一、概述

        vtkCommand是VTK中的一个重要的类，用于处理事件和回调机制。它允许用户在特定事件发生时执行自定义的操作，例如在交互操作、数据更新或渲染过程中触发某些功能。

二、主要功能

1、事件处理：vtkCommand用于监听和处理VTK管线中的各种事件

2、回调机制：通过回调函数，用户可以在事件发生时执行自定义代码

3、事件类型：VTK定义了多种事件类型，如StartEvent、EndEvent、ProgressEvent等。

三、常用事件类型

StartEvent	某个过程开始时触发
EndEvent	某个过程结束时触发
ProgressEvent	过程进行中触发，常用于更新进度条
ModifiedEvent	对象被修改时触发
PickEvent	用户进行拾起操作时触发
InteractionEvent	用户进行交互操作时触发

四、使用步骤 

1、创建一个类继承于vtkCommand，并重写Execute方法

class vtkMyCallback : public vtkCommand
{
public:
    static vtkMyCallback* New()
    {
        return new vtkMyCallback;
    }
    void Execute(vtkObject* caller, unsigned long, void*) override
    {
        auto renderer = reinterpret_cast<vtkRenderer*>(caller);
        std::cout << renderer->GetActiveCamera()->GetPosition()[0] << " "
                  << renderer->GetActiveCamera()->GetPosition()[1] << " "
                  << renderer->GetActiveCamera()->GetPosition()[2] << std::endl;
    }
    vtkMyCallback() = default;
};

2、创建vtkCommand对象 ，经对象添加到需要监听的对象中

//渲染器对象
vtkNew<vtkRenderer> ren1;

vtkNew<vtkMyCallback> mo1;
ren1->AddObserver(vtkCommand::StartEvent, mo1);

五、完整示例

namespace {
class vtkMyCallback : public vtkCommand
{
public:
    static vtkMyCallback* New()
    {
        return new vtkMyCallback;
    }
    void Execute(vtkObject* caller, unsigned long, void*) override
    {
        // Note the use of reinterpret_cast to cast the caller to the expected type.
        auto renderer = reinterpret_cast<vtkRenderer*>(caller);
        std::cout << renderer->GetActiveCamera()->GetPosition()[0] << " "
                  << renderer->GetActiveCamera()->GetPosition()[1] << " "
                  << renderer->GetActiveCamera()->GetPosition()[2] << std::endl;
    }
    vtkMyCallback() = default;
};
}

int main(int, char*[])
{
  //创建VTK命名颜色
  vtkNew<vtkNamedColors> colors;

  //创建多边形圆锥体
  vtkNew<vtkConeSource> cone;
  cone->SetHeight(3.0);
  cone->SetRadius(1.0);
  cone->SetResolution(10);

  //将多边形数据映射到圆形基于映射器
  vtkNew<vtkPolyDataMapper> coneMapper;
  coneMapper->SetInputConnection(cone->GetOutputPort());

  //创建渲染创建中的实体（几何体和属性）
  vtkNew<vtkActor> coneActor;
  coneActor->SetMapper(coneMapper);
  coneActor->GetProperty()->SetColor(colors->GetColor3d("MistyRose").GetData());

  //创建渲染器
  vtkNew<vtkRenderer> ren1;
  ren1->AddActor(coneActor);
  ren1->SetBackground(colors->GetColor3d("MidnightBlue").GetData());
  ren1->ResetCamera();

  //为渲染器创建绘制窗口
  vtkNew<vtkRenderWindow> renWin;
  renWin->AddRenderer(ren1);
  renWin->SetSize(300, 300);
  renWin->SetWindowName("Tutorial_Step2");

  //注册监听的事件及回调
  vtkNew<vtkMyCallback> mo1;
  ren1->AddObserver(vtkCommand::StartEvent, mo1);

  for (int i = 0; i < 360; ++i)
  {
    renWin->Render();
    ren1->GetActiveCamera()->Azimuth(1);
  }

  return EXIT_SUCCESS;
}

运行结果，物体旋转的同时，打印数据：

15.2107 1 0
15.2084 1 -0.265464
15.2014 1 -0.530846
15.1899 1 -0.796067
15.1737 1 -1.06105
15.1528 1 -1.3257
15.1274 1 -1.58995
15.0973 1 -1.85372
15.0627 1 -2.11692
15.0234 1 -2.37948
14.9796 1 -2.64131
14.9312 1 -2.90234
14.8783 1 -3.16248
14.8209 1 -3.42167
14.7589 1 -3.6798
14.6924 1 -3.93682
14.6215 1 -4.19264
14.5461 1 -4.44718
14.4662 1 -4.70037
14.382 1 -4.95212
14.2934 1 -5.20237
14.2004 1 -5.45103