VTK交互之Widget

交互部件

　　VTK的交互除了提供各种交互样式，还提供了功能更为强大的，可以“看得见”的交互部件，即Widget。VTK的Widget类主要包括vtk3DWidget和vtkAbstractWidget两个父类，它们都派生自vtkInteractorObserver。其中vtk3DWidget主要在三维渲染场景中生成一个可以用于控制数据的可视化实体，比如点、曲线、平面、球体等；后者是VTK里实现“交互/表达实体(Interaction/Representation)”设计的所有Widget的基类。
　　vtkAbstractWidget作为基类，只定义一些公共的API以及实现了“交互/表达实体”分离的设计机制，其中，把从vtkRenderWindowInteractor路由过来的信息交给vtkAbstractWidget的“交互”部分处理，而Widget的“表达实体”则对应一个vtkPro对象（或者是vtkWidgetRepresenttation的子类）。
　　此外，vtkAbstractWidget类提供了访问vtkWidgetEventTranslator对象的函数，即GetEventTranslator()，该对象的作用可以将VTK事件映射为Widget事件（定义于vtkWidgetEvent.h文件中），通过vtkWidgetEventTranslator类，用户可以定制符合自己使用习惯的控制Widget的事件绑定。利用类vtkWidgetCallbackMapper将相应的Widget事件与各个受保护的静态操作函数关联起来。

vtkWidgetEventTranslator* eventTranslator =  widget->GetEventTranslator();eventTranslator->SetTranslation(vtkCommand::RightButtonPressEvent, vtkWidgetEvent::Select);eventTranslator->SetTranslation(vtkCommand::RightButtonReleaseEvent, vtkWidgetEvent::EndSelect);

创建Widget交互步骤

Widget的创建以及使用基本都是类似的，一般步骤如下。

1. 实例化Widget
2. 指定渲染窗口交互器。Widget可以通过它监听用户事件。
3. 必要时使用观察者/命令模式创建回调函数。
4. 创建合适的几何表达实体，并用SetRepresentation()函数把它与Widget关联起来，或者使用Widget默认的几何表达实体。
5. 最后必须激活Widget，使其在渲染场景中显示。

示例说明

CMakeLists.txt文件代码如下：

CMAKE_MINIMUM_REQUIRED(VERSION 2.8)PROJECT(WidgetExample)FIND_PACKAGE(VTK REQUIRED)INCLUDE(${VTK_USE_FILE})ADD_EXECUTABLE(WidgetExample    WidgetExample.cpp)TARGET_LINK_LIBRARIES(WidgetExample  ${VTK_LIBRARIES})

VTKDataExample .cpp文件代码如下：

#include <vtkVersion.h>#include <vtkSmartPointer.h>#include <vtkPolyDataMapper.h>#include <vtkActor.h>#include <vtkRenderWindow.h>#include <vtkRenderer.h>#include <vtkRenderWindowInteractor.h>#include <vtkPolyData.h>#include <vtkImageData.h>#include <vtkCoordinate.h>#include <vtkSphereSource.h>#include <vtkButtonWidget.h>#include <vtkTexturedButtonRepresentation2D.h>static void CreateImage(vtkSmartPointer<vtkImageData> image,    unsigned char *color1,    unsigned char *color2);int main(int, char *[]){    // Create two images for texture    vtkSmartPointer<vtkImageData> image1 =        vtkSmartPointer<vtkImageData>::New();    vtkSmartPointer<vtkImageData> image2 =        vtkSmartPointer<vtkImageData>::New();    unsigned char banana[3] = { 227, 207, 87 };    unsigned char tomato[3] = { 255, 99, 71 };    CreateImage(image1, banana, tomato);    CreateImage(image2, tomato, banana);    // Create some geometry    vtkSmartPointer<vtkSphereSource> sphereSource =        vtkSmartPointer<vtkSphereSource>::New();    sphereSource->Update();    vtkSmartPointer<vtkPolyDataMapper> mapper =        vtkSmartPointer<vtkPolyDataMapper>::New();    mapper->SetInputConnection(sphereSource->GetOutputPort());    vtkSmartPointer<vtkActor> actor =        vtkSmartPointer<vtkActor>::New();    actor->SetMapper(mapper);    // A renderer and render window    vtkSmartPointer<vtkRenderer> renderer =        vtkSmartPointer<vtkRenderer>::New();    vtkSmartPointer<vtkRenderWindow> renderWindow =        vtkSmartPointer<vtkRenderWindow>::New();    renderWindow->AddRenderer(renderer);    // An interactor    vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =        vtkSmartPointer<vtkRenderWindowInteractor>::New();    renderWindowInteractor->SetRenderWindow(renderWindow);    // Create the widget and its representation    vtkSmartPointer<vtkTexturedButtonRepresentation2D> buttonRepresentation =        vtkSmartPointer<vtkTexturedButtonRepresentation2D>::New();    buttonRepresentation->SetNumberOfStates(2);    buttonRepresentation->SetButtonTexture(0, image1);    buttonRepresentation->SetButtonTexture(1, image2);    vtkSmartPointer<vtkButtonWidget> buttonWidget =        vtkSmartPointer<vtkButtonWidget>::New();    buttonWidget->SetInteractor(renderWindowInteractor);    buttonWidget->SetRepresentation(buttonRepresentation);    // Add the actors to the scene    renderer->AddActor(actor);    renderer->SetBackground(.1, .2, .5);    renderWindow->SetSize(640, 480);    renderWindow->Render();    // Place the widget. Must be done after a render so that the    // viewport is defined.    // Here the widget placement is in normalized display coordinates    vtkSmartPointer<vtkCoordinate> upperRight =        vtkSmartPointer<vtkCoordinate>::New();    upperRight->SetCoordinateSystemToNormalizedDisplay();    upperRight->SetValue(1.0, 1.0);    double bds[6];    double sz = 50.0;    bds[0] = upperRight->GetComputedDisplayValue(renderer)[0] - sz;    bds[1] = bds[0] + sz;    bds[2] = upperRight->GetComputedDisplayValue(renderer)[1] - sz;    bds[3] = bds[2] + sz;    bds[4] = bds[5] = 0.0;    // Scale to 1, default is .5    buttonRepresentation->SetPlaceFactor(1);    buttonRepresentation->PlaceWidget(bds);    buttonWidget->On();    // Begin mouse interaction    renderWindowInteractor->Start();    return EXIT_SUCCESS;}void CreateImage(vtkSmartPointer<vtkImageData> image,    unsigned char* color1,    unsigned char* color2){    // Specify the size of the image data    image->SetDimensions(10, 10, 1);#if VTK_MAJOR_VERSION <= 5    image->SetNumberOfScalarComponents(3);    image->SetScalarTypeToUnsignedChar();#else    image->AllocateScalars(VTK_UNSIGNED_CHAR, 3);#endif    int* dims = image->GetDimensions();    // Fill the image with    for (int y = 0; y < dims[1]; y++)    {        for (int x = 0; x < dims[0]; x++)        {            unsigned char* pixel =                static_cast<unsigned char*>(image->GetScalarPointer(x, y, 0));            if (x < 5)            {                pixel[0] = color1[0];                pixel[1] = color1[1];                pixel[2] = color1[2];            }            else            {                pixel[0] = color2[0];                pixel[1] = color2[1];                pixel[2] = color2[2];            }        }    }}

运行结果：