VTK：体绘制裁剪——Cropping技术

对于一些体积较大、结果较复杂的体画渲染效果，一旦显示其内部细节，就需要使用切割技术来渲染一些数据。vtkVolumeMapper分别提供两种裁剪技术Cropping和Clipping。 Cropping技术只支持VTKImageData切割数据。该方法在每个坐标轴上定义两个切割面，共6个切割面。将三维空间分为27个视觉区域。这些切割面只与数据的起源和像素大小有关，而不依赖于数据的任何坐标操作，因此可以使用27位数来定义每个表示一个区域。小于这些区域（xmin,ymin）每个区域的位然后根据先X方向和最后Z轴方向的顺序定义每个区域的位数。例如，当只显示中间区域时，对应的27位数为0x0002000.

vtkVolumeMapper中定义了Cropping使用接口函数Cropping切割代码下： volumeMapper->SetCropping(1)；//打开Cropping功能 volumeMapper->SetCroppingRegionPlanes(50, 150, 50, 200, 50, 150)；//在三个坐标轴上设置6个切割面的位置 volumeMapper->SetCroppingRegionFlags(0x0002000) 此外，该类还提供了设置显示区域的其他成员函数，以避免自行计算显示区域标记： SetCroppingRegionFlagsToSubVolume(); SetCroppingRegionFlagsToFence(); SetCroppingRegionFlagsToInvertedFence(); SetCroppingRegionFlagsToCross(); SetCroppingRegionFlagsToInvertedCross();

#include <vtkAutoInit.h> VTK_MODULE_INIT(vtkRenderingOpenGL2); VTK_MODULE_INIT(vtkRenderingVolumeOpenGL2); VTK_MODULE_INIT(vtkRenderingFreeType); VTK_MODULE_INIT(vtkInteractionStyle);   #include <vtkSmartPointer.h> #include <vtkStructuredPoints.h>//vtkStructuredPointsReader* -> vtkGPUVolumeRayCastMapper* #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("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());
	volumeMapper->SetCropping(1);//开启Cropping功能
	volumeMapper->SetCroppingRegionPlanes(50, 150, 50, 200, 50, 150);
	volumeMapper->SetCroppingRegionFlags(0x0002000);
	/*****************************************************************/
	//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> croppingVolume =
		vtkSmartPointer<vtkVolume>::New();
	croppingVolume->SetMapper(volumeMapper);
	croppingVolume->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> croppingRender =
		vtkSmartPointer<vtkRenderer>::New();
	croppingRender->AddVolume(croppingVolume);
	croppingRender->SetBackground(0, 1, 0);
	croppingRender->SetViewport(croppingView);
	///
	vtkSmartPointer<vtkRenderWindow> rw =
		vtkSmartPointer<vtkRenderWindow>::New();
	rw->AddRenderer(origRender);
	rw->AddRenderer(croppingRender);
	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();
	croppingRender->SetActiveCamera(origRender->GetActiveCamera());

	rw->Render();
	rwi->Start();
	return 0;
}