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{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