VTK：体绘制裁剪——Clipping技术

Clipping技术支持VTKImageData和VTKUntructuredGrid数据类型。该功能由vtkAbstractMapper3D基于这些使用的提供OpenGL硬件切割技术Mapper类，如vtkPolyDataMapper、vtkVolumeTextureMapper2D、VTKProjectedTetrahedraMapper等，当设置的切割面数量超过时OpenGL当支持数量(一般为6)时，VTK会反馈一个错误；基于软件的切割技术Mapper类，如vtkVolumeRayCastMapper没有这些限制，可以支持任何多个切割面。使用Clipping技术，图像可以沿任何方向切割，以便观察体数据的内部细节。

#include  VTK_MODULE_INIT(vtkRenderingOpenGL2); VTK_MODULE_INIT(vtkRenderingVolumeOpenGL2); VTK_MODULE_INIT(vtkRenderingFreeType); VTK_MODULE_INIT(vtkInteractionStyle);  #include  #include  #include  #include  #include  #include  #include  #include  #include  #include  #include  #include  #include   int main() { 
          vtkSmartPointer<vtkStructuredPointsReader> reader =   vtkSmartPointer<vtkStructuredPointsReader>::New();
	reader->SetFileName("data/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，只需要定义一个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。