1.基于Clipping的体绘制裁剪技术

Clipping技术支持VTKImageData和VTKUntructuredGrid数据类型。该功能由vtkAbstractMapper3D类提供，对于那些使用基于OpenGL的硬件裁剪技术的Mapper类，如vtkPolyDataMapper、vtkVolumeTextureMapper2D、VTKProjectedTetrahedraMapper等，当设置的裁剪面个数超过OpenGL支持的个数（一般为6）时，VTK会反馈一个错误；而对于基于软件的裁剪技术的Mapper类，如vtkVolumeRayCastMapper则没有这些限制，可以支持任意多个裁剪面。使用Clipping技术，可以沿着任意方向将图像切开，便于观察体数据内部细节。
下面是例程中的一个实验：
 

#include <vtkAutoInit.h>
VTK_MODULE_INIT(vtkRenderingOpenGL);
VTK_MODULE_INIT(vtkRenderingVolumeOpenGL);
VTK_MODULE_INIT(vtkRenderingFreeType);
VTK_MODULE_INIT(vtkInteractionStyle);
 
#include <vtkSmartPointer.h>
#include <vtkPlane.h>
#include <vtkStructuredPoints.h>
#include <vtkStructuredPointsReader.h>
#include <vtkGPUVolumeRayCastMapper.h>
#include <vtkVolumeProperty.h>
#include <vtkPiecewiseFunction.h>
#include <vtkColorTransferFunction.h>
#include <vtkVolume.h>
#include <vtkRenderer.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkCamera.h>
 
int main()
{
  vtkSmartPointer<vtkStructuredPointsReader> reader =
    vtkSmartPointer<vtkStructuredPointsReader>::New();
  reader->SetFileName("mummy.128.vtk");
  reader->Update();
 
  vtkSmartPointer<vtkGPUVolumeRayCastMapper> origMapper =
    vtkSmartPointer<vtkGPUVolumeRayCastMapper>::New();
  origMapper->SetInputData(reader->GetOutput());
 
  vtkSmartPointer<vtkGPUVolumeRayCastMapper> volumeMapper =
    vtkSmartPointer<vtkGPUVolumeRayCastMapper>::New();
  volumeMapper->SetInputData(reader->GetOutput());
 
  vtkSmartPointer<vtkPlane> plane =
    vtkSmartPointer<vtkPlane>::New();
  plane->SetOrigin(120, 120, 0);
  plane->SetNormal(1, 1, 0);
  volumeMapper->AddClippingPlane(plane);
 
  /*****************************************************************/
  //设置体绘制相关属性
  vtkSmartPointer<vtkVolumeProperty> volumeProperty =
    vtkSmartPointer<vtkVolumeProperty>::New();
  volumeProperty->SetInterpolationTypeToLinear(); //设置线性插值方式
  volumeProperty->ShadeOn();//开启阴影属性
  volumeProperty->SetAmbient(0.4);//设置环境温度
  volumeProperty->SetDiffuse(0.6);//设置漫反射系数
  volumeProperty->SetSpecular(0.2);//设置镜面反射系数
  //添加灰度不透明度属性
  vtkSmartPointer<vtkPiecewiseFunction> compositeOpacity =
    vtkSmartPointer<vtkPiecewiseFunction>::New();
  compositeOpacity->AddPoint(70, 0.0);
  compositeOpacity->AddPoint(90, 0.4);
  compositeOpacity->AddPoint(180, 0.6);
  volumeProperty->SetScalarOpacity(compositeOpacity);
  //添加梯度不同明度属性
  vtkSmartPointer<vtkPiecewiseFunction> gradientOpacity =
    vtkSmartPointer<vtkPiecewiseFunction>::New();
  gradientOpacity->AddPoint(10, 0.0);
  gradientOpacity->AddPoint(90, 0.5);
  gradientOpacity->AddPoint(100, 1.0);
  volumeProperty->SetGradientOpacity(gradientOpacity);
  //添加颜色传输
  vtkSmartPointer<vtkColorTransferFunction> color =
    vtkSmartPointer<vtkColorTransferFunction>::New();
  color->AddRGBPoint(0, 0, 0, 0);
  color->AddRGBPoint(64, 1.0, 0.52, 0.3);
  color->AddRGBPoint(190.0, 1.00, 1.00, 1.00);
  color->AddRGBPoint(220.0, 0.20, 0.20, 0.20);
  volumeProperty->SetColor(color);
  /***********************************************************/
  //渲染管道
  vtkSmartPointer<vtkVolume> origVolume =
    vtkSmartPointer<vtkVolume>::New();
  origVolume->SetMapper(origMapper);
  origVolume->SetProperty(volumeProperty);
 
  vtkSmartPointer<vtkVolume> clippingVolume =
    vtkSmartPointer<vtkVolume>::New();
  clippingVolume->SetMapper(volumeMapper);
  clippingVolume->SetProperty(volumeProperty);
 
  /
  double origView[4] = { 0, 0, 0.5, 1 };
  double croppingView[4] = { 0.5, 0, 1, 1 };
  vtkSmartPointer<vtkRenderer> origRender =
    vtkSmartPointer<vtkRenderer>::New();
  origRender->AddVolume(origVolume);
  origRender->SetBackground(1, 1, 0);
  origRender->SetViewport(origView);
 
  vtkSmartPointer<vtkRenderer> clippingRender =
    vtkSmartPointer<vtkRenderer>::New();
  clippingRender->AddVolume(clippingVolume);
  clippingRender->SetBackground(0, 1, 0);
  clippingRender->SetViewport(croppingView);
  ///
  vtkSmartPointer<vtkRenderWindow> rw =
    vtkSmartPointer<vtkRenderWindow>::New();
  rw->AddRenderer(origRender);
  rw->AddRenderer(clippingRender);
  rw->SetWindowName("Cropping Volume");
  rw->SetSize(640, 320);
 
  vtkSmartPointer<vtkRenderWindowInteractor> rwi =
    vtkSmartPointer<vtkRenderWindowInteractor>::New();
  rwi->SetRenderWindow(rw);
 
  origRender->GetActiveCamera()->SetPosition(0, -1, 0);
  origRender->GetActiveCamera()->SetFocalPoint(0, 0, 0);
  origRender->GetActiveCamera()->SetViewUp(0, 0, 1);
  origRender->GetActiveCamera()->Azimuth(30);
  origRender->GetActiveCamera()->Elevation(30);
  origRender->ResetCamera();
  clippingRender->SetActiveCamera(origRender->GetActiveCamera());
 
  rw->Render();
  rwi->Start();
  return 0;
}

从上面代码中可以看出，只需定义一个VTKPlane类型的裁剪平面对象，然后通过vtkAbstractMapper3D::AddClippingplane()函数将该平面添加到Mapper对象中即可。

输出结果为：

VTK_Learning_体绘制裁剪_Cripping技术_#include

转换一个角度观察：

VTK_Learning_体绘制裁剪_Cripping技术_体绘制裁剪_02