1.基于Clipping的體繪制裁剪技術

Clipping技術支持VTKImageData和VTKUntructuredGrid數據類型。該功能由vtkAbstractMapper3D類提供，對于那些使用基于OpenGL的硬件裁剪技術的Mapper類，如vtkPolyDataMapper、vtkVolumeTextureMapper2D、VTKProjectedTetrahedraMapper等，當設置的裁剪面個數超過OpenGL支持的個數（一般為6）時，VTK會反饋一個錯誤；而對于基于軟件的裁剪技術的Mapper類，如vtkVolumeRayCastMapper則沒有這些限制，可以支持任意多個裁剪面。使用Clipping技術，可以沿著任意方向將圖像切開，便于觀察體數據內部細節。 下面是例程中的一個實驗： #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);/*****************************************************************///設置體繪制相關屬性vtkSmartPointer<vtkVolumeProperty> volumeProperty =vtkSmartPointer<vtkVolumeProperty>::New();volumeProperty->SetInterpolationTypeToLinear(); //設置線性插值方式volumeProperty->ShadeOn();//開啟陰影屬性volumeProperty->SetAmbient(0.4);//設置環境溫度volumeProperty->SetDiffuse(0.6);//設置漫反射系數volumeProperty->SetSpecular(0.2);//設置鏡面反射系數//添加灰度不透明度屬性vtkSmartPointer<vtkPiecewiseFunction> compositeOpacity =vtkSmartPointer<vtkPiecewiseFunction>::New();compositeOpacity->AddPoint(70, 0.0);compositeOpacity->AddPoint(90, 0.4);compositeOpacity->AddPoint(180, 0.6);volumeProperty->SetScalarOpacity(compositeOpacity);//添加梯度不同明度屬性vtkSmartPointer<vtkPiecewiseFunction> gradientOpacity =vtkSmartPointer<vtkPiecewiseFunction>::New();gradientOpacity->AddPoint(10, 0.0);gradientOpacity->AddPoint(90, 0.5);gradientOpacity->AddPoint(100, 1.0);volumeProperty->SetGradientOpacity(gradientOpacity);//添加顏色傳輸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; }
從上面代碼中可以看出，只需定義一個VTKPlane類型的裁剪平面對象，然后通過vtkAbstractMapper3D::AddClippingplane()函數將該平面添加到Mapper對象中即可。 輸出結果為：
轉換一個角度觀察：

2.參看資料

1.《C++ primer》
2.《The VTK User’s Guide – 11thEdition》
3. ?張曉東, 羅火靈. VTK圖形圖像開發進階[M]. 機械工業出版社, 2015.

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