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前言
本文分享VTK中体绘制中的vtkLODProp3D对象，希望对各位小伙伴有所帮助！
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1. vtkLODProp3D
vtkLODProp3D与vtkVolume用法类似，两者均继承自vtkProp3D。但vtkLODProp3D支持多个Mapper、Property和Texture对象，并由它选择Mapper对象实现绘制。例如，当绘制一个数据量非常大的不规则网格数据时，可以添加一个vtkPolyDataMapper来渲染一个表面模型，作为最低级别分辨率的渲染；然后将数据采样为vtkImageData数据，并添加一个vtkVolumeTextureMapper3D进行体绘制，作为一个中等级别渲染；最后通过ZSweep技术（vtkUnstructureGridVolumeZSWeepMapper）渲染原始数据，作为最高级别的渲染。vtkLODProp3D在渲染过程中，会为每一个Mapper估计一个渲染时间，并选择一个最优的实现渲染。
其重要参数有：
1.1 获取边界包围盒
/*** Standard vtkProp method to get 3D bounds of a 3D prop*/double* GetBounds() VTK_SIZEHINT(6) override;void GetBounds(double bounds[6]) { this->vtkProp3D::GetBounds(bounds); }1.2 添加不同级别的Mapper
//@{/*** 添加不同级别的的映射器、属性、背面属性、纹理和渲染时间。* 属性和纹理字段可以设置为NULL(其他方法包含在不允许NULL变量的脚本访问中)。* time字段可以设置为0.0，表示没有提供渲染时间的初始猜测。* 返回的整数值是一个ID，稍后可以使用该ID删除该LOD，或者将其设置为所选LOD。* Add a level of detail with a given mapper, property, backface property,* texture, and guess of rendering time. The property and texture fields* can be set to NULL (the other methods are included for script access* where null variables are not allowed). The time field can be set to 0.0* indicating that no initial guess for rendering time is being supplied.* The returned integer value is an ID that can be used later to delete* this LOD, or set it as the selected LOD.*/int AddLOD(vtkMapper* m, vtkProperty* p, vtkProperty* back, vtkTexture* t, double time);int AddLOD(vtkMapper* m, vtkProperty* p, vtkTexture* t, double time);int AddLOD(vtkMapper* m, vtkProperty* p, vtkProperty* back, double time);int AddLOD(vtkMapper* m, vtkProperty* p, double time);int AddLOD(vtkMapper* m, vtkTexture* t, double time);int AddLOD(vtkMapper* m, double time);int AddLOD(vtkAbstractVolumeMapper* m, vtkVolumeProperty* p, double time);int AddLOD(vtkAbstractVolumeMapper* m, double time);int AddLOD(vtkImageMapper3D* m, vtkImageProperty* p, double time);int AddLOD(vtkImageMapper3D* m, double time);//@}1.3 获取LOD数量及当前Index
//@{/*** Get the current number of LODs.*/vtkGetMacro(NumberOfLODs, int);//@}//@{/*** Get the current index, used to determine the ID of the next LOD that is* added. Useful for guessing what IDs have been used (with NumberOfLODs,* without depending on the constructor initialization to 1000.*/vtkGetMacro(CurrentIndex, int);//@}1.4 删除指定Index的LOD
/*** Delete a level of detail given an ID. This is the ID returned by the* AddLOD method*/void RemoveLOD(int id);1.5 获取指定Index的属性
//@{/*** Methods to set / get the property of an LOD. Since the LOD could be* a volume or an actor, you have to pass in the pointer to the property* to get it. The returned property will be NULL if the id is not valid,* or the property is of the wrong type for the corresponding Prop3D.*/void SetLODProperty(int id, vtkProperty* p);void GetLODProperty(int id, vtkProperty** p);void SetLODProperty(int id, vtkVolumeProperty* p);void GetLODProperty(int id, vtkVolumeProperty** p);void SetLODProperty(int id, vtkImageProperty* p);void GetLODProperty(int id, vtkImageProperty** p);//@}1.6 设置/获取Mapper
//@{/*** Methods to set / get the mapper of an LOD. Since the LOD could be* a volume or an actor, you have to pass in the pointer to the mapper* to get it. The returned mapper will be NULL if the id is not valid,* or the mapper is of the wrong type for the corresponding Prop3D.*/void SetLODMapper(int id, vtkMapper* m);void GetLODMapper(int id, vtkMapper** m);void SetLODMapper(int id, vtkAbstractVolumeMapper* m);void GetLODMapper(int id, vtkAbstractVolumeMapper** m);void SetLODMapper(int id, vtkImageMapper3D* m);void GetLODMapper(int id, vtkImageMapper3D** m);//@}/*** Get the LODMapper as an vtkAbstractMapper3D. It is the user's* respondibility to safe down cast this to a vtkMapper or vtkVolumeMapper* as appropriate.*/vtkAbstractMapper3D* GetLODMapper(int id);1.7 获取Backface属性
//@{/*** Methods to set / get the backface property of an LOD. This method is only* valid for LOD ids that are Actors (not Volumes)*/void SetLODBackfaceProperty(int id, vtkProperty* t);void GetLODBackfaceProperty(int id, vtkProperty** t);//@}1.8 获取纹理
//@{/*** Methods to set / get the texture of an LOD. This method is only* valid for LOD ids that are Actors (not Volumes)*/void SetLODTexture(int id, vtkTexture* t);void GetLODTexture(int id, vtkTexture** t);//@}1.9 EnableLOD
//@{/*** Enable / disable a particular LOD. If it is disabled, it will not* be used during automatic selection, but can be selected as the* LOD if automatic LOD selection is off.*/void EnableLOD(int id);void DisableLOD(int id);int IsLODEnabled(int id);//@}1.10 设置LOD的级别
//@{/*** 设置特定LOD的级别。当选择一个LOD进行渲染时，因为它在分配的时间内具有最大的渲染时间，* 然后检查所有LOD，看看是否有任何LOD可以渲染得更快，但具有较低(更高分辨率/更好)的级别。* 该数量为双精度，以确保可以插入2和3之间* Set the level of a particular LOD. When a LOD is selected for* rendering because it has the largest render time that fits within* the allocated time, all LOD are then checked to see if any one can* render faster but has a lower (more resolution/better) level.* This quantity is a double to ensure that a level can be inserted* between 2 and 3.*/void SetLODLevel(int id, double level);double GetLODLevel(int id);double GetLODIndexLevel(int index);//@}1.11 获取指定Index的LOD渲染时间
//@{/*** Access method that can be used to find out the estimated render time* (the thing used to select an LOD) for a given LOD ID or index.* Value is returned in seconds.*/double GetLODEstimatedRenderTime(int id);double GetLODIndexEstimatedRenderTime(int index);//@}1.12 开启/关闭自动选择渲染的LOD
//@{/*** 开启/关闭自动选择LOD。默认为开启。* 如果它是关闭的，那么无论呈现时间或所需的更新速率如何，都会呈现SelectedLODID。* Turn on / off automatic selection of LOD.* This is on by default. If it is off, then the SelectedLODID is* rendered regardless of rendering time or desired update rate.*/vtkSetClampMacro(AutomaticLODSelection, vtkTypeBool, 0, 1);vtkGetMacro(AutomaticLODSelection, vtkTypeBool);vtkBooleanMacro(AutomaticLODSelection, vtkTypeBool);//@}1.13 设置选择的ID
//@{/*** Set the id of the LOD that is to be drawn when automatic LOD selection* is turned off.*/vtkSetMacro(SelectedLODID, int);vtkGetMacro(SelectedLODID, int);//@}1.14 返回对象
//@{/*** For some exporters and other other operations we must be* able to collect all the actors or volumes. These methods* are used in that process.*/void GetActors(vtkPropCollection*) override;void GetVolumes(vtkPropCollection*) override;//@}1.15 开始/关闭自动拾取LOD
//@{/*** 开启/关闭自动Pick的LOD。默认是开启的。* 如果它是关闭的，那么无论呈现时间或所需的更新速率如何，都会呈现SelectedLODID。* Turn on / off automatic selection of picking LOD.* This is on by default. If it is off, then the SelectedLODID is* rendered regardless of rendering time or desired update rate.*/vtkSetClampMacro(AutomaticPickLODSelection, vtkTypeBool, 0, 1);vtkGetMacro(AutomaticPickLODSelection, vtkTypeBool);vtkBooleanMacro(AutomaticPickLODSelection, vtkTypeBool);//@}1.16 设置选择Pick的LOD Index
//@{/*** Set the id of the LOD that is to be used for picking when automatic* LOD pick selection is turned off.*/void SetSelectedPickLODID(int id);vtkGetMacro(SelectedPickLODID, int);//@}注意：vtkVolumeTextureMapper3D在9.0.3及以后的版本中已不存在，由vtkOpenGLGPUVolumeRayCastMapper代替。
2. 示例
#include <vtkSmartPointer.h>
#include <vtkPolyDataMapper.h>
#include <vtkLODProp3D.h>
#include <vtkRenderWindow.h>
#include <vtkRenderer.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkPolyData.h>
#include <vtkSphereSource.h>
#include <vtkCallbackCommand.h>
#include <vtkProperty.h>void RefreshCallback( vtkObject* vtkNotUsed(caller),long unsigned int vtkNotUsed(eventId),void* clientData,void* vtkNotUsed(callData) )
{vtkSmartPointer<vtkLODProp3D> lodProp = static_cast<vtkLODProp3D*>(clientData);std::cout << "Last rendered LOD: " << lodProp->GetLastRenderedLODID() << std::endl;
}int main (int, char *[])
{// High res spherevtkSmartPointer<vtkSphereSource> highResSphereSource = vtkSmartPointer<vtkSphereSource>::New();int res = 100;highResSphereSource->SetThetaResolution(res);highResSphereSource->SetPhiResolution(res);highResSphereSource->Update();vtkSmartPointer<vtkPolyDataMapper> highResMapper = vtkSmartPointer<vtkPolyDataMapper>::New();highResMapper->SetInputConnection(highResSphereSource->GetOutputPort());// Low res spherevtkSmartPointer<vtkSphereSource> lowResSphereSource = vtkSmartPointer<vtkSphereSource>::New();vtkSmartPointer<vtkPolyDataMapper> lowResMapper = vtkSmartPointer<vtkPolyDataMapper>::New();lowResMapper->SetInputConnection(lowResSphereSource->GetOutputPort());vtkSmartPointer<vtkProperty> propertyLowRes = vtkSmartPointer<vtkProperty>::New();propertyLowRes->SetDiffuseColor(0.89, 0.81, 0.34);propertyLowRes->SetInterpolationToFlat();vtkSmartPointer<vtkProperty> propertyHighRes = vtkSmartPointer<vtkProperty>::New();propertyHighRes->SetDiffuseColor(1.0, 0.3882, 0.2784);propertyHighRes->SetInterpolationToFlat();vtkSmartPointer<vtkLODProp3D> prop = vtkSmartPointer<vtkLODProp3D>::New();prop->AddLOD(lowResMapper, propertyLowRes, 0.0);prop->AddLOD(highResMapper, propertyHighRes, 0.0);std::cout << "There are " << prop->GetNumberOfLODs() << " LODs" << std::endl;// A renderer and render windowvtkSmartPointer<vtkRenderer> renderer = vtkSmartPointer<vtkRenderer>::New();vtkSmartPointer<vtkRenderWindow> renderWindow = vtkSmartPointer<vtkRenderWindow>::New();renderWindow->AddRenderer(renderer);//prop->SetAllocatedRenderTime(1e-6,renderer);prop->SetAllocatedRenderTime(1e-10,renderer);// An interactorvtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor = vtkSmartPointer<vtkRenderWindowInteractor>::New();renderWindowInteractor->SetRenderWindow(renderWindow);// Add the actors to the scenerenderer->AddActor(prop);vtkSmartPointer<vtkCallbackCommand> refreshCallback =vtkSmartPointer<vtkCallbackCommand>::New();refreshCallback->SetCallback (RefreshCallback);refreshCallback->SetClientData(prop);renderWindow->AddObserver(vtkCommand::ModifiedEvent,refreshCallback);renderWindow->Render();// Begin mouse interactionrenderWindowInteractor->Start();return EXIT_SUCCESS;
}
结论：
感谢各位小伙伴的点赞+关注，小易会继续努力分享，一起进步！
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