, 1.00, 0.00 }, {-0.71, 0.71, 0.00 }, {-1.00, 0.00, 0.00 }, {-0.71, -0.71, 0.00 }, {0.00, -1.00, 0.00 },
{0.00, 1.00, 0.00 }, {0.00, 0.71, 0.71 }, {0.00, 0.00, 1.00 }, {0.00, -0.71, 0.71 }, {0.00, -1.00, 0.00 }
} ;
static vtkIdType lines[80][2] = {
{0, 5 }, {0, 1 }, {1, 6 }, {5, 6 }, {5, 1 }, {1, 6 }, {1, 2 }, {2, 7 },
{6, 7 }, {6, 2 }, {2, 7 }, {2, 3 }, {3, 8 }, {7, 8 }, {7, 3 }, {3, 8 },
{3, 4 }, {4, 9 }, {8, 9 }, {8, 4 }, {5, 10 }, {5, 6 }, {6, 11 }, {10, 11 },
{10, 6 }, {6, 11 }, {6, 7 }, {7, 12 }, {11, 12 }, {11, 7 }, {7, 12 }, {7, 8 },
{8, 13 }, {12, 13 }, {12, 8 }, {8, 13 }, {8, 9 }, {9, 14 }, {13, 14 }, {13, 9 },
{10, 15 }, {10, 11 }, {11, 16 }, {15, 16 }, {15, 11 }, {11, 16 }, {11, 12 }, {12, 17 },
{16, 17 }, {16, 12 }, {12, 17 }, {12, 13 }, {13, 18 }, {17, 18 }, {17, 13 }, {13, 18 },
{13, 14 }, {14, 19 }, {18, 19 }, {18, 14 }, {15, 20 }, {15, 16 }, {16, 21 }, {20, 21 },
{20, 16 }, {16, 21 }, {16, 17 }, {17, 22 }, {21, 22 }, {21, 17 }, {17, 22 }, {17, 18 },
{18, 23 }, {22, 23 }, {22, 18 }, {18, 23 }, {18, 19 }, {19, 24 }, {23, 24 }, {23, 19 }
};
static vtkIdType strips[32][3] = {
{0, 5, 1 }, {5, 1, 6 }, {1, 6, 2 }, {6, 2, 7 }, {2, 7, 3 }, {7, 3, 8 }, {3, 8, 4 }, {8, 4, 9 },
{5, 10, 6 }, {10, 6, 11 }, {6, 11, 7 }, {11, 7, 12 }, {7, 12, 8 }, {12, 8, 13 }, {8, 13, 9 }, {13, 9, 14 },
{10, 15, 11 }, {15, 11, 16 }, {11, 16, 12 }, {16, 12, 17 }, {12, 17, 13 }, {17, 13, 18 }, {13, 18, 14 }, {18, 14, 19 },
{15, 20, 16 }, {20, 16, 21 }, {16, 21, 17 }, {21, 17, 22 }, {17, 22, 18 }, {22, 18, 23 }, {18, 23, 19 }, {23, 19, 24 }
};
vtkIdType numVerts = 25;
vtkIdType numLines = 80;
vtkIdType numStrips = 32;
vtkIdType numCells = numVerts + numLines + numStrips;
vtkIdType i;
vtkPoints* points = vtkPoints::New();
points->SetNumberOfPoints(25);
for (i = 0; i < 25; i++)
{
points->InsertPoint(i, pts[i]);
}
vtkSmartPointer<vtkPolyData> poly = vtkSmartPointer<vtkPolyData>::New();
poly->AllocateExact(numCells, numCells);
poly->SetPoints(points);
points->Delete();
for (i = 0; i < numVerts; i++)
{
poly->InsertNextCell(VTK_VERTEX, 1, &i);
}
for (i = 0; i < numLines; i++)
{
poly->InsertNextCell(VTK_LINE, 2, lines[i]);
}
for (i = 0; i < numStrips; i++)
{
poly->InsertNextCell(VTK_TRIANGLE_STRIP, 3, strips[i]);
}
poly->BuildCells();
vtkNew<vtkPolyDataMapper> mapper;
mapper->SetInputData(poly);
vtkNew<vtkActor> actor;
actor->SetMapper(mapper);
actor->GetProperty()->SetLineWidth(6);
actor->GetProperty()->SetPointSize(25);
actor->GetProperty()->SetRenderLinesAsTubes(1);
actor->GetProperty()->SetRenderPointsAsSpheres(1);
actor->GetProperty()->SetColor(colors->GetColor3d("Cornsilk").GetData());
vtkNew<vtkRenderer> renderer;
vtkNew<vtkRenderWindow> renderWindow;
renderWindow->SetSize(500, 500);
renderWindow->AddRenderer(renderer);
vtkNew<vtkRenderWindowInteractor> renderWindowInteractor;
renderWindowInteractor->SetRenderWindow(renderWindow);
renderer->AddActor(actor);
renderer->SetBackground(colors->GetColor3d("DarkGreen").GetData());
renderWindow->Render();
renderWindowInteractor->Start();
getchar();
return EXIT_SUCCESS;
}运行效果图如下：
从图中可以看到绘制了点、线、由三角网渲染出来的面。
vtkUnstructuredGrid
vtkUnstructuredGrid可以表示所有单元类型（规则和不规则的），下面通过一个例子来看看它的使用。
cpp
#include <vtkAutoInit.h>
VTK_MODULE_INIT(vtkRenderingOpenGL2);
VTK_MODULE_INIT(vtkInteractionStyle);
VTK_MODULE_INIT(vtkRenderingFreeType);
VTK_MODULE_INIT(vtkRenderingVolumeOpenGL2);
#include <vtkActor.h>
#include <vtkCamera.h>
#include <vtkCellType.h>
#include <vtkDataSetMapper.h>
#include <vtkNamedColors.h>
#include <vtkNew.h>
#include <vtkPoints.h>
#include <vtkProperty.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>
#include <vtkUnstructuredGrid.h>
int main(int, char*[])
{
int i;
static double x[27][3] = {
{0, 0, 0}, {1, 0, 0}, {2, 0, 0}, {0, 1, 0}, {1, 1, 0}, {2, 1, 0},
{0, 0, 1}, {1, 0, 1}, {2, 0, 1}, {0, 1, 1}, {1, 1, 1}, {2, 1, 1},
{0, 1, 2}, {1, 1, 2}, {2, 1, 2}, {0, 1, 3}, {1, 1, 3}, {2, 1, 3},
{0, 1, 4}, {1, 1, 4}, {2, 1, 4}, {0, 1, 5}, {1, 1, 5}, {2, 1, 5},
{0, 1, 6}, {1, 1, 6}, {2, 1, 6}};
static vtkIdType pts[12][8] = {
{0, 1, 4, 3, 6, 7, 10, 9}, {1, 2, 5, 4, 7, 8, 11, 10},
{6, 10, 9, 12, 0, 0, 0, 0}, {8, 11, 10, 14, 0, 0, 0, 0},
{16, 17, 14, 13, 12, 15, 0, 0}, {18, 15, 19, 16, 20, 17, 0, 0},
{22, 23, 20, 19, 0, 0, 0, 0}, {21, 22, 18, 0, 0, 0, 0, 0},
{22, 19, 18, 0, 0, 0, 0, 0}, {23, 26, 0, 0, 0, 0, 0, 0},
{21, 24, 0, 0, 0, 0, 0, 0}, {25, 0, 0, 0, 0, 0, 0, 0}};
vtkNew<vtkNamedColors> colors;
vtkNew<vtkRenderer> renderer;
vtkNew<vtkRenderWindow> renWin;
renWin->AddRenderer(renderer);
vtkNew<vtkRenderWindowInteractor> iren;
iren->SetRenderWindow(renWin);
vtkNew<vtkPoints> points;
for (i = 0; i < 27; i++) points->InsertPoint(i, x[i]);
vtkNew<vtkUnstructuredGrid> ugrid;
ugrid->Allocate(100);
ugrid->InsertNextCell(VTK_HEXAHEDRON, 8, pts[0]);
ugrid->InsertNextCell(VTK_HEXAHEDRON, 8, pts[1]);
ugrid->InsertNextCell(VTK_TETRA, 4, pts[2]);
ugrid->InsertNextCell(VTK_TETRA, 4, pts[3]);
ugrid->InsertNextCell(VTK_POLYGON, 6, pts[4]);
ugrid->InsertNextCell(VTK_TRIANGLE_STRIP, 6, pts[5]);
ugrid->InsertNextCell(VTK_QUAD, 4, pts[6]);
ugrid->InsertNextCell(VTK_TRIANGLE, 3, pts[7]);
ugrid->InsertNextCell(VTK_TRIANGLE, 3, pts[8]);
ugrid->InsertNextCell(VTK_LINE, 2, pts[9]);
ugrid->InsertNextCell(VTK_LINE, 2, pts[10]);
ugrid->InsertNextCell(VTK_VERTEX, 1, pts[11]);
ugrid->SetPoints(points);
vtkNew<vtkDataSetMapper> ugridMapper;
ugridMapper->SetInputData(ugrid);
vtkNew<vtkActor> ugridActor;
ugridActor->SetMapper(ugridMapper);
ugridActor->GetProperty()->SetColor(colors->GetColor3d("Peacock").GetData());
ugridActor->GetProperty()->EdgeVisibilityOn();
renderer->AddActor(ugridActor);
renderer->SetBackground(colors->GetColor3d("Beige").GetData());
renderer->ResetCamera();
renderer->GetActiveCamera()->Elevation(60.0);
renderer->GetActiveCamera()->Azimuth(30.0);
renderer->GetActiveCamera()->Dolly(1.2);
renWin->SetSize(640, 480);
renWin->SetWindowName("UGrid)");
// interact with data
renWin->Render();
iren->Start();
getchar();
return EXIT_SUCCESS;
}运行效果图如下：
3 数据模型
VTK中数据模型由单元（cell） 和**点（point）**组成，点对应vtkPoints类，单元对应vtkCellArray类。
vtkPoints
vtkPoints用来表示和操作3D点。vtkPoints的数据模型是可通过（点或单元）id访问的vx-vy-vz三元组数组。
cpp
vtkPoints::vtkPoints(int dataType)
{
this->Data = vtkFloatArray::New();
this->Data->Register(this);
this->Data->Delete();
this->SetDataType(dataType);
this->Data->SetNumberOfComponents(3);
this->Data->SetName("Points");
this->Bounds[0] = this->Bounds[2] = this->Bounds[4] = VTK_DOUBLE_MAX;
this->Bounds[1] = this->Bounds[3] = this->Bounds[5] = -VTK_DOUBLE_MAX;
}从vtkPoints类构造函数中的代码可以看出，它创建了一个vtkFloatArray数据数组，NumberOfComponents为3表示其为一个三元组。
cpp
void InsertPoint(vtkIdType id, const float x[3]) VTK_EXPECTS(0 <= id)
{
this->Data->InsertTuple(id, x);
}
void InsertPoint(vtkIdType id, const double x[3]) VTK_EXPECTS(0 <= id)
{
this->Data->InsertTuple(id, x);
}
vtkIdType InsertNextPoint(const float x[3]) { return this->Data->InsertNextTuple(x); }
vtkIdType InsertNextPoint(const double x[3]) { return this->Data->InsertNextTuple(x); }
vtkIdType InsertNextPoint(double x, double y, double z);InsertPoint和InsertNextPoint内部调用的是数据数组的InsertTuple和InsertNextTuple函数。
vtkCellArray
vtkCellArray用来表示单元内部连接性的对象。其将数据集的拓扑结构存为显示连接性（connectivity）表，表中列出组成每个单元的点ID。
在vtkCellArray内部，连接性表表示为两个数组：Offsets（偏移） 和Connectivity（连接性）。Offsets是一个[numCells+1]值的数组，指示Connectivity数组中每个单元点开始的索引，最后一个值始终是Connectivity数组的长度。Connectivity数组存每个单元的点ID列表。因此，对于由两个三角形、一个四边形和一条线组成的数据集，内部数组将如下所示：
cpp
Topology:
---------
Cell 0: Triangle | point ids: {0, 1, 2}
Cell 1: Triangle | point ids: {5, 7, 2}
Cell 2: Quad | point ids: {3, 4, 6, 7}
Cell 4: Line | point ids: {5, 8}
vtkCellArray (current):
-----------------------
Offsets: {0, 3, 6, 10, 12}
Connectivity: {0, 1, 2, 5, 7, 2, 3, 4, 6, 7, 5, 8}虽然此类提供了遍历方法（旧的InitTraversal()、GetNextCell()方法和较新的方法GetCellAtId()）,但这些方法通常不是线程安全的。最好使用本地线程安全的vtkCellArrayInterator对象，可以通过以下方式获取该对象：
cpp
auto iter = vtk::TakeSmartPointer(cellArray->NewIterator());
for (iter->GoToFirstCell(); !iter->IsDoneWithTraversal(); iter->GoToNextCell())
{
// do work with iter
}（但请注意，根据内部存的类型和结构，由于额外的数据复制，单元数组迭代器可能比直接遍历单元数组慢得多。另外，如果vtkCellArray内部存储被修改，迭代器可能变得无效。）
vtkCellArray内部的数组可以存32或64位的值，尽管大多数API更喜欢使用vtkIdType来对应数组中的元素。允许将64位存储于32位vtkIdType一起使用，但太大而无法容纳32位有符号整数的值在通过API访问时将被截断。（特定的内部存储类型对性能有影响，具体取决于vtkIdType。如果内部存储等效于vtkIdType，则返回指向点"id"数组的指针的方法可以共享内部存储，否则必须执行复制内存）。
cpp
/*--------------------------------------------------------------------------*/
/* Choose an implementation for vtkIdType. */
#define VTK_HAS_ID_TYPE
#ifdef VTK_USE_64BIT_IDS
#if VTK_SIZEOF_LONG_LONG == 8
typedef long long vtkIdType;
#define VTK_ID_TYPE_IMPL VTK_LONG_LONG
#define VTK_SIZEOF_ID_TYPE VTK_SIZEOF_LONG_LONG
#define VTK_ID_MIN VTK_LONG_LONG_MIN
#define VTK_ID_MAX VTK_LONG_LONG_MAX
#define VTK_ID_TYPE_PRId "lld"
#elif VTK_SIZEOF_LONG == 8
typedef long vtkIdType;
#define VTK_ID_TYPE_IMPL VTK_LONG
#define VTK_SIZEOF_ID_TYPE VTK_SIZEOF_LONG
#define VTK_ID_MIN VTK_LONG_MIN
#define VTK_ID_MAX VTK_LONG_MAX
#define VTK_ID_TYPE_PRId "ld"
#else
#error "VTK_USE_64BIT_IDS is ON but no 64-bit integer type is available."
#endif
#else
typedef int vtkIdType;
#define VTK_ID_TYPE_IMPL VTK_INT
#define VTK_SIZEOF_ID_TYPE VTK_SIZEOF_INT
#define VTK_ID_MIN VTK_INT_MIN
#define VTK_ID_MAX VTK_INT_MAX
#define VTK_ID_TYPE_PRId "d"
#endifInsertNextCell
InsertNextCell是用来插入单元的函数，各种数据对象中都有实现该接口，用以构造本对象中的各种类型的单元。下面我们通过vtkPolyData中InsertNextCell函数的内部实现代码看下它是如何构造单元的。
cpp
vtkIdType vtkPolyData::InsertNextCell(int type, vtkIdList* pts)
{
return this->InsertNextCell(type, static_cast<int>(pts->GetNumberOfIds()), pts->GetPointer(0));
}
vtkIdType vtkPolyData::InsertNextCell(int type, int npts, const vtkIdType ptsIn[])
{
...
// Insert next cell into the lookup map:
TaggedCellId& tag = this->Cells->InsertNextCell(VTKCellType(type));
vtkCellArray* cells = this->GetCellArrayInternal(tag);
// Validate and update the internal cell id:
const vtkIdType internalCellId = cells->InsertNextCell(npts, pts);
if (internalCellId < 0)
{
vtkErrorMacro("Internal error: Invalid cell id (" << internalCellId << ").");
return -1;
}
...
// Return the dataset cell id:
return this->Cells->GetNumberOfCells() - 1;
}
inline vtkCellArray* vtkPolyData::GetCellArrayInternal(vtkPolyData::TaggedCellId tag)
{
switch (tag.GetTarget())
{
case vtkPolyData_detail::Target::Verts:
return this->Verts;
case vtkPolyData_detail::Target::Lines:
return this->Lines;
case vtkPolyData_detail::Target::Polys:
return this->Polys;
case vtkPolyData_detail::Target::Strips:
return this->Strips;
}
return nullptr; // unreachable
}vtkPolyData::InsertNextCell函数中调用：
vtkCellArray* cells = this->GetCellArrayInternal(tag);
获取当前要插入单元的类型对应的vtkCellArray。然后调用：
const vtkIdType internalCellId = cells->InsertNextCell(npts, pts);
插入单元到vtkCellArray。
cpp
inline vtkIdType vtkCellArray::InsertNextCell(vtkIdType npts, const vtkIdType* pts)
VTK_SIZEHINT(pts, npts)
{
return this->Visit(vtkCellArray_detail::InsertNextCellImpl{}, npts, pts);
}
template <typename Functor, typename... Args,
typename = typename std::enable_if<!ReturnsVoid<Functor, Args...>::value>::type>
GetReturnType<Functor, Args...> Visit(Functor&& functor, Args&&... args)
{
if (this->Storage.Is64Bit())
{
// If you get an error on the next line, a call to Visit(functor, Args...)
// is being called with arguments that do not match the functor's call
// signature. See the Visit documentation for details.
return functor(this->Storage.GetArrays64(), std::forward<Args>(args)...);
}
else
{
// If you get an error on the next line, a call to Visit(functor, Args...)
// is being called with arguments that do not match the functor's call
// signature. See the Visit documentation for details.
return functor(this->Storage.GetArrays32(), std::forward<Args>(args)...);
}
}Visit(Functor&& functor, Args&&... args)函数的第一个参数是一个InsertNextCellImpl对象（&&可以理解为std::move操作），第二个参数是一个可变参数列表。
functor(this->Storage.GetArrays64(), std::forward<Args>(args)...);调用的是InsertNextCellImpl中()操作符函数：
cpp
struct InsertNextCellImpl
{
// Insert full cell
template <typename CellStateT>
vtkIdType operator()(CellStateT& state, const vtkIdType npts, const vtkIdType pts[])
{
using ValueType = typename CellStateT::ValueType;
auto* conn = state.GetConnectivity();
auto* offsets = state.GetOffsets();
const vtkIdType cellId = offsets->GetNumberOfValues() - 1;
offsets->InsertNextValue(static_cast<ValueType>(conn->GetNumberOfValues() + npts));
for (vtkIdType i = 0; i < npts; ++i)
{
conn->InsertNextValue(static_cast<ValueType>(pts[i]));
}
return cellId;
}
...
};operator()函数的第一个参数通过this->Storage.GetArrays64()获得。
cpp
struct Storage
{
// Union type that switches 32 and 64 bit array storage
union ArraySwitch {
ArraySwitch() = default; // handled by Storage
~ArraySwitch() = default; // handle by Storage
VisitState<ArrayType32>* Int32;
VisitState<ArrayType64>* Int64;
};
Storage()
{
#ifdef VTK_USE_MEMKIND
this->Arrays =
static_cast<ArraySwitch*>(vtkObjectBase::GetCurrentMallocFunction()(sizeof(ArraySwitch)));
#else
this->Arrays = new ArraySwitch;
#endif
// Default to the compile-time setting:
#ifdef VTK_USE_64BIT_IDS
this->Arrays->Int64 = new VisitState<ArrayType64>;
this->StorageIs64Bit = true;
#else // VTK_USE_64BIT_IDS
this->Arrays->Int32 = new VisitState<ArrayType32>;
this->StorageIs64Bit = false;
#endif // VTK_USE_64BIT_IDS
#ifdef VTK_USE_MEMKIND
if (vtkObjectBase::GetUsingMemkind())
{
this->IsInMemkind = true;
}
#else
(void)this->IsInMemkind; // comp warning workaround
#endif
}
...
// Get the VisitState for 32-bit arrays
VisitState<ArrayType32>& GetArrays32()
{
assert(!this->StorageIs64Bit);
return *this->Arrays->Int32;
}
const VisitState<ArrayType32>& GetArrays32() const
{
assert(!this->StorageIs64Bit);
return *this->Arrays->Int32;
}
// Get the VisitState for 64-bit arrays
VisitState<ArrayType64>& GetArrays64()
{
assert(this->StorageIs64Bit);
return *this->Arrays->Int64;
}
const VisitState<ArrayType64>& GetArrays64() const
{
assert(this->StorageIs64Bit);
return *this->Arrays->Int64;
}
private:
// Access restricted to ensure proper union construction/destruction thru
// API.
ArraySwitch* Arrays;
bool StorageIs64Bit;
bool IsInMemkind = false;
};Storage内通过联合体（union）管理一个32位或64位的VisitState。
cpp
template <typename ArrayT>
struct VisitState
{
using ArrayType = ArrayT;
using ValueType = typename ArrayType::ValueType;
using CellRangeType = decltype(vtk::DataArrayValueRange<1>(std::declval<ArrayType>()));
// We can't just use is_same here, since binary compatible representations
// (e.g. int and long) are distinct types. Instead, ensure that ValueType
// is a signed integer the same size as vtkIdType.
// If this value is true, ValueType pointers may be safely converted to
// vtkIdType pointers via reinterpret cast.
static constexpr bool ValueTypeIsSameAsIdType = std::is_integral<ValueType>::value &&
std::is_signed<ValueType>::value && (sizeof(ValueType) == sizeof(vtkIdType));
ArrayType* GetOffsets() { return this->Offsets; }
const ArrayType* GetOffsets() const { return this->Offsets; }
ArrayType* GetConnectivity() { return this->Connectivity; }
const ArrayType* GetConnectivity() const { return this->Connectivity; }
...
friend class vtkCellArray;
protected:
VisitState()
{
this->Connectivity = vtkSmartPointer<ArrayType>::New();
this->Offsets = vtkSmartPointer<ArrayType>::New();
this->Offsets->InsertNextValue(0);
if (vtkObjectBase::GetUsingMemkind())
{
this->IsInMemkind = true;
}
}
vtkSmartPointer<ArrayType> Connectivity;
vtkSmartPointer<ArrayType> Offsets;
...
};回到InsertNextCellImpl的operator()函数。我们可以看到，函数中根据InsertNextCell传入的单元类型对应的点数（npts）在进行遍历，依次插入单元对应的点的索引集合；将conn->GetNumberOfValues() + npts（当前已经插入的索引值总数+要插入单元的元组大小）的值作为偏移值插入Offsets数组中。
4 数据属性
vtkPointData 和 vtkCellData
上一篇文章讲到数据属性通常与点和单元关联关联的（也可以通过GetFieldData()关联到整个数据模型），VTK中使用vtkPointData和vtkCellData分别表示数据点和单元的属性，它们都是vtkFieldData的子类。下面我们通过一个例子来看下它们的使用。
cpp
#include <vtkAutoInit.h>
VTK_MODULE_INIT(vtkRenderingOpenGL2);
VTK_MODULE_INIT(vtkInteractionStyle);
VTK_MODULE_INIT(vtkRenderingFreeType);
VTK_MODULE_INIT(vtkRenderingVolumeOpenGL2);
#include <vtkActor.h>
#include <vtkArrowSource.h>
#include <vtkCamera.h>
#include <vtkGlyph3D.h>
#include <vtkNamedColors.h>
#include <vtkNew.h>
#include <vtkPolyData.h>
#include <vtkPolyDataMapper.h>
#include <vtkProperty.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>
#include <vtkCubeSource.h>
#include <vtkCellArray.h>
#include <vtkFloatArray.h>
#include <vtkPointData.h>
#include <vtkCellData.h>
#include <vtkPoints.h>
int main(int, char*[])
{
vtkNew<vtkNamedColors> colors;
std::array<std::array<double, 3>, 8> pts = {{{{0, 0, 0}},
{{1, 0, 0}},
{{1, 1, 0}},
{{0, 1, 0}},
{{0, 0, 1}},
{{1, 0, 1}},
{{1, 1, 1}},
{{0, 1, 1}}}};
// The ordering of the corner points on each face.
std::array<std::array<vtkIdType, 4>, 6> ordering = {{{{0, 3, 2, 1}},
{{4, 5, 6, 7}},
{{0, 1, 5, 4}},
{{1, 2, 6, 5}},
{{2, 3, 7, 6}},
{{3, 0, 4, 7}}}};
std::array<std::array<double, 3>, 8> vertex_normals;
for(auto i = 0; i < 8; ++i)
{
for(auto j = 0; j < 3; ++j)
{
vertex_normals[i][j] = pts[i][j] - 0.5;
}
}
// We'll create the building blocks of polydata including data attributes.
vtkNew<vtkPolyData> cube;
vtkNew<vtkPoints> points;
vtkNew<vtkCellArray> polys;
vtkNew<vtkFloatArray> vertex_normals_array;
vtkNew<vtkFloatArray> scalar_array;
// Load the point, cell, and data attributes.
for (auto i = 0ul; i < pts.size(); ++i)
{
points->InsertPoint(i, pts[i].data());
}
for (auto&& i : ordering)
{
polys->InsertNextCell(vtkIdType(i.size()), i.data());
}
vertex_normals_array->SetNumberOfComponents(3);
for(auto i = 0; i < vertex_normals.size(); ++i)
{
vertex_normals_array->InsertNextTuple3(vertex_normals[i][0],
vertex_normals[i][1],
vertex_normals[i][2]);
}
scalar_array->SetNumberOfComponents(1);
for(auto i = 0; i < ordering.size(); ++i)
{
scalar_array->InsertNextTuple1(i);
}
// We now assign the pieces to the vtkPolyData.
cube->SetPoints(points);
cube->SetPolys(polys);
cube->GetPointData()->SetNormals(vertex_normals_array);
cube->GetCellData()->SetScalars(scalar_array);
vtkNew<vtkPolyData> input;
input->ShallowCopy(cube);
vtkNew<vtkArrowSource> arrowSource;
vtkNew<vtkGlyph3D> glyph3D;
glyph3D->SetSourceConnection(arrowSource->GetOutputPort());
glyph3D->SetInputData(input);
glyph3D->ScalingOn();
glyph3D->SetVectorModeToUseNormal();
glyph3D->SetScaleFactor(0.25);
glyph3D->Update();
// Visualize
vtkNew<vtkPolyDataMapper> mapper;
mapper->SetInputConnection(glyph3D->GetOutputPort());
vtkNew<vtkPolyDataMapper> cube_mapper;
cube_mapper->SetInputData(cube);
cube_mapper->SetScalarRange(cube->GetScalarRange());
vtkNew<vtkActor> actor;
actor->SetMapper(mapper);
actor->GetProperty()->SetColor(colors->GetColor3d("Gold").GetData());
vtkNew<vtkActor> cube_actor;
cube_actor->SetMapper(cube_mapper);
vtkNew<vtkRenderer> renderer;
vtkNew<vtkRenderWindow> renderWindow;
renderWindow->AddRenderer(renderer);
renderWindow->SetWindowName("OrientedGlyphs");
vtkNew<vtkRenderWindowInteractor> renderWindowInteractor;
renderWindowInteractor->SetRenderWindow(renderWindow);
renderer->AddActor(actor);
renderer->AddActor(cube_actor);
renderer->SetBackground(colors->GetColor3d("DarkGreen").GetData());
renderWindow->Render();
renderWindowInteractor->Start();
getchar();
return EXIT_SUCCESS;
}运行效果如下：
上面的代码中：
cube->GetPointData()->SetNormals(vertex_normals_array);将法向量数据数组设置给点，所以从图中可以看到箭头是在点的位置进行显示。
cube->GetCellData()->SetScalars(scalar_array);将标量数据数组设置给单元，可以看到每个单元（面）根据标量显示不同的颜色。
数据属性不仅仅只包含标量、向量，其所能支持的类型包括以下这些：
cpp
// Always keep NUM_ATTRIBUTES as the last entry
enum AttributeTypes
{
SCALARS = 0,
VECTORS = 1,
NORMALS = 2,
TCOORDS = 3,
TENSORS = 4,
GLOBALIDS = 5,
PEDIGREEIDS = 6,
EDGEFLAG = 7,
TANGENTS = 8,
RATIONALWEIGHTS = 9,
HIGHERORDERDEGREES = 10,
NUM_ATTRIBUTES
};Ghost属性
考虑如下图所示的提取外表面（face）的操作。外表面操作用于识别没有本地邻居的所有面。当我们把这些面片放置一起时，我们发现一些面被错误地识别为外部面。当两个相邻的单元被放置在单独的处理中时，这些面的错误识别就会发生。
上图提取外部面结果错误是因为处理中丢失了一些重要的全局信息，这些单独的处理过程不需要所有的数据，但需要一些不属于它们自己数据，即它们需要知道相邻的其他分区中的单元。
这个问题可以通过引入Ghost单元来解决这个局部/全局问题。Ghost单元是属于数据的一个分区并重复在其他分区上的单元。Ghost单元的引入是通过领域信息进行的，并按层次进行组织。对于给定的分区，与分区中的单元相邻但不属于分区本身的任何单元都是Ghost单元1。与不属于层次1或原始分区层次1的Ghost单元相邻的任何单元都处于层次2。递归定义更深的层次。
将Ghost引用到提取外表面的示例中，效果如下图，图中某些面仍然被分类为外表面，但是，所有这些面都附着在Ghost单元上。这些Ghost面很容易被剔除，最终结果就是合适的外表面。
下面通过一个例子来看看VTK中Ghost单元的使用：
cpp
#include <vtkAutoInit.h>
VTK_MODULE_INIT(vtkRenderingOpenGL2);
VTK_MODULE_INIT(vtkInteractionStyle);
VTK_MODULE_INIT(vtkRenderingFreeType);
VTK_MODULE_INIT(vtkRenderingVolumeOpenGL2);
#include "vtkActor.h"
#include "vtkCellData.h"
#include "vtkCellType.h"
#include "vtkDataSetSurfaceFilter.h"
#include "vtkGeometryFilter.h"
#include "vtkNew.h"
#include "vtkPoints.h"
#include "vtkPolyDataMapper.h"
#include "vtkRegressionTestImage.h"
#include "vtkRenderWindow.h"
#include "vtkRenderWindowInteractor.h"
#include "vtkRenderer.h"
#include "vtkSmartPointer.h"
#include "vtkUnsignedCharArray.h"
#include "vtkUnstructuredGrid.h"
#include "vtkFloatArray.h"
#include "vtkColorTransferFunction.h"
#include "vtkTextActor.h"
#include "vtkTextProperty.h"
#include "vtkCamera.h"
#include "vtkCallbackCommand.h"
#include "vtkRendererCollection.h"
#include "vtkActor2DCollection.h"
void CallbackFunction(vtkObject* caller, long unsigned int eventId,
void* clientData, void* callData)
{
vtkRenderWindowInteractor* iren = static_cast<vtkRenderWindowInteractor*>(caller);
vtkRenderer* renderer = iren->GetRenderWindow()->GetRenderers()->GetFirstRenderer();
if(clientData == nullptr)
return;
auto points = static_cast<vtkPoints*>(clientData);
auto ac = renderer->GetActors2D();
vtkActor2D* anActor;
vtkCollectionSimpleIterator ait;
for (ac->InitTraversal(ait); (anActor = ac->GetNextActor2D(ait));)
{
auto ta = vtkTextActor::SafeDownCast(anActor);
if(ta == nullptr) continue;
std::string text = ta->GetInput();
int idx = std::stoi(text);
auto pt = points->GetPoint(idx);
renderer->WorldToDisplay(pt[0], pt[1], pt[2]);
ta->SetDisplayPosition(pt[0], pt[1]);
}
}
int main(int argc, char* argv[])
{
vtkNew<vtkPoints> points;
points->InsertPoint(0, 0, 0, 0);
points->InsertPoint(1, 1, 0, 0);
points->InsertPoint(2, 0.5, 1, 0);
points->InsertPoint(3, 0.5, 0.5, 1);
points->InsertPoint(4, 0.5, -1, 0);
points->InsertPoint(5, 0.5, -0.5, 1);
vtkIdType v[3][4] = { { 0, 1, 2, 3 }, { 0, 4, 1, 5 }, { 5, 3, 1, 0 } };
//vtkIdType v[3][4] = { { 0, 1, 2, 3 }, { 5, 3, 1, 0 }, { 0, 4, 1, 5 } };
vtkSmartPointer<vtkUnstructuredGrid> grid = vtkSmartPointer<vtkUnstructuredGrid>::New();
grid->InsertNextCell(VTK_TETRA, 4, v[0]);
grid->InsertNextCell(VTK_TETRA, 4, v[1]);
grid->InsertNextCell(VTK_TETRA, 4, v[2]);
grid->SetPoints(points);
vtkNew<vtkFloatArray> cell_scalar_array;
cell_scalar_array->SetNumberOfComponents(1);
cell_scalar_array->InsertNextTuple1(0);
cell_scalar_array->InsertNextTuple1(3);
cell_scalar_array->InsertNextTuple1(7);
grid->GetCellData()->SetScalars(cell_scalar_array);
// vtkNew<vtkUnsignedCharArray> ghosts;
// ghosts->InsertNextValue(0);
// ghosts->InsertNextValue(1);
// ghosts->InsertNextValue(2);
// ghosts->SetName(vtkDataSetAttributes::GhostArrayName());
// grid->GetCellData()->AddArray(ghosts);
// this filter removes the ghost cells
vtkNew<vtkGeometryFilter> surfaces;
surfaces->SetInputData(grid);
surfaces->Update();
vtkNew<vtkColorTransferFunction> clrTransferFunc;
clrTransferFunc->SetColorSpaceToRGB();
clrTransferFunc->AddRGBPoint(0, 1, 0, 0);
clrTransferFunc->AddRGBPoint(3, 0, 1, 0);
clrTransferFunc->AddRGBPoint(7, 0, 1, 1);
vtkNew<vtkPolyDataMapper> mapper;
mapper->SetInputConnection(surfaces->GetOutputPort());
mapper->SetScalarRange(grid->GetScalarRange());
mapper->SetLookupTable(clrTransferFunc);
vtkNew<vtkActor> actor;
actor->SetMapper(mapper);
vtkNew<vtkCamera> camera;
camera->SetPosition(0, 0, 5);
camera->SetFocalPoint(0, 0, 0);
vtkNew<vtkRenderer> renderer;
renderer->SetActiveCamera(camera);
renderer->ResetCamera();
renderer->AddActor(actor);
vtkNew<vtkRenderWindow> renwin;
renwin->AddRenderer(renderer);
renwin->SetSize(500, 500);
vtkNew<vtkRenderWindowInteractor> iren;
iren->SetRenderWindow(renwin);
iren->Initialize();
vtkNew<vtkCallbackCommand> callback;
callback->SetCallback(CallbackFunction);
callback->SetClientData(points);
iren->AddObserver(vtkCommand::LeftButtonPressEvent, callback);
for(int i = 0; i < points->GetNumberOfPoints(); ++i)
{
auto pt = points->GetPoint(i);
std::string text = std::to_string(i);
vtkNew<vtkTextActor> ta;
ta->SetInput(text.c_str());
ta->GetTextProperty()->SetColor(0.5, 1.0, 0.0);
renderer->WorldToDisplay(pt[0], pt[1], pt[2]);
ta->SetDisplayPosition(pt[0], pt[1]);
ta->GetTextProperty()->SetFontSize(32);
renderer->AddActor(ta.Get());
}
renwin->Render();
iren->Start();
getchar();
return EXIT_SUCCESS;
}没应用ghost单元代码的情况下，效果如下图：
应用ghost单元代码的情况下，效果如下图：
可以看到vtkGeometryFilter移除了第二个Ghost单元。将第二个单元和第三个单元顺序换一下的效果图如下：
