SoGroup(3)

NAME
SoGroup - The SoGroup class is a node which managed other node instances.

The internal scene data structures in Coin are managed as directed graphs. The graphs are built by setting up a hierarchy through the use of group nodes (either of this type, or from subclasses like SoSeparator) which is then traversed when applying actions (like SoGLRenderAction) to it.

SYNOPSIS

#include <Inventor/nodes/SoGroup.h>

Inherits SoNode.

Inherited by SoArray, SoLevelOfDetail, SoLOD, SoMultipleCopy, SoPathSwitch, SoSeparator, SoSwitch, SoTransformSeparator, SoVRMLLOD, SoVRMLParent, and SoVRMLSwitch.

  Public Member Functions
virtual SoType getTypeId (void) const
SoGroup (void)
SoGroup (int nchildren)
virtual void addChild (SoNode *node)
virtual void insertChild (SoNode *child, int newchildindex)
virtual SoNode * getChild (int index) const
virtual int findChild (const SoNode *node) const
virtual int getNumChildren (void) const
virtual void removeChild (int childindex)
virtual void removeChild (SoNode *child)
virtual void removeAllChildren (void)
virtual void replaceChild (int index, SoNode *newchild)
virtual void replaceChild (SoNode *oldchild, SoNode *newchild)
virtual void doAction (SoAction *action)
virtual void GLRender (SoGLRenderAction *action)
virtual void callback (SoCallbackAction *action)
virtual void getBoundingBox (SoGetBoundingBoxAction *action)
virtual void getMatrix (SoGetMatrixAction *action)
virtual void handleEvent (SoHandleEventAction *action)
virtual void pick (SoPickAction *action)
virtual void search (SoSearchAction *action)
virtual void write (SoWriteAction *action)
virtual void getPrimitiveCount (SoGetPrimitiveCountAction *action)
virtual void audioRender (SoAudioRenderAction *action)
virtual SoChildList * getChildren (void) const

  Static Public Member Functions
static SoType getClassTypeId (void)
static void initClass (void)

  Protected Member Functions
virtual const SoFieldData * getFieldData (void) const
virtual ~SoGroup ()
virtual SbBool readInstance (SoInput *in, unsigned short flags)
virtual SbBool readChildren (SoInput *in)
virtual void copyContents (const SoFieldContainer *from, SbBool copyconnections)

  Static Protected Member Functions
static const SoFieldData ** getFieldDataPtr (void)

  Protected Attributes
SoChildList * children

  Additional Inherited Members

Detailed Description

The SoGroup class is a node which managed other node instances.

The internal scene data structures in Coin are managed as directed graphs. The graphs are built by setting up a hierarchy through the use of group nodes (either of this type, or from subclasses like SoSeparator) which is then traversed when applying actions (like SoGLRenderAction) to it. SoGroup, SoSeparator, and other classes derived from SoGroup, are the 'tools' the application programmer uses when making the layout of the scene graph.

An often asked question about SoGroup nodes is: 'Why is there no SoGroup::getParent() method?' The answer to this is that nodes in the scene graph can have multiple parents, so a simple getParent() method wouldn't work. If you have a node pointer (or other node identification) of a node that you want to remove from the scene graph, what you need to do is to use an SoSearchAction to find all paths down to the node, and then invoke SoGroup::removeChild() from all found parents of the node.

The function would look something like this:

void getParents(SoNode * node, SoNode * root, SoPathList & parents)
{
  SoSearchAction sa;
  sa.setNode(node);
  sa.setInterest(SoSearchAction::ALL);
  sa.apply(root);
  parents = sa.getPaths();
}

Or if you know that your node of interest has only a single parent:

SoGroup * getParent(SoNode * node, SoNode * root)
{
  SoSearchAction sa;
  sa.setNode(node);
  sa.setInterest(SoSearchAction::FIRST);
  sa.apply(root);
  SoPath * p = sa.getPath();
  assert(p && "not found");
  if (p->getLength() < 2) { return NULL; } // no parent
  return (SoGroup *)p->getNodeFromTail(1);
}

An important note about a potential problem using SoGroup nodes which it is not common to stumble on, but which makes hard to find bugs when one does: you should not change the scene graph layout during any action traversal, as that is not allowed by the internal Coin code. I.e. do not use addChild(), removeChild(), insertChild() or replaceChild() from any callback that is triggered directly or indirectly from an action traversal. The most common way of getting hit by this error, would be something like the following (simplified) example:

#include <Inventor/Qt/SoQt.h>
#include <Inventor/Qt/viewers/SoQtExaminerViewer.h>
#include <Inventor/nodes/SoEventCallback.h>
#include <Inventor/nodes/SoSeparator.h>
#include <Inventor/nodes/SoCone.h>
#include <Inventor/manips/SoPointLightManip.h>
#include <Inventor/events/SoMouseButtonEvent.h>
SoPointLightManip * global_pointlightmanip;
SoSeparator * global_root;
// Remove pointlight when clicking right mouse button.
static void
mySelectionC(void * ud, SoEventCallback * n)
{
  const SoMouseButtonEvent * mbe = (SoMouseButtonEvent*) n->getEvent();
  if ((mbe->getButton() == SoMouseButtonEvent::BUTTON2) &&
      (mbe->getState() == SoButtonEvent::DOWN)) {
    if (global_pointlightmanip) {
      global_root->removeChild(global_pointlightmanip);
      global_pointlightmanip = NULL;
    }
  }
}
int
main(int argc, char ** argv)
{
  QWidget * window = SoQt::init(argv[0]);
  global_root = new SoSeparator;
  global_root->ref();
  SoEventCallback * ecb = new SoEventCallback;
  ecb->addEventCallback(SoMouseButtonEvent::getClassTypeId(), mySelectionC, 0);
  global_root->addChild(ecb);
  global_root->addChild(new SoCone);
  global_pointlightmanip = new SoPointLightManip;
  global_root->addChild(global_pointlightmanip);
  SoQtExaminerViewer * viewer = new SoQtExaminerViewer(window);
  viewer->setSceneGraph(global_root);
  viewer->show();
  SoQt::show(window);
  SoQt::mainLoop();
  global_root->unref();
  delete viewer;
  return 0;
}

What happens in the above case is this: when clicking with the right mouse button, the SoQtExaminerViewer converts the Qt event to a Coin event, which is sent down the scene graph with an SoHandleEventAction. The action traversal reaches the 'global_root' SoSeparator node, where it sees that it should further traverse 3 child nodes (first the SoEventCallback, then the SoCone, then the SoPointLightManip). When it then traverses the SoEventCallback, the mySelectionC() callback will be invoked, which removes the last child. But the SoHandleEventAction will still continue it's traversal as if the global_root node has 3 children -- and the code will crash.

(This exact example would perhaps be straight-forward to handle internally in Coin, but there are other ways to change the scene graph layout that are very difficult to handle properly. So in general, changing layout during action traversal is not allowed.)

What to do in these cases is to change the code inside the callback to not do any operations that immediately changes the layout of the scene graph, but to delay it for after the traversal is done. This can e.g. be done by using a Coin sensor.

FILE FORMAT/DEFAULTS:

Group {
}

Constructor & Destructor Documentation

  SoGroup::SoGroup (void)
Default constructor.

  SoGroup::SoGroup (int nchildren)
Constructor.

The argument should be the approximate number of children which is expected to be inserted below this node. The number need not be exact, as it is only used as a hint for better memory resource allocation.

  SoGroup::~SoGroup () [protected], [virtual]
Destructor.

Member Function Documentation

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

Usage example:

void foo(SoNode * node)
{
  if (node->getTypeId() == SoFile::getClassTypeId()) {
    SoFile * filenode = (SoFile *)node;  // safe downward cast, knows the type
  }
}

For application programmers wanting to extend the library with new nodes, engines, nodekits, draggers or others: this method needs to be overridden in all subclasses. This is typically done as part of setting up the full type system for extension classes, which is usually accomplished by using the pre-defined macros available through for instance Inventor/nodes/SoSubNode.h (SO_NODE_INIT_CLASS and SO_NODE_CONSTRUCTOR for node classes), Inventor/engines/SoSubEngine.h (for engine classes) and so on.

For more information on writing Coin extensions, see the class documentation of the toplevel superclasses for the various class groups.

Implements SoBase.

Reimplemented in SoExtSelection, SoVRMLSwitch, SoSelection, SoWWWAnchor, SoVRMLAnchor, SoGeoSeparator, SoSwitch, SoShadowGroup, SoVRMLCollision, SoVRMLGroup, SoVRMLLOD, SoLocateHighlight, SoSeparator, SoVRMLBillboard, SoVRMLParent, SoBlinker, SoLOD, SoArray, SoLevelOfDetail, SoVRMLTransform, SoMultipleCopy, SoPathSwitch, SoAnnotation, and SoTransformSeparator.

  const SoFieldData * SoGroup::getFieldData (void) const [protected], [virtual]
Returns a pointer to the class-wide field data storage object for this instance. If no fields are present, returns NULL.

Reimplemented from SoFieldContainer.

Reimplemented in SoExtSelection, SoVRMLSwitch, SoSelection, SoWWWAnchor, SoVRMLAnchor, SoGeoSeparator, SoSwitch, SoShadowGroup, SoVRMLCollision, SoVRMLGroup, SoVRMLLOD, SoLocateHighlight, SoSeparator, SoVRMLBillboard, SoVRMLParent, SoBlinker, SoLOD, SoArray, SoLevelOfDetail, SoVRMLTransform, SoMultipleCopy, SoPathSwitch, SoAnnotation, and SoTransformSeparator.

  void SoGroup::addChild (SoNode * node) [virtual]
Append a child node to the list of children nodes this group node is managing.

Please note that this method is not virtual in the original SGI Inventor API.

Reimplemented in SoVRMLSwitch, SoVRMLLOD, and SoVRMLParent.

  void SoGroup::insertChild (SoNode * child, int newchildindex) [virtual]
Insert a child node at position newchildindex.

newchildindex must be <= this->getNumChildren()

Please note that this method is not virtual in the original SGI Inventor API.

Reimplemented in SoVRMLSwitch, SoVRMLLOD, and SoVRMLParent.

  SoNode * SoGroup::getChild (int index) const [virtual]
Returns pointer to child node at index.

Please note that this method is not virtual in the original SGI Inventor API.

Reimplemented in SoVRMLSwitch, SoVRMLLOD, and SoVRMLParent.

  int SoGroup::findChild (const SoNode * node) const [virtual]
Returns index in our list of children for child node, or -1 if node is not a child of this group node.

Please note that this method is not virtual in the original SGI Inventor API.

Reimplemented in SoVRMLSwitch, SoVRMLLOD, and SoVRMLParent.

  int SoGroup::getNumChildren (void) const [virtual]
Returns number of child nodes managed by this group.

Please note that this method is not virtual in the original SGI Inventor API.

Reimplemented in SoVRMLSwitch, SoVRMLLOD, and SoVRMLParent.

  void SoGroup::removeChild (int childindex) [virtual]
Remove node at childindex in our list of children.

Please note that this method is not virtual in the original SGI Inventor API.

Reimplemented in SoVRMLSwitch, SoVRMLLOD, and SoVRMLParent.

  void SoGroup::removeChild (SoNode * child) [virtual]
Remove child from the set of children managed by this group node. Will decrease the reference count of child by 1.

This is a convenience method. It will simply call findChild() with child as argument, and then call removeChild(int) if the child is found.

Please note that this method is not virtual in the original SGI Inventor API.

Reimplemented in SoVRMLSwitch, SoVRMLLOD, and SoVRMLParent.

  void SoGroup::removeAllChildren (void) [virtual]
Do not manage the children anymore. Will dereference all children by 1 as they are removed.

Please note that this method is not virtual in the original SGI Inventor API.

Reimplemented in SoVRMLSwitch, SoVRMLLOD, and SoVRMLParent.

  void SoGroup::replaceChild (int index, SoNode * newchild) [virtual]
Replace child at index with newChild.

Dereferences the child previously at index, and increases the reference count of newChild by 1.

index must be < this->getNumChildren()

Please note that this method is not virtual in the original SGI Inventor API.

Reimplemented in SoVRMLSwitch, SoVRMLLOD, and SoVRMLParent.

  void SoGroup::replaceChild (SoNode * oldchild, SoNode * newchild) [virtual]
Replace oldchild with newchild.

Dereferences oldchild by 1, and increases the reference count of newchild by 1.

This is a convenience method. It will simply call findChild() with oldchild as argument, and call replaceChild(int, SoNode*) if the child is found.

Please note that this method is not virtual in the original SGI Inventor API.

Reimplemented in SoVRMLSwitch, SoVRMLLOD, and SoVRMLParent.

  void SoGroup::doAction (SoAction * action) [virtual]
This function performs the typical operation of a node for any action.

Reimplemented from SoNode.

Reimplemented in SoVRMLSwitch, SoVRMLTransform, SoVRMLLOD, SoVRMLGroup, SoVRMLParent, SoArray, SoSeparator, SoSwitch, SoVRMLBillboard, SoLOD, SoLevelOfDetail, SoMultipleCopy, SoPathSwitch, and SoTransformSeparator.

  void SoGroup::GLRender (SoGLRenderAction * action) [virtual]
Action method for the SoGLRenderAction.

This is called during rendering traversals. Nodes influencing the rendering state in any way or who wants to throw geometry primitives at OpenGL overrides this method.

Reimplemented from SoNode.

Reimplemented in SoVRMLSwitch, SoVRMLLOD, SoVRMLGroup, SoArray, SoSeparator, SoSwitch, SoVRMLBillboard, SoLOD, SoVRMLCollision, SoLevelOfDetail, SoMultipleCopy, SoPathSwitch, SoTransformSeparator, and SoAnnotation.

  void SoGroup::callback (SoCallbackAction * action) [virtual]
Action method for SoCallbackAction.

Simply updates the state according to how the node behaves for the render action, so the application programmer can use the SoCallbackAction for extracting information about the scene graph.

Reimplemented from SoNode.

Reimplemented in SoVRMLSwitch, SoVRMLTransform, SoVRMLLOD, SoVRMLGroup, SoSeparator, SoArray, SoSwitch, SoPathSwitch, SoVRMLBillboard, SoGeoSeparator, SoLOD, SoLevelOfDetail, SoMultipleCopy, and SoTransformSeparator.

  void SoGroup::getBoundingBox (SoGetBoundingBoxAction * action) [virtual]
Action method for the SoGetBoundingBoxAction.

Calculates bounding box and center coordinates for node and modifies the values of the action to encompass the bounding box for this node and to shift the center point for the scene more towards the one for this node.

Nodes influencing how geometry nodes calculates their bounding box also overrides this method to change the relevant state variables.

Reimplemented from SoNode.

Reimplemented in SoVRMLSwitch, SoVRMLLOD, SoVRMLTransform, SoVRMLGroup, SoArray, SoSeparator, SoLOD, SoSwitch, SoGeoSeparator, SoVRMLBillboard, SoLevelOfDetail, SoMultipleCopy, SoPathSwitch, SoBlinker, and SoTransformSeparator.

  void SoGroup::getMatrix (SoGetMatrixAction * action) [virtual]
Action method for SoGetMatrixAction.

Updates action by accumulating with the transformation matrix of this node (if any).

Reimplemented from SoNode.

Reimplemented in SoVRMLSwitch, SoVRMLTransform, SoVRMLGroup, SoArray, SoSeparator, SoSwitch, SoGeoSeparator, SoVRMLBillboard, SoMultipleCopy, SoPathSwitch, and SoTransformSeparator.

  void SoGroup::handleEvent (SoHandleEventAction * action) [virtual]
Action method for SoHandleEventAction.

Inspects the event data from action, and processes it if it is something which this node should react to.

Nodes influencing relevant state variables for how event handling is done also overrides this method.

Reimplemented from SoNode.

Reimplemented in SoExtSelection, SoSelection, SoVRMLSwitch, SoSeparator, SoArray, SoWWWAnchor, SoVRMLAnchor, SoLocateHighlight, SoSwitch, SoMultipleCopy, and SoPathSwitch.

  void SoGroup::pick (SoPickAction * action) [virtual]
Action method for SoPickAction.

Does common processing for SoPickAction action instances.

Reimplemented from SoNode.

Reimplemented in SoVRMLSwitch, SoArray, SoSwitch, SoVRMLBillboard, SoMultipleCopy, SoPathSwitch, and SoTransformSeparator.

  void SoGroup::search (SoSearchAction * action) [virtual]
Action method for SoSearchAction.

Compares the search criteria from the action to see if this node is a match. Searching is done by matching up all criteria set up in the SoSearchAction -- if any of the requested criteria is a miss, the search is not deemed successful for the node.

See also:
    SoSearchAction

Reimplemented from SoNode.

Reimplemented in SoVRMLSwitch, SoVRMLGroup, SoVRMLLOD, SoSeparator, SoArray, SoVRMLParent, SoSwitch, SoVRMLBillboard, SoMultipleCopy, and SoPathSwitch.

  void SoGroup::write (SoWriteAction * action) [virtual]
Action method for SoWriteAction.

Writes out a node object, and any connected nodes, engines etc, if necessary.

Reimplemented from SoNode.

Reimplemented in SoVRMLSwitch, SoVRMLGroup, SoVRMLLOD, SoVRMLParent, SoSwitch, and SoBlinker.

  void SoGroup::getPrimitiveCount (SoGetPrimitiveCountAction * action) [virtual]
Action method for the SoGetPrimitiveCountAction.

Calculates the number of triangle, line segment and point primitives for the node and adds these to the counters of the action.

Nodes influencing how geometry nodes calculates their primitive count also overrides this method to change the relevant state variables.

Reimplemented from SoNode.

Reimplemented in SoVRMLGroup, SoVRMLLOD, SoVRMLTransform, SoSeparator, SoArray, SoVRMLParent, SoSwitch, SoLOD, SoGeoSeparator, SoMultipleCopy, SoPathSwitch, and SoTransformSeparator.

  void SoGroup::audioRender (SoAudioRenderAction * action) [virtual]
Action method for SoAudioRenderAction.

Does common processing for SoAudioRenderAction action instances.

Reimplemented from SoNode.

Reimplemented in SoVRMLSwitch, SoVRMLGroup, SoVRMLLOD, SoVRMLTransform, SoSeparator, SoArray, SoSwitch, SoLOD, SoMultipleCopy, SoPathSwitch, SoLevelOfDetail, and SoTransformSeparator.

  SoChildList * SoGroup::getChildren (void) const [virtual]
Returns list of children.

Reimplemented from SoNode.

Reimplemented in SoVRMLSwitch, SoVRMLLOD, and SoVRMLParent.

  SbBool SoGroup::readInstance (SoInput * in, unsigned short flags) [protected], [virtual]
This method is mainly intended for internal use during file import operations.

It reads a definition of an instance from the input stream in. The input stream state points to the start of a serialized / persistant representation of an instance of this class type.

TRUE or FALSE is returned, depending on if the instantiation and configuration of the new object of this class type went ok or not. The import process should be robust and handle corrupted input streams by returning FALSE.

flags is used internally during binary import when reading user extension nodes, group nodes or engines.

Reimplemented from SoNode.

Reimplemented in SoVRMLSwitch, SoVRMLLOD, SoSeparator, and SoVRMLParent.

  SbBool SoGroup::readChildren (SoInput * in) [protected], [virtual]
Read all children of this node from in and attach them below this group in left-to-right order. Returns FALSE upon read error.

  void SoGroup::copyContents (const SoFieldContainer * from, SbBool copyconnections) [protected], [virtual]
Makes a deep copy of all data of from into this instance, except external scenegraph references if copyconnections is FALSE.

This is the protected method that should be overridden by extension node / engine / dragger / whatever subclasses which needs to account for internal data that are not handled automatically.

For copying nodes from application code, you should not invoke this function directly, but rather call the SoNode::copy() function:

SoNode * mynewnode = templatenode->copy();

The same also goes for engines.

Make sure that when you override the copyContents() method in your extension class that you also make it call upwards to it's parent superclass in the inheritance hierarchy, as copyContents() in for instance SoNode and SoFieldContainer does important work. It should go something like this:

void
MyCoinExtensionNode::copyContents(const SoFieldContainer * from,
                                  SbBool copyconnections)
{
  // let parent superclasses do their thing (copy fields, copy
  // instance name, etc etc)
  SoNode::copyContents(from, copyconnections);
  // [..then copy internal data..]
}

Reimplemented from SoNode.

Reimplemented in SoVRMLSwitch, SoVRMLLOD, and SoVRMLParent.

Member Data Documentation

  SoChildList * SoGroup::children [protected]
List of managed child nodes.

Author

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