VTK笔记——Widget简介

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很多时候，3D模型软件需要和用户进行交互，比如按钮单击，鼠标移动，滚轮缩放，快捷键控制等等。在VTK中，widget可以为这些复杂的交互提供便利。比如，vtkBoxWidget2 允许你在屏幕上移动box，它提供了平移box，旋转和缩放这个box的操作。当然，你会说，这些可以用vtkCubeSource 和指定的vtkInteractorStyle来实现，没错，但相比而言，widget以一种更一般，更便利和更独立的方式提供了所有的这些操作。

widget包含两个重要的组成部分：Interaction和Representation.

Interaction

Interaction是一些名叫vtk*Widget的类（比如vtkBoxWidget2）。它包含了交互的所有选项和事件处理。

Representation

Representation是显示并与之交互的一类对象，以名叫vtk*Representation.

用法

创建一个widget:

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vtkSmartPointer<vtkBoxWidget2> boxWidget =
  vtkSmartPointer<vtkBoxWidget2>::New();
boxWidget->SetInteractor( renderWindowInteractor );

大多数widget都有默认的representation。如果你想改变它，可以手动创建一个representation并设置到widget.

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 vtkSmartPointer<vtkBoxRepresentation> boxRep =
vtkSmartPointer<vtkBoxRepresentation>::New();
 boxRep->SetPlaceFactor(1);
 boxRep->PlaceWidget(actor->GetBounds());
 boxWidget->SetRepresentation(boxRep);

事件处理

往往你希望响应用户在widget上所作的操作，那这时候就需要定义一个vtkCommand的子类，并在一个类似于vtkCallbackFunction回调函数的方法Execute中来处理这些操作。

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class vtkBoxCallback : public vtkCommand
{
public:
  static vtkBoxCallback *New()
  {
    return new vtkBoxCallback;
  }

  vtkSmartPointer<vtkActor> m_actor;

  void SetActor(vtkSmartPointer<vtkActor> actor)
  {
    m_actor = actor;
  }

  virtual void Execute(vtkObject *caller, unsigned long, void*)
  {
    vtkSmartPointer<vtkBoxWidget2> boxWidget =
      dynamic_cast<vtkBoxWidget2*>(caller);

    vtkSmartPointer<vtkTransform> t =
      vtkSmartPointer<vtkTransform>::New();

	dynamic_cast<vtkBoxRepresentation*>(boxWidget->GetRepresentation())->GetTransform(t);
	this->m_actor->SetUserTransform(t);
  }

  vtkBoxCallback(){}
};

绑定事件

将自定义的事件添加到widget上，需要创建vtkCommand对象并调用widget的AddObserver方法。

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vtkSmartPointer<vtkBoxCallback> boxCallback =
  vtkSmartPointer<vtkBoxCallback>::New();
boxCallback->SetActor(actor);
boxWidget->AddObserver(vtkCommand::InteractionEvent, boxCallback);

启用Widget

使用Widget时，一定要注意顺序：

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boxWidget->On();

renderWindowInteractor->Start();

效果

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示例代码

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#include <vtkSmartPointer.h>
#include <vtkConeSource.h>
#include <vtkPolyDataMapper.h>
#include <vtkActor.h>
#include <vtkRenderer.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkInteractorStyleTrackballCamera.h>
#include <vtkBoxWidget2.h>
#include <vtkBoxRepresentation.h>
#include <vtkCommand.h>
#include <vtkTransform.h>

class vtkBoxCallback : public vtkCommand
{
public:
  static vtkBoxCallback *New()
  {
    return new vtkBoxCallback;
  }

  vtkSmartPointer<vtkActor> m_actor;

  void SetActor(vtkSmartPointer<vtkActor> actor)
  {
    m_actor = actor;
  }

  virtual void Execute(vtkObject *caller, unsigned long, void*)
  {
    vtkSmartPointer<vtkBoxWidget2> boxWidget =
      dynamic_cast<vtkBoxWidget2*>(caller);

    vtkSmartPointer<vtkTransform> t =
      vtkSmartPointer<vtkTransform>::New();

	dynamic_cast<vtkBoxRepresentation*>(boxWidget->GetRepresentation())->GetTransform(t);
	this->m_actor->SetUserTransform(t);
  }

  vtkBoxCallback(){}
};

int main(int argc, char* argv[])
{
  vtkSmartPointer<vtkConeSource> coneSource =
    vtkSmartPointer<vtkConeSource>::New();
  coneSource->SetHeight(1.5);

  vtkSmartPointer<vtkPolyDataMapper> mapper =
    vtkSmartPointer<vtkPolyDataMapper>::New();
  mapper->SetInputConnection(coneSource->GetOutputPort());

  vtkSmartPointer<vtkActor> actor = vtkSmartPointer<vtkActor>::New();
  actor->SetMapper(mapper);

  vtkSmartPointer<vtkRenderer> renderer =
    vtkSmartPointer<vtkRenderer>::New();
  renderer->AddActor(actor);
  renderer->ResetCamera(); 

  vtkSmartPointer<vtkRenderWindow> renderWindow =
    vtkSmartPointer<vtkRenderWindow>::New();
  renderWindow->AddRenderer(renderer);

  vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
    vtkSmartPointer<vtkRenderWindowInteractor>::New();
  renderWindowInteractor->SetRenderWindow(renderWindow);

  vtkSmartPointer<vtkInteractorStyleTrackballCamera> style =
    vtkSmartPointer<vtkInteractorStyleTrackballCamera>::New();
  renderWindowInteractor->SetInteractorStyle(style);

  vtkSmartPointer<vtkBoxWidget2> boxWidget =
    vtkSmartPointer<vtkBoxWidget2>::New();
  boxWidget->SetInteractor(renderWindowInteractor);

  vtkSmartPointer<vtkBoxRepresentation> boxRep =
	vtkSmartPointer<vtkBoxRepresentation>::New();
  boxRep->SetPlaceFactor(1);
  boxRep->PlaceWidget(actor->GetBounds());
  boxWidget->SetRepresentation(boxRep);
  
  vtkSmartPointer<vtkBoxCallback> boxCallback =
    vtkSmartPointer<vtkBoxCallback>::New();
  boxCallback->SetActor(actor);
  boxWidget->AddObserver(vtkCommand::InteractionEvent, boxCallback);

  boxWidget->On();

  renderWindowInteractor->Start();

  return 0;
}

Ref

VTK Widgets Tutorials
VTKExamples-Widgets
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