SoGroup Class Reference
[Node Classes]

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. More...

#include <Inventor/nodes/SoGroup.h>

Inheritance diagram for SoGroup:

List of all members.

Public Member Functions
	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 void	initClass (void)
	Sets up initialization for data common to all instances of this class, like submitting necessary information to the Coin type system.
Protected Member Functions
virtual	~SoGroup ()
virtual SbBool	readInstance (SoInput *in, unsigned short flags)
virtual SbBool	readChildren (SoInput *in)
virtual void	copyContents (const SoFieldContainer *from, SbBool copyconnections)
virtual SoNotRec	createNotRec (void)
void	setOperation (const SoNotRec::OperationType opType=SoNotRec::UNSPECIFIED, const SoNode cc=NULL, const SoNode pc=NULL, const int ci=-1)
Protected Attributes
SoChildList *	children

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.