VTK_Learning_体绘制讨论_梯度不透明度传输函数

深藏阁楼爱情的钟 2023-07-12 09:23 15阅读 0赞

# 1.梯度不透明度函数 #

> 梯度不透明度函数是将梯度模值映射为一个不透明度乘子，从而增强过渡区域的显示效果。  
> 该函数也是使用vtkPiecewiseFunction类。例如，在不同材料的临界区域，如空气到软组织，或者软组织到骨头的临界区，梯度值会比较大，而材料的内部梯度值则会相对比较小。  
> vtkVolumeProperty中通过如下函数设置和获取梯度不透明度函数：
> 
>     void SetGradientOpacity(vtkPiecewiseFunction* function);
>     vtkPiecewiseFunction* GetGradientOpacity();
> 
> ## 1.1 添加梯度不透明度函数标准代码片段及理解 ##
> 
>     vtkSmartPointer<vtkPiecewiseFunction> gradientOpacity =
>     		vtkSmartPointer<vtkPiecewiseFunction>::New();
>     	gradientOpacity->AddPoint(10, 0.0);
>     	gradientOpacity->AddPoint(90, 0.5);
>     	gradientOpacity->AddPoint(100, 1.0);
>     	volumeProperty->SetGradientOpacity(gradientOpacity);
> 
> 上述代码中将梯度小于10的点的不透明度乘子设为0，即完全透明。当梯度大小为10时，不透明度为0；梯度大小为90时，不透明度乘子为0.5；梯度大小在10~90时，不透明度乘子通过线性映射至0~0.5之间的数值；同理，当梯度大小在90~100之间时，不透明度乘子通过线性映射至0.5~1.0之间；梯度值大于100时，岂不透明度乘子为1.
> 
> ##    1.2 不同梯度不透明度传输函数实验 ##
> 
> 示例代码如下：
> 
>     #include <vtkAutoInit.h>
>     VTK_MODULE_INIT(vtkRenderingOpenGL);
>     VTK_MODULE_INIT(vtkRenderingVolumeOpenGL);
>     VTK_MODULE_INIT(vtkRenderingFreeType);
>     VTK_MODULE_INIT(vtkInteractionStyle);
>      
>     #include <vtkSmartPointer.h>
>     #include <vtkStructuredPointsReader.h>
>     #include <vtkStructuredPoints.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> volumeMapper1 =
>     		vtkSmartPointer<vtkGPUVolumeRayCastMapper>::New();
>     	volumeMapper1->SetInputData(reader->GetOutput());
>      
>     	vtkSmartPointer<vtkGPUVolumeRayCastMapper> volumeMapper2 =
>     		vtkSmartPointer<vtkGPUVolumeRayCastMapper>::New();
>     	volumeMapper2->SetInputData(reader->GetOutput());
>     	/****************************************************************/
>     	vtkSmartPointer<vtkVolumeProperty> volumeProperty1 =
>     		vtkSmartPointer<vtkVolumeProperty>::New();
>     	volumeProperty1->SetInterpolationTypeToLinear(); //设置线性插值
>     	volumeProperty1->ShadeOn();//开启阴影功能 
>     	volumeProperty1->SetAmbient(0.4);//设置环境温度系数
>     	volumeProperty1->SetDiffuse(0.6);//设置漫反射系数
>     	volumeProperty1->SetSpecular(0.2);//设置镜面反射系数
>      
>     	vtkSmartPointer<vtkVolumeProperty> volumeProperty2 =
>     		vtkSmartPointer<vtkVolumeProperty>::New();
>     	volumeProperty2->SetInterpolationTypeToLinear(); //设置线性插值
>     	volumeProperty2->ShadeOn();//开启阴影功能 
>     	volumeProperty2->SetAmbient(0.4);//设置环境光强系数
>     	volumeProperty2->SetDiffuse(0.6);//设置漫反射系数
>     	volumeProperty2->SetSpecular(0.2);//设置镜面反射系数
>      
>     	vtkSmartPointer<vtkPiecewiseFunction> compositeOpacity =
>     		vtkSmartPointer<vtkPiecewiseFunction>::New();
>     	compositeOpacity->AddPoint(50, 0.0);
>     	compositeOpacity->AddPoint(120, 0.5);
>     	compositeOpacity->AddPoint(200, 1.0);
>     	volumeProperty1->SetScalarOpacity(compositeOpacity);
>     	volumeProperty2->SetScalarOpacity(compositeOpacity);
>     	//
>     	//梯度不透明度函数1
>     	vtkSmartPointer<vtkPiecewiseFunction> gradientOpacity1 =
>     		vtkSmartPointer<vtkPiecewiseFunction>::New();
>     	gradientOpacity1->AddPoint(1, 0.0);
>     	gradientOpacity1->AddPoint(70, 0.5);
>     	gradientOpacity1->AddPoint(130, 1.0);
>     	volumeProperty1->SetGradientOpacity(gradientOpacity1);
>     	
>     	//梯度不透明度函数2
>     	vtkSmartPointer<vtkPiecewiseFunction> gradientOpacity2 =
>     		vtkSmartPointer<vtkPiecewiseFunction>::New();
>     	gradientOpacity2->AddPoint(120, 0.0);
>     	gradientOpacity2->AddPoint(150, 0.2);
>     	gradientOpacity2->AddPoint(180, 0.4);
>     	volumeProperty2->SetGradientOpacity(gradientOpacity2);
>     	
>     	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);
>     	volumeProperty1->SetColor(color);
>     	volumeProperty2->SetColor(color);
>     	/****************************************************************/
>     	vtkSmartPointer<vtkVolume> volume1 =
>     		vtkSmartPointer<vtkVolume>::New();
>     	volume1->SetMapper(volumeMapper1);
>     	volume1->SetProperty(volumeProperty1);
>      
>     	vtkSmartPointer<vtkVolume> volume2 =
>     		vtkSmartPointer<vtkVolume>::New();
>     	volume2->SetMapper(volumeMapper2);
>     	volume2->SetProperty(volumeProperty2);
>     	//
>     	double View1[4] = { 0, 0, 0.5, 1 };
>     	double View2[4] = { 0.5, 0, 1, 1 };
>     	vtkSmartPointer<vtkRenderer> render1 =
>     		vtkSmartPointer<vtkRenderer>::New();
>     	render1->AddVolume(volume1);
>     	render1->SetViewport(View1);
>     	render1->SetBackground(1, 1, 0);
>      
>     	vtkSmartPointer<vtkRenderer> render2 =
>     		vtkSmartPointer<vtkRenderer>::New();
>     	render2->AddVolume(volume2);
>     	render2->SetViewport(View2);
>     	render2->SetBackground(0, 1, 0);
>      
>     	vtkSmartPointer<vtkRenderWindow> rw =
>     		vtkSmartPointer<vtkRenderWindow>::New();
>     	rw->AddRenderer(render1);
>     	rw->AddRenderer(render2);
>     	rw->SetSize(640, 320);
>     	rw->SetWindowName("Differ Gradient Opacity Function");
>      
>     	vtkSmartPointer<vtkRenderWindowInteractor> rwi =
>     		vtkSmartPointer<vtkRenderWindowInteractor>::New();
>     	rwi->SetRenderWindow(rw);
>      
>     	render1->GetActiveCamera()->SetPosition(0, -1, 0);
>     	render1->GetActiveCamera()->SetFocalPoint(0, 0, 0);
>     	render1->GetActiveCamera()->SetViewUp(0, 0, 1);
>     	render1->GetActiveCamera()->Azimuth(30);
>     	render1->GetActiveCamera()->Elevation(30);
>     	render1->ResetCamera();
>     	render2->SetActiveCamera(render1->GetActiveCamera());
>      
>     	rw->Render();
>     	rwi->Start();
>     	return 0;
>     }
> 
> 输出结果为：
> 
> ![20170207201143709][]

[20170207201143709]: https://img-blog.csdn.net/20170207201143709