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SoElement.3coin2

NAME

SoElement -

SoElement is the abstract base class for all elements.

Elements are part of the design for scenegraph traversal in Coin.

SYNOPSIS

#include <Inventor/elements/SoElement.h>

Inherited by SoAccumulatedElement, SoFloatElement, SoInt32Element, SoOverrideElement, and SoReplacedElement.

Public Member Functions

const SoType getTypeId (void) const

int getStackIndex (void) const

virtual void init (SoState *state)

virtual void push (SoState *state)

virtual void pop (SoState *state, const SoElement *prevTopElement)

virtual SbBool matches (const SoElement *element) const =0

virtual SoElement * copyMatchInfo (void) const =0

void setDepth (const int depth)

int getDepth (void) const

virtual void print (FILE *file=stdout) const

virtual ~SoElement ()

Static Public Member Functions

static void initClass (void)

static SoType getClassTypeId (void)

static int getClassStackIndex (void)

static void initElements (void)

static int getNumStackIndices (void)

static SoType getIdFromStackIndex (const int stackIndex)

Protected Member Functions

SoElement (void)

void capture (SoState *const state) const

virtual void captureThis (SoState *state) const

void setTypeId (const SoType typeId)

void setStackIndex (const int index)

SoElement * getNextInStack (void) const

SoElement * getNextFree (void) const

Static Protected Member Functions

static SoElement * getElement (SoState *const state, const int stackIndex)

static const SoElement * getConstElement (SoState *const state, const int stackIndex)

static int createStackIndex (const SoType id)

Protected Attributes

SoType typeId

int stackIndex

int depth

Static Protected Attributes

static int classStackIndex

static SoTypeList * stackToType

Friends

class SoState

Detailed Description

SoElement is the abstract base class for all elements.

Elements are part of the design for scenegraph traversal in Coin.

It works like this: any traversal action instantiates and keeps a single SoState instance during traversal. The SoState instance uses SoElement objects as 'memory units' to keep track of the current state for any feature of the scenegraph nodes.

As an example, consider the SoPointSize node: when the SoPointSize node is traversed by for instance a SoGLRenderAction, it will itself push a SoPointSizeElement onto the SoGLRenderAction's SoState stack. Later, when a SoPointSet node occurs in the scenegraph, it will request the current pointsize value from the SoState by reading off the value of it's SoPointSizeElement.

SoSeparator nodes will push and pop elements on and off the state stack, so anything that changes state below a SoSeparator node will not influence anything above the SoSeparator.

For more information on the theoretical underpinnings of this traversal design, you should consider reading available literature on the so-called 'Visitor pattern'. We recommend 'Design Patterns', by Gamma, Helm, Johnson, Vlissides (aka the 'Gang Of Four'). This book actually uses the Inventor API traversal mechanism as the case study for explaining the Visitor pattern.

For extending the Coin library with your own classes, we strongly recommend that you make yourself acquainted with the excellent «The Inventor Toolmaker» book (ISBN 0-201-62493-1), which describes the tasks involved in detail. This book was written by the original SGI Inventor designers and explains many of the underlying design ideas, aswell as having lots of hands-on examples on how to extend the Coin toolkit in ways that are true to the fundamental design ideas. («The Inventor Toolmaker» is also available at SGI's online library, at no cost. See Download The Inventor Toolmaker.) Reading the sourcecode of the built-in classes in Coin should also provide very helpful.

The following is a complete example on how to extend Coin with your own traversal elements. First, the class declaration of the new element (ie the header include file):

   // [texturefilenameelement.h]
   #ifndef TEXTUREFILENAMEELEMENT_H
   #define TEXTUREFILENAMEELEMENT_H
 
   #include <Inventor/elements/SoReplacedElement.h>
   #include <Inventor/SbString.h>
 
   class TextureFilenameElement : public SoReplacedElement {
     typedef SoReplacedElement inherited;
 
     SO_ELEMENT_HEADER(TextureFilenameElement);
   public:
     static void initClass(void);
 
     virtual void init(SoState * state);
     static void set(SoState * const state, SoNode * const node,
                     const SbString & filename);
     static const SbString & get(SoState * const state);
     static const TextureFilenameElement * getInstance(SoState * state);
 
   protected:
     virtual ~TextureFilenameElement();
     virtual void setElt(const SbString & filename);
 
   private:
     SbString filename;
   };
 
   #endif // !TEXTUREFILENAMEELEMENT_H
 

The implementation of the element:

   // [texturefilenameelement.cpp]
   //
   // The purpose of the code in this file is to demonstrate how you can
   // make your own elements for scene graph traversals.
   //
   // Code by Peder Blekken <pederb@sim.no>, 1999-12-09. Copyright
   // Systems in Motion.
 
   #include 'texturefilenameelement.h'
 
 
   SO_ELEMENT_SOURCE(TextureFilenameElement);
 
 
   void
   TextureFilenameElement::initClass(void)
   {
     SO_ELEMENT_INIT_CLASS(TextureFilenameElement, inherited);
   }
 
   void
   TextureFilenameElement::init(SoState * state)
   {
     this->filename = '<none>';
   }
 
   TextureFilenameElement::~TextureFilenameElement()
   {
   }
 
   void
   TextureFilenameElement::set(SoState * const state, SoNode * const node,
                               const SbString & filename)
   {
     TextureFilenameElement * elem = (TextureFilenameElement *)
       SoReplacedElement::getElement(state, classStackIndex, node);
     elem->setElt(filename);
   }
 
   const SbString &
   TextureFilenameElement::get(SoState * const state)
   {
     return TextureFilenameElement::getInstance(state)->filename;
   }
 
   void
   TextureFilenameElement::setElt(const SbString & filename)
   {
     this->filename = filename;
   }
 
   const TextureFilenameElement *
   TextureFilenameElement::getInstance(SoState * state)
   {
     return (const TextureFilenameElement *)
       SoElement::getConstElement(state, classStackIndex);
   }
 

And a small, stand-alone test application putting the new element to use:

   // [lstextures.cpp]
   //
   // The purpose of this file is to make a small wrapper 'tool' around
   // the TextureFilenameElement extension element, just for showing
   // example code on how to make use of a user-defined custom element.
   //
   // The code goes like this:
   //
   // We initialize the element, enable it for the SoCallbackAction, read
   // a scene graph file, set callbacks on SoTexture2 and all shape nodes
   // and applies the SoCallbackAction. The callbacks will then print out
   // the texture filename information from the TextureFilenameElement
   // each time an interesting node is hit.
   //
   //
   // Code by Peder Blekken <pederb@sim.no>. Cleaned up, integrated in
   // Coin distribution and commented by Morten Eriksen <mortene@sim.no>.
   // 1999-12-09. Copyright Systems in Motion.
 
   #include <Inventor/SoDB.h>
   #include <Inventor/SoInput.h>
   #include <Inventor/actions/SoCallbackAction.h>
   #include <Inventor/nodes/SoSeparator.h>
   #include <Inventor/nodes/SoTexture2.h>
   #include <Inventor/nodes/SoShape.h>
   #include <Inventor/misc/SoState.h>
   #include <stdio.h>
 
   #include 'texturefilenameelement.h'
 
 
   SoCallbackAction::Response
   pre_tex2_cb(void * data, SoCallbackAction * action, const SoNode * node)
   {
     const SbString & filename = ((SoTexture2 *)node)->filename.getValue();
     TextureFilenameElement::set(action->getState(), (SoNode *)node, filename);
 
     (void)fprintf(stdout, '=> New texture: %s,
                   filename.getLength() == 0 ?
                   '<inlined>' : filename.getString());
 
     return SoCallbackAction::CONTINUE;
   }
 
   SoCallbackAction::Response
   pre_shape_cb(void * data, SoCallbackAction * action, const SoNode * node)
   {
     const SbString & filename =
       TextureFilenameElement::get(action->getState());
 
     (void)fprintf(stdout, '   Texturemap on %s: %s,
                   node->getTypeId().getName().getString(),
                   filename.getLength() == 0 ?
                   '<inlined>' : filename.getString());
 
     return SoCallbackAction::CONTINUE;
   }
 
   void
   usage(const char * appname)
   {
     (void)fprintf(stderr, 'tUsage: %s <modelfile.iv>n', appname);
     (void)fprintf(stderr,
                   '    Lists all texture filenames in the model file,
                   '    and on which shape nodes they are used.n'
                   '    The purpose of this example utility is simply to
                   '    show how to create and use an extension element for
                   '    scene graph traversal.n');
   }
 
   int
   main(int argc, char ** argv)
   {
     if (argc != 2) {
       usage(argv[0]);
       exit(1);
     }
 
     SoDB::init();
 
     TextureFilenameElement::initClass();
     SO_ENABLE(SoCallbackAction, TextureFilenameElement);
 
     SoInput input;
     if (!input.openFile(argv[1])) {
       (void)fprintf(stderr, 'ERROR: couldn't open file ``%s''., argv[1]);
       exit(1);
     }
 
     SoSeparator * root = SoDB::readAll(&input);
     if (root) {
       root->ref();
       SoCallbackAction cbaction;
       cbaction.addPreCallback(SoTexture2::getClassTypeId(), pre_tex2_cb, NULL);
       cbaction.addPreCallback(SoShape::getClassTypeId(), pre_shape_cb, NULL);
       cbaction.apply(root);
       root->unref();
       return 0;
     }
     return 1;
   }
 

 

Constructor & Destructor Documentation

SoElement::~SoElement () [virtual]The destructor.

SoElement::SoElement (void) [protected]The constructor. To create element instances, use SoType::createInstance() for the elements type identifier..

Member Function Documentation

void SoElement::initClass (void) [static]Initialize relevant common data for all instances, like the type system.

Reimplemented in SoAccumulatedElement, SoOverrideElement, SoFloatElement, SoInt32Element, SoGLColorIndexElement, SoGLLineWidthElement, SoGLPointSizeElement, SoLineWidthElement, SoPointSizeElement, SoReplacedElement, SoListenerPositionElement, SoListenerOrientationElement, SoListenerGainElement, and SoListenerDopplerElement.

References SoType::badType(), classStackIndex, SoType::createType(), and initElements().

Referenced by SoDB::init(), and initElements().

SoType SoElement::getClassTypeId (void) [static]This static method returns the class type.

Referenced by SoAction::initClass().

int SoElement::getClassStackIndex (void) [static]This static method returns the state stack index for the class.

References classStackIndex.

Referenced by SoAction::initClass().

const SoType SoElement::getTypeId (void) constReturns the type identification of an object derived from a class inheriting SoElement. This is used for run-time type checking and 'downward' casting.

For a more thorough explanation of the run-time type identification functionality, see the documentation of SoBase::getTypeId().

References typeId.

Referenced by SoReplacedElement::copyMatchInfo(), SoOverrideElement::copyMatchInfo(), SoInt32Element::copyMatchInfo(), SoFloatElement::copyMatchInfo(), SoAccumulatedElement::copyMatchInfo(), SoState::getElement(), SoState::print(), SoReplacedElement::print(), SoInt32Element::print(), SoFloatElement::print(), and print().

int SoElement::getStackIndex (void) constReturns the stack index for an element instance.

References stackIndex.

Referenced by SoState::SoState().

void SoElement::init (SoState * state) [virtual]This function initializes the element type in the given SoState. It is called for the first element of each enabled element type in SoState objects.

Reimplemented in SoAccumulatedElement, SoOverrideElement, SoFloatElement, SoInt32Element, SoGLColorIndexElement, SoGLLineWidthElement, SoGLPointSizeElement, SoLineWidthElement, SoPointSizeElement, SoReplacedElement, SoListenerPositionElement, SoListenerOrientationElement, SoListenerGainElement, and SoListenerDopplerElement.

Referenced by SoReplacedElement::init(), SoOverrideElement::init(), SoInt32Element::init(), SoFloatElement::init(), SoAccumulatedElement::init(), and SoState::SoState().

void SoElement::push (SoState * state) [virtual]This method is called every time a new element is required in one of the stacks. This happens when a writable element is requested, using SoState::getElement() or indirectly SoElement::getElement(), and the depth of the current element is less than the state depth.

Override this method if your element needs to copy data from the previous top of stack. The push() method is called on the new element, and the previous element can be found using SoElement::getNextInStack().

Reimplemented in SoAccumulatedElement, SoOverrideElement, SoGLLineWidthElement, and SoGLPointSizeElement.

Referenced by SoState::getElement(), SoOverrideElement::push(), and SoAccumulatedElement::push().

void SoElement::pop (SoState * state, const SoElement * prevTopElement) [virtual]This method is callled when the state is popped, and the depth of the element is bigger than the current state depth. pop() is called on the new top of stack, and a pointer to the previous top of stack is passed in prevTopElement.

Override this method if you need to copy some state information from the previous top of stack.

Referenced by SoState::pop().

SbBool SoElement::matches (const SoElement * element) const [pure virtual]This function returns TRUE is the element matches another element (of the same class), with respect to cache validity.

If the application programmer's extension element has a matches() function, it should also have a copyMatchInfo() function.

SoElement * SoElement::copyMatchInfo (void) const [pure virtual]This function creates a copy of the element that contains enough information to enable the matches() function to work.

Used to help with scenegraph traversal caching operations.

Implemented in SoAccumulatedElement, SoOverrideElement, SoFloatElement, SoInt32Element, and SoReplacedElement.

void SoElement::initElements (void) [static]This function initializes all the built-in Coin element classes.

References initClass().

Referenced by initClass().

int SoElement::getNumStackIndices (void) [static]Returns the number of allocated element stack index slots.

References SbPList::getLength().

Referenced by SoState::SoState().

SoType SoElement::getIdFromStackIndex (const int stackIndex) [static]Returns the SoType identifier for the element class with element state stack index stackIndex.

void SoElement::setDepth (const int deptharg)Sets the depth value of the element instance in the state stack.

References depth.

Referenced by SoState::getElement(), and SoState::SoState().

int SoElement::getDepth (void) constReturns the state stack depth value of the element instance.

References depth.

Referenced by SoState::getElement().

void SoElement::print (FILE * file = stdout) const [virtual]This function is for printing element information, and is used mostly for debugging purposes.

Reimplemented in SoOverrideElement, SoFloatElement, SoInt32Element, SoReplacedElement, SoListenerPositionElement, SoListenerOrientationElement, and SoListenerDopplerElement.

References SoType::getName(), SbName::getString(), and getTypeId().

SoElement * SoElement::getElement (SoState *const state, const int stackIndex) [inline, static, protected]This method returns the top instance (in the state stack) of the element class with stack index stackIndex.

The retuned instance is writable. To make this instance, some lazy evaluation may have to be perfomed, so use getConstElement() instead if the instance shouldn't be modified.

If no instance is available and can not be made, NULL is returned.

See also:

const SoElement * SoElement::getConstElement(SoState * const state, const int stackIndex)

References SoState::getElement().

Referenced by SoReplacedElement::getElement(), SoListenerPositionElement::set(), SoListenerOrientationElement::set(), SoFloatElement::set(), SoListenerDopplerElement::setDopplerFactor(), and SoListenerDopplerElement::setDopplerVelocity().

void const SoElement * SoElement::getConstElement (SoState *const state, const int stackIndex) [inline, static, protected]This method returns a reference to the top element of the class with stack index stackIndex. The returned element is non-mutable.

(Don't try to be clever and cast away the constness -- if the returned instance is modified, strange, hard to find and generally wonderful bugs will most likely start to happen.)

If no instance can be returned, NULL is returned.

See also:

SoElement * SoElement::getElement(SoState * const state, const int stackIndex)

References capture(), and SoState::getConstElement().

Referenced by SoListenerPositionElement::get(), SoListenerOrientationElement::get(), SoInt32Element::get(), SoFloatElement::get(), SoListenerDopplerElement::getDopplerFactor(), SoListenerDopplerElement::getDopplerVelocity(), SoListenerPositionElement::isSetByListener(), and SoListenerOrientationElement::isSetByListener().

void SoElement::capture (SoState *const state) const [inline, protected]This function does whatever is necessary in the state for caching purposes. If should be called by subclasses of SoElement whenever any value in the element is accessed.

References captureThis(), and SoState::isCacheOpen().

Referenced by getConstElement(), SoGLPointSizeElement::push(), and SoGLLineWidthElement::push().

void SoElement::captureThis (SoState * state) const [protected, virtual]Adds the element to the cache.

Reimplemented in SoAccumulatedElement.

Referenced by capture(), and SoAccumulatedElement::captureThis().

void SoElement::setTypeId (const SoType typeIdarg) [protected]Sets the type identifier of an instance.

Note that this is fundamentally different from the SoNode run-time type system.

References typeId.

void SoElement::setStackIndex (const int stackIndexarg) [protected]Sets the stack index in an instance. Used in constructors of derived elements.

References stackIndex.

int SoElement::createStackIndex (const SoType typeId) [static, protected]Returns the value of a new available stack index.

References SoTypeList::append(), SoType::canCreateInstance(), and SbPList::getLength().

SoElement * SoElement::getNextInStack (void) const [protected]Returns the next element down in the stack. Should be used in push() to get the previous element.

This method has a slightly misleading name, but we didn't change it to stay compatible with the original SGI Inventor API.

Referenced by SoAccumulatedElement::captureThis(), SoOverrideElement::push(), SoGLPointSizeElement::push(), and SoGLLineWidthElement::push().

SoElement * SoElement::getNextFree (void) const [protected]Returns the next free element, ie the next element up in the stack.

Member Data Documentation

int SoElement::classStackIndex [static, protected]This is the static state stack index for the class.

Referenced by SoPointSizeElement::get(), SoListenerPositionElement::get(), SoListenerOrientationElement::get(), SoListenerGainElement::get(), SoLineWidthElement::get(), getClassStackIndex(), SoListenerDopplerElement::getDopplerFactor(), SoListenerDopplerElement::getDopplerVelocity(), SoGLColorIndexElement::getInstance(), initClass(), SoListenerPositionElement::isSetByListener(), SoListenerOrientationElement::isSetByListener(), SoPointSizeElement::set(), SoListenerPositionElement::set(), SoListenerOrientationElement::set(), SoListenerGainElement::set(), SoLineWidthElement::set(), SoListenerDopplerElement::setDopplerFactor(), and SoListenerDopplerElement::setDopplerVelocity().

SoType SoElement::typeId [protected]The element's unique SoType type identification.

Referenced by getTypeId(), and setTypeId().

int SoElement::stackIndex [protected]The index in the state stack for this particular element instance.

Referenced by getStackIndex(), and setStackIndex().

SoTypeList * SoElement::stackToType [static, protected]Provides mapping from state stack indices to element types.

int SoElement::depth [protected]The depth of the element instance in the state stack.

Referenced by getDepth(), and setDepth().

Author

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