1 Visualization {#occt_user_guides__visualization}
2 ========================
5 @section occt_visu_1 Introduction
7 Visualization in Open CASCADE Technology is based on the separation of:
8 * on the one hand -- the data which stores the geometry and topology of the entities you want to display and select, and
9 * 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).
11 Presentations are managed through the **Presentation** component, and selection through the **Selection** component.
13 **Application Interactive Services** (AIS) provides the means to create links between an application GUI viewer and the packages, which are used to manage selection and presentation, which makes management of these functionalities in 3D more intuitive and consequently, more transparent.
15 *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.
17 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.
19 The the following packages are used to display 3D objects:
27 The packages used to display 3D objects are also applicable for visualization of 2D objects.
29 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.
31 @figure{visualization_image003.png,"Key concepts and packages in visualization",400}
33 To answer different needs of CASCADE users, this User's Guide offers the following three paths in reading it.
35 * If the 3D services proposed in AIS meet your requirements, you need only read chapter 3 @ref occt_visu_3 "AIS: Application Interactive Services".
36 * If you need more detail, for example, a selection filter on another type of entity -- you should read chapter 2 @ref occt_visu_2 "Fundamental Concepts", chapter 3 @ref occt_visu_3 "AIS: Application Interactive Services", and 4 @ref occt_visu_4 "3D Presentations". You may want to begin with the chapter presenting AIS.
38 For advanced information on visualization algorithms, see our <a href="http://www.opencascade.com/content/tutorial-learning">E-learning & Training</a> offerings.
40 @section occt_visu_2 Fundamental Concepts
42 @subsection occt_visu_2_1 Presentation
44 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.
46 @subsubsection occt_visu_2_1_1 Structure of the Presentation
48 Displaying an object on the screen involves three kinds of entities:
49 * a presentable object, the *AIS_InteractiveObject*
51 * an interactive context, the *AIS_InteractiveContext*.
53 #### The presentable object
55 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.
57 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.
59 Each object to be presented individually must be presentable or associated with a presentable object.
63 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.
65 #### The Interactive Context
67 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.
69 @subsubsection occt_visu_2_1_2 Presentation packages
71 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.
73 * *AIS* package provides all classes to implement interactive objects (presentable and selectable entities).
74 * *PrsMgr* package provides low level services and is only to be used when you do not want to use the services provided by AIS. It contains all classes needed to implement the presentation process: abstract classes *Presentation* and *PresentableObject* and concrete class *PresentationManager3d*.
75 * *StdPrs* package provides ready-to-use standard presentation algorithms for specific geometries: points, curves and shapes of the geometry and topology toolkits.
76 * *Prs3d* package provides 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, etc.
77 * *V3d* package provides the services supported by the 3D viewer.
78 * *Graphic3d* package provides resources to create 3D graphic structures.
79 * *Visual3d* package contains classes implementing commands for 3D viewer.
80 * *DsgPrs* package provides tools for display of dimensions, relations and XYZ trihedrons.
82 @subsubsection occt_visu_2_1_3 A Basic Example: How to display a 3D object
85 Handle(V3d_Viewer) theViewer;
86 Handle(AIS_InteractiveContext) aContext = new AIS_InteractiveContext (theViewer);
88 BRepPrimAPI_MakeWedge aWedgeMaker (theWedgeDX, theWedgeDY, theWedgeDZ, theWedgeLtx);
89 TopoDS_Solid aShape = aWedgeMaker.Solid();
90 Handle(AIS_Shape) aShapePrs = new AIS_Shape (aShape); // creation of the presentable object
91 aContext->Display (aShapePrs); // display the presentable object in the 3d viewer
94 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.
96 @figure{visualization_image004.svg,"Processes involved in displaying a presentable shape",400}
98 @subsection occt_visu_2_2 Selection
100 Standard OCCT selection algorithm is represented by 2 parts: dynamic and static. Dynamic selection causes objects to be automatically highlighted as the mouse cursor moves over them. Static selection allows to pick particular object (or objects) for further processing.
102 There are 3 different selection types:
103 - **Point selection** -- allows picking and highlighting a single object (or its part) located under the mouse cursor;
104 - **Rectangle selection** -- allows picking objects or parts located under the rectangle defined by the start and end mouse cursor positions;
105 - **Polyline selection** -- allows picking objects or parts located under a user-defined non-self-intersecting polyline.
107 For OCCT selection algorithm, all selectable objects are represented as a set of sensitive zones, called **sensitive entities**. When the mouse cursor moves in the view, the sensitive entities of each object are analyzed for collision.
109 @subsubsection occt_visu_2_2_1 Terms and notions
111 This section introduces basic terms and notions used throughout the algorithm description.
113 #### Sensitive entity
115 Sensitive entities in the same way as entity owners are links between objects and the selection mechanism.
117 The purpose of entities is to define what parts of the object will be selectable in particular. Thus, any object that is meant to be selectable must be split into sensitive entities (one or several). For instance, to apply face selection to an object it is necessary to explode it into faces and use them for creation of a sensitive entity set.
119 @figure{visualization_image005.png,"Example of a shape divided into sensitive entities",400}
121 Depending on the user's needs, sensitive entities may be atomic (point or edge) or complex. Complex entities contain many sub-elements that can be handled by detection mechanism in a similar way (for example, a polyline stored as a set of line segments or a triangulation).
123 Entities are used as internal units of the selection algorithm and do not contain any topological data, hence they have a link to an upper-level interface that maintains topology-specific methods.
127 Each sensitive entity stores a reference to its owner, which is a class connecting the entity and the corresponding selectable object. Besides, owners can store any additional information, for example, the topological shape of the sensitive entity, highlight colors and methods, or if the entity is selected or not.
131 To simplify the handling of different selection modes of an object, sensitive entities linked to their owners are organized into sets, called **selections**.
132 Each selection contains entities created for a certain mode along with the sensitivity and update states.
134 #### Selectable object
136 Selectable object stores information about all created selection modes and sensitive entities.
138 All successors of a selectable object must implement the method that splits its presentation into sensitive entities according to the given mode. The computed entities are arranged in one selection and added to the list of all selections of this object. No selection will be removed from the list until the object is deleted permanently.
140 For all standard OCCT shapes, zero mode is supposed to select the whole object (but it may be redefined easily in the custom object). For example, the standard OCCT selection mechanism and *AIS_Shape* determine the following modes:
141 - 0 -- selection of the entire object *(AIS_Shape)*;
142 - 1 -- selection of the vertices;
143 - 2 -- selection of the edges;
144 - 3 -- selection of the wires;
145 - 4 -- selection of the faces;
146 - 5 -- selection of the shells;
147 - 6 -- selection of the constituent solids.
149 @figure{visualization_image006.png,"Hierarchy of references from sensitive entity to selectable object",400}
151 @figure{visualization_image007.png,"The principle of entities organization within the selectable object",400}
155 For each OCCT viewer there is a **Viewer selector** class instance. It provides a high-level API for the whole selection algorithm and encapsulates the processing of objects and sensitive entities for each mouse pick.
156 The viewer selector maintains activation and deactivation of selection modes, launches the algorithm, which detects candidate entities to be picked, and stores its results, as well as implements an interface for keeping selection structures up-to-date.
158 #### Selection manager
160 Selection manager is a high-level API to manipulate selection of all displayed objects. It handles all viewer selectors, activates and deactivates selection modes for the objects in all or particular selectors, manages computation and update of selections for each object. Moreover, it keeps selection structures updated taking into account applied changes.
162 @figure{visualization_image008.png,"The relations chain between viewer selector and selection manager",400}
164 @subsubsection occt_visu_2_2_2 Algorithm
166 All three types of OCCT selection are implemented as a single concept, based on the search for overlap between frustum and sensitive entity through 3-level BVH tree traversal.
168 #### Selection Frustum
170 The first step of each run of selection algorithm is to build the selection frustum according to the currently activated selection type.
172 For the point or the rectangular selection the base of the frustum is a rectangle built in conformity with the pixel tolerance or the dimensions of a user-defined area, respectively. For the polyline selection, the polygon defined by the constructed line is triangulated and each triangle is used as the base for its own frustum. Thus, this type of selection uses a set of triangular frustums for overlap detection.
174 The frustum length is limited by near and far view volume planes and each plane is built parallel to the corresponding view volume plane.
176 @figure{visualization_image009.png,"",400}
178 The image above shows the rectangular frustum: a) after mouse move or click, b) after applying the rectangular selection.
180 @figure{visualization_image010.png,"",400}
182 In the image above triangular frustum is set: a) by a user-defined polyline, b) by triangulation of the polygon based on the given polyline, c) by a triangular frustum based on one of the triangles.
186 To maintain selection mechanism at the viewer level, a speedup structure composed of 3 BVH trees is used.
188 The first level tree is constructed of axis-aligned bounding boxes of each selectable object. Hence, the root of this tree contains the combination of all selectable boundaries even if they have no currently activated selections. Objects are added during the display of *AIS_InteractiveObject* and will be removed from this tree only when the object is destroyed. The 1st level BVH tree is build on demand simultaneously with the first run of the selection algorithm.
190 The second level BVH tree consists of all sensitive entities of one selectable object. The 2nd level trees are built automatically when the default mode is activated and rebuilt whenever a new selection mode is calculated for the first time.
192 The third level BVH tree is used for complex sensitive entities that contain many elements: for example, triangulations, wires with many segments, point sets, etc. It is built on demand for sensitive entities with under 800K sub-elements.
194 @figure{visualization_image022.png,"Selection BVH tree hierarchy: from the biggest object-level (first) to the smallest complex entity level (third)",400}
196 #### Stages of the algorithm
198 The algorithm includes pre-processing and three main stages.
202 Implies calculation of the selection frustum and its main characteristics.
204 ##### First stage -- traverse of the first level BVH tree
206 After successful building of the selection frustum, the algorithm starts traversal of the object-level BVH tree. The nodes containing axis-aligned bounding boxes are tested for overlap with the selection frustum following the terms of *separating axis theorem (SAT)*. When the traversal goes down to the leaf node, it means that a candidate object with possibly overlapping sensitive entities has been found. If no such objects have been detected, the algorithm stops and it is assumed that no object needs to be selected. Otherwise it passes to the next stage to process the entities of the found selectable object.
208 ##### Second stage -- traversal of the second level BVH tree
210 At this stage it is necessary to determine if there are candidates among all sensitive entities of one object.
212 First of all, at this stage the algorithm checks if there is any transformation applied for the current object. If it has its own location, then the correspondingly transformed frustum will be used for further calculations. At the next step the nodes of the second level BVH tree of the given object are visited to search for overlapping leaves. If no such leafs have been found, the algorithm returns to the second stage. Otherwise it starts processing the found entities by performing the following checks:
213 - activation check - the entity may be inactive at the moment as it belongs to deactivated selection;
214 - tolerance check - current selection frustum may be too large for further checks as it is always built with the maximum tolerance among all activated entities. Thus, at this step the frustum may be scaled.
216 After these checks the algorithm passes to the last stage.
218 ##### Third stage -- overlap or inclusion test of a particular sensitive entity
220 If the entity is atomic, a simple SAT test is performed. In case of a complex entity, the third level BVH tree is traversed. The quantitative characteristics (like depth, distance to the center of geometry) of matched sensitive entities is analyzed and clipping planes are applied (if they have been set). The result of detection is stored and the algorithm returns to the second stage.
222 @subsubsection occt_visu_2_2_3 Packages and classes
224 Selection is implemented as a combination of various algorithms divided among several packages -- *SelectBasics*, *Select3D*, *SelectMgr* and *StdSelect*.
228 *SelectBasics* package contains basic classes and interfaces for selection. The most notable are:
229 - *SelectBasics_SensitiveEntity* -- the base definition of a sensitive entity;
230 - *SelectBasics_EntityOwner* -- the base definition of the an entity owner -- the link between the sensitive entity and the object to be selected;
231 - *SelectBasics_PickResult* -- the structure for storing quantitative results of detection procedure, for example, depth and distance to the center of geometry;
232 - *SelectBasics_SelectingVolumeManager* -- the interface for interaction with the current selection frustum.
234 Each custom sensitive entity must inherit at least *SelectBasics_SensitiveEntity*.
238 *Select3D* package provides a definition of standard sensitive entities, such as:
250 Each basic sensitive entity inherits *Select3D_SensitiveEntity*, which is a child class of *SelectBasics_SensitiveEntity*.
251 The package also contains two auxiliary classes, *Select3D_SensitivePoly* and *Select3D_SensitiveSet*.
253 *Select3D_SensitiveSet* -- a base class for all complex sensitive entities that require the third level BVH usage. It implements traverse of the tree and defines an interface for the methods that check sub-entities.
255 *Select3D_SensitivePoly* -- describes an arbitrary point set and implements basic functions for selection. It is important to know that this class does not perform any internal data checks. Hence, custom implementations of sensitive entity inherited from *Select3D_SensitivePoly* must satisfy the terms of Separating Axis Theorem to use standard OCCT overlap detection methods.
259 *SelectMgr* package is used to maintain the whole selection process. For this purpose, the package provides the following services:
260 - activation and deactivation of selection modes for all selectable objects;
261 - interfaces to compute selection mode of the object;
262 - definition of selection filter classes;
263 - keeping selection BVH data up-to-date.
265 A brief description of the main classes:
266 - *SelectMgr_FrustumBase*, *SelectMgr_Frustum*, *SelectMgr_RectangularFrustum*, *SelectMgr_TriangluarFrustum* and *SelectMgr_TriangularFrustumSet* -- interfaces and implementations of selecting frustums, these classes implement different SAT tests for overlap and inclusion detection. They also contain methods to measure characteristics of detected entities (depth, distance to center of geometry);
267 - *SelectMgr_SensitiveEntity*, *SelectMgr_Selection* and *SelectMgr_SensitiveEntitySet* -- store and handle sensitive entities; *SelectMgr_SensitiveEntitySet* implements a primitive set for the second level BVH tree;
268 - *SelectMgr_SelectableObject* and *SelectMgr_SelectableObjectSet* -- describe selectable objects. They also manage storage, calculation and removal of selections. *SelectMgr_SelectableObjectSet* implements a primitive set for the first level BVH tree;
269 - *SelectMgr_ViewerSelector* -- encapsulates all logics of the selection algorithm and implements the third level BVH tree traverse;
270 - *SelectMgr_SelectionManager* -- manages activation/deactivation, calculation and update of selections of every selectable object, and keeps BVH data up-to-date.
274 *StdSelect* package contains the implementation of some *SelectMgr* classes and tools for creation of selection structures. For example,
275 - *StdSelect_BRepOwner* -- defines an entity owner with a link to its topological shape and methods for highlighting;
276 - *StdSelect_BRepSelectionTool* -- contains algorithms for splitting standard AIS shapes into sensitive primitives;
277 - *StdSelect_ViewerSelector3d* -- an example of *SelectMgr_ViewerSelecor* implementation, which is used in a default OCCT selection mechanism;
278 - *StdSelect_FaceFilter*, *StdSelect_EdgeFilter* -- implementation of selection filters.
280 @subsubsection occt_visu_2_2_4 Examples of usage
282 The first code snippet illustrates the implementation of *SelectMgr_SelectableObject::ComputeSelection()* method in a custom interactive object. The method is used for computation of user-defined selection modes.
283 Let us assume it is required to make a box selectable in two modes -- the whole shape (mode 0) and each of its edges (mode 1).
284 To select the whole box, the application can create a sensitive primitive for each face of the interactive object. In this case, all primitives share the same owner -- the box itself.
285 To select box's edge, the application must create one sensitive primitive per edge. Here all sensitive entities cannot share the owner since different geometric primitives must be highlighted as the result of selection procedure.
288 void InteractiveBox::ComputeSelection (const Handle(SelectMgr_Selection)& theSel,
289 const Standard_Integer theMode)
293 case 0: // creation of face sensitives for selection of the whole box
295 Handle(SelectMgr_EntityOwner) anOwner = new SelectMgr_EntityOwner (this, 5);
296 for (Standard_Integer aFaceIter = 1; aFaceIter <= myNbFaces; ++aFaceIter)
298 Select3D_TypeOfSensitivity aSensType = myIsInterior;
299 theSel->Add (new Select3D_SensitiveFace (anOwner, myFaces[aFaceIter]->PointArray(), aSensType));
303 case 1: // creation of edge sensitives for selection of box edges only
305 for (Standard_Integer anEdgeIter = 1; anEdgeIter <= 12; ++anEdgeIter)
307 // 1 owner per edge, where 6 is a priority of the sensitive
308 Handle(MySelection_EdgeOwner) anOwner = new MySelection_EdgeOwner (this, anEdgeIter, 6);
309 theSel->Add (new Select3D_SensitiveSegment (anOwner, myFirstPnt[anEdgeIter]), myLastPnt[anEdgeIter]));
317 The algorithms for creating selection structures store sensitive primitives in *SelectMgr_Selection* instance. Each *SelectMgr_Selection* sequence in the list of selections of the object must correspond to a particular selection mode.
318 To describe the decomposition of the object into selectable primitives, a set of ready-made sensitive entities is supplied in *Select3D* package. Custom sensitive primitives can be defined through inheritance from *SelectBasics_SensitiveEntity*.
319 To make custom interactive objects selectable or customize selection modes of existing objects, the entity owners must be defined. They must inherit *SelectMgr_EntityOwner* interface.
321 Selection structures for any interactive object are created in *SelectMgr_SelectableObject::ComputeSelection()* method.
322 The example below shows how computation of different selection modes of the topological shape can be done using standard OCCT mechanisms, implemented in *StdSelect_BRepSelectionTool*.
325 void MyInteractiveObject::ComputeSelection (const Handle(SelectMgr_Selection)& theSelection,
326 const Standard_Integer theMode)
330 case 0: StdSelect_BRepSelectionTool::Load (theSelection, this, myShape, TopAbs_SHAPE); break;
331 case 1: StdSelect_BRepSelectionTool::Load (theSelection, this, myShape, TopAbs_VERTEX); break;
332 case 2: StdSelect_BRepSelectionTool::Load (theSelection, this, myShape, TopAbs_EDGE); break;
333 case 3: StdSelect_BRepSelectionTool::Load (theSelection, this, myShape, TopAbs_WIRE); break;
334 case 4: StdSelect_BRepSelectionTool::Load (theSelection, this, myShape, TopAbs_FACE); break;
339 The *StdSelect_BRepSelectionTool* class provides a high level API for computing sensitive entities of the given type (for example, face, vertex, edge, wire and others) using topological data from the given *TopoDS_Shape*.
341 The traditional way of highlighting selected entity owners adopted by Open CASCADE Technology assumes that each entity owner highlights itself on its own. This approach has two drawbacks:
343 - each entity owner has to maintain its own *Prs3d_Presentation* object, that results in a considerable memory overhead;
344 - drawing selected owners one by one is not efficient from the visualization point of view.
346 Therefore, to overcome these limitations, OCCT has an alternative way to implement the highlighting of a selected presentation. Using this approach, the interactive object itself will be responsible for the highlighting, not the entity owner.
348 On the basis of *SelectMgr_EntityOwner::IsAutoHilight()* return value, *AIS_InteractiveContext* object either uses the traditional way of highlighting (in case if *IsAutoHilight()* returns TRUE) or groups such owners according to their selectable objects and finally calls *SelectMgr_SelectableObject::HilightSelected()* or *SelectMgr_SelectableObject::ClearSelected()*, passing a group of owners as an argument.
350 Hence, an application can derive its own interactive object and redefine virtual methods *HilightSelected()*, *ClearSelected()* and *HilightOwnerWithColor()* from *SelectMgr_SelectableObject*. *SelectMgr_SelectableObject::GetHilightPresentation* and *SelectMgr_SelectableObject::GetSelectPresentation* methods can be used to optimize filling of selection and highlight presentations according to the user's needs.
351 The *AIS_InteractiveContext::HighlightSelected()* method can be used for efficient redrawing of the selection presentation for a given interactive object from an application code.
353 After all the necessary sensitive entities are computed and packed in *SelectMgr_Selection* instance with the corresponding owners in a redefinition of *SelectMgr_SelectableObject::ComputeSelection()* method, it is necessary to register the prepared selection in *SelectMgr_SelectionManager* through the following steps:
354 - if there was no *AIS_InteractiveContext* opened, create an interactive context and display the selectable object in it;
355 - load the selectable object to the selection manager of the interactive context using *AIS_InteractiveContext::Load()* method. If the selection mode passed as a parameter to this method is not equal to -1, *ComputeSelection()* for this selection mode will be called;
356 - activate or deactivate the defined selection mode using *AIS_InteractiveContext::Activate()* or *AIS_InteractiveContext::Deactivate()* methods.
358 After these steps, the selection manager of the created interactive context will contain the given object and its selection entities, and they will be involved in the detection procedure.
360 The code snippet below illustrates the above steps. It also contains the code to start the detection procedure and parse the results of selection.
363 // Suppose there is an instance of class InteractiveBox from the previous sample.
364 // It contains an implementation of method InteractiveBox::ComputeSelection() for selection
365 // modes 0 (whole box must be selected) and 1 (edge of the box must be selectable)
366 Handle(InteractiveBox) theBox;
367 Handle(AIS_InteractiveContext) theContext;
368 // To prevent automatic activation of the default selection mode
369 theContext->SetAutoActivateSelection (false);
370 theContext->Display (theBox, false);
372 // Load a box to the selection manager without computation of any selection mode
373 theContext->Load (theBox, -1, true);
374 // Activate edge selection
375 theContext->Activate (theBox, 1);
377 // Run the detection mechanism for activated entities in the current mouse coordinates and in the current view.
378 // Detected owners will be highlighted with context highlight color
379 theContext->MoveTo (aXMousePos, aYMousePos, myView);
380 // Select the detected owners
381 theContext->Select();
382 // Iterate through the selected owners
383 for (theContext->InitSelected(); theContext->MoreSelected() && !aHasSelected; theContext->NextSelected())
385 Handle(AIS_InteractiveObject) anIO = theContext->SelectedInteractive();
388 // deactivate all selection modes for aBox1
389 theContext->Deactivate (aBox1);
392 It is also important to know, that there are 2 types of detection implemented for rectangular selection in OCCT:
393 - <b>inclusive</b> detection. In this case the sensitive primitive is considered detected only when all its points are included in the area defined by the selection rectangle;
394 - <b>overlap</b> detection. In this case the sensitive primitive is considered detected when it is partially overlapped by the selection rectangle.
396 The standard OCCT selection mechanism uses inclusion detection by default. To change this, use the following code:
399 // Assume there is a created interactive context
400 const Handle(AIS_InteractiveContext) theContext;
401 // Retrieve the current viewer selector
402 const Handle(StdSelect_ViewerSelector3d)& aMainSelector = theContext->MainSelector();
403 // Set the flag to allow overlap detection
404 aMainSelector->AllowOverlapDetection (true);
407 @section occt_visu_3 Application Interactive Services
408 @subsection occt_visu_3_1 Introduction
410 Application Interactive Services allow managing presentations and dynamic selection in a viewer in a simple and transparent manner.
411 The central entity for management of visualization and selections is the **Interactive Context**. It is connected to the main viewer.
413 Interactive context by default starts at **Neutral Point** with each selectable object picked as a whole, but the user might activate **Local Selection** for specific objects to make selectable parts of the objects.
414 Local/global selection is managed by a list of selection modes activated for each displayed object with 0 (default selection mode) usually meaning Global (entire object) selection.
416 **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.
418 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.
419 When an Interactive Object is visualized, the required graphic attributes are taken from its own **Drawer** (*Prs3d_Drawer*) if it has the required custom attributes or otherwise from the context drawer.
421 @figure{visualization_image017.png,"",360}
423 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 only within at the Neutral Point, others only within Local Selection. It is possible to program custom filters and load them into the interactive context.
425 @subsection occt_visu_3_2 Interactive objects
427 Entities which are visualized and selected in the AIS viewer are objects. They connect the underlying reference geometry of a model to its graphic representation in *AIS*. You can use the predefined OCCT classes of standard interactive objects, for which all necessary functions have already been programmed, or, if you are an advanced user, you can implement your own classes of interactive objects.
429 @subsubsection occt_visu_3_2_1 Presentations
431 An interactive object can have as many presentations as its creator wants to give it.
432 3D presentations are managed by **Presentation Manager** (*PrsMgr_PresentationManager*). As this is transparent in AIS, the user does not have to worry about it.
434 A presentation is identified by an index (*Display Mode*) and by the reference to the Presentation Manager, which it depends on.
435 By convention, the default mode of representation for the Interactive Object has index 0.
437 @figure{visualization_image018.png,"",360}
439 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.
441 If you are creating your own type of interactive object, you must implement the Compute function in one of the following ways:
446 void PackageName_ClassName::Compute (const Handle(PrsMgr_PresentationManager3d)& thePresentationManager,
447 const Handle(Prs3d_Presentation)& thePresentation,
448 const Standard_Integer theMode);
451 #### For hidden line removal (HLR) mode in 3D:
453 void PackageName_ClassName::Compute (const Handle(Prs3d_Projector)& theProjector,
454 const Handle(Prs3d_Presentation)& thePresentation);
457 @subsubsection occt_visu_3_2_2 Hidden Line Removal
459 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.
461 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:
463 * Initially by using one of the values of the enumeration *PrsMgr_TypeOfPresentation*:
464 * *PrsMgr_TOP_AllView*,
465 * *PrsMgr_TOP_ProjectorDependant*
467 * Later by using the function *PrsMgr_PresentableObject::SetTypeOfPresentation*
469 *AIS_Shape* class is an example of an interactive object that supports HLR representation.
470 The type of the HLR algorithm is stored in *Prs3d_Drawer* of the shape. It is a value of the *Prs3d_TypeOfHLR* enumeration and can be set to:
471 * *Prs3d_TOH_PolyAlgo* for a polygonal algorithm based on the shape's triangulation;
472 * *Prs3d_TOH_Algo* for an exact algorithm that works with the shape's real geometry;
473 * *Prs3d_TOH_NotSet* if the type of algorithm is not set for the given interactive object instance.
475 The type of the HLR algorithm used for *AIS_Shape* can be changed by calling the *AIS_Shape::SetTypeOfHLR()* method.
476 The current HLR algorithm type can be obtained using *AIS_Shape::TypeOfHLR()* method is to be used.
478 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*.
479 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.
481 @subsubsection occt_visu_3_2_3 Presentation modes
483 There are four types of interactive objects in AIS:
484 * the "construction element" or Datum,
485 * the Relation (dimensions and constraints)
487 * the None type (when the object is of an unknown type).
489 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:
490 * *AIS_InteractiveObject::Type*
491 * *AIS_InteractiveObject::Signature*.
493 **Note** that some signatures are already used by "standard" objects provided in AIS (see the @ref occt_visu_3_5 "List of Standard Interactive Object Classes").
495 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.
496 Consequently, to get information about this class it is necessary to use virtual function *AIS_InteractiveObject::AcceptDisplayMode*.
500 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.
504 At dynamic detection, the presentation echoed by the Interactive Context, is by default the presentation already on the screen.
506 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.
508 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).
510 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.
514 If you do not 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.
516 Let us take for example the class called *IShape* representing an interactive object:
519 myPk_IShape::myPK_IShape (const TopoDS_Shape& theShape, PrsMgr_TypeOfPresentation theType)
520 : AIS_InteractiveObject (theType), myShape (theShape) { SetHilightMode (0); }
522 void myPk_IShape::Compute (const Handle(PrsMgr_PresentationManager3d)& thePrsMgr,
523 const Handle(Prs3d_Presentation)& thePrs,
524 const Standard_Integer theMode)
528 // algo for calculation of wireframe presentation
529 case 0: StdPrs_WFDeflectionShape::Add (thePrs, myShape, myDrawer); return;
530 // algo for calculation of shading presentation
531 case 1: StdPrs_ShadedShape::Add (thePrs, myShape, myDrawer); return;
535 void myPk_IShape::Compute (const Handle(Prs3d_Projector)& theProjector,
536 const Handle(Prs3d_Presentation)& thePrs)
538 // Hidden line mode calculation algorithm
539 StdPrs_HLRPolyShape::Add (thePrs, myShape, myDrawer, theProjector);
543 @subsubsection occt_visu_3_2_4 Selection
545 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 interactive object or shape which has been detected (see @ref occt_visu_2_2 "Selection" chapter).
547 The set of sensitive primitives, which correspond to a given mode, is stocked in a **Selection** (*SelectMgr_Selection*).
549 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*. However, it can be modified in the custom interactive objects using method *SelectMgr_SelectableObject::setGlobalSelMode()*.
551 The calculation of selection primitives (or sensitive entities) is done in a virtual function *ComputeSelection*. It should be implemented for each type of interactive object that is assumed to have different selection modes using the function *AIS_InteractiveObject::ComputeSelection*.
552 A detailed explanation of the mechanism and the manner of implementing this function has been given in @ref occt_visu_2_2 "Selection" chapter.
554 There are some examples of selection mode calculation for the most widely used interactive object in OCCT -- *AIS_Shape* (selection by vertex, by edges, etc). To create new classes of interactive objects with the same selection behavior as *AIS_Shape* -- such as vertices and edges -- you must redefine the virtual function *AIS_InteractiveObject::AcceptShapeDecomposition*.
556 @subsubsection occt_visu_3_2_5 Graphic attributes
558 Graphic attributes manager, or *Prs3d_Drawer*, stores graphic attributes for specific interactive objects and for interactive objects controlled by interactive context.
560 Initially, all drawer attributes are filled out with the predefined values which will define the default 3D object appearance.
561 When an interactive object is visualized, the required graphic attributes are first taken from its own drawer if one exists, or from the context drawer if no specific drawer for that type of object exists.
563 Keep in mind the following points concerning graphic attributes:
564 * Each interactive object can have its own visualization attributes.
565 * 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.)
566 * 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.
568 @figure{visualization_image020.svg,"Redefinition of virtual functions for changes in AIS_Shape and AIS_TextLabel.",360}
570 The following virtual functions provide settings for color, width, material and transparency:
571 * *AIS_InteractiveObject::UnsetColor*
572 * *AIS_InteractiveObject::SetWidth*
573 * *AIS_InteractiveObject::UnsetWidth*
574 * *AIS_InteractiveObject::SetMaterial*
575 * *AIS_InteractiveObject::UnsetMaterial*
576 * *AIS_InteractiveObject::SetTransparency*
577 * *AIS_InteractiveObject::UnsetTransparency*
579 These methods can be used as a shortcut assigning properties in common way, but result might be not available.
580 Some interactive objects might not implement these methods at all or implement only a sub-set of them.
581 Direct modification of *Prs3d_Drawer* properties returned by *AIS_InteractiveObject::Attributes* can be used for more precise and predictable configuration.
583 It is important to know which functions may imply the recalculation of presentations of the object.
584 If the presentation mode of an interactive object is to be updated, a flag from *PrsMgr_PresentableObject* indicates this.
585 The mode can be updated using the functions *Display* and *Redisplay* in *AIS_InteractiveContext*.
587 @subsubsection occt_visu_3_2_6 Complementary Services
589 When you use complementary services for interactive objects, pay special attention to the cases mentioned below.
591 #### Change the location of an interactive object
593 The following functions allow "moving" the representation and selection of Interactive Objects in a view without recalculation (and modification of the original shape).
594 * *AIS_InteractiveContext::SetLocation*
595 * *AIS_InteractiveContext::ResetLocation*
596 * *AIS_InteractiveContext::HasLocation*
597 * *AIS_InteractiveContext::Location*
599 #### Connect an interactive object to an applicative entity
601 Each Interactive Object has functions that allow attributing it an *Owner* in form of a *Transient*.
602 * *AIS_InteractiveObject::SetOwner*
603 * *AIS_InteractiveObject::HasOwner*
604 * *AIS_InteractiveObject::Owner*
606 An interactive object can therefore be associated or not with an applicative entity, without affecting its behavior.
608 **NOTE:** Don't be confused by owners of another kind - *SelectBasics_EntityOwner* used for identifying selectable parts of the object or object itself.
610 #### Resolving coincident topology
612 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.
614 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.
616 The methods *AIS_InteractiveObject::SetPolygonOffsets* and *AIS_InteractiveContext::SetPolygonOffsets* allow setting up the polygon offsets.
618 @subsubsection occt_visu_3_2_7 Object hierarchy
620 Each *PrsMgr_PresentableObject* has a list of objects called *myChildren*.
621 Any transformation of *PrsMgr_PresentableObject* is also applied to its children. This hierarchy does not propagate to *Graphic3d* level and below.
623 *PrsMgr_PresentableObject* sends its combined (according to the hierarchy) transformation down to *Graphic3d_Structure*.
624 The materials of structures are not affected by the hierarchy.
626 Object hierarchy can be controlled by the following API calls:
627 * *PrsMgr_PresentableObject::AddChild*;
628 * *PrsMgr_PresentableObject::RemoveChild*.
630 @subsubsection occt_visu_3_2_8 Instancing
632 The conception of instancing operates the object hierarchy as follows:
633 * Instances are represented by separated *AIS* objects.
634 * Instances do not compute any presentations.
636 Classes *AIS_ConnectedInteractive* and *AIS_MultipleConnectedInteractive* are used to implement this conception.
638 *AIS_ConnectedInteractive* is an object instance, which reuses the geometry of the connected object but has its own transformation and visibility flag. This connection is propagated down to *OpenGl* level, namely to *OpenGl_Structure*. *OpenGl_Structure* can be connected only to a single other structure.
640 *AIS_ConnectedInteractive* can be referenced to any *AIS_InteractiveObject* in general. When it is referenced to another *AIS_ConnectedInteractive*, it just copies the reference.
642 *AIS_MultipleConnectedInteractive* represents an assembly, which does not have its own presentation. The assemblies are able to participate in the object hierarchy and are intended to handle a grouped set of instanced objects. It behaves as a single object in terms of selection. It applies high level transformation to all sub-elements since it is located above in the hierarchy.
644 All *AIS_MultipleConnectedInteractive* are able to have child assemblies. Deep copy of object instances tree is performed if one assembly is attached to another.
646 Note that *AIS_ConnectedInteractive* cannot reference *AIS_MultipleConnectedInteractive*. *AIS_ConnectedInteractive* copies sensitive entities of the origin object for selection, unlike *AIS_MultipleConnectedInteractive* that re-uses the entities of the origin object.
648 Instances can be controlled by the following DRAW commands:
649 * *vconnect* : Creates and displays *AIS_MultipleConnectedInteractive* object from input objects and location.
650 * *vconnectto* : Makes an instance of object with the given position.
651 * *vdisconnect* : Disconnects all objects from an assembly or disconnects an object by name or number.
652 * *vaddconnected* : Adds an object to the assembly.
653 * *vlistconnected* : Lists objects in the assembly.
655 Have a look at the examples below:
661 vconnectto s2 3 0 0 s # make instance
665 See how proxy *OpenGl_Structure* is used to represent instance:
667 @figure{/user_guides/visualization/images/visualization_image029.png,"",240}
669 The original object does not have to be displayed in order to make instance. Also selection handles transformations of instances correctly:
676 vdisplay s # p is not displayed
678 vconnect x 3 0 0 s p # make assembly
682 @figure{/user_guides/visualization/images/visualization_image030.png,"",420}
684 Here is the example of a more complex hierarchy involving sub-assemblies:
692 vsetlocation s 0 2.5 0
697 vconnectto b1 -2 0 0 b
699 vconnect z2 4 0 0 d d2
700 vconnect z3 6 0 0 z z2
704 @subsection occt_visu_3_3 Interactive Context
706 @subsubsection occt_visu_3_3_1 Rules
708 The Interactive Context allows managing in a transparent way the graphic and **selectable** behavior of interactive objects in one or more viewers. Most functions which allow modifying the attributes of interactive objects, and which were presented in the preceding chapter, will be looked at again here.
710 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.
713 Handle(AIS_Shape) aShapePrs = new AIS_Shape (theShape);
714 myIntContext->Display (aShapePrs, AIS_Shaded, 0, false, aShapePrs->AcceptShapeDecomposition());
715 myIntContext->SetColor(aShapePrs, Quantity_NOC_RED);
721 Handle(AIS_Shape) aShapePrs = new AIS_Shape (theShape);
722 aShapePrs->SetColor (Quantity_NOC_RED);
723 aShapePrs->SetDisplayMode (AIS_Shaded);
724 myIntContext->Display (aShapePrs);
727 @subsubsection occt_visu_3_3_2 Groups of functions
729 **Neutral Point** and **Local Selection** constitute the two operating modes or states of the **Interactive Context**, which is the central entity which pilots visualizations and selections.
730 The **Neutral Point**, which is the default mode, allows easily visualizing and selecting interactive objects, which have been loaded into the context.
731 Activating **Local Selection** for specific Objects allows selecting of their sub-parts.
733 @subsubsection occt_visu_3_3_3 Management of the Interactive Context
735 An interactive object can have a certain number of specific graphic attributes, such as visualization mode, color, and material. Correspondingly, the interactive context has a set of graphic attributes, the *Drawer*, which is valid by default for the objects it controls.
736 When an interactive object is visualized, the required graphic attributes are first taken from the object's own *Drawer* if it exists, or from the context drawer if otherwise.
738 The following adjustable settings allow personalizing the behavior of presentations and selections:
739 * Default Drawer, containing all the color and line attributes which can be used by interactive objects, which do not have their own attributes.
740 * Default Visualization Mode for interactive objects. By default: *mode 0*;
741 * Highlight color of entities detected by mouse movement. By default: *Quantity_NOC_CYAN1*;
742 * Pre-selection color. By default: *Quantity_NOC_GREEN*;
743 * Selection color (when you click on a detected object). By default: *Quantity_NOC_GRAY80*;
745 All of these settings can be modified by functions proper to the Context.
746 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.
748 Let us examine the case of two interactive objects: *theObj1* and *theObj2*:
751 theCtx->Display (theObj1, false);
752 theCtx->Display (theObj2, true); // TRUE for viewer update
753 theCtx->SetDisplayMode (theObj1, 3, false);
754 theCtx->SetDisplayMode (2, true);
755 // theObj2 is visualised in mode 2 (if it accepts this mode)
756 // theObj1 stays visualised in its mode 3
759 *PresentationManager* and *Selector3D*, which manage the presentation and selection of present interactive objects, are associated to the main Viewer.
761 @subsection occt_visu_3_4 Local Selection
763 @subsubsection occt_visu_3_4_1 Selection Modes
765 The Local Selection is defined by index (Selection Mode). The Selection Modes implemented by a specific interactive object and their meaning should be checked within the documentation of this class.
766 See, for example, *MeshVS_SelectionModeFlags* for *MeshVS_Mesh* object.
768 *AIS_Shape* is the most used interactive object. It provides API to manage selection operations on the constituent elements of shapes (selection of vertices, edges, faces, etc.). The Selection Mode for a specific shape type (*TopAbs_ShapeEnum*) is returned by method *AIS_Shape::SelectionMode()*.
770 The method *AIS_InteractiveObject::Display()* without a Selection Mode argument activates the default Selection Mode of the object.
771 The methods *AIS_InteractiveContext::Activate()* and *AIS_InteractiveContext::Deactivate()* activate and deactivate a specific Selection Mode.
773 More than one Selection Mode can be activated at the same time (but default 0 mode for selecting entire object is exclusive - it cannot be combined with others).
774 The list of active modes can be retrieved using function *AIS_InteractiveContext::ActivatedModes*.
776 @subsubsection occt_visu_3_4_2 Filters
778 To define an environment of dynamic detection, you can use standard filter classes or create your own.
779 A filter questions the owner of the sensitive primitive to determine if it has the desired qualities. If it answers positively, it is kept. If not, it is rejected.
781 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 selector answer *OK*. If so, it is kept, otherwise it is rejected.
782 You can create a custom class of filter objects by implementing the deferred function *SelectMgr_Filter::IsOk()*.
784 In *SelectMgr*, there are also Composition filters (AND Filters, OR Filters), which allow combining several filters. In Interactive Context, all filters that you add are stored in an OR filter (which answers *OK* if at least one filter answers *OK*).
786 There are Standard filters, which have already been implemented in several packages:
787 * *StdSelect_EdgeFilter* -- for edges, such as lines and circles;
788 * *StdSelect_FaceFilter* -- for faces, such as planes, cylinders and spheres;
789 * *StdSelect_ShapeTypeFilter* -- for shape types, such as compounds, solids, shells and wires;
790 * *AIS_TypeFilter* -- for types of interactive objects;
791 * *AIS_SignatureFilter* -- for types and signatures of interactive objects;
792 * *AIS_AttributeFilter* -- for attributes of Interactive Objects, such as color and width.
794 There are several functions to manipulate filters:
795 * *AIS_InteractiveContext::AddFilter* adds a filter passed as an argument.
796 * *AIS_InteractiveContext::RemoveFilter* removes a filter passed as an argument.
797 * *AIS_InteractiveContext::RemoveFilters* removes all present filters.
798 * *AIS_InteractiveContext::Filters* gets the list of filters active in a context.
803 // shading visualization mode, no specific mode, authorization for decomposition into sub-shapes
804 const TopoDS_Shape theShape;
805 Handle(AIS_Shape) aShapePrs = new AIS_Shape (theShape);
806 myContext->Display (aShapePrs, AIS_Shaded, -1, true, true);
808 // activates decomposition of shapes into faces
809 const int aSubShapeSelMode = AIS_Shape::SelectionMode (TopAbs_Face);
810 myContext->Activate (aShapePrs, aSubShapeSelMode);
812 Handle(StdSelect_FaceFilter) aFil1 = new StdSelect_FaceFilter (StdSelect_Revol);
813 Handle(StdSelect_FaceFilter) aFil2 = new StdSelect_FaceFilter (StdSelect_Plane);
814 myContext->AddFilter (aFil1);
815 myContext->AddFilter (aFil2);
817 // only faces of revolution or planar faces will be selected
818 myContext->MoveTo (thePixelX, thePixelY, myView);
821 @subsubsection occt_visu_3_4_6 Selection
823 Dynamic detection and selection are put into effect in a straightforward way. There are only a few conventions and functions to be familiar with:
824 * *AIS_InteractiveContext::MoveTo* -- passes mouse position to Interactive Context selectors.
825 * *AIS_InteractiveContext::Select* -- stores what has been detected at the last *MoveTo*. Replaces the previously selected object. Empties the stack if nothing has been detected at the last move.
826 * *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.
827 * *AIS_InteractiveContext::Select* -- selects everything found in the surrounding area.
828 * *AIS_InteractiveContext::ShiftSelect* -- selects what was not previously in the list of selected, deselects those already present.
830 Highlighting of detected and selected entities is automatically managed by the Interactive Context. The Highlight colors are those dealt with above. You can nonetheless disconnect this automatic mode if you want to manage this part yourself:
832 AIS_InteractiveContext::SetAutomaticHilight
833 AIS_InteractiveContext::AutomaticHilight
836 You can question the Interactive context by moving the mouse. The following functions can be used:
837 * *AIS_InteractiveContext::HasDetected* -- checks if there is a detected entity;
838 * *AIS_InteractiveContext::DetectedOwner* -- returns the (currently highlighted) detected entity.
840 After using the *Select* and *ShiftSelect* functions, you can explore the list of selections. The following functions can be used:
841 * *AIS_InteractiveContext::InitSelected* -- initializes an iterator;
842 * *AIS_InteractiveContext::MoreSelected* -- checks if the iterator is valid;
843 * *AIS_InteractiveContext::NextSelected* -- moves the iterator to the next position;
844 * *AIS_InteractiveContext::SelectedOwner* -- returns an entity at the current iterator position.
846 The owner object *SelectMgr_EntityOwner* is a key object identifying the selectable entity in the viewer (returned by methods *AIS_InteractiveContext::DetectedOwner* and *AIS_InteractiveContext::SelectedOwner*).
847 The Interactive Object itself can be retrieved by method *SelectMgr_EntityOwner::Selectable*, while identifying a sub-part depends on the type of Interactive Object.
848 In case of *AIS_Shape*, the (sub)shape is returned by method *StdSelect_BRepOwner::Shape*.
852 for (myAISCtx->InitSelected(); myAISCtx->MoreSelected(); myAISCtx->NextSelected())
854 Handle(SelectMgr_EntityOwner) anOwner = myAISCtx->SelectedOwner();
855 Handle(AIS_InteractiveObject) anObj = Handle(AIS_InteractiveObject)::DownCast (anOwner->Selectable());
856 if (Handle(StdSelect_BRepOwner) aBRepOwner = Handle(StdSelect_BRepOwner)::DownCast (anOwner))
858 // to be able to use the picked shape
859 TopoDS_Shape aShape = aBRepOwner->Shape();
864 @subsection occt_visu_3_5 Standard Interactive Object Classes
866 Interactive Objects are selectable and viewable objects connecting graphic representation and the underlying reference geometry.
868 They are divided into four types:
869 * the **Datum** -- a construction geometric element;
870 * the **Relation** -- a constraint on the interactive shape and the corresponding reference geometry;
871 * the **Object** -- a topological shape or connection between shapes;
872 * **None** -- a token, that instead of eliminating the object, tells the application to look further until it finds an acceptable object definition in its generation.
874 Inside these categories, there is a possibility of additional characterization by means of a signature. The signature provides an index to the further characterization. By default, the **Interactive Object** has a *None* type and a signature of 0 (equivalent to *None*).
875 If you want to give a particular type and signature to your interactive object, you must redefine the two virtual methods: *Type* and *Signature*.
877 @subsubsection occt_visu_3_5_1 Datum
879 The **Datum** groups together the construction elements such as lines, circles, points, trihedrons, plane trihedrons, planes and axes.
881 *AIS_Point, AIS_Axis, AIS_Line, AIS_Circle, AIS_Plane* and *AIS_Trihedron* have four selection modes:
882 * mode 0 : selection of a trihedron;
883 * mode 1 : selection of the origin of the trihedron;
884 * mode 2 : selection of the axes;
885 * mode 3 : selection of the planes XOY, YOZ, XOZ.
887 when you activate one of modes: 1 2 3 4, you pick AIS objects of type:
889 * *AIS_Axis* (and information on the type of axis);
890 * *AIS_Plane* (and information on the type of plane).
892 *AIS_PlaneTrihedron* offers three selection modes:
893 * mode 0 : selection of the whole trihedron;
894 * mode 1 : selection of the origin of the trihedron;
895 * mode 2 : selection of the axes -- same remarks as for the Trihedron.
897 For the presentation of planes and trihedra, the default length unit is millimeter and the default value for the representation of axes is 10. To modify these dimensions, you must temporarily recover the object **Drawer**. From it, take the *DatumAspect()* and change the value *FirstAxisLength*. Finally, recalculate the presentation.
899 @subsubsection occt_visu_3_5_2 Object
901 The **Object** type includes topological shapes, and connections between shapes.
903 *AIS_Shape* has two visualization modes:
904 * mode 0 : Line (default mode)
905 * mode 1 : Shading (depending on the type of shape)
907 *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.
908 *AIS_MultipleConnectedInteractive* is an object connected to a list of interactive objects (which can also be Connected objects. It does not require memory-hungry presentation calculations).
910 *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.
912 The class *AIS_ColoredShape* allows using custom colors and line widths for *TopoDS_Shape* objects and their sub-shapes.
915 AIS_ColoredShape aColoredShape = new AIS_ColoredShape (theShape);
917 // setup color of entire shape
918 aColoredShape->SetColor (Quantity_NOC_RED);
920 // setup line width of entire shape
921 aColoredShape->SetWidth (1.0);
923 // set transparency value
924 aColoredShape->SetTransparency (0.5);
926 // customize color of specified sub-shape
927 aColoredShape->SetCustomColor (theSubShape, Quantity_NOC_BLUE1);
929 // customize line width of specified sub-shape
930 aColoredShape->SetCustomWidth (theSubShape, 0.25);
933 The presentation class *AIS_PointCloud* can be used for efficient drawing of large arbitrary sets of colored points. It uses *Graphic3d_ArrayOfPoints* to pass point data into OpenGl graphic driver to draw a set points as an array of "point sprites". The point data is packed into vertex buffer object for performance.
934 - The type of point marker used to draw points can be specified as a presentation aspect.
935 - The presentation provides selection by a bounding box of the visualized set of points. It supports two display / highlighting modes: points or bounding box.
937 @figure{point_cloud.png,"A random colored cloud of points",240}
941 Handle(Graphic3d_ArrayOfPoints) aPoints = new Graphic3d_ArrayOfPoints (2000, Standard_True);
942 aPoints->AddVertex (gp_Pnt(-40.0, -40.0, -40.0), Quantity_Color (Quantity_NOC_BLUE1));
943 aPoints->AddVertex (gp_Pnt (40.0, 40.0, 40.0), Quantity_Color (Quantity_NOC_BLUE2));
945 Handle(AIS_PointCloud) aPntCloud = new AIS_PointCloud();
946 aPntCloud->SetPoints (aPoints);
949 The draw command *vpointcloud* builds a cloud of points from shape triangulation.
950 This command can also draw a sphere surface or a volume with a large amount of points (more than one million).
952 @subsubsection occt_visu_3_5_3 Relations
954 The **Relation** is made up of constraints on one or more interactive shapes and the corresponding reference geometry. For example, you might want to constrain two edges in a parallel relation. This constraint is considered as an object in its own right, and is shown as a sensitive primitive. This takes the graphic form of a perpendicular arrow marked with the || symbol and lying between the two edges.
956 The following relations are provided by *AIS*:
957 * *AIS_ConcentricRelation*
959 * *AIS_IdenticRelation*
960 * *AIS_ParallelRelation*
961 * *AIS_PerpendicularRelation*
963 * *AIS_SymmetricRelation*
964 * *AIS_TangentRelation*
966 The list of relations is not exhaustive.
968 @subsubsection occt_visu_3_5_4 Dimensions
969 * *AIS_AngleDimension*
970 * *AIS_Chamf3dDimension*
971 * *AIS_DiameterDimension*
972 * *AIS_DimensionOwner*
973 * *AIS_LengthDimension*
974 * *AIS_OffsetDimension*
975 * *AIS_RadiusDimension*
977 @subsubsection occt_visu_3_5_5 MeshVS_Mesh
979 *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.
981 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.
983 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.
985 You can add/remove builders using the following methods:
987 MeshVS_Mesh::AddBuilder (const Handle(MeshVS_PrsBuilder)& theBuilder, Standard_Boolean theToTreatAsHilighter);
988 MeshVS_Mesh::RemoveBuilder (const Standard_Integer theIndex);
989 MeshVS_Mesh::RemoveBuilderById (const Standard_Integer theId);
992 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:
999 It is also possible to display deformed mesh in wireframe, shading or shrink modes usung:
1001 MeshVS_DMF_DeformedPrsWireFrame
1002 MeshVS_DMF_DeformedPrsShading
1003 MeshVS_DMF_DeformedPrsShrink
1006 The following methods represent different kinds of data:
1008 MeshVS_DMF_VectorDataPrs
1009 MeshVS_DMF_NodalColorDataPrs
1010 MeshVS_DMF_ElementalColorDataPrs
1011 MeshVS_DMF_TextDataPrs
1012 MeshVS_DMF_EntitiesWithData
1015 The following methods provide selection and highlighting:
1017 MeshVS_DMF_SelectionPrs
1018 MeshVS_DMF_HilightPrs
1021 *MeshVS_DMF_User* is a user-defined mode.
1023 These values will be used by the presentation builder.
1024 There is also a set of selection modes flags that can be grouped in a combination of bits:
1028 * *MeshVS_SMF_Volume*
1029 * *MeshVS_SMF_Element* -- groups *0D, Link, Face* and *Volume* as a bit mask;
1031 * *MeshVS_SMF_All* -- groups *Element* and *Node* as a bit mask;
1033 * *MeshVS_SMF_Group*
1035 Such an object, for example, can be used for displaying the object and stored in the STL file format:
1038 // read the data and create a data source
1039 Handle(Poly_Triangulation) aSTLMesh = RWStl::ReadFile (aFileName);
1040 Handle(XSDRAWSTLVRML_DataSource) aDataSource = new XSDRAWSTLVRML_DataSource (aSTLMesh);
1043 Handle(MeshVS_Mesh) aMeshPrs = new MeshVS();
1044 aMeshPrs->SetDataSource (aDataSource);
1046 // use default presentation builder
1047 Handle(MeshVS_MeshPrsBuilder) aBuilder = new MeshVS_MeshPrsBuilder (aMeshPrs);
1048 aMeshPrs->AddBuilder (aBuilder, true);
1051 *MeshVS_NodalColorPrsBuilder* allows representing a mesh with a color scaled texture mapped on it.
1052 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.
1053 The following example demonstrates how you can do this (check if the view has been set up to display textures):
1056 // assign nodal builder to the mesh
1057 Handle(MeshVS_NodalColorPrsBuilder) aBuilder = new MeshVS_NodalColorPrsBuilder (theMeshPrs, MeshVS_DMF_NodalColorDataPrs | MeshVS_DMF_OCCMask);
1058 aBuilder->UseTexture (true);
1060 // prepare color map
1061 Aspect_SequenceOfColor aColorMap;
1062 aColorMap.Append (Quantity_NOC_RED);
1063 aColorMap.Append (Quantity_NOC_BLUE1);
1065 // assign color scale map values (0..1) to nodes
1066 TColStd_DataMapOfIntegerReal aScaleMap;
1068 // iterate through the nodes and add an node id and an appropriate value to the map
1069 aScaleMap.Bind (anId, aValue);
1071 // pass color map and color scale values to the builder
1072 aBuilder->SetColorMap (aColorMap);
1073 aBuilder->SetInvalidColor (Quantity_NOC_BLACK);
1074 aBuilder->SetTextureCoords (aScaleMap);
1075 aMesh->AddBuilder (aBuilder, true);
1078 @subsection occt_visu_3_6 Dynamic Selection
1080 The dynamic selection represents the topological shape, which you want to select, by decomposition of *sensitive primitives* -- the sub-parts of the shape that will be detected and highlighted. The sets of these primitives are handled by the powerful three-level BVH tree selection algorithm.
1082 For more details on the algorithm and examples of usage, refer to @ref occt_visu_2_2 "Selection" chapter.
1084 @section occt_visu_4 3D Presentations
1086 @subsection occt_visu_4_1 Glossary of 3D terms
1088 * **Group** -- a set of primitives and attributes on those primitives. Primitives and attributes may be added to a group but cannot be removed from it, unless erased globally. A group can have a pick identity.
1089 * **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.
1090 * **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.
1091 * **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.
1092 * **View** -- is defined by a view orientation, a view mapping, and a context view.
1093 * **Viewer** -- manages a set of views.
1094 * **View orientation** -- defines the manner in which the observer looks at the scene in terms of View Reference Coordinates.
1095 * **View mapping** -- defines the transformation from View Reference Coordinates to the Normalized Projection Coordinates. This follows the Phigs scheme.
1096 * **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.
1098 @subsection occt_visu_4_2 Graphic primitives
1100 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, such as polylines, planar polygons with or without holes, text and markers, and attributes, such as color, transparency, reflection, line type, line width, and text font. 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.
1102 Graphic structures can be:
1107 * Connected to form a tree hierarchy of structures, created by transformations.
1109 There are classes for:
1110 * Visual attributes for lines, faces, markers, text, materials,
1111 * Vectors and vertices,
1112 * Graphic objects, groups, and structures.
1114 @subsubsection occt_visu_4_2_2 Structure hierarchies
1116 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.
1118 @subsubsection occt_visu_4_2_3 Graphic primitives
1120 * Have one or more vertices,
1121 * Have a type, a scale factor, and a color,
1122 * Have a size, shape, and orientation independent of transformations.
1124 * Has at least three vertices,
1125 * Has nodal normals defined for shading,
1126 * Has interior attributes -- style, color, front and back material, texture and reflection ratio.
1127 * **Polylines** or **Segments**
1128 * Have two or more vertices,
1129 * Have the following attributes -- type, width scale factor, color.
1131 * Has geometric and non-geometric attributes,
1132 * Geometric attributes -- character height, character up vector, text path, horizontal and vertical alignment, orientation, three-dimensional position, zoomable flag
1133 * Non-geometric attributes -- text font, character spacing, character expansion factor, color.
1135 @subsubsection occt_visu_4_2_4 Primitive arrays
1137 The different types of primitives could be presented with the following primitive arrays:
1138 * *Graphic3d_ArrayOfPoints,*
1139 * *Graphic3d_ArrayOfPolylines,*
1140 * *Graphic3d_ArrayOfSegments,*
1141 * *Graphic3d_ArrayOfTriangleFans,*
1142 * *Graphic3d_ArrayOfTriangles,*
1143 * *Graphic3d_ArrayOfTriangleStrips.*
1145 The *Graphic3d_ArrayOfPrimitives* is a base class for these primitive arrays.
1146 Method set *Graphic3d_ArrayOfPrimitives::AddVertex* allows adding vertices to the primitive array with their attributes (color, normal, texture coordinates).
1147 You can also modify the values assigned to the vertex or query these values by the vertex index.
1149 The following example shows how to define an array of points:
1153 Handle(Graphic3d_ArrayOfPoints) anArray = new Graphic3d_ArrayOfPoints (theVerticiesMaxCount);
1155 // add vertices to the array
1156 anArray->AddVertex (10.0, 10.0, 10.0);
1157 anArray->AddVertex (0.0, 10.0, 10.0);
1159 // add the array to the structure
1160 Handle(Graphic3d_Group) aGroup = thePrs->NewGroup();
1161 aGroup->AddPrimitiveArray (anArray);
1162 aGroup->SetGroupPrimitivesAspect (myDrawer->PointAspect()->Aspect());
1165 If the primitives share the same vertices (polygons, triangles, etc.) then you can define them as indices of the vertices array.
1166 The method *Graphic3d_ArrayOfPrimitives::AddEdge* allows defining the primitives by indices. This method adds an "edge" in the range *[1, VertexNumber()]* in the array.
1167 It is also possible to query the vertex defined by an edge using method *Graphic3d_ArrayOfPrimitives::Edge*.
1169 The following example shows how to define an array of triangles:
1173 Standard_Boolean hasNormals = false;
1174 Standard_Boolean hasColors = false;
1175 Standard_Boolean hasTextureCrds = false;
1176 Handle(Graphic3d_ArrayOfTriangles) anArray = new Graphic3d_ArrayOfTriangles (theVerticesMaxCount, theEdgesMaxCount, hasNormals, hasColors, hasTextureCrds);
1177 // add vertices to the array
1178 anArray->AddVertex (-1.0, 0.0, 0.0); // vertex 1
1179 anArray->AddVertex ( 1.0, 0.0, 0.0); // vertex 2
1180 anArray->AddVertex ( 0.0, 1.0, 0.0); // vertex 3
1181 anArray->AddVertex ( 0.0,-1.0, 0.0); // vertex 4
1183 // add edges to the array
1184 anArray->AddEdge (1); // first triangle
1185 anArray->AddEdge (2);
1186 anArray->AddEdge (3);
1187 anArray->AddEdge (1); // second triangle
1188 anArray->AddEdge (2);
1189 anArray->AddEdge (4);
1191 // add the array to the structure
1192 Handle(Graphic3d_Group) aGroup = thePrs->NewGroup();
1193 aGroup->AddPrimitiveArray (anArray);
1194 aGroup->SetGroupPrimitivesAspect (myDrawer->ShadingAspect()->Aspect());
1197 @subsubsection occt_visu_4_2_5 Text primitive
1199 *TKOpenGL* toolkit renders text labels using texture fonts. *Graphic3d* text primitives have the following features:
1200 * fixed size (non-zoomable) or zoomable,
1201 * can be rotated to any angle in the view plane,
1202 * support unicode charset.
1204 The text attributes for the group could be defined with the *Graphic3d_AspectText3d* attributes group.
1205 To add any text to the graphic structure you can use the following methods:
1207 void Graphic3d_Group::Text (const Standard_CString theText,
1208 const Graphic3d_Vertex& thePoint,
1209 const Standard_Real theHeight,
1210 const Quantity_PlaneAngle theAngle,
1211 const Graphic3d_TextPath theTp,
1212 const Graphic3d_HorizontalTextAlignment theHta,
1213 const Graphic3d_VerticalTextAlignment theVta,
1214 const Standard_Boolean theToEvalMinMax);
1217 The meaning of these parameters is as follows:
1218 * *theText* - the text string,
1219 * *thePoint* - the three-dimensional position of the text,
1220 * *theHeight* - the text height,
1221 * *theAngle* - the text orientation (at the moment, this parameter has no effect, but you can specify the text orientation through the *Graphic3d_AspectText3d* attributes).
1222 * *theTp* defines the text path,
1223 * *theHta* - the horizontal alignment of the text,
1224 * *theVta* - the vertical alignment of the text.
1226 You can pass FALSE as *theToEvalMinMax* if you do not want the graphic3d structure boundaries to be affected by the text position.
1228 **Note** that the text orientation angle can be defined by *Graphic3d_AspectText3d* attributes.
1230 void Graphic3d_Group::Text (const Standard_CString theText,
1231 const Graphic3d_Vertex& thePoint,
1232 const Standard_Real theHeight,
1233 const Standard_Boolean theToEvalMinMax);
1234 void Graphic3d_Group::Text (const TCcollection_ExtendedString& theText,
1235 const Graphic3d_Vertex& thePoint,
1236 const Standard_Real theHeight,
1237 const Quantity_PlaneAngle theAngle,
1238 const Graphic3d_TextPath theTp,
1239 const Graphic3d_HorizontalTextAlignment theHta,
1240 const Graphic3d_VerticalTextAlignment theVta,
1241 const Standard_Boolean theToEvalMinMax);
1242 void Graphic3d_Group::Text (const TCcollection_ExtendedString& theText,
1243 const Graphic3d_Vertex& thePoint,
1244 const Standard_Real theHeight,
1245 const Standard_Boolean theToEvalMinMax);
1251 Handle(Graphic3d_Group) aGroup = thePrs->NewGroup();
1253 // change the text aspect
1254 Handle(Graphic3d_AspectText3d) aTextAspect = new Graphic3d_AspectText3d();
1255 aTextAspect->SetTextZoomable (true);
1256 aTextAspect->SetTextAngle (45.0);
1257 aGroup->SetPrimitivesAspect (aTextAspect);
1259 // add a text primitive to the structure
1260 Graphic3d_Vertex aPoint (1, 1, 1);
1261 aGroup->Text (Standard_CString ("Text"), aPoint, 16.0);
1264 @subsubsection occt_visu_4_2_6 Materials
1266 A *Graphic3d_MaterialAspect* is defined by:
1268 * Diffuse reflection -- a component of the object color;
1269 * Ambient reflection;
1270 * Specular reflection -- a component of the color of the light source;
1273 The following items are required to determine the three colors of reflection:
1275 * Coefficient of diffuse reflection;
1276 * Coefficient of ambient reflection;
1277 * Coefficient of specular reflection.
1279 @subsubsection occt_visu_4_2_7 Textures
1281 A *texture* is defined by a name.
1282 Three types of texture are available:
1285 * Environment mapping.
1287 @subsubsection occt_visu_4_2_8 Shaders
1289 OCCT visualization core supports GLSL shaders. Shaders can be assigned to a generic presentation by its drawer attributes (Graphic3d aspects). To enable custom shader for a specific AIS_Shape in your application, the following API functions can be used:
1292 // Create shader program
1293 Handle(Graphic3d_ShaderProgram) aProgram = new Graphic3d_ShaderProgram();
1295 // Attach vertex shader
1296 aProgram->AttachShader (Graphic3d_ShaderObject::CreateFromFile (Graphic3d_TOS_VERTEX, "<Path to VS>"));
1298 // Attach fragment shader
1299 aProgram->AttachShader (Graphic3d_ShaderObject::CreateFromFile (Graphic3d_TOS_FRAGMENT, "<Path to FS>"));
1301 // Set values for custom uniform variables (if they are)
1302 aProgram->PushVariable ("MyColor", Graphic3d_Vec3 (0.0f, 1.0f, 0.0f));
1304 // Set aspect property for specific AIS_Shape
1305 theAISShape->Attributes()->ShadingAspect()->Aspect()->SetShaderProgram (aProgram);
1308 @subsection occt_visu_4_3 Graphic attributes
1310 @subsubsection occt_visu_4_3_1 Aspect package overview
1312 The *Aspect* package provides classes for the graphic elements in the viewer:
1313 * Groups of graphic attributes;
1314 * Edges, lines, background;
1317 * Enumerations for many of the above.
1319 @subsection occt_visu_4_4 3D view facilities
1321 @subsubsection occt_visu_4_4_1 Overview
1323 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.
1325 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, etc.) in any particular view.
1327 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:
1328 * Default parameters of the viewer,
1329 * Views (orthographic, perspective),
1330 * Lighting (positional, directional, ambient, spot, headlight),
1332 * Instantiated sequences of views, planes, light sources, graphic structures, and picks,
1333 * Various package methods.
1335 @subsubsection occt_visu_4_4_2 A programming example
1337 This sample TEST program for the *V3d* Package uses primary packages *Xw* and *Graphic3d* and secondary packages *Visual3d, Aspect, Quantity* and *math*.
1340 // create a default display connection
1341 Handle(Aspect_DisplayConnection) aDispConnection = new Aspect_DisplayConnection();
1342 // create a Graphic Driver
1343 Handle(OpenGl_GraphicDriver) aGraphicDriver = new OpenGl_GraphicDriver (aDispConnection);
1344 // create a Viewer to this Driver
1345 Handle(V3d_Viewer) VM = new V3d_Viewer (aGraphicDriver);
1346 VM->SetDefaultBackgroundColor (Quantity_NOC_DARKVIOLET);
1347 VM->SetDefaultViewProj (V3d_Xpos);
1348 // Create a structure in this Viewer
1349 Handle(Graphic3d_Structure) aStruct = new Graphic3d_Structure (VM->Viewer());
1351 // Type of structure
1352 aStruct->SetVisual (Graphic3d_TOS_SHADING);
1354 // Create a group of primitives in this structure
1355 Handle(Graphic3d_Group) aPrsGroup = new Graphic3d_Group (aStruct);
1357 // Fill this group with one quad of size 100
1358 Handle(Graphic3d_ArrayOfTriangleStrips) aTriangles = new Graphic3d_ArrayOfTriangleStrips (4);
1359 aTriangles->AddVertex (-100./2., -100./2., 0.0);
1360 aTriangles->AddVertex (-100./2., 100./2., 0.0);
1361 aTriangles->AddVertex ( 100./2., -100./2., 0.0);
1362 aTriangles->AddVertex ( 100./2., 100./2., 0.0);
1363 aPrsGroup->AddPrimitiveArray (aTriangles);
1364 aPrsGroup->SetGroupPrimitivesAspect (new Graphic3d_AspectFillArea3d());
1366 // Create Ambient and Infinite Lights in this Viewer
1367 Handle(V3d_AmbientLight) aLight1 = new V3d_AmbientLight (VM, Quantity_NOC_GRAY50);
1368 Handle(V3d_DirectionalLight) aLight2 = new V3d_DirectionalLight (VM, V3d_XnegYnegZneg, Quantity_NOC_WHITE);
1370 // Create a 3D quality Window with the same DisplayConnection
1371 Handle(Xw_Window) aWindow = new Xw_Window (aDispConnection, "Test V3d", 0.5, 0.5, 0.5, 0.5);
1373 // Map this Window to this screen
1376 // Create a Perspective View in this Viewer
1377 Handle(V3d_View) aView = new V3d_View (VM);
1378 aView->Camera()->SetProjectionType (Graphic3d_Camera::Projection_Perspective);
1379 // Associate this View with the Window
1380 aView ->SetWindow (aWindow);
1381 // Display ALL structures in this View
1382 VM->Viewer()->Display();
1383 // Finally update the Visualization in this View
1385 // Fit view to object size
1389 @subsubsection occt_visu_4_4_3 Define viewing parameters
1391 View projection and orientation in OCCT *V3d_View* are driven by camera. The camera calculates and supplies projection and view orientation matrices for rendering by OpenGL. The allows to the user to control all projection parameters. The camera is defined by the following properties:
1393 * **Eye** -- defines the observer (camera) position. Make sure the Eye point never gets between the Front and Back clipping planes.
1395 * **Center** -- defines the origin of View Reference Coordinates (where camera is aimed at).
1397 * **Direction** -- defines the direction of camera view (from the Eye to the Center).
1399 * **Distance** -- defines the distance between the Eye and the Center.
1401 * **Front** Plane -- defines the position of the front clipping plane in View Reference Coordinates system.
1403 * **Back** Plane -- defines the position of the back clipping plane in View Reference Coordinates system.
1405 * **ZNear** -- defines the distance between the Eye and the Front plane.
1407 * **ZFar** -- defines the distance between the Eye and the Back plane.
1409 Most common view manipulations (panning, zooming, rotation) are implemented as convenience methods of *V3d_View* class, however *Graphic3d_Camera* class can also be used directly by application developers:
1413 // rotate camera by X axis on 30.0 degrees
1415 aTrsf.SetRotation (gp_Ax1 (gp_Pnt (0.0, 0.0, 0.0), gp_Dir (1.0, 0.0, 0.0)), 30.0);
1416 aView->Camera()->Transform (aTrsf);
1419 @subsubsection occt_visu_4_4_4 Orthographic Projection
1421 @figure{view_frustum.png,"Perspective and orthographic projection",420}
1423 The following code configures the camera for orthographic rendering:
1426 // Create an orthographic View in this Viewer
1427 Handle(V3d_View) aView = new V3d_View (VM);
1428 aView->Camera()->SetProjectionType (Graphic3d_Camera::Projection_Orthographic);
1429 // update the Visualization in this View
1433 @subsubsection occt_visu_4_4_5 Perspective Projection
1435 **Field of view (FOVy)** -- defines the field of camera view by y axis in degrees (45° is default).
1437 @figure{camera_perspective.png,"Perspective frustum",420}
1439 The following code configures the camera for perspective rendering:
1442 // Create a perspective View in this Viewer
1443 Handle(V3d_View) aView = new V3d_View(VM);
1444 aView->Camera()->SetProjectionType (Graphic3d_Camera::Projection_Perspective);
1449 @subsubsection occt_visu_4_4_6 Stereographic Projection
1451 **IOD** -- defines the intraocular distance (in world space units).
1453 There are two types of IOD:
1454 * _IODType_Absolute_ : Intraocular distance is defined as an absolute value.
1455 * _IODType_Relative_ : Intraocular distance is defined relative to the camera focal length (as its coefficient).
1457 **Field of view (FOV)** -- defines the field of camera view by y axis in degrees (45° is default).
1459 **ZFocus** -- defines the distance to the point of stereographic focus.
1461 @figure{stereo.png,"Stereographic projection",420}
1463 To enable stereo projection, your workstation should meet the following requirements:
1465 * The graphic card should support quad buffering.
1466 * You need active 3D glasses (LCD shutter glasses).
1467 * The graphic driver needs to be configured to impose quad buffering for newly created OpenGl contexts; the viewer and the view should be created after that.
1469 In stereographic projection mode the camera prepares two projection matrices to display different stereo-pictures for the left and for the right eye. In a non-stereo camera this effect is not visible because only the same projection is used for both eyes.
1471 To enable quad buffering support you should provide the following settings to the graphic driver *opengl_caps*:
1474 Handle(OpenGl_GraphicDriver) aDriver = new OpenGl_GraphicDriver();
1475 OpenGl_Caps& aCaps = aDriver->ChangeOptions();
1476 aCaps.contextStereo = Standard_True;
1479 The following code configures the camera for stereographic rendering:
1482 // Create a Stereographic View in this Viewer
1483 Handle(V3d_View) aView = new V3d_View(VM);
1484 aView->Camera()->SetProjectionType (Graphic3d_Camera::Projection_Stereo);
1485 // Change stereo parameters
1486 aView->Camera()->SetIOD (IODType_Absolute, 5.0);
1487 // Finally update the Visualization in this View
1491 @subsubsection occt_visu_4_4_7 View frustum culling
1493 The algorithm of frustum culling on CPU-side is activated by default for 3D viewer. This algorithm allows skipping the presentation outside camera at the rendering stage, providing better performance. The following features support this method:
1494 * *Graphic3d_Structure::CalculateBoundBox()* is used to calculate axis-aligned bounding box of a presentation considering its transformation.
1495 * *V3d_View::SetFrustumCulling* enables or disables frustum culling for the specified view.
1496 * Classes *OpenGl_BVHClipPrimitiveSet* and *OpenGl_BVHTreeSelector* handle the detection of outer objects and usage of acceleration structure for frustum culling.
1497 * *BVH_BinnedBuilder* class splits several objects with null bounding box.
1499 @subsubsection occt_visu_4_4_9 View background styles
1500 There are three types of background styles available for *V3d_View*: solid color, gradient color and image.
1502 To set solid color for the background you can use the following method:
1504 void V3d_View::SetBackgroundColor (const Quantity_Color& theColor);
1507 The gradient background style could be set up with the following method:
1509 void V3d_View::SetBgGradientColors (const Quantity_Color& theColor1,
1510 const Quantity_Color& theColor2,
1511 const Aspect_GradientFillMethod theFillStyle,
1512 const Standard_Boolean theToUpdate = false);
1515 The *theColor1* and *theColor2* parameters define the boundary colors of interpolation, the *theFillStyle* parameter defines the direction of interpolation.
1517 To set the image as a background and change the background image style you can use the following method:
1519 void V3d_View::SetBackgroundImage (const Standard_CString theFileName,
1520 const Aspect_FillMethod theFillStyle,
1521 const Standard_Boolean theToUpdate = false);
1524 The *theFileName* parameter defines the image file name and the path to it, the *theFillStyle* parameter defines the method of filling the background with the image. The methods are:
1525 * *Aspect_FM_NONE* -- draws the image in the default position;
1526 * *Aspect_FM_CENTERED* -- draws the image at the center of the view;
1527 * *Aspect_FM_TILED* -- tiles the view with the image;
1528 * *Aspect_FM_STRETCH* -- stretches the image over the view.
1530 @subsubsection occt_visu_4_4_10 Dumping a 3D scene into an image file
1532 The 3D scene displayed in the view can be dumped into image file with resolution independent from window size (using offscreen buffer).
1533 The *V3d_View* has the following methods for dumping the 3D scene:
1535 Standard_Boolean V3d_View::Dump (const Standard_CString theFile,
1536 const Image_TypeOfImage theBufferType);
1538 Dumps the scene into an image file with the view dimensions.
1539 The raster image data handling algorithm is based on the *Image_AlienPixMap* class. The supported extensions are ".png", ".bmp", ".jpg" and others supported by **FreeImage** library.
1540 The value passed as *theBufferType* argument defines the type of the buffer for an output image *(RGB, RGBA, floating-point, RGBF, RGBAF)*. Method returns TRUE if the scene has been successfully dumped.
1543 Standard_Boolean V3d_View::ToPixMap (Image_PixMap& theImage,
1544 const V3d_ImageDumpOptions& theParams);
1546 Dumps the displayed 3d scene into a pixmap with a width and height passed through parameters structure *theParams*.
1548 @subsubsection occt_visu_4_4_13 Ray tracing support
1550 OCCT visualization provides rendering by real-time ray tracing technique. It is allowed to switch easily between usual rasterization and ray tracing rendering modes. The core of OCCT ray tracing is written using GLSL shaders. The ray tracing has a wide list of features:
1556 * Support of non-polygon objects, such as lines, text, highlighting, selection.
1557 * Performance optimization using 2-level bounding volume hierarchy (BVH).
1559 The ray tracing algorithm is recursive (Whitted's algorithm). It uses BVH effective optimization structure. The structure prepares optimized data for a scene geometry for further displaying it in real-time. The time-consuming re-computation of the BVH is not necessary for view operations, selections, animation and even editing of the scene by transforming location of the objects. It is only necessary when the list of displayed objects or their geometry changes.
1560 To make the BVH reusable it has been added into an individual reusable OCCT package *TKMath/BVH*.
1562 There are several ray-tracing options that user can switch on/off:
1563 * Maximum ray tracing depth
1565 * Specular reflections
1566 * Adaptive anti aliasing
1567 * Transparency shadow effects
1571 Graphic3d_RenderingParams& aParams = aView->ChangeRenderingParams();
1572 // specifies rendering mode
1573 aParams.Method = Graphic3d_RM_RAYTRACING;
1574 // maximum ray-tracing depth
1575 aParams.RaytracingDepth = 3;
1576 // enable shadows rendering
1577 aParams.IsShadowEnabled = true;
1578 // enable specular reflections.
1579 aParams.IsReflectionEnabled = true;
1580 // enable adaptive anti-aliasing
1581 aParams.IsAntialiasingEnabled = true;
1582 // enable light propagation through transparent media.
1583 aParams.IsTransparentShadowEnabled = true;
1588 @subsubsection occt_visu_4_4_14 Display priorities
1590 Structure display priorities control the order, in which structures are drawn. When you display a structure you specify its priority. The lower is the value, the lower is the display priority. When the display is regenerated, the structures with the lowest priority are drawn first. The structures with the same display priority are drawn in the same order as they have been displayed. OCCT supports eleven structure display priorities.
1592 @subsubsection occt_visu_4_4_15 Z-layer support
1594 OCCT features depth-arranging functionality called z-layer. A graphical presentation can be put into a z-layer. In general, this function can be used for implementing "bring to front" functionality in a graphical application.
1599 // set z-layer to an interactive object
1600 Handle(AIS_InteractiveContext) theContext;
1601 Handle(AIS_InteractiveObject) theInterObj;
1602 Standard_Integer anId = 3;
1603 aViewer->AddZLayer (anId);
1604 theContext->SetZLayer (theInterObj, anId);
1607 For each z-layer, it is allowed to:
1608 * Enable / disable depth test for layer.
1609 * Enable / disable depth write for layer.
1610 * Enable / disable depth buffer clearing.
1611 * Enable / disable polygon offset.
1613 You can get the options using getter from *V3d_Viewer*. It returns *Graphic3d_ZLayerSettings* for a given *LayerId*.
1617 // change z-layer settings
1618 Graphic3d_ZLayerSettings aSettings = aViewer->ZLayerSettings (anId);
1619 aSettings.SetEnableDepthTest (true);
1620 aSettings.SetEnableDepthWrite(true);
1621 aSettings.SetClearDepth (true);
1622 aSettings.SetPolygonOffset (Graphic3d_PolygonOffset());
1623 aViewer->SetZLayerSettings (anId, aSettings);
1626 Another application for Z-Layer feature is treating visual precision issues when displaying objects far from the World Center.
1627 The key problem with such objects is that visualization data is stored and manipulated with single precision floating-point numbers (32-bit).
1628 Single precision 32-bit floating-point numbers give only 6-9 significant decimal digits precision,
1629 while double precision 64-bit numbers give 15-17 significant decimal digits precision, which is sufficient enough for most applications.
1631 When moving an Object far from the World Center, float number steadily eats precision.
1632 The camera Eye position adds leading decimal digits to the overall Object transformation, which discards smaller digits due to floating point number nature.
1633 For example, the object of size 0.0000123 moved to position 1000 has result transformation 1000.0000123,
1634 which overflows single precision floating point - considering the most optimistic scenario of 9 significant digits (but it is really not this case), the result number will be 1000.00001.
1636 This imprecision results in visual artifacts of two kinds in the 3D Viewer:
1638 * Overall per-vertex Object distortion.
1639 This happens when each vertex position has been defined within World Coordinate system.
1640 * The object itself is not distorted, but its position in the World is unstable and imprecise - the object jumps during camera manipulations.
1641 This happens when vertices have been defined within Local Coordinate system at the distance small enough to keep precision within single precision float,
1642 however Local Transformation applied to the Object is corrupted due to single precision float.
1644 The first issue cannot be handled without switching the entire presentation into double precision (for each vertex position).
1645 However, visualization hardware is much faster using single precision float number rather than double precision - so this is not an option in most cases.
1646 The second issue, however, can be negated by applying special rendering tricks.
1648 So, to apply this feature in OCCT, the application:
1650 * Defines Local Transformation for each object to fit the presentation data into single precision float without distortion.
1651 * Spatially splits the world into smaller areas/cells where single precision float will be sufficient.
1652 The size of such cell might vary and depends on the precision required by application (e.g. how much user is able to zoom in camera within application).
1653 * Defines a Z-Layer for each spatial cell containing any object.
1654 * Defines the Local Origin property of the Z-Layer according to the center of the cell.
1657 Graphic3d_ZLayerSettings aSettings = aViewer->ZLayerSettings (anId);
1658 aSettings.SetLocalOrigin (400.0, 0.0, 0.0);
1660 * Assigns a presentable object to the nearest Z-Layer.
1662 Note that Local Origin of the Layer is used only for rendering - everything outside will be still defined in the World Coordinate System,
1663 including Local Transformation of the Object and Detection results.
1664 E.g., while moving the presentation between Z-layers with different Local Origins, the Object will stay at the same place - only visualization quality will vary.
1666 @subsubsection occt_visu_4_4_16 Clipping planes
1668 The ability to define custom clipping planes could be very useful for some tasks. OCCT provides such an opportunity.
1670 The *Graphic3d_ClipPlane* class provides the services for 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:
1673 Graphic3d_ClipPlane::Graphic3d_ClipPlane (const gp_Pln& thePlane)
1674 void Graphic3d_ClipPlane::SetEquation (const gp_Pln& thePlane)
1675 Graphic3d_ClipPlane::Graphic3d_ClipPlane (const Equation& theEquation)
1676 void Graphic3d_ClipPlane::SetEquation (const Equation& theEquation)
1677 gp_Pln Graphic3d_ClipPlane::ToPlane() const
1680 The clipping planes can be activated with the following method:
1682 void Graphic3d_ClipPlane::SetOn (const Standard_Boolean theIsOn)
1685 The number of clipping planes is limited. You can check the limit value via method *Graphic3d_GraphicDriver::InquireLimit()*;
1688 // get the limit of clipping planes for the current view
1689 Standard_Integer aMaxClipPlanes = aView->Viewer()->Driver()->InquireLimit (Graphic3d_TypeOfLimit_MaxNbClipPlanes);
1692 Let us see for example how to create a new clipping plane with custom parameters and add it to a view or to an object:
1694 // create a new clipping plane
1695 const Handle(Graphic3d_ClipPlane)& aClipPlane = new Graphic3d_ClipPlane();
1696 // change equation of the clipping plane
1697 Standard_Real aCoeffA = ...
1698 Standard_Real aCoeffB = ...
1699 Standard_Real aCoeffC = ...
1700 Standard_Real aCoeffD = ...
1701 aClipPlane->SetEquation (gp_Pln (aCoeffA, aCoeffB, aCoeffC, aCoeffD));
1703 aClipPlane->SetCapping (aCappingArg == "on");
1704 // set the material with red color of clipping plane
1705 Graphic3d_MaterialAspect aMat = aClipPlane->CappingMaterial();
1706 Quantity_Color aColor (1.0, 0.0, 0.0, Quantity_TOC_RGB);
1707 aMat.SetAmbientColor (aColor);
1708 aMat.SetDiffuseColor (aColor);
1709 aClipPlane->SetCappingMaterial (aMat);
1710 // set the texture of clipping plane
1711 Handle(Graphic3d_Texture2Dmanual) aTexture = ...
1712 aTexture->EnableModulate();
1713 aTexture->EnableRepeat();
1714 aClipPlane->SetCappingTexture (aTexture);
1715 // add the clipping plane to an interactive object
1716 Handle(AIS_InteractiveObject) aIObj = ...
1717 aIObj->AddClipPlane (aClipPlane);
1718 // or to the whole view
1719 aView->AddClipPlane (aClipPlane);
1720 // activate the clipping plane
1721 aClipPlane->SetOn(Standard_True);
1727 @subsubsection occt_visu_4_4_17 Automatic back face culling
1729 Back face culling reduces the rendered number of triangles (which improves the performance) and eliminates artifacts at shape boundaries. However, this option can be used only for solid objects, where the interior is actually invisible from any point of view. Automatic back-face culling mechanism is turned on by default, which is controlled by *V3d_View::SetBackFacingModel()*.
1731 The following features are applied in *StdPrs_ToolShadedShape::IsClosed()*, which is used for definition of back face culling in *ShadingAspect*:
1732 * disable culling for free closed Shells (not inside the Solid) since reversed orientation of a free Shell is a valid case;
1733 * enable culling for Solids packed into a compound;
1734 * ignore Solids with incomplete triangulation.
1736 Back face culling is turned off at TKOpenGl level in the following cases:
1737 * clipping/capping planes are in effect;
1738 * for translucent objects;
1739 * with hatching presentation style.
1741 @subsection occt_visu_4_5 Examples: creating a 3D scene
1743 To create 3D graphic objects and display them in the screen, follow the procedure below:
1744 1. Create attributes.
1745 2. Create a 3D viewer.
1747 4. Create an interactive context.
1748 5. Create interactive objects.
1749 6. Create primitives in the interactive object.
1750 7. Display the interactive object.
1752 @subsubsection occt_visu_4_5_1 Create attributes
1757 Quantity_Color aBlack (Quantity_NOC_BLACK);
1758 Quantity_Color aBlue (Quantity_NOC_MATRABLUE);
1759 Quantity_Color aBrown (Quantity_NOC_BROWN4);
1760 Quantity_Color aFirebrick (Quantity_NOC_FIREBRICK);
1761 Quantity_Color aForest (Quantity_NOC_FORESTGREEN);
1762 Quantity_Color aGray (Quantity_NOC_GRAY70);
1763 Quantity_Color aMyColor (0.99, 0.65, 0.31, Quantity_TOC_RGB);
1764 Quantity_Color aBeet (Quantity_NOC_BEET);
1765 Quantity_Color aWhite (Quantity_NOC_WHITE);
1768 Create line attributes.
1771 Handle(Graphic3d_AspectLine3d) anAspectBrown = new Graphic3d_AspectLine3d();
1772 Handle(Graphic3d_AspectLine3d) anAspectBlue = new Graphic3d_AspectLine3d();
1773 Handle(Graphic3d_AspectLine3d) anAspectWhite = new Graphic3d_AspectLine3d();
1774 anAspectBrown->SetColor (aBrown);
1775 anAspectBlue ->SetColor (aBlue);
1776 anAspectWhite->SetColor (aWhite);
1779 Create marker attributes.
1781 Handle(Graphic3d_AspectMarker3d aFirebrickMarker = new Graphic3d_AspectMarker3d();
1782 // marker attributes
1783 aFirebrickMarker->SetColor (Firebrick);
1784 aFirebrickMarker->SetScale (1.0);
1785 aFirebrickMarker->SetType (Aspect_TOM_BALL);
1787 // it is a preferred way (supports full-color images on modern hardware).
1788 aFirebrickMarker->SetMarkerImage (theImage)
1791 Create facet attributes.
1793 Handle(Graphic3d_AspectFillArea3d) aFaceAspect = new Graphic3d_AspectFillArea3d();
1794 Graphic3d_MaterialAspect aBrassMaterial (Graphic3d_NOM_BRASS);
1795 Graphic3d_MaterialAspect aGoldMaterial (Graphic3d_NOM_GOLD);
1796 aFaceAspect->SetInteriorStyle (Aspect_IS_SOLID);
1797 aFaceAspect->SetInteriorColor (aMyColor);
1798 aFaceAspect->SetDistinguishOn ();
1799 aFaceAspect->SetFrontMaterial (aGoldMaterial);
1800 aFaceAspect->SetBackMaterial (aBrassMaterial);
1801 aFaceAspect->SetEdgeOn();
1804 Create text attributes.
1806 Handle(Graphic3d_AspectText3d) aTextAspect = new Graphic3d_AspectText3d (aForest, Graphic3d_NOF_ASCII_MONO, 1.0, 0.0);
1809 @subsubsection occt_visu_4_5_2 Create a 3D Viewer (a Windows example)
1812 // create a default connection
1813 Handle(Aspect_DisplayConnection) aDisplayConnection;
1814 // create a graphic driver from default connection
1815 Handle(OpenGl_GraphicDriver) aGraphicDriver = new OpenGl_GraphicDriver (aDisplayConnection);
1817 myViewer = new V3d_Viewer (aGraphicDriver);
1818 // set parameters for V3d_Viewer
1819 // defines default lights -
1820 // positional-light 0.3 0.0 0.0
1821 // directional-light V3d_XnegYposZpos
1822 // directional-light V3d_XnegYneg
1824 a3DViewer->SetDefaultLights();
1825 // activates all the lights defined in this viewer
1826 a3DViewer->SetLightOn();
1827 // set background color to black
1828 a3DViewer->SetDefaultBackgroundColor (Quantity_NOC_BLACK);
1832 @subsubsection occt_visu_4_5_3 Create a 3D view (a Windows example)
1834 It is assumed that a valid Windows window may already be accessed via the method *GetSafeHwnd()* (as in case of MFC sample).
1836 Handle(WNT_Window) aWNTWindow = new WNT_Window (GetSafeHwnd());
1837 myView = myViewer->CreateView();
1838 myView->SetWindow (aWNTWindow);
1841 @subsubsection occt_visu_4_5_4 Create an interactive context
1844 myAISContext = new AIS_InteractiveContext (myViewer);
1847 You are now able to display interactive objects such as an *AIS_Shape*.
1850 TopoDS_Shape aShape = BRepAPI_MakeBox (10, 20, 30).Solid();
1851 Handle(AIS_Shape) anAISShape = new AIS_Shape (aShape);
1852 myAISContext->Display (anAISShape);
1855 @subsubsection occt_visu_4_5_5 Create your own interactive object
1857 Follow the procedure below to compute the presentable object:
1859 1. Build a presentable object inheriting from *AIS_InteractiveObject* (refer to the Chapter on @ref occt_visu_2_1 "Presentable Objects").
1860 2. Reuse the *Prs3d_Presentation* provided as an argument of the compute methods.
1862 **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.
1864 Let us look at the example of compute methods
1867 void MyPresentableObject::Compute (const Handle(PrsMgr_PresentationManager3d)& thePrsManager,
1868 const Handle(Prs3d_Presentation)& thePrs,
1869 const Standard_Integer theMode)
1874 void MyPresentableObject::Compute (const Handle(Prs3d_Projector)& theProjector,
1875 const Handle(Prs3d_Presentation)& thePrs)
1881 @subsubsection occt_visu_4_5_6 Create primitives in the interactive object
1883 Get the group used in *Prs3d_Presentation*.
1886 Handle(Graphic3d_Group) aGroup = thePrs->NewGroup();
1889 Update the group attributes.
1892 aGroup->SetGroupPrimitivesAspect (anAspectBlue);
1895 Create two triangles in *aGroup*.
1898 Standard_Integer aNbTria = 2;
1899 Handle(Graphic3d_ArrayOfTriangles) aTriangles = new Graphic3d_ArrayOfTriangles (3 * aNbTria, 0, true);
1900 for (Standard_Integer aTriIter = 1; aTriIter <= aNbTria; ++aTriIter)
1902 aTriangles->AddVertex (aTriIter * 5., 0., 0., 1., 1., 1.);
1903 aTriangles->AddVertex (aTriIter * 5 + 5, 0., 0., 1., 1., 1.);
1904 aTriangles->AddVertex (aTriIter * 5 + 2.5, 5., 0., 1., 1., 1.);
1906 aGroup->AddPrimitiveArray (aTriangles);
1907 aGroup->SetGroupPrimitivesAspect (new Graphic3d_AspectFillArea3d());
1910 Use the polyline function to create a boundary box for the *thePrs* structure in group *aGroup*.
1913 Standard_Real Xm, Ym, Zm, XM, YM, ZM;
1914 thePrs->MinMaxValues (Xm, Ym, Zm, XM, YM, ZM);
1916 Handle(Graphic3d_ArrayOfPolylines) aPolylines = new Graphic3d_ArrayOfPolylines (16, 4);
1917 aPolylines->AddBound (4);
1918 aPolylines->AddVertex (Xm, Ym, Zm);
1919 aPolylines->AddVertex (Xm, Ym, ZM);
1920 aPolylines->AddVertex (Xm, YM, ZM);
1921 aPolylines->AddVertex (Xm, YM, Zm);
1922 aPolylines->AddBound (4);
1923 aPolylines->AddVertex (Xm, Ym, Zm);
1924 aPolylines->AddVertex (XM, Ym, Zm);
1925 aPolylines->AddVertex (XM, Ym, ZM);
1926 aPolylines->AddVertex (XM, YM, ZM);
1927 aPolylines->AddBound (4);
1928 aPolylines->AddVertex (XM, YM, Zm);
1929 aPolylines->AddVertex (XM, Ym, Zm);
1930 aPolylines->AddVertex (XM, YM, Zm);
1931 aPolylines->AddVertex (Xm, YM, Zm);
1932 aPolylines->AddBound (4);
1933 aPolylines->AddVertex (Xm, YM, ZM);
1934 aPolylines->AddVertex (XM, YM, ZM);
1935 aPolylines->AddVertex (XM, Ym, ZM);
1936 aPolylines->AddVertex (Xm, Ym, ZM);
1938 aGroup->AddPrimitiveArray(aPolylines);
1939 aGroup->SetGroupPrimitivesAspect (new Graphic3d_AspectLine3d());
1942 Create text and markers in group *aGroup*.
1945 static char* texte[3] =
1947 "Application title",
1949 "My company address."
1951 Handle(Graphic3d_ArrayOfPoints) aPtsArr = new Graphic3d_ArrayOfPoints (2, 1);
1952 aPtsArr->AddVertex (-40.0, -40.0, -40.0);
1953 aPtsArr->AddVertex (40.0, 40.0, 40.0);
1954 aGroup->AddPrimitiveArray (aPtsArr);
1955 aGroup->SetGroupPrimitivesAspect (new Graphic3d_AspectText3d());
1957 Graphic3d_Vertex aMarker (0.0, 0.0, 0.0);
1958 for (int i = 0; i <= 2; i++)
1960 aMarker.SetCoord (-(Standard_Real )i * 4 + 30,
1961 (Standard_Real )i * 4,
1962 -(Standard_Real )i * 4);
1963 aGroup->Text (texte[i], Marker, 20.);
1968 @section occt_visu_5 Mesh Visualization Services
1970 *MeshVS* (Mesh Visualization Service) component extends 3D visualization capabilities of Open CASCADE Technology. It provides flexible means of displaying meshes along with associated pre- and post-processor data.
1972 From a developer's point of view, it is easy to integrate the *MeshVS* component into any mesh-related application with the following guidelines:
1974 * Derive a data source class from the *MeshVS_DataSource* class.
1975 * Re-implement its virtual methods, so as to give the *MeshVS* component access to the application data model. This is the most important part of the job, since visualization performance is affected by performance of data retrieval methods of your data source class.
1976 * Create an instance of *MeshVS_Mesh* class.
1977 * Create an instance of your data source class and pass it to a *MeshVS_Mesh* object through the *SetDataSource()* method.
1978 * Create one or several objects of *MeshVS_PrsBuilder*-derived classes (standard, included in the *MeshVS* package, or your custom ones).
1979 * Each *PrsBuilder* is responsible for drawing a *MeshVS_Mesh* presentation in a certain display mode(s) specified as a *PrsBuilder* constructor's argument. Display mode is treated by *MeshVS* classes as a combination of bit flags (two least significant bits are used to encode standard display modes: wireframe, shading and shrink).
1980 * Pass these objects to the *MeshVS_Mesh::AddBuilder()* method. *MeshVS_Mesh* takes advantage of improved selection highlighting mechanism: it highlights its selected entities itself, with the help of so called "highlighter" object. You can set one of *PrsBuilder* objects to act as a highlighter with the help of a corresponding argument of the *AddBuilder()* method.
1982 Visual attributes of the *MeshVS_Mesh* object (such as shading color, shrink coefficient and so on) are controlled through *MeshVS_Drawer* object. It maintains a map "Attribute ID --> attribute value" and can be easily extended with any number of custom attributes.
1984 In all other respects, *MeshVS_Mesh* is very similar to any other class derived from *AIS_InteractiveObject* and it should be used accordingly (refer to the description of *AIS package* in the documentation).