VTK_Learning_體繪製裁剪_Cripping技術

1.基於Clipping的體繪製裁剪技術

Clipping技術支持VTKImageData和VTKUntructuredGrid數據類型。該功能由vtkAbstractMapper3D類提供，對於那些使用基於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（一般爲6）時，VTK會反饋一個錯誤；而對於基於軟件的裁剪技術的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，可以沿着任意方向將圖像切開，便於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);
 
	/*****************************************************************/
	//設置體繪製相關屬性
	vtkSmartPointer<vtkVolumeProperty> volumeProperty =
		vtkSmartPointer<vtkVolumeProperty>::New();
	volumeProperty->SetInterpolationTypeToLinear(); //設置線性插值方式
	volumeProperty->ShadeOn();//開啓陰影屬性
	volumeProperty->SetAmbient(0.4);//設置環境溫度
	volumeProperty->SetDiffuse(0.6);//設置漫反射係數
	volumeProperty->SetSpecular(0.2);//設置鏡面反射係數
	//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，然後通過vtkAbstractMapper3D::AddClippingplane()函數將該平面添加到Mapper對象中即可。

輸出結果爲：

轉換一個角度觀察：