Element Classes

The element classes in Coin are the containers of state information during action traversals of scene graphs. More...

Classes
class	SoAccumulatedElement
	The SoAccumulatedElement class is an abstract class for storing accumulated state. More...
class	SoAmbientColorElement
	The SoAmbientColorElement class is yet to be documented. More...
class	SoAnnoText3CharOrientElement
	The SoAnnoText3CharOrientElement class is yet to be documented. More...
class	SoAnnoText3FontSizeHintElement
	The SoAnnoText3FontSizeHintElement class is yet to be documented. More...
class	SoAnnoText3RenderPrintElement
	The SoAnnoText3RenderPrintElement class is yet to be documented. More...
class	SoBBoxModelMatrixElement
	The SoBBoxModelMatrixElement class keeps track of the current model matrix during a scene graph traversal. It is used by amongst others the SoGetBoundingBoxAction class. More...
class	SoBumpMapCoordinateElement
	The SoBumpMapCoordinateElement class is yet to be documented. More...
class	SoBumpMapElement
	The SoBumpMapElement class is yet to be documented. More...
class	SoBumpMapMatrixElement
	The SoBumpMapMatrixElement class is used to manage the bump map matrix stack. More...
class	SoCacheElement
	The SoCacheElement class stores and manages the open caches. More...
class	SoCacheHintElement
	The SoCacheHintElement class is yet to be documented. More...
class	SoClipPlaneElement
	The SoClipPlaneElement class is used to manage the clip plane stack. More...
class	SoComplexityElement
	The SoComplexityElement class contains the current shape complexity for a graph traverser. More...
class	SoComplexityTypeElement
	The SoComplexityTypeElement class is yet to be documented. More...
class	SoCoordinateElement
	The SoCoordinateElement class is yet to be documented. More...
class	SoCreaseAngleElement
	The SoCreaseAngleElement class stores the crease angle during a scene graph traversal. More...
class	SoCullElement
	The SoCullElement class is used internally for render and pick culling. More...
class	SoDecimationPercentageElement
	The SoDecimationPercentageElement class is yet to be documented. More...
class	SoDecimationTypeElement
	The SoDecimationTypeElement class is yet to be documented. More...
class	SoDepthBufferElement
	The SoDepthBufferElement controls the depth buffer settings. More...
class	SoDiffuseColorElement
	The SoDiffuseColorElement class is yet to be documented. More...
class	SoDrawStyleElement
	The SoDrawStyleElement class is yet to be documented. More...
class	SoElement
	SoElement is the abstract base class for all elements. More...
class	SoEmissiveColorElement
	The SoEmissiveColorElement class is yet to be documented. More...
class	SoEnvironmentElement
	The SoEnvironmentElement class is yet to be documented. More...
class	SoFloatElement
	SoFloatElement is an abstract base class for elements that consists of a single float value. More...
class	SoFocalDistanceElement
	The SoFocalDistanceElement class is yet to be documented. More...
class	SoFontNameElement
	The SoFontNameElement class is yet to be documented. More...
class	SoFontSizeElement
	The SoFontSizeElement class is yet to be documented. More...
class	SoGeoElement
	The SoGeoElement class is yet to be documented. More...
class	SoGLCacheContextElement
	The SoGLCacheContextElement class handles the OpenGL cache for a context. More...
class	SoGLClipPlaneElement
	The SoGLClipPlaneElement class is yet to be documented. More...
class	SoGLColorIndexElement
	The SoGLColorIndexElement class sets the current OpenGL color. More...
class	SoGLCoordinateElement
	The SoGLCoordinateElement class is yet to be documented. More...
class	SoGLDepthBufferElement
	The SoGLDepthBufferElement controls the OpenGL depth buffer. More...
class	SoGLDisplayList
	The SoGLDisplayList class stores and manages OpenGL display lists. More...
class	SoGLDrawStyleElement
	The SoGLDrawStyleElement updates the current draw style in OpenGL. More...
class	SoGLEnvironmentElement
	The SoGLEnvironmentElement class is for setting GL fog etc. More...
class	SoGLLazyElement
	The SoGLLazyElement class is meant to optimize GL rendering. More...
class	SoGLLightIdElement
	The SoGLLightIdElement class is yet to be documented. More...
class	SoGLLinePatternElement
	The SoGLLinePatternElement class changes the line stipple pattern of the OpenGL render state. More...
class	SoGLLineWidthElement
	The SoGLLineWidthElement class changes the line width setting of the OpenGL render state. More...
class	SoGLModelMatrixElement
	The SoGLModelMatrixElement class is yet to be documented. More...
class	SoGLMultiTextureCoordinateElement
	The SoGLMultiTextureCoordinateElement class stores the current gltexture coordinates for several units. More...
class	SoGLMultiTextureEnabledElement
	The SoGLMultiTextureEnabledElement class is an element which controls whether texturing is enabled or not. More...
class	SoGLMultiTextureImageElement
	The SoGLMultiTextureImageElement class is used to control the current GL texture for texture units. More...
class	SoGLMultiTextureMatrixElement
	The SoGLMultiTextureMatrixElement class is used to update the OpenGL texture matrix. More...
class	SoGLNormalElement
	The SoGLNormalElement class is yet to be documented. More...
class	SoGLPointSizeElement
	The SoGLPointSizeElement class changes the point size setting of the OpenGL render state. More...
class	SoGLPolygonOffsetElement
	The SoGLPolygonOffsetElement class is yet to be documented. More...
class	SoGLProjectionMatrixElement
	The SoGLProjectionMatrixElement class is yet to be documented. More...
class	SoGLRenderPassElement
	The SoGLRenderPassElement class is yet to be documented. More...
class	SoGLShadowCullingElement
	The SoGLShadowCullingElement class is yet to be documented. More...
class	SoGLShapeHintsElement
	The SoGLShapeHintsElement class is yet to be documented. More...
class	SoGLUpdateAreaElement
	The SoGLUpdateAreaElement class is yet to be documented. More...
class	SoGLVBOElement
	The SoGLVBOElement class is used to store VBO state. More...
class	SoGLVertexAttributeElement
	The SoGLVertexAttributeElement class is yet to be documented. More...
class	SoGLViewingMatrixElement
	The SoGLViewingMatrixElement class is used to store the current viewing matrix. More...
class	SoGLViewportRegionElement
	The SoGLViewportRegionElement class is yet to be documented. More...
class	SoInt32Element
	The SoInt32Element class is the base class for elements that simply store a 32-bit integer. More...
class	SoLazyElement
	The SoLazyElement class is used to handle material and shape properties. More...
class	SoLightAttenuationElement
	The SoLightAttenuationElement class is yet to be documented. More...
class	SoLightElement
	The SoLightElement class manages the currently active light sources. More...
class	SoLightModelElement
	The SoLightModelElement class is yet to be documented. More...
class	SoLinePatternElement
	The SoLinePatternElement class defines the line stipple pattern. More...
class	SoLineWidthElement
	The SoLineWidthElement class changes the line width setting of the render state. More...
class	SoListenerDopplerElement
	The SoListenerDopplerElement holds the Doppler velocity and factor of the current listener. More...
class	SoListenerGainElement
	The SoListenerGainElement class stores the SoListener gain during a scene graph traversal. More...
class	SoListenerOrientationElement
	The SoListenerOrientationElement holds the orientation of the current listener. More...
class	SoListenerPositionElement
	The SoListenerPositionElement holds the position of the current listener. More...
class	SoLocalBBoxMatrixElement
	The SoLocalBBoxMatrixElement class is yet to be documented. More...
class	SoMaterialBindingElement
	The SoMaterialBindingElement class is yet to be documented. More...
class	SoModelMatrixElement
	The SoModelMatrixElement class is used to manage the current transformation. More...
class	SoMultiTextureCoordinateElement
	The SoMultiTextureCoordinateElement class is yet to be documented. More...
class	SoMultiTextureEnabledElement
	The SoMultiTextureEnabledElement class is an element which stores whether texturing is enabled or not. More...
class	SoMultiTextureImageElement
	The SoMultiTextureImageElement class is yet to be documented. More...
class	SoMultiTextureMatrixElement
	The SoMultiTextureMatrixElement class is used to manage the texture matrix stack for texture units > 0. More...
class	SoNodeVisualize
	The SoNodeVisualize class is yet to be documented. More...
class	SoNormalBindingElement
	The SoNormalBindingElement is yet to be documented. More...
class	SoNormalElement
	The SoNormalElement class is yet to be documented. More...
class	SoOverrideElement
	The SoOverrideElement maintains a list of overridable elements and a list over which elements should be overridden. More...
class	SoPickRayElement
	The SoPickRayElement class is yet to be documented. More...
class	SoPickStyleElement
	The SoPickStyleElement is yet to be documented. More...
class	SoPointSizeElement
	The SoPointSizeElement changes the point size setting of the render state. More...
class	SoPolygonOffsetElement
	The SoPolygonOffsetElement class is yet to be documented. More...
class	SoProfileCoordinateElement
	The SoProfileCoordinateElement class is yet to be documented. More...
class	SoProfileElement
	The SoProfileElement class is yet to be documented. More...
class	SoProfilerTopEngine
	The SoProfilerTopEngine class is yet to be documented. More...
class	SoProjectionMatrixElement
	The SoProjectionMatrixElement class is yet to be documented. More...
class	SoReplacedElement
	The SoReplacedElement class is an abstract element superclass. More...
class	SoShadowStyleElement
	The SoShadowStyleElement class is yet to be documented. More...
class	SoShapeHintsElement
	The SoShapeHintsElement class is yet to be documented. More...
class	SoShapeStyleElement
	The SoShapeStyleElement class is yet to be documented. More...
class	SoShininessElement
	The SoShininessElement class is yet to be documented. More...
class	SoSoundElement
	The SoSoundElement is used for optimizing audio rendering and for turning off inactive SoVRMLSound nodes. More...
class	SoSpecularColorElement
	The SoSpecularColorElement is yet to be documented. More...
class	SoSwitchElement
	The SoSwitchElement class is yet to be documented. More...
class	SoTextOutlineEnabledElement
	The SoTextOutlineEnabledElement class is yet to be documented. More...
class	SoTextureCombineElement
	The SoTextureCombineElement class is yet to be documented. More...
class	SoTextureCoordinateBindingElement
	The SoTextureCoordinateBindingElement class is yet to be documented. More...
class	SoTextureOverrideElement
	The SoTextureOverrideElement makes it possible to override texture elements. More...
class	SoTextureQualityElement
	The SoTextureQualityElement is yet to be documented. More...
class	SoTextureUnitElement
	The SoTextureUnitElement class is yet to be documented. More...
class	SoTransparencyElement
	The SoTransparencyElement is yet to be documented. More...
class	SoUnitsElement
	The SoUnitsElement class is yet to be documented. More...
class	SoVertexAttributeBindingElement
	The SoVertexAttributeBindingElement class is yet to be documented. More...
class	SoVertexAttributeElement
	The SoVertexAttributeElement class is yet to be documented. More...
class	SoViewingMatrixElement
	The SoViewingMatrixElement class stores the world-to-camera transformation. More...
class	SoViewportRegionElement
	The SoViewportRegionElement class is yet to be documented. More...
class	SoViewVolumeElement
	The SoViewVolumeElement class is yet to be documented. More...
class	SoWindowElement
	The SoWindowElement class is used to store current window attributes. More...

Detailed Description

The element classes in Coin are the containers of state information during action traversals of scene graphs.

One element usually corresponds to one item of information, or sometimes a group of related information values. The elements work like a stack that is pushed and popped as the action traverses in and out of SoSeparator nodes, and the action will always just inspect the top of the stack when it needs to know a value.

Elements are internal implementation details of the workings of nodes and actions, and is not something one needs to worry about before writing ones own extension nodes. Writing extension elements is even more removed from plain Open Inventor usage, but is fully possible for the experienced Open Inventor developer.

The Element Classes

Elements are mostly internal to Coin, unless you create new extension nodes over Coin. Then you will probably need to know about them.
Elements are part of the design for scene graph 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 scene graph 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 scene graph, it will request the current point size value from the SoState by reading off the value of its 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, as well 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 source code of the built-in classes in Coin should also prove 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 (i.e. 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>. Copyright (C)
// Kongsberg Oil & Gas Technologies.
 
#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, standalone 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>. Copyright (C) Kongsberg Oil & Gas Technologies.
 
#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 <cstdio>
 
#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\n",
                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\n",
                node->getTypeId().getName().getString(),
                filename.getLength() == 0 ?
                "<inlined>" : filename.getString());
 
  return SoCallbackAction::CONTINUE;
}
 
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);
  }
 
  SoDB::init();
 
  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;
}