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SoElement Class Referenceabstract

SoElement is the abstract base class for all elements.Elements are part of the design for scenegraph traversal in Coin. More...

#include <Inventor/elements/SoElement.h>

Inheritance diagram for SoElement:
SoAccumulatedElement SoFloatElement SoInt32Element SoOverrideElement SoReplacedElement SoLineWidthElement SoListenerGainElement SoPointSizeElement SoGLColorIndexElement SoListenerDopplerElement SoListenerOrientationElement SoListenerPositionElement SoGLLineWidthElement SoGLPointSizeElement

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 SoElementcopyMatchInfo (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)
 
SoElementgetNextInStack (void) const
 
SoElementgetNextFree (void) const
 

Static Protected Member Functions

static SoElementgetElement (SoState *const state, const int stackIndex)
 
static const SoElementgetConstElement (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 SoTypeListstackToType
 

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 *)
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 *)
}

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"
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\n",
filename.getLength() == 0 ?
"<inlined>" : filename.getString());
}
pre_shape_cb(void * data, SoCallbackAction * action, const SoNode * node)
{
const SbString & filename =
TextureFilenameElement::get(action->getState());
(void)fprintf(stdout, " Texturemap on %s: %s\n",
filename.getLength() == 0 ?
"<inlined>" : filename.getString());
}
void
usage(const char * appname)
{
(void)fprintf(stderr, "\n\tUsage: %s <modelfile.iv>\n\n", appname);
(void)fprintf(stderr,
"\tLists all texture filenames in the model file,\n"
"\tand on which shape nodes they are used.\n\n"
"\tThe purpose of this example utility is simply to\n"
"\tshow how to create and use an extension element for\n"
"\tscene graph traversal.\n\n");
}
int
main(int argc, char ** argv)
{
if (argc != 2) {
usage(argv[0]);
exit(1);
}
TextureFilenameElement::initClass();
SO_ENABLE(SoCallbackAction, TextureFilenameElement);
SoInput input;
if (!input.openFile(argv[1])) {
(void)fprintf(stderr, "ERROR: couldn't open file ``%s''.\n", 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::~SoElement ( )
virtual

The destructor.

◆ SoElement()

SoElement::SoElement ( void  )
protected

The constructor. To create element instances, use SoType::createInstance() for the elements type identifier..

Member Function Documentation

◆ initClass()

void SoElement::initClass ( void  )
static

Initialize relevant common data for all instances, like the type system.

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

Referenced by SoDB::init().

◆ getClassTypeId()

SoType SoElement::getClassTypeId ( void  )
static

This static method returns the class type.

◆ getClassStackIndex()

int SoElement::getClassStackIndex ( void  )
static

This static method returns the state stack index for the class.

References classStackIndex.

◆ getTypeId()

const SoType SoElement::getTypeId ( void  ) const

Returns 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 SoFloatElement::copyMatchInfo(), SoReplacedElement::copyMatchInfo(), SoInt32Element::copyMatchInfo(), SoAccumulatedElement::copyMatchInfo(), SoOverrideElement::copyMatchInfo(), SoState::getElement(), SoFloatElement::matches(), SoInt32Element::matches(), SoFloatElement::print(), SoInt32Element::print(), SoReplacedElement::print(), SoState::print(), and print().

◆ getStackIndex()

int SoElement::getStackIndex ( void  ) const

Returns the stack index for an element instance.

References stackIndex.

Referenced by SoState::SoState().

◆ init()

void SoElement::init ( SoState state)
virtual

◆ push()

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 SoOverrideElement, SoAccumulatedElement, SoGLPointSizeElement, and SoGLLineWidthElement.

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

◆ pop()

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.

Reimplemented in SoGLPointSizeElement, and SoGLLineWidthElement.

Referenced by SoState::pop().

◆ matches()

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.

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

◆ copyMatchInfo()

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 SoOverrideElement, SoAccumulatedElement, SoInt32Element, SoReplacedElement, and SoFloatElement.

◆ initElements()

void SoElement::initElements ( void  )
static

This function initializes all the built-in Coin element classes.

References SoListenerPositionElement::initClass(), SoListenerDopplerElement::initClass(), SoListenerOrientationElement::initClass(), and SoOverrideElement::initClass().

Referenced by initClass().

◆ getNumStackIndices()

int SoElement::getNumStackIndices ( void  )
static

Returns the number of allocated element stack index slots.

References SbPList::getLength(), and stackToType.

Referenced by SoState::SoState().

◆ getIdFromStackIndex()

SoType SoElement::getIdFromStackIndex ( const int  stackIndex)
static

Returns the SoType identifier for the element class with element state stack index stackIndex.

References stackIndex, and stackToType.

◆ setDepth()

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().

◆ getDepth()

int SoElement::getDepth ( void  ) const

Returns the state stack depth value of the element instance.

References depth.

Referenced by SoState::getElement().

◆ print()

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, SoListenerDopplerElement, SoReplacedElement, SoListenerPositionElement, SoListenerOrientationElement, SoInt32Element, and SoFloatElement.

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

◆ getElement()

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

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(), and stackIndex.

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

◆ getConstElement()

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

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(), SoState::getConstElement(), and stackIndex.

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

◆ capture()

void SoElement::capture ( SoState *const  state) const
inlineprotected

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(), SoGLLineWidthElement::push(), and SoGLPointSizeElement::push().

◆ captureThis()

void SoElement::captureThis ( SoState state) const
protectedvirtual

Adds the element to the cache.

Reimplemented in SoAccumulatedElement.

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

◆ setTypeId()

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.

◆ setStackIndex()

void SoElement::setStackIndex ( const int  stackIndexarg)
protected

Sets the stack index in an instance. Used in constructors of derived elements.

References stackIndex.

◆ createStackIndex()

int SoElement::createStackIndex ( const SoType  typeId)
staticprotected

Returns the value of a new available stack index.

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

◆ getNextInStack()

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(), SoGLLineWidthElement::push(), SoGLPointSizeElement::push(), and SoOverrideElement::push().

◆ getNextFree()

SoElement * SoElement::getNextFree ( void  ) const
protected

Returns the next free element, ie the next element up in the stack.

Member Data Documentation

◆ classStackIndex

int SoElement::classStackIndex
staticprotected

This is the static state stack index for the class.

Referenced by getClassStackIndex(), and initClass().

◆ typeId

SoType SoElement::typeId
protected

The element's unique SoType type identification.

Referenced by createStackIndex(), getTypeId(), and setTypeId().

◆ stackIndex

int SoElement::stackIndex
protected

The index in the state stack for this particular element instance.

Referenced by getConstElement(), SoReplacedElement::getElement(), getElement(), getIdFromStackIndex(), getStackIndex(), SoFloatElement::set(), and setStackIndex().

◆ stackToType

SoTypeList * SoElement::stackToType
staticprotected

Provides mapping from state stack indices to element types.

Referenced by createStackIndex(), getIdFromStackIndex(), getNumStackIndices(), and initClass().

◆ depth

int SoElement::depth
protected

The depth of the element instance in the state stack.

Referenced by getDepth(), and setDepth().


The documentation for this class was generated from the following files:

Copyright © 1998-2007 by Systems in Motion AS. All rights reserved.

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