Visualization {#user_guides__visualization} ======================== @tableofcontents @section occt_visu_1 Introduction This manual provides basic documentation on setting up and using Visualization. For advanced information on Visualization and its applications, see our offerings on our web site (Training and E-Learning) at http://www.opencascade.org/support/training/ Visualization in Open CASCADE Technology is based on the separation of: * on the one hand - the data which stores the geometry and topology of the entities you want to display and select, and * on the other hand - its **presentation** (what you see when an object is displayed in a scene) and **selection** (possibility to choose the whole object or its sub-parts interactively to apply application-defined operations to the selected entities). @subsection occt_visu_1_1 Open CASCADE Technology Visualization and the Organization of this guide Presentations are managed through the Presentation component, and selection through the Selection component. To make management of these functionalities in 3D more intuitive and consequently, more transparent, *Application Interactive Services* have been created. *AIS* uses the notion of the *interactive object*, a displayable and selectable entity, which represents an element from the application data. As a result, in 3D, you, the user, have no need to be familiar with any functions underlying AIS unless you want to create your own interactive objects or selection filters. If, however, you require types of interactive objects and filters other than those provided, you will need to know the mechanics of presentable and selectable objects, specifically how to implement their virtual functions. To do this requires familiarity with such fundamental concepts as the sensitive primitive and the presentable object. The packages used to display 3D objects are the following: * AIS * StdPrs * Prs3d * PrsMgr * V3d * Graphic3d If you are concerned with 2D visualization, you must familiarize yourself with the fundamental concepts of presentation as outlined in the section on this subject in chapter Fundamental Concepts. In brief, the packages used to display 3D objects are applicable for visualization of 2D objects too. The figure below presents a schematic overview of the relations between the key concepts and packages in visualization. Naturally, "Geometry & Topology" is just an example of application data that can be handled by *AIS*, and application-specific interactive objects can deal with any kind of data. @image html visualization_image003.png "Key concepts and packages in visualization" @image latex visualization_image003.png "Key concepts and packages in visualization" To answer different needs of CASCADE users, this user’s guide offers the following three paths in reading it.   * If the 3D services proposed in AIS meet your requirements, you need only read chapter 3 AIS: Application Interactive Services. * If you need more detail, for example, a selection filter on another type of entity - you should read chapter 2 Fundamental Concepts, chapter 3 AIS: Application Interactive Services, and possibly chapters 4 and 5 3D Presentations and 3D Resources. You may want to begin with the chapter presenting AIS. @section occt_visu_2  Fundamental Concepts @subsection occt_visu_2_1 Presentation In Open CASCADE Technology, presentation services are separated from the data, which they represent, which is generated by applicative algorithms. This division allows you to modify a geometric or topological algorithm and its resulting objects without modifying the visualization services. @subsubsection occt_visu_2_1_1 Structure of the Presentation Displaying an object on the screen involves three kinds of entities: * a presentable object, the *AIS_InteractiveObject* * a viewer * an interactive context, the *AIS_InteractiveContext*.

The presentable object

The purpose of a presentable object is to provide the graphical representation of an object in the form of *Graphic3d* structure. On the first display request, it creates this structure by calling the appropriate algorithm and retaining this framework for further display. Standard presentation algorithms are provided in the *StdPrs* and *Prs3d* packages. You can, however, write specific presentation algorithms of your own, provided that they create presentations made of structures from the *Graphic3d* packages. You can also create several presentations of a single presentable object: one for each visualization mode supported by your application. Each object to be presented individually must be presentable or associated with a presentable object.

The viewer

The viewer allows interactively manipulating views of the object. When you zoom, translate or rotate a view, the viewer operates on the graphic structure created by the presentable object and not on the data model of the application. Creating Graphic3d structures in your presentation algorithms allows you to use the 3D viewers provided in Open CASCADE Technology for 3D visualisation.

The Interactive Context

The interactive context controls the entire presentation process from a common high-level API. When the application requests the display of an object, the interactive context requests the graphic structure from the presentable object and sends it to the viewer for displaying. @subsubsection occt_visu_2_1_2 Presentation packages Presentation involves at least the *AIS, PrsMgr, StdPrs* and *V3d* packages. Additional packages such as *Prs3d* and *Graphic3d* may be used if you need to implement your own presentation algorithms. * *AIS* package provides all classes to implement interactive objects (presentable and selectable entities). * *PrsMgr* package provides all the classes needed to implement the presentation process: the *Presentation* and *PresentableObject* abstract classes and *PresentationManager3d* concrete class. * *StdPrs* package provides ready-to-use standard presentation algorithms of points, curves and shapes of the geometry and topology toolkits. * *V3d* package provides the services supported by the 3D viewer. * *Prs3d* package provides some generic presentation algorithms such as wireframe, shading and hidden line removal associated with a Drawer class which controls the attributes of the presentation to be created in terms of color, line type, thickness, and so on. * *Graphic3d* package provides resources to create 3D graphic structures. @subsubsection occt_visu_2_1_3 A Basic Example: How to display a 3D object ~~~~~ Void Standard_Real dx  = ...; //Parameters Void Standard_Real dy  = ...; //to build a wedge Void Standard_Real dz  = ...; Void Standard_Real ltx = ...; Handle(V3d_Viewer)aViewer = ...; Handle(AIS_InteractiveContext)aContext; aContext = new AIS_InteractiveContext(aViewer); BRepPrimAPI_MakeWedge w(dx, dy, dz, ltx); TopoDS_Solid & = w.Solid(); Handle(AIS_Shape) anAis = new AIS_Shape(S); //creation of the presentable object aContext - Display(anAis); //Display the presentable object in the 3d viewer. ~~~~~ The shape is created using the *BRepPrimAPI_MakeWedge* command. An *AIS_Shape* is then created from the shape. When calling the *Display* command, the interactive context calls the Compute method of the presentable object to calculate the presentation data and transfer it to the viewer. See figure below. @image html visualization_image004.png "Processes involved in displaying a presentable shape" @image latex visualization_image004.png "Processes involved in displaying a presentable shape" @subsection occt_visu_2_2 Selection Objects that may be selected graphically, are displayed as sets of sensitive primitives, which provide sensitive zones in 2D graphic space. These zones are sorted according to their position on the screen when starting the selection process. @image html visualization_image006.png "A model" @image latex visualization_image006.png "A model" The position of the mouse is also associated with a sensitive zone. When moving within the window where objects are displayed, the areas touched by the zone of the mouse are analyzed. The owners of these areas are then highlighted or signaled by other means such as the name of the object highlighted in a list. That way, you are informed of the identity of the detected element. @image html visualization_image007.png "Modeling faces with sensitive primitives" @image latex visualization_image007.png "Modeling faces with sensitive primitives" @image html visualization_image008.png "In a dynamic selection, each sensitive polygon is represented by its bounding rectangle"   @image latex visualization_image008.png "In a dynamic selection, each sensitive polygon is represented by its bounding rectangle" @image html visualization_image009.png "Reference to the sensitive primitive, then to the owner" @image latex visualization_image009.png "Reference to the sensitive primitive, then to the owner" @subsubsection occt_visu_2_2_1 The Sensitive Primitive The sensitive primitive along with the entity owner allows defining what can be made selectable, and providing the link between the applicative object and the sensitive zones defined by the 2D bounding boxes. To be dynamically selectable, an object has to be represented either as a sensitive primitive or a set of them, e.g. 2D boxes that will be included in a sorting algorithm. The use of 2D boxes allows a pre-selection of the detected entities. After pre-selection, the algorithm checks which sensitive primitives are actually detected. When detected, the primitives provide their owners’ identity. @image html visualization_image010.png "Example of sensitive primitives" @image latex visualization_image010.png "Example of sensitive primitives" In the example, the sensitive line segment proposes a bounding box to the selector. During selection, positions 1 and 2 of the mouse detect the box but after sorting, only position 2 retains the line segment as selected by the algorithm. When the Box associated with the position of the mouse intersects the Box of a sensitive primitive, the owner of the sensitive primitive is called and its presentation is highlighted. The notion of sensitive primitive is important for the developer when defining his own classes of sensitive primitives for the chosen selection modes. The classes must contain *Areas* and *Matches* functions. The former provides the list of 2D sensitive boxes representing the sensitive primitive at pre-selection and the latter determines if the detection of the primitive by the 2D boxes is valid. @subsubsection occt_visu_2_2_2 Dynamic Selection Dynamic selection causes objects in a view to be automatically highlighted as the mouse cursor moves over them. This allows the user to be certain that the picked object is the correct one. Dynamic Selection is based on the following two concepts: * a Selectable Object (*AIS_InteractiveObject*) * an Interactive Context

Selectable Object

A selectable object presents a given number of selection modes which can be redefined, and which will be activated or deactivated in the selection manager’s selectors. Note that the selection mode of a selectable object, can refer to the selection mode of the object itself or to the selection mode of its part. For each selection mode, a *SelectMgr_Selection* object class is included in the selectable object. (Each selection mode establishes a priority of selection for each class of selectable object defined.) The notion of **Selection** is comparable to the notion of **Display**. Just as a display contains a set of graphic primitives that allow display of the entity in a specific display mode, a **Selection** contains a set of sensitive primitives, which allow detection of the entities they are associated with.

Interactive Context

The interactive context is used to manage both selectable objects and selection processes. Selection modes may be activated or de-activated for given selectable objects. Information is then provided about the status of activated/de-activated selection modes for a given object in a given selector. See also AIS: Application Interactive Services. Let us consider, for example, a 3D selectable shape object, which corresponds to a topological shape. For this class, seven selection modes can be defined: * mode 0 - selection of the shape itself * mode 1 - selection of vertices * mode 2 - selection of edges * mode 3 - selection of wires * mode 4 - selection of faces * mode 5 - selection of shells * mode 6 - selection of solids * mode 7 - selection of compsolids * mode 8 - selection of compounds Selection 2 includes the sensitive primitives that model all the edges of the shape. Each of these primitives contains a reference to the edge it represents. The selections may be calculated before any activation and are graph independent as long as they are not activated in a given selector. Activation of selection mode 3 in a selector associated with a view V leads to the projection of the 3D sensitive primitives contained in the selection; then the 2D areas which represent the 2D bounding boxes of these primitives are provided to the sorting process of the selector containing all the detectable areas. To deactivate selection mode 3 remove all those 2D areas. @subsubsection occt_visu_2_2_3 Selection Packages The following selection packages exist : *SelectBasics*, *SelectMgr*, *Select3D*, *StdSelect*. *SelectBasics* package contains the basic classes of the selection: * the main definition of a sensitive primitive: *SensitiveEntity* * the definition of a sensitive primitive owner: *EntityOwner* * the algorithm used for sorting sensitive boxes: *SortAlgo* *EntityOwner* is used to establish a link from *SensitiveEntity* to application-level objects. For example, *SelectMgr_EntityOwner* (see below) class holds a pointer to corresponding *SelectableObject*. *SelectMgr* package is used to manage the whole dynamic selection process. It contains the *SelectableObject*, Entity Owner containing a link to its SelectableObject,* *Selection*, *SelectionManager*, and *ViewSelector* classes. There are also implementations of *ViewerSelector* interface for 3D selection in *StdSelect* package: *ViewerSelector3d*. *Select3D* package contains all 3D standard sensitive primitives such as point, curve and face. All these classes inherit from 3D *SensitiveEntry* from *SelectBasics* with an additional method, which allows recovery of the bounding boxes in the 2D graphic selection space, if required. This package also includes the 3D-2D projector. *StdSelect* package provides standard uses of the classes described above and main tools used to prevent the developer from redefining the selection objects. In particular, *StdSelect* includes standard means for selection of topological objects (shapes). @subsubsection occt_visu_2_2_4 How to use dynamic selection Several operations must be performed prior to using dynamic selection: 1. Implement specific sensitive primitives if those defined in Select3D are not sufficient. These primitives must inherit from *SensitiveEntity* from *SelectBasics* or from a suitable Select3D sensitive entity class when a projection from 3D to 2D is necessary. 2. Define all the owner types, which will be used, and the classes of selectable objects, i.e. the number of possible selection modes for these objects and the calculation of the decomposition of the object into sensitive primitives of all the primitives describing this mode. It is possible to define only one default selection mode for a selectable object if this object is to be selectable in a unique way. 3. Install the process, which provides the user with the identity of the owner of the detected entities in the selection loop. When all these steps have been carried out, follow the procedure below: 1. Create an interactive context. 2. Create the selectable objects and calculate their various possible selections. 3. Load these selectable objects in the interactive context. The objects may be common to all the selectors, i.e. they will be seen by all the selectors in the selection manager, or local to one selector or more. 4. Activate or deactivate the objects’ selection modes in the selector(s). When activating a selection mode in a selector for a given object, the manager sends the order to make the sensitive primitives in this selector selectable. If the primitives are to projected from 3D to 2D, the selector calls the specific method used to carry out this projection. At this stage, the selection of selectable entities in the selectors is available. The selection loop informs constantly the selectors with the position of the mouse and questions them about the detected entities. Let us suppose that you create an application that displays houses in a viewer of the V3d package and you want to select houses or parts of these houses (windows, doors, etc.) in the graphic window. You define a selectable object called *House* and propose four possible selection modes for this object: 1. selection of the house itself; 2. selection of the rooms 3. selection of the walls 4. selection of the doors. You have to write the method, which calculates the four selections above, i.e. the sensitive primitives which are activated when the mode is. You must define the class *Owner* specific to your application. This class will contain the reference to the house element it represents: wall, door or room. It inherits from *EntityOwner* from *SelectMgr*. For example, let us consider a house with the following representation: @image html visualization_image011.png "Selection of rooms in a house" @image latex visualization_image011.png "Selection of rooms in a house" To build the selection, which corresponds to the mode "selection of the rooms" (selection 2 in the list of selection modes), use the following procedure: ~~~~~ Void House::ComputeSelection (Const Handle(SelectMgr_Selection)& Sel,  const Standard_Integer mode {  switch(mode){  case 0: //Selection of the rooms {  for(Standard_Integer i = 1; i = myNbRooms; i++)  { //for every room, create an instance of the owner, the given room and its name. Handle(RoomOwner) aRoomOwner = new RoomOwner (Room(i), NameRoom(i)); //Room() returns a room and NameRoom() returns its name. Handle(Select3d_SensitiveBox) aSensitiveBox; aSensitiveBox = new Select3d_SensitiveBox (aRoomOwner, Xmin, Ymin, Zmin, Xmax, Ymax, Zmax);  Sel - Add(aSensitiveBox);  }  break;  Case 1: ... //Selection of the doors  } //Switch ) // ComputeSelection ~~~~~ @image html visualization_image012.png "Activated sensitive boxes corresponding to selection mode 0 (selection of rooms)" @image latex visualization_image012.png "Activated sensitive boxes corresponding to selection mode 0 (selection of rooms)" @image html visualization_image013.png "Activated sensitive rectangles in the selector during dynamic selection in view 1" @image latex visualization_image013.png "Activated sensitive rectangles in the selector during dynamic selection in view 1" @image html visualization_image014.png "Activated sensitive polygons corresponding to selection mode 1 (selection of doors)" @image latex visualization_image014.png "Activated sensitive polygons corresponding to selection mode 1 (selection of doors)" @image html visualization_image015.png "Sensitive rectangles in the selector during dynamic selection in view 2" @image latex visualization_image015.png "Sensitive rectangles in the selector during dynamic selection in view 2" @section occt_visu_3 Application Interactive Services @subsection occt_visu_3_1 Introduction Application Interactive Services allow managing presentations and dynamic selection in a viewer in a simple and transparent manner. The central entity for management of visualization and selections is the **Interactive Context**. It is connected to the main viewer (and if need be, the trash bin viewer). It has two operating modes: the Neutral Point and the local visualization and selection context. The neutral point, which is the default mode, allows easily visualizing and selecting interactive objects loaded into the context. **Local Contexts** can be opened to prepare and use a temporary selection environment without disturbing the neutral point. It is possible to choose the interactive objects, which you want to act on, the selection modes, which you want to activate, and the temporary visualizations, which you will execute. When the operation is finished, you close the current local context and return to the state in which you were before opening it (neutral point or previous local context). **Interactive Objects** are the entities, which are visualized and selected. You can use classes of standard interactive objects for which all necessary functions have already been programmed, or you can implement your own classes of interactive objects, by respecting a certain number of rules and conventions described below. @image html visualization_image016.png @image latex visualization_image016.png An Interactive Object is a "virtual" entity, which can be presented and selected. An Interactive Object can have a certain number of specific graphic attributes, such as visualization mode, color and material. When an Interactive Object is visualized, the required graphic attributes are taken from its own **Drawer** if it has the required custom attributes or otherwise from the context drawer. @image html visualization_image017.png @image latex visualization_image017.png It can be necessary to filter the entities to be selected. Consequently there are **Filter** entities, which allow refining the dynamic detection context. Some of these filters can be used at the Neutral Point, others only in an open local context. It is possible to program custom filters and load them into the interactive context. @subsection occt_visu_3_2 Interactive objects @subsubsection occt_visu_3_2_1 Presentations An interactive object can have as many presentations as its creator wants to give it. 3D presentations are managed by PresentationManager3D. As this is transparent in AIS, the user does not have to worry about it. A presentation is identified by an index and by the reference to the Presentation Manager which it depends on. By convention, the default mode of representation for the Interactive Object has index 0. @image html visualization_image018.png @image latex visualization_image018.png Calculation of different presentations of an interactive object is done by the *Compute* functions inheriting from *PrsMgr_ PresentableObject::Compute* functions. They are automatically called by *PresentationManager* at a visualization or an update request. If you are creating your own type of interactive object, you must implement the Compute function in one of the following ways: #### For 3D: ~~~~~ void PackageName_ClassName::Compute (const Handle(PrsMgr_PresentationManager3d)& aPresentationManager,  const Handle(Prs3d_Presentation)& aPresentation,  const Standard_Integer aMode = 0); ~~~~~ #### For hidden line removal (HLR) mode in 3D: ~~~~~ void PackageName_ClassName::Compute (const Handle(Prs3d_Projector)& aProjector,  const Handle(Prs3d_Presentation)& aPresentation); ~~~~~ @subsubsection occt_visu_3_2_2 Hidden Line Removal The view can have two states: the normal mode or the computed mode (Hidden Line Removal mode). When the latter is active, the view looks for all presentations displayed in the normal mode, which have been signalled as accepting HLR mode. An internal mechanism allows calling the interactive object’s own *Compute*, that is projector function. By convention, the Interactive Object accepts or rejects the representation of HLR mode. It is possible to make this declaration in one of two ways: * Initially by using one of the values of the enumeration *PrsMgr_TypeOfPresentation*: * *PrsMgr_TOP_AllView*, * *PrsMgr_TOP_ProjectorDependant* * Later by using the function *PrsMgr_PresentableObject::SetTypeOfPresentation* *AIS_Shape* class is an example of an interactive object that supports HLR representation. It supports two types of the HLR algorithm: * the polygonal algorithm based on the shape’s triangulation; * the exact algorithm that works with the shape’s real geometry. The type of the HLR algorithm is stored in *AIS_Drawer* of the shape. It is a value of the *Prs3d_TypeOfHLR* enumeration and can be set to: * *Prs3d_TOH_PolyAlgo* for a polygonal algorithm; * *Prs3d_TOH_Algo* for an exact algorithm; * *Prs3d_TOH_NotSet* if the type of algorithm is not set for the given interactive object instance. The type of the HLR algorithm used for *AIS_Shape* can be changed by calling the *AIS_Shape::SetTypeOfHLR()* method. The current HLR algorithm type can be obtained using *AIS_Shape::TypeOfHLR()* method is to be used. These methods get the value from the drawer of *AIS_Shape*. If the HLR algorithm type in the *AIS_Drawer* is set to *Prs3d_TOH_NotSet*, the *AIS_Drawer* gets the value from the default drawer of *AIS_InteractiveContext*. So it is possible to change the default HLR algorithm used by all newly displayed interactive objects. The value of the HLR algorithm type stored in the context drawer can be *Prs3d_TOH_Algo* or *Prs3d_TOH_PolyAlgo*. The polygonal algorithm is the default one. @subsubsection occt_visu_3_2_3 Presentation modes There are four types of interactive objects in AIS: * the "construction element" or Datum, * the Relation (dimensions and constraints) * the Object * the None type (when the object is of an unknown type). Inside these categories, additional characterization is available by means of a signature (an index.) By default, the interactive object has a NONE type and a signature of 0 (equivalent to NONE.) If you want to give a particular type and signature to your interactive object, you must redefine two virtual functions: * *AIS_InteractiveObject::Type* * *AIS_InteractiveObject::Signature*. **Note** that some signatures are already used by "standard" objects provided in AIS (see the list of Standard Interactive Object Classes). The interactive context can have a default mode of representation for the set of interactive objects. This mode may not be accepted by a given class of objects. Consequently, to get information about this class it is necessary to use virtual function *AIS_InteractiveObject::AcceptDisplayMode*. #### Display Mode The functions *AIS_InteractiveContext::SetDisplayMode* and *AIS_InteractiveContext::UnsetDisplayMode* allow setting a custom display mode for an objects, which can be different from that proposed by the interactive context. #### Highlight Mode At dynamic detection, the presentation echoed by the Interactive Context, is by default the presentation already on the screen. The functions *AIS_InteractiveObject::SetHilightMode* and *AIS_InteractiveObject::UnSetHilightMode* allow specifying the display mode used for highlighting (so called highlight mode), which is valid independently from the active representation of the object. It makes no difference whether this choice is temporary or definitive. Note that the same presentation (and consequently the same highlight mode) is used for highlighting *detected* objects and for highlighting *selected* objects, the latter being drawn with a special *selection color* (refer to the section related to *Interactive Context* services). For example, you want to systematically highlight the wireframe presentation of a shape - non regarding if it is visualized in wireframe presentation or with shading. Thus, you set the highlight mode to *0* in the constructor of the interactive object. Do not forget to implement this representation mode in the *Compute* functions. #### Infinite Status If you don’t want an object to be affected by a *FitAll* view, you must declare it infinite; you can cancel its "infinite" status using *AIS_InteractiveObject::SetInfiniteState* and *AIS_InteractiveObject::IsInfinite* functions. Let us take for example the class called *IShape* representing an interactive object : ~~~~~ myPk_IShape::myPK_IShape (const TopoDS_Shape& SH, PrsMgr_TypeOfPresentation aType): AIS_InteractiveObject(aType), myShape(SH), myDrwr(new AIS_Drawer()) {SetHilightMode(0);}  void myPk_IShape::Compute (const Handle(PrsMgr_PresentationManager3d) & PM, const Handle(Prs3d_Presentation)& P,   const Standard_Integer TheMode) { switch (TheMode){ case 0: StdPrs_WFDeflectionShape::Add (P,myShape,myDrwr); //algo for calculation of wireframe presentation break; case 1: StdPrs_ShadedShape::Add (P,myShape,myDrwr); //algo for calculation of shading presentation. break; } } void myPk_IsShape::Compute (const Handle(Prs3d_Projector)& Prj, const Handle(Prs3d_Presentation) P) { StdPrs_HLRPolyShape::Add(P,myShape,myDrwr); //Hidden line mode calculation algorithm } ~~~~~ @subsubsection occt_visu_3_2_4 Selection An interactive object can have an indefinite number of selection modes, each representing a "decomposition" into sensitive primitives; each primitive has an Owner (*SelectMgr_EntityOwner*) which allows identifying the exact entity which has been detected (see Dynamic Selection chapter). The set of sensitive primitives, which correspond to a given mode, is stocked in a SELECTION (*SelectMgr_Selection*). Each Selection mode is identified by an index. By Convention, the default selection mode that allows us to grasp the Interactive object in its entirety is mode *0*. The calculation of Selection primitives (or sensitive primitives) is done by the intermediary of a virtual function, *ComputeSelection*. This should be implemented for each type of interactive object on which you want to make different type selections using the function *AIS_ConnectedInteractive::ComputeSelection*. A detailed explanation of the mechanism and the manner of implementing this function has been given in Dynamic Selection chapter. Moreover, just as the most frequently manipulated entity is *TopoDS_Shape*, the most used Interactive Object is *AIS_Shape*. You will see below activation functions for standard selection modes are proposed in the Interactive context (selection by vertex, by edges etc). To create new classes of interactive object with the same behavior as *AIS_Shape* - such as vertices and edges - you must redefine the virtual function *AIS_ConnectedInteractive::AcceptShapeDecomposition*. You can change the default selection mode index of an Interactive Object using the following functions: * *AIS_InteractiveObject::HasSelectionMode* checks if there is a selection mode; * *AIS_InteractiveObject::SelectionMode* check the current selection mode; * *AIS_InteractiveContext::SetSelectionMode* sets a selection mode; * *AIS_InteractiveContext::UnsetSelectionMode* unsets a selection mode. These functions can be useful if you decide that the *0* mode used by default will not do. In the same way, you can temporarily change the priority of certain interactive objects for selection of 0 mode to facilitate detecting them graphically using the following functions: * *AIS_InteractiveObject::HasSelectionPriority* checks if there is a selection priority setting for the owner; * *AIS_InteractiveObject::SelectionPriority* checks the current priority; * *AIS_InteractiveObject::SetSelectionPriority* sets a priority; * *AIS_InteractiveObject::UnsetSelectionPriority* unsets the priority.      @subsubsection occt_visu_3_2_5 Graphic attributes Keep in mind the following points concerning graphic attributes: * Each interactive object can have its own visualization attributes. * The set of graphic attributes of an interactive object is stocked in an *AIS_Drawer*, which is only a *Prs3d_Drawer* with the possibility of a link to another drawer * By default, the interactive object takes the graphic attributes of the context in which it is visualized (visualization mode, deflection values for the calculation of presentations, number of isoparameters, color, type of line, material, etc.) * In the *AIS_InteractiveObject* abstract class, standard attributes including color, line thickness, material, and transparency have been privileged. Consequently, there is a certain number of virtual functions, which allow acting on these attributes. Each new class of interactive object can redefine these functions and change the behavior of the class. @image html visualization_image019.png "Figure 13. Redefinition of virtual functions for changes in AIS_Point" @image latex visualization_image019.png "Figure 13. Redefinition of virtual functions for changes in AIS_Point" @image html visualization_image020.png "Figure 14. Redefinition of virtual functions for changes in AIS_Shape." @image latex visualization_image020.png "Figure 14. Redefinition of virtual functions for changes in AIS_Shape." The following virtual functions provide settings for color, width, material and transparency: * *AIS_InteractiveObject::UnsetColor* * *AIS_InteractiveObject::SetWidth* * *AIS_InteractiveObject::UnsetWidth* * *AIS_InteractiveObject::SetMaterial (const Graphic3d_NameOfPhysicalMaterial & aName)* * *AIS_InteractiveObject::SetMaterial  (const Graphic3d_MaterialAspect & aMat)* * *AIS_InteractiveObject::UnsetMaterial* * *AIS_InteractiveObject::SetTransparency* * *AIS_InteractiveObject::UnsetTransparency* For other types of attribute, it is appropriate to change the Drawer of the object directly using: * *AIS_InteractiveObject::SetAttributes* * *AIS_InteractiveObject::UnsetAttributes* It is important to know which functions may imply the recalculation of presentations of the object. If the presentation mode of an interactive object is to be updated, a flag from *PrsMgr_PresentableObject* indicates this. The mode can be updated using the functions *Display* and *Redisplay* in *AIS_InteractiveContext*. @subsubsection occt_visu_3_2_6 Complementary Services When you use complementary services for interactive objects, pay special attention to the cases mentioned below. #### Change the location of an interactive object The following functions allow temporarily "moving" the representation and selection of Interactive Objects in a view without recalculation. * *AIS_InteractiveContext::SetLocation* * *AIS_InteractiveContext::ResetLocation* * *AIS_InteractiveContext::HasLocation* * *AIS_InteractiveContext::Location* #### Connect an interactive object to an applicative entity Each Interactive Object has functions that allow attributing it an *Owner* in form of a *Transient*. * *AIS_InteractiveObject::SetOwner* * *AIS_InteractiveObject::HasOwner* * *AIS_InteractiveObject::Owner* An interactive object can therefore be associated or not with an applicative entity, without affecting its behavior. #### Resolving coincident topology Due to the fact that the accuracy of three-dimensional graphics coordinates has a finite resolution the elements of topological objects can coincide producing the effect of "popping" some elements one over another. To the problem when the elements of two or more Interactive Objects are coincident you can apply the polygon offset. It is a sort of graphics computational offset, or depth buffer offset, that allows you to arrange elements (by modifying their depth value) without changing their coordinates. The graphical elements that accept this kind of offsets are solid polygons or displayed as boundary lines and points. The polygons could be displayed as lines or points by setting the appropriate interior style. The method *AIS_InteractiveObject::SetPolygonOffsets (const Standard_Integer aMode, const Standard_Real aFactor, const Standard_Real aUnits)* allows setting up the polygon offsets. The parameter *aMode* can contain various combinations of *Aspect_PolygonOffsetMode* enumeration elements: * *Aspect_POM_None* * *Aspect_POM_Off* * Aspect_POM_Fill * Aspect_POM_Line * Aspect_POM_Point * Aspect_POM_All The combination of these elements defines the polygon display modes that will use the given offsets. You can switch off the polygon offsets by passing *Aspect_POM_Off*. Passing *Aspect_POM_None* allows changing the *aFactor* and *aUnits* values without changing the mode. If *aMode* is different from *Aspect_POM_Off*, the *aFactor* and *aUnits* arguments are used by the graphics renderer to calculate the depth offset value: ~~~~~ offset = aFactor * m + aUnits * r ~~~~~ where *m* is the maximum depth slope for the currently displayed polygons, r is the minimum depth resolution (implementation-specific). Negative offset values move polygons closer to the viewer while positive values shift polygons away. **Warning** This method has a side effect – it creates its own shading aspect if not yet created, so it is better to set up the object shading aspect first. You can use the following functions to obtain the current settings for polygon offsets: ~~~~~ void AIS_InteractiveObject::PolygonOffsets (Standard_Integer &aMode,  Standard_Real &aFactor,  Standard_Real &aUnits) Standard_Boolean AIS_InteractiveObject::HasPolygonOffsets() ~~~~~ The same operation could be performed for the interactive object known by the *AIS_InteractiveContext* with the following methods: ~~~~~ void AIS_InteractiveContext::SetPolygonOffsets (const Handle(AIS_InteractiveObject) &anObj,  const Standard_Integer aMode,  const Standard_Real aFactor,  const Standard_Real aUnits) void AIS_InteractiveContext::PolygonOffsets (const Handle(AIS_InteractiveObject) &anObj,  Standard_Integer &aMode,  Standard_Real &aFactor,  Standard_Real &aUnits) Standard_Boolean     AIS_InteractiveContext::HasPolygonOffsets (const Handle(AIS_InteractiveObject) &anObj) ~~~~~ @subsection occt_visu_3_3 Interactive Context @subsubsection occt_visu_3_3_1 Rules The Interactive Context allows us to manage in a transparent way, the graphic and "selectable" behavior of interactive objects in one or more viewers. Most functions which allow us to modify the attributes of interactive objects, and which were presented in the preceding chapter, will be looked at again here. There is one essential rule to follow: the modification of an interactive object, which is already known by the Context, must be done using Context functions. You can only directly call the functions available for an interactive object if it has not been loaded into an Interactive Context. ~~~~~ Handle (AIS_Shape) TheAISShape = new AIS_Shape (ashape); myIntContext-Display(TheAISShape); myIntContext-SetDisplayMode(TheAISShape ,1); myIntContext-SetColor(TheAISShape,Quantity_NOC_RED); ~~~~~ You can also write ~~~~~ Handle (AIS_Shape) TheAISShape = new AIS_Shape (ashape); TheAISShape-SetColor(Quantity_NOC_RED); TheAISShape-SetDisplayMode(1); myIntContext-Display(TheAISShape); ~~~~~ @subsubsection occt_visu_3_3_2 Groups of functions You must distinguish two states in the Interactive Context: * No Open Local Context; which will be referred to as Neutral Point. * One or several open local contexts, each representing a temporary state of selection and presentation. Some functions can only be used in open Local Context; others in closed local context; others do not have the same behavior in one state as in the other. The Interactive Context is composed of many functions, which can be conveniently grouped according to the theme: * management proper to the context; * management in the local context; * presentations and selection in open/closed context; * selection strictly speaking. @subsubsection occt_visu_3_3_3 Management of the Interactive Context The Interactive Context is made up of a Principal Viewer and, optionally, a trash bin or "Collector" Viewer. It also has a group of adjustable settings allowing you to personalize the behavior of presentations and selections: * Default Drawer, containing all the color and line attributes which can be used by interactive objects, which do not have their own attributes. * Default Visualization Mode for interactive objects. By default: *mode 0* ; * Highlight color of entities detected by mouse movement. By default: *Quantity_NOC_CYAN1*; * Pre-selection color. By default: *Quantity_NOC_GREEN*; * Selection color (when you click on a detected object). By default: *Quantity_NOC_GRAY80*; * Sub-Intensity color. By default: *Quantity_NOC_GRAY40*. All of these settings can be modified by functions proper to the Context. When you change a graphic attribute pertaining to the Context (visualization mode, for example), all interactive objects, which do not have the corresponding appropriate attribute, are updated. Let us examine the case of two interactive objects: *obj1* and *obj2*: ~~~~~ TheCtx-Display(obj1,Standard_False); // False = no viewer update TheCtx-Display(obj2,Standard_True); // True = viewer update TheCtx-SetDisplayMode(obj1,3,Standard_False); TheCtx-SetDisplayMode(2); // obj2 is visualised in mode 2 (if it accepts this mode) // obj1 stays visualised in its mode 3. ~~~~~ *PresentationManager3D* and a *Selector3D* which manage the presentation and selection of present interactive objects, are associated to the main Viewer. The same is true of the optional Collector. @subsection occt_visu_3_4 Local Context @subsubsection occt_visu_3_4_1 Rules and Conventions * Opening a local context allows preparing an environment for temporary presentations and selections, which will disappear once the local context is closed. * It is possible to open several local contexts, but only the last one will be active. * When you close a local context, the previous one, which is still on the stack, is activated again. If none is left, you return to Neutral Point. * Each local context has an index created when the context opens. You should close the local context, which you have opened. The interactive object, which is used the most by applications, is *AIS_Shape*. Consequently, standard functions are available which allow you to easily prepare selection operations on the constituent elements of shapes (selection of vertices, edges, faces etc) in an open local context. The selection modes specific to "Shape" type objects are called **Standard Activation Mode**. These modes are only taken into account in open local context and only act on interactive objects which have redefined the virtual function *AcceptShapeDecomposition()* so that it returns *TRUE*. * Objects, which are temporarily in a local context, are not recognized by other local contexts a priori. Only objects visualized in Neutral Point are recognized by all local contexts. * The state of a temporary interactive object in a local context can only be modified while another local context is open. **Warning** The specific modes of selection only concern the interactive objects, which are present in the Main Viewer. In the Collector, you can only locate interactive objects, which answer positively to the positioned filters when a local context is open, however, they are never decomposed in standard mode. @subsubsection occt_visu_3_4_2 Management of Local Context The local context can be opened using method *AIS_InteractiveContext::OpenLocalContext*. The following options are available: * *UseDisplayedObjects*: allows loading the interactive objects visualized at Neutral Point in the opened local context. If* FALSE*, the local context is empty after being opened. If *TRUE*, the objects at Neutral Point are modified by their default selection mode. * *AllowShapeDecomposition*: *AIS_Shape* allows or prevents decomposition in standard shape location mode of objects at Neutral Point, which are type-privileged (see Selection chapter). This Flag is only taken into account when *UseDisplayedObjects* is *TRUE*. * *AcceptEraseOfObjects*: authorises other local contexts to erase the interactive objects present in this context. This option is rarely used. The last option has no current use. This function returns the index of the created local context. It should be kept and used when the context is closed. To load objects visualized at Neutral Point into a local context or remove them from it use methods ~~~~~ AIS_InteractiveContext::UseDisplayedObjects AIS_InteractiveContext::NotUseDisplayedObjects ~~~~~ Closing Local Contexts is done by: ~~~~~ AIS_InteractiveContext::CloseLocalContext AIS_InteractiveContext::CloseAllContexts ~~~~~ *Warning* When the index isn’t specified in the first function, the current Context is closed. This option can be dangerous, as other Interactive Functions can open local contexts without necessarily warning the user. For greater security, you have to close the context with the index given on opening. To get the index of the current context, use function "AIS_InteractiveContext::IndexOfCurrentLocal". It allows closing all open local contexts at one go. In this case, you find yourself directly at Neutral Point. When you close a local context, all temporary interactive objects are deleted, all selection modes concerning the context are cancelled, and all content filters are emptied. @subsubsection occt_visu_3_4_3 Presentation in a Neutral Point You must distinguish between the Neutral Point and the Open Local Context states. Although the majority of visualization functions can be used in both situations, their behavior is different. Neutral Point should be used to visualize the interactive objects, which represent and select an applicative entity. Visualization and Erasing orders are straightforward: ~~~~~ AIS_InteractiveContext::Display (const Handle(AIS_InteractiveObject)& anIobj,  const Standard_Boolean updateviewer=Standard_True); AIS_InteractiveContext::Display (const Handle(AIS_InteractiveObject)& anIobj,  const Standard_Integer amode,  const Standard_Integer aSelectionMode,  const Standard_Boolean updateviewer = Standard_True,  const Standard_Boolean allowdecomposition = Standard_True); AIS_InteractiveContext::Erase AIS_InteractiveContext::EraseMode AIS_InteractiveContext::ClearPrs AIS_InteractiveContext::Redisplay AIS_InteractiveContext::Remove AIS_InteractiveContext::EraseAll AIS_InteractiveContext::Hilight AIS_InteractiveContext::HilightWithColor ~~~~~ Bear in mind the following points: * It is recommended to display and erase interactive objects when no local context is opened, and open a local context for local selection only. * The first *Display* function among the two ones available in *InteractiveContext* visualizes the object in its default mode (set with help of SetDisplayMode() method of InteractiveObject prior to Display() call), or in the default context mode, if applicable. If it has neither, the function displays it in 0 presentation mode. The object’s default selection mode is automatically activated (0 mode by convention). * Activating the displayed object by default can be turned off with help of *SetAutoActivateSelection()* method. This might be efficient if you are not interested in selection immediately after displaying an object. * The second *Display* function should only be used in Neutral Point to visualize a supplementary mode for the object, which you can erase by *EraseMode (...)*. You activate the selection mode. This is passed as an argument. By convention, if you do not want to activate a selection mode, you must set the *SelectionMode* argument to -1. This function is especially interesting in open local context, as we will see below. * In Neutral Point, it is not advisable to activate other selection modes than the default selection one. It is preferable to open a local context in order to activate particular selection modes. * When you call *Erase *(Interactive object) function, the *PutIncollector* argument, which is FALSE by default, allows you to visualize the object directly in the Collector and makes it selectable (by activation of 0 mode). You can nonetheless block its passage through the Collector by changing the value of this option. In this case, the object is present in the Interactive Context, but is not seen anywhere. * *Erase()* with *putInCollector = Standard_True* might be slow as it computes again the object presentation in the Collector. Set *putInCollector* to *Standard_False* if you simply want to hide the object’s presentation temporarily. * Visualization attributes and graphic behavior can be modified through a set of functions similar to those for the interactive object (color, thickness of line, material, transparency, locations, etc.) The context then manages immediate and deferred updates. * Call *Remove()* method of *InteractiveContext* as soon as the interactive object is no longer needed and you want to destroy it.. Otherwise, references to *InteractiveObject* are kept by *InteractiveContext*, and the *Object* is not destroyed, which results in memory leaks. In general, if the presentation of an interactive object can be computed quickly, it is recommended to *Remove()* it instead of using *Erase()* method. @subsubsection occt_visu_3_4_4 Presentation in Local Context In open local context, the *Display* functions presented above can be as well. **WARNING** The function *AIS_InteractiveObject::Display* automatically activates the object’s default selection mode. When you only want to visualize an Interactive Object in open Context, you must call the function *AIS_InteractiveContext::Display*. You can activate or deactivate specific selection modes in the local open context in several different ways: Use the Display functions with the appropriate modes. ~~~~~ AIS_InteractiveContext::ActivateStandardMode //can be used only if a Local Context is opened. AIS_InteractiveContext::DeactivateStandardMode AIS_InteractiveContext::ActivatedStandardModes AIS_InteractiveContext::SetShapeDecomposition ~~~~~ This activates the corresponding selection mode for all objects in Local Context, which accept decomposition into sub-shapes. Every new Object which has been loaded into the interactive context and which meets the decomposition criteria is automatically activated according to these modes. **WARNING** If you have opened a local context by loading an object with the default options *(AllowShapeDecomposition = Standard_True)*, all objects of the "Shape" type are also activated with the same modes. You can change the state of these "Standard" objects by using *SetShapeDecomposition(Status)*. Load an interactive object by the function *AIS_InteractiveContext::Load*. This function allows loading an Interactive Object whether it is visualized or not with a given selection mode, and/or with the necessary decomposition option. If *AllowDecomp=TRUE* and obviously, if the interactive object is of the "Shape" type, these "standard" selection modes will be automatically activated as a function of the modes present in the Local Context. Use *AIS_InteractiveContext::Activate* and *AIS_InteractiveContext::Deactivate* to directly activate/deactivate selection modes on an object. @subsubsection occt_visu_3_4_5 Filters When Interactive objects have been "prepared" in the local context, you can add rejection filters. The root class of objects is *SelectMgr_Filter*. The principle behind it is straightforward: a filter tests to see whether the owners *(SelectMgr_EntityOwner)* detected in mouse position by the Local context selector answer *OK*. If so, it is kept, otherwise it is rejected. You can create a custom class of filter objects by implementing the deferred function *IsOk()*: ~~~~~ class MyFilter : public SelectMgr_Filter { }; virtual Standard_Boolean MyFilter::IsOk (const Handle(SelectMgr_EntityOwner)& anObj) const = 0; ~~~~~ In *SelectMgr*, there are also Composition filters (AND Filters, OR Filters), which allow combining several filters. In InteractiveContext , all filters that you add are stocked in an OR filter (which answers *OK* if at least one filter answers *OK*). There are Standard filters, which have already been implemented in several packages: * *StdSelect_EdgeFilter* - for edges, such as lines and circles; * *StdSelect_FaceFilter* - for faces, such as planes, cylinders and spheres; * *StdSelect_ShapeTypeFilter* - for shape types, such as compounds, solids, shells and wires; * *AIS_TypeFilter* - for types of interactive objects; * *AIS_SignatureFilter* - for types and signatures of interactive objects; * *AIS_AttributeFilter* - for attributes of Interactive Objects, such as color and width. As there are specific behaviors on shapes, each new Filter class must, if necessary, redefine *AIS_LocalContext::ActsOn* function, which informs the Local Context if it acts on specific types of sub-shapes. By default, this function answers *FALSE*. **WARNING** Only type filters are activated in Neutral Point to make it possible to identify a specific type of visualized object. For filters to come into play, one or more object selection modes must be activated. There are several functions to manipulate filters: * *AIS_InteractiveContext::AddFilter* adds a filter passed as an argument.   * *AIS_InteractiveContext::RemoveFilter* removes a filter passed as an argument. * *AIS_InteractiveContext::RemoveFilters* removes all present filters. * *AIS_InteractiveContext::Filters* gets the list of filters active in a local context.

Example

~~~~~ myContext-OpenLocalContext(Standard_False); // no object in neutral point is loaded myContext-ActivateStandardMode(TopAbs_Face); //activates decomposition of shapes into faces. Handle (AIS_Shape) myAIShape = new AIS_Shape ( ATopoShape); myContext-Display(myAIShape,1,-1,Standard_True,Standard_True); //shading visualization mode, no specific mode, authorization for //decomposition into sub-shapes. At this Stage, myAIShape is decomposed into faces... Handle(StdSelect_FaceFilter) Fil1= new StdSelect_FaceFilter(StdSelect_Revol); Handle(StdSelect_FaceFilter) Fil2= new       StdSelect_FaceFilter(StdSelect_Plane); myContext-AddFilter(Fil1); myContext-AddFilter(Fil2); //only faces of revolution or planar faces will be selected myContext-MoveTo( xpix,ypix,Vue); // detects the mouse position ~~~~~ @subsubsection occt_visu_3_4_6 Selection in the Local Context Dynamic detection and selection are put into effect in a straightforward way. There are only a few conventions and functions to be familiar with. The functions are the same in neutral point and in open local context: * *AIS_InteractiveContext::MoveTo* - passes mouse position to Interactive Context selectors * *AIS_InteractiveContext::Select* - stocks what has been detected on the last *MoveTo*. Replaces the previously selected object. Empties the stack if nothing has been detected at the last move * *AIS_InteractiveContext::ShiftSelect* - if the object detected at the last move was not already selected, it is added to the list of the selected objects. If not, it is withdrawn. Nothing happens if you click on an empty area. * *AIS_InteractiveContext::Select* selects everything found in the surrounding area. * *AIS_InteractiveContext::ShiftSelect* selects what was not previously in the list of selected, deselects those already present. Highlighting of detected and selected entities is automatically managed by the Interactive Context, whether you are in neutral point or Local Context. The Highlight colors are those dealt with above. You can nonetheless disconnect this automatic mode if you want to manage this part yourself : ~~~~~ AIS_InteractiveContext::SetAutomaticHilight AIS_InteractiveContext::AutomaticHilight ~~~~~ If there is no open local context, the objects selected are called **current objects**. If there is a local context, they are called **selected objects**. Iterators allow entities to be recovered in either case. A set of functions allows manipulating the objects, which have been placed in these different lists. **WARNING** When a Local Context is open, you can select entities other than interactive objects (vertices, edges etc.) from decompositions in standard modes, or from activation in specific modes on specific interactive objects. Only interactive objects are stocked in the list of selected objects. You can question the Interactive context by moving the mouse. The following functions can be used: * *AIS_InteractiveContext::HasDetected* informs if something has been detected; * *AIS_InteractiveContext::HasDetectedShape* informs if it is a shape; * *AIS_InteractiveContext::DetectedShape* gets the shape if the detected entity is an object; * *AIS_InteractiveContext::DetectedInteractive* gets the interactive object if the detected entity is an object. After using the *Select* and *ShiftSelect* functions in Neutral Point, you can explore the list of selections, referred to as current objects in this context. The following functions can be used: * *AIS_InteractiveContext::InitCurrent* initiates a scan of this list; * *AIS_InteractiveContext::MoreCurrent* extends the scan; * *AIS_InteractiveContext::NextCurrent* resumes the scan; * *AIS_InteractiveContext::Current* gets the name of the current object detected in the scan; * *AIS_InteractiveContext::FirstCurrentObject* gets the first current interactive object; * *AIS_InteractiveContext::HilightCurrents* highlights current objects; * *AIS_InteractiveContext::UnhilightCurrents* removes highlight from current objects; * *AIS_InteractiveContext::ClearCurrents* empties the list of current objects in order to update it; * *AIS_InteractiveContext::IsCurrent* finds the current object. In the Local Context, you can explore the list of selected objects available. The following functions can be used: * *AIS_InteractiveContext::InitSelected* initiates the list of objects; * *AIS_InteractiveContext::MoreSelected* extends the list of objects; * *AIS_InteractiveContext::NextSelected* resumes a scan; * *AIS_InteractiveContext::SelectedShape* gets the name of the selected object; * *AIS_InteractiveContext::HasSelectedShape* checks if the selected shape is obtained; * *AIS_InteractiveContext::Interactive* gets the picked interactive object; * *AIS_InteractiveContext::HasApplicative* checks if the applicative object has an owner from Interactive attributed to it; * *AIS_InteractiveContext::Applicative* gets the owner of the detected applicative entity; * *AIS_InteractiveContext::IsSelected* gets the name of the selected object.

Example

~~~~~ myAISCtx-InitSelected(); while (myAISCtx-MoreSelected()) { if (myAISCtx-HasSelectedShape) { TopoDS_Shape ashape = myAISCtx-SelectedShape(); // to be able to use the picked shape             } else { Handle_AIS_InteractiveObject aniobj = myAISCtx-Interactive(); // to be able to use the picked interactive object } myAISCtx-NextSelected(); } ~~~~~ You have to ask whether you have selected a shape or an interactive object before you can recover the entity in the Local Context or in the iteration loop. If you have selected a Shape from *TopoDS* on decomposition in standard mode, the *Interactive()* function returns the interactive object, which provided the selected shape. Other functions allow you to manipulate the content of Selected or Current Objects: * *AIS_InteractiveContext::EraseSelected* erases the selected objects; * *AIS_InteractiveContext::DisplaySelected* displays them; * *AIS_InteractiveContext::SetSelected* puts the objects in the list of selections; * *AIS_InteractiveContext::SetSelectedCurrent* takes the list of selected objects from a local context and puts it into the list of current objects in Neutral Point; * *AIS_InteractiveContext::AddOrRemoveSelected* adds or removes an object from the list of selected entities; * *AIS_InteractiveContext::HilightSelected* highlights the selected object; * *AIS_InteractiveContext::UnhilightSelected* removes highlighting from the selected object; * *AIS_InteractiveContext::ClearSelected* empties the list of selected objects. You can highlight and remove highlighting from a current object, and empty the list of current objects using the following functions: ~~~~~ AIS_InteractiveContext::HilightCurrents AIS_InteractiveContext::UnhilightCurrents AIS_InteractiveContext::ClearCurrents ~~~~~ When you are in an open Local Context, you may need to keep "temporary" interactive objects. This is possible using the following functions: * *AIS_InteractiveContext::KeepTemporary* transfers the characteristics of the interactive object seen in its local context (visualization mode, etc.) to the neutral point. When the local context is closed, the object does not disappear. * *AIS_InteractiveContext::SetSelectedCurrent* allows the selected object to become the current object when you close the local context. You can also want to use function *AIS_InteractiveContext::ClearLocalContext* to modify in a general way the state of the local context before continuing a selection (emptying objects, removing filters, standard activation modes). @subsubsection occt_visu_3_4_7 Recommendations The possibilities of use for local contexts are numerous depending on the type of operation that you want to perform: * working on all visualized interactive objects, * working on only a few objects, * working on a single object. When you want to work on one type of entity, you should open a local context with the option *UseDisplayedObjects* set to FALSE. Some functions which allow you to recover the visualized interactive objects, which have a given Type, and Signature from the "Neutral Point" are: ~~~~~ AIS_InteractiveContext::DisplayedObjects (AIS_ListOfInteractive& aListOfIO) const; AIS_InteractiveContext::DisplayedObjects (const AIS_KindOfInteractive WhichKind, const Standard_Integer WhichSignature; AIS_ListOfInteractive& aListOfIO) const; ~~~~~ At this stage, you only have to load the functions *Load, Activate,* and so on. When you open a Local Context with default options, you must keep the following points in mind: * The Interactive Objects visualized at Neutral Point are activated with their default selection mode. You must deactivate those, which you do not want to use. * The Shape Type Interactive Objects are automatically decomposed into sub-shapes when standard activation modes are launched. * The "temporary" Interactive Objects present in the Local Contexts are not automatically taken into account. You have to load them manually if you want to use them. The stages could be the following: 1. Open a Local Context with the right options; 2. Load/Visualize the required complementary objects with the desired activation modes. 3. Activate Standard modes if necessary 4. Create its filters and add them to the Local Context 5. Detect/Select/recover the desired entities 6. Close the Local Context with the adequate index. It is useful to create an **interactive editor**, to which you pass the Interactive Context. This allow setting up different contexts of selection/presentation according to the operation, which you want to perform. Let us assume that you have visualized several types of interactive objects: *AIS_Points*, *AIS_Axes*, *AIS_Trihedrons*, and *AIS_Shapes*. For your applicative function, you need an axis to create a revolved object. You could obtain this axis by identifying: * an axis which is already visualized, * 2 points, * a rectilinear edge on the shapes which are present, * a cylindrical face on the shapes (You will take the axis of this face) ~~~~~ myIHMEditor::myIHMEditor (const Handle(AIS_InteractiveContext)& Ctx,  ....) :  myCtx(Ctx), ... { } myIHMEditor::PrepareContext() { myIndex =myCtx-OpenLocalContext(); //the filters Handle(AIS_SignatureFilter) F1 = new  AIS_SignatureFilter(AIS_KOI_Datum,AIS_SD_Point); //filter on the points Handle(AIS_SignatureFilter) F2 = new AIS_SignatureFilter(AIS_KOI_Datum,AIS_SD_Axis); //filters on the axes. Handle(StdSelect_FaceFilter) F3 = new StdSelect_FaceFilter(AIS_Cylinder); //cylindrical face filters //... // activation of standard modes on the shapes.. myCtx-ActivateStandardMode(TopAbs_FACE); myCtx-ActivateStandardMode(TopAbs_VERTEX); myCTX-Add(F1); myCTX-Add(F2); myCTX-Add(F3); // at this point, you can call the selection/detection function } void myIHMEditor::MoveTo(xpix,ypix,Vue) { myCTX-MoveTo(xpix,ypix,vue); // the highlight of what is detected is automatic. } Standard_Boolean myIHMEditor::Select() { // returns true if you should continue the selection myCTX-Select(); myCTX-InitSelected(); if(myCTX-MoreSelected())  {  if(myCTX-HasSelectedShape()) { const TopoDS_Shape& sh = myCTX-SelectedShape(); if( vertex){ if(myFirstV...) { //if it’s the first vertex, you stock it, then you deactivate the faces and only keep the filter on the points: mypoint1 = ....; myCtx-RemoveFilters(); myCTX-DeactivateStandardMode(TopAbs_FACE); myCtx-Add(F1); // the filter on the AIS_Points myFirstV = Standard_False; return Standard_True;  } else  { mypoint2 =...; // construction of the axis return Standard_False; }  }  else   { //it is a cylindrical face : you recover the axis; visualize it; and stock it. return Standard_False; }   } // it is not a shape but is no doubt a point. else { Handle(AIS_InteractiveObject) SelObj = myCTX-SelectedInteractive(); if(SelObj-Type()==AIS_KOI_Datum) { if(SelObj-Signature()==1) { if (firstPoint) { mypoint1 =... return Standard_True; } else { mypoint2 = ...; //construction of the axis, visualization, stocking return Standard_False; } } else { // you have selected an axis; stock the axis return Standard_False; } } } } } void myIHMEditor::Terminate() { myCtx->CloseLocalContext(myIndex); ... } ~~~~~ @subsection occt_visu_3_5 Standard Interactive Object Classes @subsubsection occt_visu_3_5_1 Datums *AIS_Point, AIS_Axis, AIS_Line, AIS_Circle, AIS_Plane* and *AIS_Trihedron* have four selection modes: * mode 0 : selection of a trihedron; * mode 1 : selection of the origin of the trihedron; * mode 2 : selection of the axes; * mode 3 : selection of the planes XOY, YOZ, XOZ. when you activate one of modes: 1 2 3 4, you pick AIS objects of type: * *AIS_Point* * *AIS_Axis* (and information on the type of axis) * *AIS_Plane* (and information on the type of plane). *AIS_PlaneTrihedron* offers three selection modes: * mode 0 : selection of the whole trihedron; * mode 1 : selection of the origin of the trihedron; * mode 2 : selection of the axes - same remarks as for the Trihedron. For the presentation of planes and trihedra, the default unit of length is millimeter, and the default value for the representation of axes is 100. If you modify these dimensions, you must temporarily recover the object **Drawer**. From it, take the *Aspects* in which the values for length are stored (*PlaneAspect* for the plane, *FirstAxisAspect* for trihedra), and change these values inside these Aspects. Finally, recalculate the presentation. @subsubsection occt_visu_3_5_2 Objects *AIS_Shape* has three visualization modes : * mode 0 : Line (default mode) * mode 1 : Shading (depending on the type of shape) * mode 2 : Bounding Box And at maximum seven selection modes, depending on the shape complexity: * mode 0 : selection of the *AIS_Shape*; * mode 1 : selection of the vertices; * mode 2 : selection of the edges; * mode 3 : selection of the wires; * mode 4 : selection of the faces; * mode 5 : selection of the shells; * mode 6 : selection of the constituent solids. * *AIS_Triangulation* is a simple interactive object for displaying triangular mesh contained in *Poly_Triangulation* container. * *AIS_ConnectedInteractive* is an Interactive Object connecting to another interactive object reference, and located elsewhere in the viewer makes it possible not to calculate presentation and selection, but to deduce them from your object reference. * *AIS_ConnectedShape* is an object connected to interactive objects having a shape; this class has the same decompositions as *AIS_Shape*. What’s more, it allows a presentation of hidden parts, which are calculated automatically from the shape of its reference. * *AIS_MultipleConnectedInteractive* is an object connected to a list of interactive objects (which can also be Connected objects. It does not require memory hungry calculations of presentation) * *AIS_MultipleConnectedShape* is an interactive Object connected to a list of interactive objects having a Shape (AIS_Shape, AIS_ConnectedShape, AIS_MultipleConnectedShape). The presentation of hidden parts is calculated automatically. * *AIS_TexturedShape* is an Interactive Object that supports texture mapping. It is constructed as a usual AIS_Shape, but has additional methods that allow to map a texture on it. * *MeshVS_Mesh* is an Interactive Object that represents meshes, it has a data source that provides geometrical information (nodes, elements) and can be built up from the source data with a custom presentation builder. @subsubsection occt_visu_3_5_3 Relations * *AIS_ConcentricRelation* * *AIS_FixRelation* * *AIS_IdenticRelation* * *AIS_ParallelRelation* * *AIS_PerpendicularRelation* * *AIS_Relation* * *AIS_SymmetricRelation* * *AIS_TangentRelation* The list of relations is not exhaustive. @subsubsection occt_visu_3_5_4 Dimensions * *AIS_AngleDimension* * *AIS_Chamf3dDimension* * *AIS_DiameterDimension* * *AIS_DimensionOwner* * *AIS_LengthDimension* * *AIS_OffsetDimension* * *AIS_RadiusDimension* @subsubsection occt_visu_3_5_5 MeshVS_Mesh *MeshVS_Mesh* is an Interactive Object that represents meshes. This object differs from the *AIS_Shape* as its geometrical data is supported by the data source *MeshVS_DataSource* that describes nodes and elements of the object. As a result, you can provide your own data source. However, the *DataSource* does not provide any information on attributes, for example nodal colors, but you can apply them in a special way – by choosing the appropriate presentation builder. The presentations of *MeshVS_Mesh* are built with the presentation builders *MeshVS_PrsBuilder*. You can choose between the builders to represent the object in a different way. Moreover, you can redefine the base builder class and provide your own presentation builder. You can add/remove builders using the following methods: ~~~~~ MeshVS_Mesh::AddBuilder (const Handle (MeshVS_PrsBuilder) &Builder, Standard_Boolean TreatAsHilighter) MeshVS_Mesh::RemoveBuilder (const Standard_Integer Index) MeshVS_Mesh::RemoveBuilderById (const Standard_Integer Id) ~~~~~ There is a set of reserved display and highlighting mode flags for *MeshVS_Mesh*. Mode value is a number of bits that allows selecting additional display parameters and combining the following mode flags, which allow displaying mesh in wireframe, shading and shrink modes: ~~~~~ MeshVS_DMF_WireFrame MeshVS_DMF_Shading MeshVS_DMF_Shrink ~~~~~ It is also possible to display deformed mesh in wireframe, shading or shrink modes usung : ~~~~~ MeshVS_DMF_DeformedPrsWireFrame MeshVS_DMF_DeformedPrsShading MeshVS_DMF_DeformedPrsShrink ~~~~~ The following methods represent different kinds of data : ~~~~~ MeshVS_DMF_VectorDataPrs MeshVS_DMF_NodalColorDataPrs MeshVS_DMF_ElementalColorDataPrs MeshVS_DMF_TextDataPrs MeshVS_DMF_EntitiesWithData ~~~~~ The following methods provide selection and highlighting : ~~~~~ MeshVS_DMF_SelectionPrs MeshVS_DMF_HilightPrs ~~~~~ *MeshVS_DMF_User* is a user-defined mode. These values will be used by the presentation builder. There is also a set of selection modes flags that can be grouped in a combination of bits: * *MeshVS_SMF_0D* * *MeshVS_SMF_Link* * *MeshVS_SMF_Face* * *MeshVS_SMF_Volume* * *MeshVS_SMF_Element* - groups *0D, Link, Face* and *Volume* as a bit mask ; * *MeshVS_SMF_Node* * *MeshVS_SMF_All* - groups *Element* and *Node* as a bit mask; * *MeshVS_SMF_Mesh* * *MeshVS_SMF_Group* Such an object, for example, can be used for displaying the object and stored in the STL file format: ~~~~~ // read the data and create a data source Handle (StlMesh_Mesh) aSTLMesh = RWStl::ReadFile (aFileName); Handle (XSDRAWSTLVRML_DataSource) aDataSource = new XSDRAWSTLVRML_DataSource (aSTLMesh); // create mesh Handle (MeshVS_Mesh) aMesh = new MeshVS(); aMesh-SetDataSource (aDataSource); // use default presentation builder Handle (MeshVS_MeshPrsBuilder) aBuilder = new MeshVS_MeshPrsBuilder (aMesh); aMesh-AddBuilder (aBuilder, Standard_True); ~~~~~ *MeshVS_NodalColorPrsBuilder* allows representing a mesh with a color scaled texture mapped on it. To do this you should define a color map for the color scale, pass this map to the presentation builder, and define an appropriate value in the range of 0.0 – 1.0 for every node. The following example demonstrates how you can do this (check if the view has been set up to display textures): ~~~~~ // assign nodal builder to the mesh Handle (MeshVS_NodalColorPrsBuilder) aBuilder = new MeshVS_NodalColorPrsBuilder     (aMesh,MeshVS_DMF_NodalColorDataPrs | MeshVS_DMF_OCCMask); aBuilder-UseTexture (Standard_True); // prepare color map Aspect_SequenceOfColor aColorMap; aColorMap.Append ((Quantity_NameOfColor) Quantity_NOC_RED); aColorMap.Append ((Quantity_NameOfColor) Quantity_NOC_BLUE1); // assign color scale map values (0..1) to nodes TColStd_DataMapOfIntegerReal aScaleMap; … // iterate through the nodes and add an node id and an appropriate value to the map aScaleMap.Bind (anId, aValue);   // pass color map and color scale values to the builder aBuilder-SetColorMap (aColorMap); aBuilder-SetInvalidColor (Quantity_NOC_BLACK); aBuilder-SetTextureCoords (aScaleMap); aMesh-AddBuilder (aBuilder, Standard_True); ~~~~~ @subsection occt_visu_3_6 Dynamic Selection The idea of dynamic selection is to represent the entities, which you want to select by a bounding box in the actual 2D space of the selection view. The set of these zones is ordered by a powerful sorting algorithm. To then find the applicative entities actually detected at this position, all you have to do is read which rectangles are touched at mouse position (X,Y) of the view, and judiciously reject some of the entities which have provided these rectangles. @subsubsection occt_visu_3_6_1 How to go from the objects to 2D boxes An intermediary stage consists in representing what you can make selectable by means of sensitive primitives and owners, entities of a high enough level to be known by the selector mechanisms. The sensitive primitive is capable of: * giving a 2D bounding box to the selector. * answering the rejection criteria positively or negatively by a "Matches" function. * being projected from 3D in the 2D space of the view if need be. * returning the owner which it will represent in terms of selection. A set of standard sensitive primitives exists in Select3D packages for 3D primitives. The owner is the entity, which makes it possible to link the sensitive primitives and the objects that you really wanted to detect. It stocks the diverse information, which makes it possible to find objects. An owner has a priority (*5* by default), which you can change to make one entity more selectable than another. @image html visualization_image021.png @image latex visualization_image021.png @subsubsection occt_visu_3_6_2 Implementation in an interactive/selectable object Define the number of selection modes possible, i.e. what you want to identify by activating each of the selection modes. For example: for an interactive object representing a topological shape: * mode 0: selection of the interactive object itself; * mode 1: selection of the vertices; * mode 2: selection of the edges; * mode 3: selection of the wires; * mode 4: selection of the detectable faces. For each selection mode of an interactive object, "model" is the set of entities, which you want to locate by these primitives and these owners. There is an "owner" root class, *SelectMgr_EntityOwner*, containing a reference to a selectable object, which has created it. If you want to stock its information, you have to create classes derived from this root class. Example: for shapes, there is the *StdSelect_BRepOwner* class, which can save a *TopoDS* shape as a field as well as the Interactive Object. The set of sensitive primitives which has been calculated for a given mode is stocked in *SelectMgr_Selection*. For an Interactive object, the modeling is done in the *ComputeSelection* virtual function. Let us consider an example of an interactive object representing a box. We are interested in two location modes: * mode 0: location of the whole box. * mode 1: location of the edges on the box. For the first mode, all sensitive primitives will have the same owner, which will represent the interactive object. In the second case, we have to create an owner for each edge, and this owner will have to contain the index for the edge, which it represents. You will create a class of owner, which derives from *SelectMgr_EntityOwner*. The *ComputeSelection* function for the interactive box can have the following form: ~~~~~ void InteractiveBox::ComputeSelection (const Handle(SelectMgr_Selection)& Sel,  const Standard_Integer Mode) { switch(Mode) { case 0: //locating the whole box by making its faces sensitive... { Handle(SelectMgr_EntityOwner) Ownr = new SelectMgr_EntityOwner(this,5); for(Standard_Integer I=1;I=Nbfaces;I++) { //Array is a TColgp_Array1OfPnt: which represents the array of vertices. Sensitivity is Select3D_TypeOfSensitivity value Sel-Add(new Select3D_SensitiveFace(Ownr,Array,Sensitivity)); } break;    }   case 1: // locates the edges { for(Standard_Integer i=1;i=12;i++) { // 1 owner per edge... Handle(mypk_EdgeOwner) Ownr = new mypk_EdgeOwner(this,i,6); //6-priority Sel-Add(new Select3D_SensitiveSegment (Ownr,firstpt(i),lastpt(i))); } break; } } } ~~~~~ Selectable objects are loaded in the selection manager, which has one or more selectors; in general, we suggest assigning one selector per viewer. All you have to do afterwards is to activate or deactivate the different selection modes for selectable objects. The *SelectionManager* looks after the call to the *ComputeSelection* functions for different objects. NOTE: This procedure is completely hidden if you use the AIS Interactive Context

Example

~~~~~ //We have several " interactive boxes " box1, box2, box3; Handle(SelectMgr_SelectionManager) SM = new SelectMgr_SelectionManager(); Handle(StdSelect_ViewerSelector3d) VS = new StdSelect_ViewerSelector3d(); SM-Add(VS); SM-Load(box1);SM-Load(box2);SM-Load(box3); // box load. SM-Activate(box1,0,VS); // activates mode 0 of box 1 in the selector VS SM-Activate(box1,1,VS); M-Activate(box3,1,VS); VS-Pick(xpix,ypix,vue3d) // detection of primitives by mouse position. Handle(EntityOwner) POwnr = VS-OnePicked(); // picking of the "best" owner detected for(VS-Init();VS-More();VS-Next()) { VS-Picked(); // picking of all owners detected   } SM-Deactivate(box1); // deactivate all active modes of box1 ~~~~~ @section occt_visu_4 3D Presentations @subsection occt_visu_4_1 Glossary of 3D terms * **Anti-aliasing** This mode attempts to improve the screen resolution by drawing lines and curves in a mixture of colors so that to the human eye the line or curve is smooth. The quality of the result is linked to the quality of the algorithm used by the workstation hardware. * **Depth-cueing** Reduces the color intensity for the portion of an object further away from the eye to give the impression of depth. This is used for wireframe objects. Shaded objects do not require this. * **Group** - a set of primitives and attributes on those primitives. Primitives and attributes may be added to a group but cannot be removed from a group, except by erasing them globally. A group can have a pick identity. * **Light** There are five kinds of light source - ambient, headlight, directional, positional and spot. The light is only activated in a shading context in a view. * **Primitive** - a drawable element. It has a definition in 3D space. Primitives can either be lines, faces, text, or markers. Once displayed markers and text remain the same size. Lines and faces can be modified e.g. zoomed. Primitives must be stored in a group. * **Structure** - manages a set of groups. The groups are mutually exclusive. A structure can be edited, adding or removing groups. A structure can reference other structures to form a hierarchy. It has a default (identity) transformation and other transformations may be applied to it (rotation, translation, scale, etc). It has no default attributes for the primitive lines, faces, markers, and text. Attributes may be set in a structure but they are overridden by the attributes in each group. Each structure has a display priority associated with it, which rules the order in which it is redrawn in a 3D viewer. If the visualization mode is incompatible with the view it is not displayed in that view, e.g. a shading-only object is not visualized in a wireframe view. * **View** - is defined by a view orientation, a view mapping, and a context view. * **Viewer** - manages a set of views. * **View orientation** - defines the manner in which the observer looks at the scene in terms of View Reference Coordinates. * **View mapping** - defines the transformation from View Reference Coordinates to the Normalized Projection Coordinates. This follows the Phigs scheme. * **Z-Buffering** -= a form of hidden surface removal in shading mode only. This is always active for a view in the shading mode. It cannot be suppressed. @subsection occt_visu_4_2 Creating a 3D scene To create 3D graphic objects and display them on the screen, follow the procedure below: 1. Create attributes. 2. Create a 3D viewer.. 3. Create a view. 4. Create an interactive context. 5. Create interactive objects. 6. Create primitives in the interactive object 7. Display the interactive object. @subsubsection occt_visu_4_2_1 Create attributes Create colors. ~~~~~ Quantity_Color Black (Quantity_NOC_BLACK); Quantity_Color Blue (Quantity_NOC_MATRABLUE); Quantity_Color Brown (Quantity_NOC_BROWN4); Quantity_Color Firebrick (Quantity_NOC_FIREBRICK); Quantity_Color Forest (Quantity_NOC_FORESTGREEN); Quantity_Color Gray (Quantity_NOC_GRAY70); Quantity_Color MyColor (0.99, 0.65, 0.31, Quantity_TOC_RGB); Quantity_Color Beet (Quantity_NOC_BEET); Quantity_Color White (Quantity_NOC_WHITE); ~~~~~ Create line attributes. ~~~~~ Handle(Graphic3d_AspectLine3d) CTXLBROWN = new Graphic3d_AspectLine3d (); Handle(Graphic3d_AspectLine3d) CTXLBLUE = new Graphic3d_AspectLine3d (); Handle(Graphic3d_AspectLine3d) CTXLWHITE = new Graphic3d_AspectLine3d(); CTXLBROWN-SetColor (Brown); CTXLBLUE-SetColor (Blue); CTXLWHITE-SetColor (White); ~~~~~ Create marker attributes. ~~~~~ Handle(Graphic3d_AspectMarker3d) CTXMFIREBRICK = new Graphic3d_AspectMarker3d(); CTXMFIREBRICK-SetColor (Firebrick); CTXMFIREBRICK-SetScale (1.0); CTXMFIREBRICK-SetType (Aspect_TOM_BALL); ~~~~~ Create facet attributes. ~~~~~ Handle(Graphic3d_AspectFillArea3d) CTXF = new Graphic3d_AspectFillArea3d (); Graphic3d_MaterialAspect BrassMaterial (Graphic3d_NOM_BRASS); Graphic3d_MaterialAspect GoldMaterial (Graphic3d_NOM_GOLD); CTXF-SetInteriorStyle (Aspect_IS_SOLID); CTXF-SetInteriorColor (MyColor); CTXF-SetDistinguishOn (); CTXF-SetFrontMaterial (GoldMaterial); CTXF-SetBackMaterial (BrassMaterial); CTXF-SetEdgeOn (); ~~~~~ Create text attributes. ~~~~~ Handle(Graphic3d_AspectText3d) CTXT = new Graphic3d_AspectText3d (Forest, Graphic3d_NOF_ASCII_MONO, 1., 0.); ~~~~~ @subsubsection occt_visu_4_2_2 Create a 3D Viewer (a Windows example) ~~~~~ Handle(Aspect_DisplayConnection) aDisplayConnection; Handle(Graphic3d_GraphicDriver) aGraphicDriver = Graphic3d::InitGraphicDriver (aDisplayConnection); TCollection_ExtendedString aName("3DV"); myViewer = new V3d_Viewer (aGraphicDriver,aName.ToExtString (), ""); myViewer - SetDefaultLights (); myViewer - SetLightOn (); ~~~~~ @subsubsection occt_visu_4_2_3 Create a 3D view (a Windows example) It is assumed that a valid Windows window may already be accessed via the method *GetSafeHwnd()*. ~~~~~ Handle (WNT_Window) aWNTWindow; aWNTWindow = new WNT_Window (GetSafeHwnd()); myView = myViewer -> CreateView(); myView -> SetWindow (a WNTWindow); ~~~~~ @subsubsection occt_visu_4_2_4 Create an interactive context ~~~~~ myAISContext = new AIS_InteractiveContext (myViewer); ~~~~~ You are now able to display interactive objects such as an *AIS_Shape*. ~~~~~ TopoDS_Shape aShape = BRepAPI_MakeBox(10,20,30)_Solid(); Handle (AIS_Shape) aAISShape = new AIS_Shape(aShape); myAISContext - Display (aAISShape); ~~~~~ @subsubsection occt_visu_4_2_5 Create your own interactive object Follow the procedure below to compute the presentable object: 1. Build a presentable object inheriting from *AIS_InteractiveObject* (refer to the Chapter on Presentable Objects). 2. Reuse the *Prs3d_Presentation* provided as an argument of the compute methods. **Note** that there are two compute methods: one for a standard representation, and the other for a degenerated representation, i.e. in hidden line removal and wireframe modes. Let us look at the example of compute methods ~~~~~ Void myPresentableObject::Compute (const Handle(PrsMgr_PresentationManager3d)& aPresentationManager, const Handle(Prs3d_Presentation)& aPrs, const Standard_Integer aMode) ( //... ) void myPresentableObject::Compute (const Handle(Prs3d_Projector)&, const Handle(Prs3d_Presentation)& aPrs) ( //... ) ~~~~~ @subsubsection occt_visu_4_2_6 Create primitives in the interactive object Get the group used in *Prs3d_Presentation*. ~~~~~ Handle(Graphic3d_Group) TheGroup = Prs3d_Root::CurrentGroup(aPrs); ~~~~~ Update the group attributes. ~~~~~ TheGroup - SetPrimitivesAspect(CTXLBLUE); ~~~~~ Create two triangles in *TheGroup*. ~~~~~ Standard_Integer aNbTria = 2; Handle(Graphic3d_ArrayOfTriangles) aTriangles = new Graphic3d_ArrayOfTriangles(3 * aNbTria, 0, Standard_True); Standard_Integer anIndex; for (anIndex = 1; anIndex = aNbTria; nt++) {   aTriangles-AddVertex(anIndex * 5., 0., 0., 1., 1., 1.);   aTriangles-AddVertex(anIndex * 5 + 5, 0., 0., 1., 1., 1.);   aTriangles-AddVertex(anIndex * 5 + 2.5, 5., 0., 1., 1., 1.); } TheGroup-BeginPrimitives (); mygroup-AddPrimitiveArray(aTriangles); TheGroup-EndPrimitives (); ~~~~~ The *BeginPrimitives()* and *EndPrimitives()* methods are used when creating a set of various primitives in the same group. Use the polyline function to create a boundary box for the *Struct* structure in group *TheGroup*. ~~~~~ Standard_Real Xm, Ym, Zm, XM, YM, ZM; Struct-MinMaxValues (Xm, Ym, Zm, XM, YM, ZM); Handle(Graphic3d_ArrayOfPolylines) aPolylines = new Graphic3d_ArrayOfPolylines(16, 4); aPolylines-AddBound (4); aPolylines-AddVertex (Xm, Ym, Zm); aPolylines-AddVertex (Xm, Ym, ZM); aPolylines-AddVertex (Xm, YM, ZM); aPolylines-AddVertex (Xm, YM, Zm); aPolylines-AddBound (4); aPolylines-AddVertex (Xm, Ym, Zm); aPolylines-AddVertex (XM, Ym, Zm); aPolylines-AddVertex (XM, Ym, ZM); aPolylines-AddVertex (XM, YM, ZM); aPolylines-AddBound (4); aPolylines-AddVertex (XM, YM, Zm); aPolylines-AddVertex (XM, Ym, Zm); aPolylines-AddVertex (XM, YM, Zm); aPolylines-AddVertex (Xm, YM, Zm); aPolylines-AddBound (4); aPolylines-AddVertex (Xm, YM, ZM); aPolylines-AddVertex (XM, YM, ZM); aPolylines-AddVertex (XM, Ym, ZM); aPolylines-AddVertex (Xm, Ym, ZM); TheGroup-BeginPrimitives (); TheGroup-AddPrimitiveArray(aPolylines); TheGroup-EndPrimitives (); ~~~~~ Create text and markers in group *TheGroup*. ~~~~~ static char *texte[3] = {  "Application title", "My company", "My company address." }; Graphic3d_Array1OfVertex Tpts8 (0, 1); Tpts8(0).SetCoord (-40.0, -40.0, -40.0); Tpts8(1).SetCoord (40.0, 40.0, 40.0); TheGroup-MarkerSet (Tpts8); Graphic3d_Vertex Marker (0.0, 0.0, 0.0); for (i=0; i=2; i++) {   Marker.SetCoord (-(Standard_Real)i*4 + 30,                     (Standard_Real)i*4,                    -(Standard_Real)i*4);   TheGroup-Text (texte[i], Marker, 20.); } ~~~~~ @section occt_visu_5 3D Resources The 3D resources include the *Graphic3d* and *V3d* packages. @subsection occt_visu_5_1 Graphic3D Package @subsubsection occt_visu_5_1_1 Overview The *Graphic3d* package is used to create 3D graphic objects in a 3D viewer. These objects called **structures** are made up of groups of primitives and attributes. A group is the smallest editable element of a structure. A transformation can be applied to a structure. Structures can be connected to form a tree of structures, composed by transformations. Structures are globally manipulated by the viewer. @subsubsection occt_visu_5_1_2 Provided services Graphic structures can be: * Displayed, * Highlighted, * Erased, * Transformed, * Connected to form a tree. There are classes for: * Visual attributes for lines, faces, markers, text, materials, * Vectors and vertices, * Graphic objects, groups, and structures. @subsubsection occt_visu_5_1_3 About the primitives * **Markers** * Have one or more vertices, * Have a type, a scale factor, and a color, * Have a size, shape, and orientation independent of transformations. * **Polygons** * Have one closed boundary, * Have at least three vertices, * Are planar and have a normal, * Have interior attributes - style, color, front and back material, texture and reflection ratio, * Have a boundary with the following attributes - type, width scale factor, color. The boundary is only drawn when the interior style is hollow. * **Polygons with holes** * Have multiple closed boundaries, each one with at least three vertices, * Are planar and have a normal, * Have interior attributes - style, color, front and back material, * Have a boundary with the following attributes - type, width scale factor, color. The boundary is only drawn when the interior style is hollow. * **Polylines** * Have two or more vertices, * Have the following attributes - type, width scale factor, color. * **Text** * Has geometric and non-geometric attributes, * Geometric attributes - character height, character up vector, text path, horizontal and vertical alignment, orientation, three-dimensional position, zoomable flag * Non-geometric attributes - text font, character spacing, character expansion factor, color. @subsubsection occt_visu_5_1_4 Primitive arrays Primitive arrays are a more efficient approach to describe and display the primitives from the aspects of memory usage and graphical performance. The key feature of the primitive arrays is that the primitive data is not duplicated. For example, two polygons could share the same vertices, so it is more efficient to keep the vertices in a single array and specify the polygon vertices with indices of this array. In addition to such kind of memory savings, the OpenGl graphics driver provides the Vertex Buffer Objects (VBO). VBO is a sort of video memory storage that can be allocated to hold the primitive arrays, thus making the display operations more efficient and releasing the RAM memory. The Vertex Buffer Objects are enabled by default, but VBOs availability depends on the implementation of OpenGl. If the VBOs are unavailable or there is not enough video memory to store the primitive arrays, the RAM memory will be used to store the arrays. The Vertex Buffer Objects can be disabled at the application level. You can use the method *Graphic3d_GraphicDriver::EnableVBO (const Standard_Boolean status)* to enable/disable VBOs: The following example shows how to disable the VBO support: ~~~~~ *// get the graphic driver* Handle (Graphic3d_GraphicDriver) aDriver =   myAISContext-CurrentViewer()-Driver(); *// disable VBO support* aDriver-EnableVBO (Standard_False); ~~~~~ **Note** that the use of Vertex Buffer Objects requires the application level primitive data provided by the *Graphic3d_ArrayOfPrimitives* to be transferred to the video memory. *TKOpenGl* transfers the data and releases the *Graphic3d_ArrayOfPrimitives* internal pointers to the primitive data. Thus it might be necessary to pay attention to such kind of behaviour, as the pointers could be modified (nullified) by the *TKOpenGl*. The different types of primitives could be presented with the following primitive arrays: * *Graphic3d_ArrayOfPoints,* * *Graphic3d_ArrayOfPolygons,* * *Graphic3d_ArrayOfPolylines,* * *Graphic3d_ArrayOfQuadrangles,* * *Graphic3d_ArrayOfQuadrangleStrips,* * *Graphic3d_ArrayOfSegments,* * *Graphic3d_ArrayOfTriangleFans,* * *Graphic3d_ArrayOfTriangles,* * *Graphic3d_ArrayOfTriangleStrips.* The *Graphic3d_ArrayOfPrimitives* is a base class for these primitive arrays. Method *Graphic3d_ArrayOfPrimitives::AddVertex* allows adding There is a set of similar methods to add vertices to the primitive array. These methods take vertex coordinates as an argument and allow you to define the color, the normal and the texture coordinates assigned to the vertex. The return value is the actual number of vertices in the array. You can also modify the values assigned to the vertex or query these values by the vertex index: * *void Graphic3d_ArrayOfPrimitives::SetVertice* * *void Graphic3d_ArrayOfPrimitives::SetVertexColor* * *void Graphic3d_ArrayOfPrimitives::SetVertexNormal* * *void Graphic3d_ArrayOfPrimitives::SetVertexTexel* * *gp_Pnt Graphic3d_ArrayOfPrimitives::Vertices* * *gp_Dir  Graphic3d_ArrayOfPrimitives::VertexNormal* * *gp_Pnt3d Graphic3d_ArrayOfPrimitives::VertexTexel* * *Quantity_Color Graphic3d_ArrayOfPrimitives::VertexColor* * *void Graphic3d_ArrayOfPrimitives::Vertices* * *void Graphic3d_ArrayOfPrimitives::VertexNormal* * *void Graphic3d_ArrayOfPrimitives::VertexTexel* * *void Graphic3d_ArrayOfPrimitives::VertexColor* The following example shows how to define an array of points: ~~~~~ // create an array Handle (Graphic3d_ArrayOfPoints) anArray = new Graphic3d_ArrayOfPoints (aVerticiesMaxCount); // add vertices to the array anArray-AddVertex (10.0, 10.0, 10.0); anArray-AddVertex (0.0, 10.0, 10.0); // add the array to the structure Handle (Graphic3d_Group) aGroup = Prs3d_Root::CurrentGroup (aPrs); aGroup-BeginPrimitives (); aGroup-AddPrimitiveArray (anArray); aGroup-EndPrimitives (); ~~~~~ If the primitives share the same vertices (polygons, triangles, etc.) then you can define them as indices of the vertices array. The method *Graphic3d_ArrayOfPrimitives::AddEdge* allows defining the primitives by indices. This method adds an "edge" in the range [1, VertexNumber() ] in the array. It is also possible to query the vertex defined by an edge using method *Graphic3d_ArrayOfPrimitives::Edge* The following example shows how to define an array of triangles: ~~~~~ // create an array Standard_Boolean IsNormals     = Standard_False; Standard_Boolean IsColors      = Standard_False; Standard_Boolean IsTextureCrds = Standard_False; Handle (Graphic3d_ArrayOfTriangles) anArray =           new Graphic3d_ArrayOfTriangles (aVerticesMaxCount,                                           aEdgesMaxCount,                                           IsNormals,                                           IsColors,                                           IsTextureCrds); // add vertices to the array anArray-AddVertex (-1.0, 0.0, 0.0);   // vertex 1 anArray-AddVertex ( 1.0, 0.0, 0.0);   // vertex 2 anArray-AddVertex ( 0.0, 1.0, 0.0);   // vertex 3 anArray-AddVertex ( 0.0,-1.0, 0.0);   // vertex 4 // add edges to the array anArray-AddEdge (1);  // first triangle anArray-AddEdge (2); anArray-AddEdge (3); anArray-AddEdge (1);  // second triangle anArray-AddEdge (2); anArray-AddEdge (4); // add the array to the structure Handle (Graphic3d_Group) aGroup = Prs3d_Root::CurrentGroup (aPrs); aGroup-BeginPrimitives (); aGroup-AddPrimitiveArray (anArray); aGroup-EndPrimitives (); ~~~~~ If the primitive array presents primitives built from sequential sets of vertices, for example polygons, then you can specify the bounds, or the number of vertices for each primitive. You can use the method *Graphic3d_ArrayOfPrimitives::AddBound* to define the bounds and the color for each bound. This method returns the actual number of bounds. It is also possible to set the color and query the number of edges in the bound and bound color. ~~~~~ Standard_Integer Graphic3d_ArrayOfPrimitives::Bound Quantity_Color Graphic3d_ArrayOfPrimitives::BoundColor void Graphic3d_ArrayOfPrimitives::BoundColor ~~~~~ The following example shows how to define an array of polygons: ~~~~~ // create an array Standard_Boolean IsNormals      = Standard_False; Standard_Boolean IsVertexColors = Standard_False; Standard_Boolean IsFaceColors   = Standard_False; Standard_Boolean IsTextureCrds  = Standard_False; Handle (Graphic3d_ArrayOfPolygons) anArray =           new Graphic3d_ArrayOfPolygons (aVerticesMaxCount,                                          aBoundsMaxCount,                                          aEdgesMaxCount,                                          IsNormals,                                          IsVertexColors,                                          IsFaceColors,                                          IsTextureCrds); // add bounds to the array, first polygon anArray-AddBound (3); anArray-AddVertex (-1.0, 0.0, 0.0);   anArray-AddVertex ( 1.0, 0.0, 0.0);   anArray-AddVertex ( 0.0, 1.0, 0.0);   // add bounds to the array, second polygon anArray-AddBound (4); anArray-AddVertex (-1.0, 0.0, 0.0);   anArray-AddVertex ( 1.0, 0.0, 0.0);   anArray-AddVertex ( 1.0,-1.0, 0.0);   anArray-AddVertex (-1.0,-1.0, 0.0);   // add the array to the structure Handle (Graphic3d_Group) aGroup = Prs3d_Root::CurrentGroup (aPrs); aGroup-BeginPrimitives (); aGroup-AddPrimitiveArray (anArray); aGroup-EndPrimitives (); ~~~~~ There are also several helper methods. You can get the type of the primitive array: ~~~~~ Graphic3d_TypeOfPrimitiveArray Graphic3d_ArrayOfPrimitives::Type Standard_CString Graphic3d_ArrayOfPrimitives::StringType ~~~~~ and check if the primitive array provides normals, vertex colors and vertex texels (texture coordinates): ~~~~~ Standard_Boolean Graphic3d_ArrayOfPrimitives::HasVertexNormals Standard_Boolean Graphic3d_ArrayOfPrimitives::HasVertexColors Standard_Boolean Graphic3d_ArrayOfPrimitives::HasVertexTexels ~~~~~ or get the number of vertices, edges and bounds: ~~~~~ Standard_Integer Graphic3d_ArrayOfPrimitives::VertexNumber Standard_Integer Graphic3d_ArrayOfPrimitives::EdgeNumber Standard_Integer Graphic3d_ArrayOfPrimitives::BoundNumber ~~~~~ @subsubsection occt_visu_5_1_5 Materials A *material* is defined by : * Transparency, * Diffuse reflection - a component of the object color; * Ambient reflection; * Specular reflection - a component of the color of the light source. The following items are required to determine the three colors of reflection: * Color, * Coefficient of diffuse reflection, * Coefficient of ambient reflection, * Coefficient of specular reflection. @subsubsection occt_visu_5_1_6 Textures A *texture* is defined by a name. Three types of texture are available: * 1D, * 2D, * Environment mapping. @subsubsection occt_visu_5_1_7 Graphic3d text The OpenGl graphics driver uses advanced text rendering powered by FTGL library. This library provides vector text rendering, as a result the text can be rotated and zoomed without quality loss. *Graphic3d* text primitives have the following features: * fixed size (non-zoomable) or zoomable, * can be rotated to any angle in the view plane, * support unicode charset. The text attributes for the group could be defined with the *Graphic3d_AspectText3d* attributes group. To add any text to the graphic structure you can use the following methods: ~~~~~ void Graphic3d_Group::Text (const Standard_CString AText,  const Graphic3d_Vertex& APoint,  const Standard_Real AHeight,  const Quantity_PlaneAngle AAngle,  const Graphic3d_TextPath ATp,  const Graphic3d_HorizontalTextAlignment AHta,  const Graphic3d_VerticalTextAlignment AVta,  const Standard_Boolean EvalMinMax), ~~~~~ *AText* parameter is the text string, *APoint* is the three-dimensional position of the text, *AHeight* is the text height, *AAngle* is the orientation of the text (at the moment, this parameter has no effect, but you can specify the text orientation through the *Graphic3d_AspectText3d* attributes). *ATp* parameter defines the text path, *AHta* is the horizontal alignment of the text, *AVta* is the vertical alignment of the text. You can pass *Standard_False* as *EvalMinMax* if you don’t want the graphic3d structure boundaries to be affected by the text position. **Note** that the text orientation angle can be defined by *Graphic3d_AspectText3d* attributes. ~~~~~ void Graphic3d_Group::Text (const Standard_CString AText,  const Graphic3d_Vertex& APoint,  const Standard_Real AHeight,  const Standard_Boolean EvalMinMax) void Graphic3d_Group::Text (const TCcollection_ExtendedString &AText, const Graphic3d_Vertex& APoint,  const Standard_Real AHeight,  const Quantity_PlaneAngle AAngle,  const Graphic3d_TextPath ATp,  const Graphic3d_HorizontalTextAlignment AHta,  const Graphic3d_VerticalTextAlignment AVta,  const Standard_Boolean EvalMinMax) void Graphic3d_Group::Text (const TCcollection_ExtendedString &AText,  const Graphic3d_Vertex& APoint,  const Standard_Real AHeight,  const Standard_Boolean EvalMinMax) ~~~~~ See the example: ~~~~~ // get the group Handle (Graphic3d_Group) aGroup = Prs3d_Root::CurrentGroup (aPrs); // change the text aspect Handle(Graphic3d_AspectText3d) aTextAspect = new Graphic3d_AspectText3d (); aTextAspect-SetTextZoomable (Standard_True); aTextAspect-SetTextAngle (45.0); aGroup-SetPrimitivesAspect (aTextAspect); // add a text primitive to the structure Graphic3d_Vertex aPoint (1, 1, 1); aGroup-Text (Standard_CString ("Text"), aPoint, 16.0); ~~~~~ @subsubsection occt_visu_5_1_8 Display priorities Structure display priorities control the order in which structures are drawn. When you display a structure you specify its priority. The lower the value, the lower the display priority. When the display is regenerated the structures with the lowest priority are drawn first. For structures with the same display priority the order in which they were displayed determines the drawing order. OCCT supports eleven structure display priorities. @subsubsection occt_visu_5_1_9 About structure hierarchies The root is the top of a structure hierarchy or structure network. The attributes of a parent structure are passed to its descendants. The attributes of the descendant structures do not affect the parent. Recursive structure networks are not supported. @subsection occt_visu_5_2 V3d Package @subsubsection occt_visu_5_2_1 Overview The *V3d* package provides the resources to define a 3D viewer and the views attached to this viewer (orthographic, perspective). This package provides the commands to manipulate the graphic scene of any 3D object visualized in a view on screen. A set of high-level commands allows the separate manipulation of parameters and the result of a projection (Rotations, Zoom, Panning, etc.) as well as the visualization attributes (Mode, Lighting, Clipping, Depth-cueing, etc.) in any particular view. @subsubsection occt_visu_5_2_2 Provided services The *V3d* package is basically a set of tools directed by commands from the viewer front-end. This tool set contains methods for creating and editing classes of the viewer such as: * Default parameters of the viewer, * Views (orthographic, perspective), * Lighting (positional, directional, ambient, spot, headlight), * Clipping planes (note that only Z-clipping planes can work with the Phigs interface), * Instantiated sequences of views, planes, light sources, graphic structures, and picks, * Various package methods. @subsubsection occt_visu_5_2_3 A programming example This sample TEST program for the *V3d* Package uses primary packages *Xw* and *Graphic3d* and secondary packages *Visual3d, Aspect, Quantity, Phigs* and *math*. ~~~~~ //Create a default display connection Handle(Aspect_DisplayConnection) aDisplayConnection = new Aspect_DisplayConnection(); //Create a Graphic Driver from the default *Aspect_DisplayConnection* Handle(Graphic3d_GraphicDriver) GD = Graphic3d::InitGraphicDriver (aDisplayConnection); //Create a Viewer to this Driver Handle(V3d_Viewer) VM = new V3d_Viewer(GD, 400., // Space size V3d_Xpos,// Default projection Quantity_NOC_DARKVIOLET, // Default background V3d_ZBUFFER, // Type of visualization V3d_GOURAUD, // Shading model V3d_WAIT); // Update mode *// Create a structure in this Viewer * Handle(Graphic3d_Structure) S = new Graphic3d_Structure(VM-Viewer()) ; *// Type of structure * S-SetVisual (Graphic3d_TOS_SHADING); *// Create a group of primitives in this structure* Handle(Graphic3d_Group) G = new Graphic3d_Group(S) ; *// Fill this group with one polygon of size 100* Graphic3d_Array1OfVertex Points(0,3) ; Points(0).SetCoord(-100./2.,-100./2.,-100./2.) ; Points(1).SetCoord(-100./2., 100./2.,-100./2.) ; Points(2).SetCoord( 100./2., 100./2.,-100./2.) ; Points(3).SetCoord( 100./2.,-100./2.,-100./2.) ; Normal.SetCoord(0.,0.,1.) ; G-Polygon(Points,Normal) ; *// Create Ambient and Infinite Lights in this Viewer* Handle(V3d_AmbientLight) L1 = new V3d_AmbientLight (VM,Quantity_NOC_GRAY50) ; Handle(V3d_DirectionalLight) L2 = new V3d_DirectionalLight (VM,V3d_XnegYnegZneg,Quantity_NOC_WHITE) ; *// Create a 3D quality Window with the same DisplayConnection* Handle(Xw_Window) W = new Xw_Window(aDisplayConnection,"Test V3d",0.5,0.5,0.5,0.5) ; *// Map this Window to this screen*  W-Map() ; *// Create a Perspective View in this Viewer* Handle(V3d_PerspectiveView) V = new V3d_PerspectiveView(VM); *// Set the Eye position* V-SetEye(100.,100.,100.) ; *// Associate this View with the Window * V-SetWindow(W) ; *// Activate ALL defined Lights in this View * V-SetLightOn() ; *// Display ALL structures in this View * (VM-Viewer())-Display() ; *// Finally update the Visualization in this View * V-Update() ; ~~~~~ @subsubsection occt_visu_5_2_4 Glossary of view transformations The following terms are used to define view orientation, i.e. transformation from World Coordinates (WC) to the View Reference Coordinates system (VRC): * **View Reference Point (VRP)** - defines the origin of View Reference Coordinates. * **View Reference Plane Normal (VPN)** - defines the normal of projection plane of the view. * **View Reference Up Vector (VUP)** - defines the vertical of observer of the view. The following terms are used to define view mapping, i.e. transformation from View Reference Coordinates (VRC) to the Normalized Projection Coordinates (NPC): * **Projection type** - Orthographic or perspective. * **Projection Reference Point (PRP)** - Defines the observer position. * **Front Plane Distance (FPD)** - Defines the position of the front clipping plane in View Reference Coordinates system. * **Back Plane Distance (BPD)** Defines the position of the back clipping plane in View Reference Coordinates system. * **View Plane Distance (VPD)** Defines the position of the view projection plane in View Reference Coordinates system. View plane must be located between front and back clipping planes. * **Window Limits** Defines the visible part of the view projection plane (left, right, top and bottom boundaries: *Umin, Umax, Vmax* and *Vmin* respectively) in View Reference Coordinates. The *V3d_View* API uses the following terms to define view orientation and mapping: * **At** - Position of View Reference Point (VRP) in World Coordinates * **Eye** - Position of the observer (projection reference point) in World Coordinates. Influences to the view projection vector and depth value. * **Proj** - View projection vector (VPN) * **Up** - Position of the high point / view up vector (VUP) * **Depth** - Distance between Eye and At point * **ZSize** - Distance between front and back clipping planes * **Size** - Window size in View Reference Coordinates * **Focal Reference point** - Position of Projection Reference Point (PRP) in World Coordinates * **Focale** - Distance between Projection Reference Point (PRP) and View projection plane @subsubsection occt_visu_5_2_5 Management of perspective projection The perspective projection allows definition of viewing volume as a truncated pyramid (frustum) with apex at the Projection Reference Point. In the View Reference Coordinate system it can be presented by the following picture: @image html visualization_image023.png "View Reference Coordinate System, perspective viewing volume and view mapping parameter" @image latex visualization_image023.png "View Reference Coordinate System, perspective viewing volume and view mapping parameter"   During panning, window limits are changed, as if a sort of "frame" through which the user sees a portion of the view plane was moved over the view. The perspective frustum itself remains unchanged. The perspective projection is defined by two parameters: * *Depth* value defines distance between Projection Reference Point and the nearest (front) clipping plane. * *ZSize* defines distance between Front and Back clipping planes. The influence of this parameter is caused by the OCCT specific to center viewing volume around View Reference Point so the front and back plane distances were the same: *FPD = BPD = ZSize / 2*. **Note** that the closer the displayed object to the Projection Reference Point the more visible its perspective distortion. Thus, in order to get a good perspective it is recommended to set **ZSize** value comparable with the expected model size and small Depth value. However, very small Depth values might lead to inaccuracy of "fit all" operation and to non-realistic perspective distortion. Let us see the example: ~~~~~ // Create a Perspective View in Viewer VM Handle(V3d_PerspectiveView) V = new V3d_PerspectiveView(VM); // Set the ZSize V-SetZSize(2000.) ; // Set the Depth value V-SetDepth(20.) ; // Set the current mapping as default to be used by Reset() operation V-SetViewMappingDefault() ; ~~~~~ As an alternative to manual setting of perspective parameters the *V3d_View::DepthFitAll* function can be used. ~~~~~ // Display  shape in Viewer VM Handle(AIS_InteractiveContext) aContext = new AIS_InteractiveContext(VM); aContext-Display(shape); // Create a Perspective View in Viewer VM Handle(V3d_PerspectiveView) V = new V3d_PerspectiveView(VM); // Set automatically the perspective parameters V-DepthFitAll() ; // Fit view to object size V-FitAll(); // Set the current mapping as default to be used by Reset() operation V-SetViewMappingDefault() ; ~~~~~ It is necessary to take into account that during rotation Z size of the view might be modified automatically to fit the model into the viewing volume. Make sure the Eye point never gets between the Front and Back clipping planes. In perspective view, changing Z size results in changed perspective effect. To avoid this, an application should specify the maximum expected Z size using *V3d_View::SetZSize()* method in advance. *V3d_View::FitAll()* with *FitZ = Standard_True* and *V3d_View::ZFitAll()* also change the perspective effect and should therefore be used with precautions similar to those for rotation. @subsubsection occt_visu_5_2_6 Underlay and overlay layers management In addition to interactive 3d graphics displayed in the view you can display an underlying and overlying graphics: text, color scales, drawings. All *V3d* view graphical objects in the overlay are managed by the default layer manager (*V3d_LayerMgr*). The *V3d* view has a basic layer manager capable of displaying the color scale, but you can redefine this class to provide your own overlay and underlay graphics. The method *V3d_View::SetLayerMgr(const Handle (V3d_LayerMgr)& aMgr)* allows assigning a custom layer manager to the *V3d* view. There are three virtual methods to prepare graphics in the manager for further drawing (set up layer dimensions, draw static graphics). These methods can be redefined: ~~~~~ void V3d_LayerMgr::Begin () void V3d_LayerMgr::Redraw () void V3d_LayerMgr::End () ~~~~~ The layer manager controls layers (*Visual3d_Layer*) and layer items (*Visual3d_LayerItem*). Both the overlay and underlay layers can be created by the layer manager. The layer entity is presented by the *Visual3d_Layer* class. This entity provides drawing services in the layer, for example: ~~~~~ void Visual3d_Layer::DrawText void Visual3d_Layer::DrawRectangle void Visual3d_Layer::SetColor void Visual3d_Layer::SetViewport ~~~~~ The following example demonstrates how to draw overlay graphics by the *V3d_LayerMgr*: ~~~~~ // redefined method of V3d_LayerMgr void MyLayerMgr::Redraw () {   Quantity_Color aRed (Quantity_NOC_RED);   myOverlayLayer-SetColor (aRed);   myOverlayLayer-DrawRectangle (0, 0, 100, 100); } ~~~~~ The layer contains layer items that will be displayed on view redraw. Such items are *Visual3d_LayerItem* entities. To manipulate *Visual3d_LayerItem* entities assigned to the layer’s internal list you can use the following methods: ~~~~~ void Visual3d_Layer::AddLayerItem (const Handle (Visual3d_LayerItem)& Item) void Visual3d_Layer::RemoveLayerItem (const Handle (Visual3d_LayerItem)& Item)  void Visual3d_Layer::RemoveAllLayerItems () const Visual3d_NListOfLayerItem& Visual3d_Layer::GetLayerItemList ()   ~~~~~ The layer’s items are rendered when the method *void Visual3d_Layer::RenderLayerItems()* is called by the graphical driver. The *Visual3d_LayerItem* has virtual methods that are used to render the item: ~~~~~ void Visual3d_LayerItem::RedrawLayerPrs () void Visual3d_LayerItem::ComputeLayerPrs () ~~~~~ The item presentation can be computed before drawing by the *ComputeLayerPrs* method to save time on redraw. It also has an additional flag that is used to tell that the presentation should be recomputed: ~~~~~ void Visual3d_LayerItem::SetNeedToRecompute (const Standard_Boolean NeedToRecompute) Standard_Boolean Visual3d_LayerItem::IsNeedToRecompute ~~~~~ An example of *Visual3d_LayerItem* is *V3d_ColorScaleLayerItem* that represents the color scale entity as the layer’s item. The *V3d_ColorScaleLayerItem* sends render requests to the color scale entity represented by it. As this entity (*V3d_ColorScale*) is assigned to the *V3d_LayerMgr* it uses its overlay layer’s services for drawing:

Example

~~~~~ // tell V3d_ColorScale to draw itself void V3d_ColorScaleLayerItem::RedrawLayerPrs () {   Visual3d_LayerItem::RedrawLayerPrs ()   if (!MyColorScale.IsNull ())     MyColorScale-DrawScale (); } // V3d_ColorScale has a reference to a LayerMgr void V3d_ColorScale::DrawScale () {     // calls *V3d_ColorScale::PaintRect, V3d_ColorScale::PaintText, etc … } // PaintRect method uses overlay layer of LayerMgr to draw a rectangle void V3d_ColorScale::PaintRect        (const Standard_Integer X, const Standard_Integer Y,         const Standard_Integer W, const Standard_Integer H,         const Quantity_Color aColor,         const Standard_Boolean aFilled) {   const Handle (Visual3d_Layer)& theLayer =                                  myLayerMgr-Overlay ();     …   theLayer-SetColor (aColor);   theLayer-DrawRectangle (X, Y, W, H);    … } ~~~~~ @subsubsection occt_visu_5_2_7 View background styles There are three types of background styles available for *V3d_view*: solid color, gradient color and image. To set solid color for the background you can use the following methods: ~~~~~ void V3d_View::SetBackgroundColor (const Quantity_TypeOfColor Type,  const Quantity_Parameter V1,  const Quantity_Parameter V2,  const Quantity_Parameter V3) ~~~~~ This method allows you to specify the background color in RGB (red, green, blue) or HLS (hue, lightness, saturation) color spaces, so the appropriate values of the Type parameter are *Quantity_TOC_RGB* and *Quantity_TOC_HLS*. **Note** that the color value parameters *V1,V2,V3* should be in the range between *0.0-1.0.* ~~~~~ void V3d_View::SetBackgroundColor(const Quantity_Color &Color) void V3d_View::SetBackgroundColor(const Quantity_NameOfColor Name) ~~~~~ The gradient background style could be set up with the following methods: ~~~~~ void V3d_View::SetBgGradientColors (const Quantity_Color& Color1,  const Quantity_Color& Color2,  const Aspect_GradientFillMethod FillStyle,  const Standard_Boolean update) void V3d_View::SetBgGradientColors (const Quantity_NameOfColor Color1,  const Quantity_NameOfColor Color2,  const Aspect_GradientFillMethod FillStyle,  const Standard_Boolean update) ~~~~~ The *Color1* and *Color2* parameters define the boundary colors of interpolation, the *FillStyle* parameter defines the direction of interpolation. You can pass *Standard_True* as the last parameter to update the view. The fill style can be also set with the method *void V3d_View::SetBgGradientStyle(const Aspect_GradientFillMethod AMethod, const Standard_Boolean update)*. To get the current background color you can use the following methods: ~~~~~ void V3d_View::BackgroundColor (const Quantity_TypeOfColor Type,  Quantity_Parameter &V1,  Quantity_Parameter &V2,  Quantity_Parameter &V3) Quantity_Color V3d_View::BackgroundColor() void V3d_View::GradientBackgroundColors(Quantity_Color& Color1, Quantity_Color& Color2) Aspect_GradientBackground GradientBackground() ~~~~~ To set the image as a background and change the background image style you can use the following methods: ~~~~~ * void V3d_View::SetBackgroundImage (const Standard_CString FileName,  const Aspect_FillMethod FillStyle,  const Standard_Boolean update) * void V3d_View::SetBgImageStyle (const Aspect_FillMethod FillStyle,  const Standard_Boolean update) ~~~~~ The *FileName* parameter defines the image file name and the path to it, the *FillStyle* parameter defines the method of filling the background with the image. The methods are: * *Aspect_FM_NONE* -  draws the image in the default position; * *Aspect_FM_CENTERED* - draws the image at the center of the view; * *Aspect_FM_TILED* tiles the view with the image; * *Aspect_FM_STRETCH* stretches the image over the view. @subsubsection occt_visu_5_2_8 User-defined clipping planes The ability to define custom clipping planes could be very useful for some tasks. The *V3d* view provides such an opportunity. The *V3d_Plane* class provides the services of clipping planes: it holds the plane equation coefficients and provides its graphical representation. To set and get plane equation coefficients you can use the following methods: ~~~~~ void V3d_Plane::SetPlane (const Quantity_Parameter A,  const Quantity_Parameter B,  const Quantity_Parameter C,  const Quantity_Parameter D) void V3d_Plane::Plane (Quantity_Parameter& A,  Quantity_Parameter& B,  Quantity_Parameter& C,  Quantity_Parameter& D) ~~~~~  *V3d_Plane* also provides display services: ~~~~~ * void V3d_Plane::Display (const Handle(V3d_View)& aView,  const Quantity_Color& aColor) * void V3d_Plane::Erase () * Standard_Boolean V3d_Plane::IsDisplayed () ~~~~~ The *Display* method could be redefined to provide custom representation of the clipping plane. The clipping planes could be activated with the methods *void V3d_View::SetPlaneOn (const Handle(V3d_Plane)& MyPlane)* and *void V3d_View::SetPlaneOn()* The first method appends the given *V3d_Plane* to the internal list of user-defined clipping planes of a view and activates it. If the plane is already in the list, it becomes activated. The second method activates all of the planes defined for the view. The clipping planes could be deactivated with the similar methods *void V3d_View::SetPlaneOff(const Handle(V3d_Plane)& MyPlane)* and *void V3d_View::SetPlaneOff()* The only difference is that these methods remove the user-defined clipping planes from the internal list. Thus, the view retains only active clipping planes. You can iterate through the active planes using the following methods: * *void V3d_View::InitActivePlanes()* - sets the iterator to the beginning of the internal list of clipping planes; * *Standard_Boolean V3d_View::MoreActivePlanes()* returns *Standard_True* if there are more active planes to return; * *void V3d_View::NextActivePlanes()* sets the iterator to the next active plane in the list; * *Handle(V3d_Plane) V3d_View::ActivePlane()* returns the active plane or check if a certain clipping plane has been activated with method *Standard_Boolean V3d_View::IsActivePlane (const Handle (V3d_Plane)& aPlane)* The number of clipping planes is limited. The method *Standard_Boolean V3d_View::IfMorePlanes()* allows checking if it is possible to activate at least one more plane in the view or the limit has been reached.

Example

~~~~~ // try to use an existing clipping plane or create a new one Handle(V3d_Plane) aCustomPlane; myView-InitActivePlanes (); if (myView-MoreActivePlanes ())   aCustomPlane = myView-ActivePlane (); else   aCustomPlane = new V3d_Plane (); // calculate new coefficients Standard_Real a, b, c, d; Standard_Real x = 0.0, y = 0.0, z = 10.0; Standard_Real dx = 0.0, dy = 0.0, dz = 1.0; gp_Pln aPln (gp_Pnt (x, y, z), gp_Dir (dx, dy, dz)); aPln.Coefficients (a, b, c, d); // update plane aCustomPlane-SetPlane (a, b, c, d); myView-SetPlaneOn (aCustomPlane); ~~~~~ @subsubsection occt_visu_5_2_9 Dumping a 3D scene into an image file The 3D scene displayed in the view could be dumped in high resolution into an image file. The high resolution (8192x8192 on some implementations) is achieved using the Frame Buffer Objects (FBO) provided by the graphic driver. Frame Buffer Objects enable off-screen rendering into a virtual view to produce images in the background mode (without displaying any graphics on the screen). The *V3d_View* has the following methods for dumping the 3D scene: * *Standard_Boolean V3d_View::Dump (const Standard_CString theFile, const Image_TypeOfImage theBufferType)* - dumps the scene into an image file with the view dimensions. * *Standard_Boolean V3d_View::Dump (const Standard_CString theFile, const Aspect_FormatOfSheetPaper theFormat, const Image_TypeOfImage theBufferType)* - allows making the dimensions of the output image compatible to a certain format of printing paper passed by *theFormat* argument. These methods dump the 3D scene into an image file passed by its name and path as theFile. The raster image data handling algorithm is based on the Image_PixMap class. The supported extensions are ".png", ".bmp", ".png", ".png". The value passed as *theBufferType* argument defines the type of the buffer for an output image *(RGB, RGBA, floating-point, RGBF, RGBAF)*. Both methods return *Standard_True* if the scene has been successfully dumped. **Note** that dumping the image for a paper format with large dimensions is a memory consuming operation, it might be necessary to take care of preparing enough free memory to perform this operation. * Handle_Image_PixMap V3d_View::ToPixMap (const Standard_Integer theWidth, const Standard_Integer theHeight, const Image_TypeOfImage theBufferType, const Standard_Boolean theForceCentered)* allows dumping the displayed 3d scene into a pixmap with a width and height passed as *theWidth* and theHeight arguments. The value passed as *theBufferType* argument defines the type of the buffer for a pixmap *(RGB, RGBA, floating-point, RGBF, RGBAF)*. The last parameter allows centering the 3D scene on dumping. All these methods assume that you have created a view and displayed a 3d scene in it. However, the window used for such a view could be virtual, so you can dump the 3d scene in the background mode without displaying it on the screen. To use such an opportunity you can perform the following steps: * Create display connection; * Initialize graphic driver; * Create a window; * Set up the window as virtual, *Aspect_Window::SetVirtual()* ; * Create a view and an interactive context; * Assign the virtual window to the view; * Display a 3D scene; * Use one of the functions described above to dump the 3D scene. The following example demonstrates this procedure for *WNT_Window* : ~~~~~ // create a dummy display connection Handle(Aspect_DisplayConnection) aDisplayConnection; // create a graphic driver Handle (Graphic3d_GraphicDriver) aDriver = Graphic3d::InitGraphicDriver (aDisplayConnection); // create a window Standard_Integer aDefWidth  = 800; Standard_Integer aDefHeight = 600; Handle (WNT_WClass) aWClass =              new WNT_WClass ("Virtual Class",DefWindowProc,                              CS_VREDRAW | CS_HREDRAW, 0, 0,                              ::LoadCursor (NULL, IDC_ARROW)); Handle (WNT_Window) aWindow =              new WNT_Window ("VirtualWnd",  aWClass,                              WS_OVERLAPPEDWINDOW, 0, 0,                              aDefWidth, aDefHeight); // set up the window as virtual aWindow-SetVirtual (Standard_True); // create a view and an interactive context Handle (V3d_Viewer) aViewer =              new V3d_Viewer (aDriver,                              Standard_ExtString ("Virtual")); Handle (AIS_InteractiveContext) aContext =              new AIS_InteractiveContext (aViewer); Handle (V3d_View) aView = aViewer-CreateView (); // assign the virtual window to the view aView-SetWindow (aWindow); // display a 3D scene Handle (AIS_Shape) aBox =              new AIS_Shape (BRepPrimAPI_MakeBox (5, 5, 5)); aContext-Display (aBox); aView-FitAll(); // dump the 3D scene into an image file aView-Dump ("3dscene.png"); ~~~~~ @subsubsection occt_visu_5_2_10 Printing a 3D scene The contents of a view can be printed out. Moreover, the OpenGl graphic driver used by the v3d view supports printing in high resolution. The print method uses the OpenGl frame buffer (Frame Buffer Object) for rendering the view contents and advanced print algorithms that allow printing in, theoretically, any resolution. The method *void V3d_View::Print(const Aspect_Handle hPrnDC, const Standard_Boolean showDialog, const Standard_Boolean showBackground, const Standard_CString  filename, const Aspect_PrintAlgo printAlgorithm)* prints the view contents: *hPrnDC* is the printer device handle. You can pass your own printer handle or "NULL" to select the printer by the default dialog. In that case you can use the default dialog or pass "Standard_False" as the showDialog argument to select the default printer automatically. You can define the filename for the printer driver if you want to print out the result into a file. If you do not want to print the background, you can pass *Standard_False* as the *showBackground* argument. The *printAlgorithm* argument allows choosing between two print algorithms that define how the 3d scene is mapped to the print area when the maximum dimensions of the frame buffer are smaller than the dimensions of the print area by choosing *Aspect_PA_STRETCH* or *Aspect_PA_TILE* The first value defines the stretch algorithm: the scene is drawn with the maximum possible frame buffer dimensions and then is stretched to the whole printing area. The second value defines *TileSplit* algorithm: covering the whole printing area by rendering multiple parts of the viewer. **Note** that at the moment printing is implemented only for Windows. @subsubsection occt_visu_5_2_11 Vector image export The 3D content of a view can be exported to the vector image file format. The vector image export is powered by the GL2PS library. You can export your 3D scenes into a file format supported by the GL2PS library: PostScript (PS), Encapsulated PostScript (EPS), Portable Document Format (PDF), Scalable Vector Graphics (SVG), LaTeX file format and Portable LaTeX Graphics (PGF). The method *void Visual3d_View::Export (const Standard_CString FileName, const Graphic3d_ExportFormat Format, const Graphic3d_SortType aSortType, const Standard_Real Precision, const Standard_Address ProgressBarFunc, const Standard_Address ProgressObject)* of *Visual3d_View* class allows exporting a 3D scene: The *FileName* defines the output image file name and the *Format* argument defines the output file format: * Graphic3d_EF_PostScript (PS), * Graphic3d_EF_EhnPostScript (EPS), * Graphic3d_EF_TEX (TEX), * Graphic3d_EF_PDF (PDF), * Graphic3d_EF_SVG (SVG), * Graphic3d_EF_PGF (PGF) The *aSortType* parameter defines *GL2PS* sorting algorithm for the primitives. The *Precision, ProgressBarFunc* and *ProgressObject* parameters are implemented for future uses and at the moment have no effect. The *Export* method supports only basic 3d graphics and has several limitations: * Rendering large scenes could be slow and can lead to large output files; * Transparency is only supported for PDF and SVG output; * Textures and some effects are not supported by the GL2PS library. @section occt_visu_6 Graphic Attributes @subsection occt_visu_6_1 Aspect Package The *Aspect* package provides classes for the graphic elements in the viewer: * Color maps, * Pixels, * Groups of graphic attributes, * Edges, lines, background, * Font classes, * Width map classes, * Marker map classes, * Type of Line map classes, * Window, * Driver, PlotterDriver (inherited by PS_Driver), WindowDriver, * Enumerations for many of the above, * Array instantiations for edges, * Array instantiations for map entries for color, type, font, width, and marker.