SoGetBoundingBoxAction(3)

NAME
SoGetBoundingBoxAction - The SoGetBoundingBoxAction class calculates bounding boxes for nodes and subgraphs.

SYNOPSIS

#include <Inventor/actions/SoGetBoundingBoxAction.h>

Inherits SoAction.

  Public Types
enum ResetType { TRANSFORM = 0x1, BBOX = 0x2, ALL = TRANSFORM | BBOX }

  Public Member Functions
virtual SoType getTypeId (void) const
SoGetBoundingBoxAction (const SbViewportRegion &vp)
virtual ~SoGetBoundingBoxAction (void)
void setViewportRegion (const SbViewportRegion &newregion)
const SbViewportRegion & getViewportRegion (void) const
SbBox3f getBoundingBox (void) const
SbXfBox3f & getXfBoundingBox (void)
const SbVec3f & getCenter (void) const
void setInCameraSpace (const SbBool flag)
SbBool isInCameraSpace (void) const
void setResetPath (const SoPath *path, const SbBool resetbefore=TRUE, const ResetType what=ALL)
const SoPath * getResetPath (void) const
SbBool isResetPath (void) const
SbBool isResetBefore (void) const
SoGetBoundingBoxAction::ResetType getWhatReset (void) const
void checkResetBefore (void)
void checkResetAfter (void)
void extendBy (const SbBox3f &box)
void extendBy (const SbXfBox3f &box)
void setCenter (const SbVec3f &center, const SbBool transformcenter)
SbBool isCenterSet (void) const
void resetCenter (void)

  Static Public Member Functions
static SoType getClassTypeId (void)
static void addMethod (const SoType type, SoActionMethod method)
static void enableElement (const SoType type, const int stackindex)
static void initClass (void)

  Protected Member Functions
virtual const SoEnabledElementsList & getEnabledElements (void) const
virtual void beginTraversal (SoNode *node)

  Static Protected Member Functions
static SoEnabledElementsList * getClassEnabledElements (void)
static SoActionMethodList * getClassActionMethods (void)

  Additional Inherited Members

Detailed Description

The SoGetBoundingBoxAction class calculates bounding boxes for nodes and subgraphs. If this action is applied to a path or scene graph root, it will calculate the bounding box and the center point of the geometry contained within the scene.

You don't have to apply an SoGetBoundingBoxAction to the root of a scene. When using the action, you will get the bounding box of the node you are applying it to and that node's sub-tree in the scene graph (if any).

The calculated bounding box will be in the local coordinates of that sub-tree. If applying it to a scene graph root node, the calculated bounding box will be in global coordinates.

The use of bounding boxes is ubiquitous within the Coin library. It is needed for the correct execution of and for performance enhancements during rendering, picking, caching, culling, etc.

SoSeparator nodes are aggressively caching the results of bounding box calculations, so that they are really only re-calculated whenever the scene graph rooted below any SoSeparator node has been modified. This means that applying this action to scene graphs, or parts of scene graphs, should be very quick on successive runs for 'static' parts of the scene.

Note that the algorithm used is not guaranteed to always give an exact bounding box: it combines bounding boxes in pairs and extends one of them to contain the other. Since the boxes need not be parallel to the principal axes the new box might not be a perfect fit for the box not extended (its coordinate system has been changed).

Note also that what is returned from getBoundingBox() will be projected so as to be oriented along the principal axes, which can often cause it to become quite a lot larger than what it was before projection. For client code to obtain the best bounding box that Coin can calculate (and which will usually be exact), you need to use the getXfBoundingBox() method after having applied the SoGetBoundingBoxAction.

See also
    SoSeparator::boundingBoxCaching

Member Enumeration Documentation

  enum SoGetBoundingBoxAction::ResetType
This API member is considered internal to the library, as it is not likely to be of interest to the application programmer.

Constructor & Destructor Documentation

  SoGetBoundingBoxAction::SoGetBoundingBoxAction (const SbViewportRegion & vp)
Constructor.

It might seem unnecessary to have to pass in a viewport region argument to calculate bounding boxes, but there is a good reason for this: a few shape nodes needs to know the viewport region to calculate their bounding box -- these include SoText2 and SoImage, among others.

What is particular about these shapes is that they are fundamentally 2D shapes, but they are being rendered on the screen 'surface' as if they were in a 3D scene. (This is possible because we can match each pixel's depth value against the 3D shapes in the scene.)

To compute an accurate 3D bounding box of a shape rendered in 2D on the screen 'surface', you need to 'de-project' the screen space area it occupies to a 2D rectangle placed at some depth in the scene. This 'de-projecting' operation needs to know about the dimensions of the viewport.

Also, some 3D shapes like for instance SoNurbsSurface, get slightly distorted if there's an SoComplexity node in the scene graph with the SoComplexity::value field set to SCREEN_SPACE. Then it is also necessary to know the viewport region to find out how to accurately calculate the bounding box of those shapes.

You would usually want to pass in a viewport region equal to the layout of the current render area canvas. If you have a viewer or So@Gui@RenderArea available, you can get hold of the viewport region data simply by doing

const SbViewportRegion & vpreg = viewer->getViewportRegion();

(If you don't have a viewer or render area available in your application at the point where you want to get the bounding box, it probably doesn't matter much what you set it to. The accuracy of the bounding box calculation might be slightly wrong versus the actual rendered appearance of the scene, but this is usually not noticeable.)

  SoGetBoundingBoxAction::~SoGetBoundingBoxAction (void) [virtual]
Destructor.

Member Function Documentation

  SoType SoGetBoundingBoxAction::getTypeId (void) const [virtual]
Returns the type identification of an object derived from a class inheriting SoAction. This is used for runtime type checking and 'downward' casting.

Implements SoAction.

  SoType SoGetBoundingBoxAction::getClassTypeId (void) [static]
This static method returns the SoType object associated with objects of this class.

  void SoGetBoundingBoxAction::addMethod (const SoType type, SoActionMethod method) [static]
This API member is considered internal to the library, as it is not likely to be of interest to the application programmer.

  void SoGetBoundingBoxAction::enableElement (const SoType type, const int stackindex) [static]
This API member is considered internal to the library, as it is not likely to be of interest to the application programmer.

  const SoEnabledElementsList & SoGetBoundingBoxAction::getEnabledElements (void) const [protected], [virtual]
Returns list of enabled elements.

Reimplemented from SoAction.

  SoEnabledElementsList * SoGetBoundingBoxAction::getClassEnabledElements (void) [static], [protected]
Returns list of enabled elements for this class. The enabledElements and methods variables are protected in the original OIV API. This is not such a good idea, since exposed static class member variables is a major grievance with regard to Win32 DLLs. This function is an extension for Coin, and it is not available in the original SGI Open Inventor v2.1 API.

  SoActionMethodList * SoGetBoundingBoxAction::getClassActionMethods (void) [static], [protected]
Returns list of action methods for this class. The enabledElements and methods variables are protected in the original OIV API. This is not such a good idea, since exposed static class member variables is a major grievance with regard to Win32 DLLs. This function is an extension for Coin, and it is not available in the original SGI Open Inventor v2.1 API.

  void SoGetBoundingBoxAction::initClass (void) [static]
Initializes the runtime type system for this class, and sets up the enabled elements and action method list.

  void SoGetBoundingBoxAction::setViewportRegion (const SbViewportRegion & newregion)
Set a new viewport region with this method, if it has changed from the one passed in with the constructor.

  const SbViewportRegion & SoGetBoundingBoxAction::getViewportRegion (void) const
Returns the viewport region used by the action instance.

  SbBox3f SoGetBoundingBoxAction::getBoundingBox (void) const
Returns the projected bounding box after (or during) traversal.

  SbXfBox3f & SoGetBoundingBoxAction::getXfBoundingBox (void)
Returns the bounding box and transformation matrix to global coordinates. Use after (or during) traversal.

  const SbVec3f & SoGetBoundingBoxAction::getCenter (void) const
Returns center point of scene after the action has been applied.

This might differ from the geometric center of the bounding box, as shape nodes may 'weight' the center point according to various criteria (i.e. a faceset could for instance weight the center point according to the area within its bounding box where there are more polygons).

  void SoGetBoundingBoxAction::setInCameraSpace (const SbBool on)
Sets whether the returned bounding box should be calculated in the coordinate system of the camera space or not.

  SbBool SoGetBoundingBoxAction::isInCameraSpace (void) const
Returns whether the bounding box returned is to be in camera space.

  void SoGetBoundingBoxAction::setResetPath (const SoPath * path, const SbBool resetbefore = TRUE, const ResetType what = ALL)
Forces the computed bounding box to be reset and the transformation to be identity before or after the tail node of path, depending on the resetbefore argument. NULL can be specified for the path argument to disable this behavior.

See also
    getResetPath(), isResetPath(), isResetBefore(), getWhatReset()

  const SoPath * SoGetBoundingBoxAction::getResetPath (void) const
Returns the reset path (or NULL).

See also
    setResetPath(), isResetPath(), isResetBefore(), getWhatReset()

  SbBool SoGetBoundingBoxAction::isResetPath (void) const
Returns whether a reset path is set or not.

See also
    setResetPath(), getResetPath(), isResetBefore(), getWhatReset()

  SbBool SoGetBoundingBoxAction::isResetBefore (void) const
Returns whether the bounding box and transformation is reset before or after the tail node of the reset path.

See also
    setResetPath(), getResetPath(), isResetPath(), getWhatReset()

  SoGetBoundingBoxAction::ResetType SoGetBoundingBoxAction::getWhatReset (void) const
Returns what type of reset has been specified for the reset path.

See also
    setResetPath(), getResetPath(), isResetPath(), isResetBefore()

  void SoGetBoundingBoxAction::checkResetBefore (void)
This API member is considered internal to the library, as it is not likely to be of interest to the application programmer.
Called before node traversal of each node (from SoNode action method).

  void SoGetBoundingBoxAction::checkResetAfter (void)
This API member is considered internal to the library, as it is not likely to be of interest to the application programmer.
Called after node traversal of each node (from SoNode action method).

  void SoGetBoundingBoxAction::extendBy (const SbBox3f & box)
Extend bounding box by the given box. Called from nodes during traversal.

Should usually not be of interest to application programmers, unless you're extending Coin with your own shapenode extension classes.

  void SoGetBoundingBoxAction::extendBy (const SbXfBox3f & box)
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

  void SoGetBoundingBoxAction::setCenter (const SbVec3f & centerarg, const SbBool transformcenter)
This API member is considered internal to the library, as it is not likely to be of interest to the application programmer.
Set a new center point during traversal.

  SbBool SoGetBoundingBoxAction::isCenterSet (void) const
This API member is considered internal to the library, as it is not likely to be of interest to the application programmer.
Query about the center point during traversal.

  void SoGetBoundingBoxAction::resetCenter (void)
This API member is considered internal to the library, as it is not likely to be of interest to the application programmer.
Reset the scene center point during traversal.

  void SoGetBoundingBoxAction::beginTraversal (SoNode * node) [protected], [virtual]
This virtual method is called from SoAction::apply(), and is the entry point for the actual scene graph traversal.

It can be overridden to initialize the action at traversal start, for specific initializations in the action subclasses inheriting SoAction.

Default method just calls traverse(), which any overridden implementation of the method must do too (or call SoAction::beginTraversal()) to trigger the scene graph traversal.

Reimplemented from SoAction.

Author

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