SoLevelOfDetail Class Reference
Node Classes

The SoLevelOfDetail class is used to choose a child based on projected size. More...

`#include <Inventor/nodes/SoLevelOfDetail.h>`

Inheritance diagram for SoLevelOfDetail:

## Public Member Functions

virtual SoType | getTypeId (void) const
| SoLevelOfDetail (void)
| SoLevelOfDetail (int numchildren)
virtual void | doAction (SoAction *action)
virtual void | callback (SoCallbackAction *action)
virtual void | GLRender (SoGLRenderAction *action)
virtual void | rayPick (SoRayPickAction *action)
virtual void | getBoundingBox (SoGetBoundingBoxAction *action)
virtual void | audioRender (SoAudioRenderAction *action)
virtual void | notify (SoNotList *nl)
Public Member Functions inherited from SoGroup
| 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 | 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 SoChildList * | getChildren (void) const
virtual void | addWriteReference (SoOutput *out, SbBool isfromfield=FALSE)
Public Member Functions inherited from SoNode
void | setOverride (const SbBool state)
SbBool | isOverride (void) const
void | setNodeType (const NodeType type)
NodeType | getNodeType (void) const
virtual SoNode * | copy (SbBool copyconnections=FALSE) const
virtual SbBool | affectsState (void) const
virtual void | GLRenderBelowPath (SoGLRenderAction *action)
virtual void | GLRenderInPath (SoGLRenderAction *action)
virtual void | GLRenderOffPath (SoGLRenderAction *action)
virtual void | grabEventsSetup (void)
virtual void | grabEventsCleanup (void)
virtual void | startNotify (void)
SbUniqueId | getNodeId (void) const
virtual void | writeInstance (SoOutput *out)
virtual SoNode * | addToCopyDict (void) const
virtual SoFieldContainer * | copyThroughConnection (void) const
Public Member Functions inherited from SoFieldContainer
void | setToDefaults (void)
SbBool | hasDefaultValues (void) const
SbBool | fieldsAreEqual (const SoFieldContainer *container) const
void | copyFieldValues (const SoFieldContainer *container, SbBool copyconnections=FALSE)
SbBool | set (const char *const fielddata)
void | get (SbString &fielddata)
virtual int | getFields (SoFieldList &l) const
virtual int | getAllFields (SoFieldList &l) const
virtual SoField * | getField (const SbName &name) const
virtual SoField * | getEventIn (const SbName &name) const
virtual SoField * | getEventOut (const SbName &name) const
SbBool | getFieldName (const SoField *const field, SbName &name) const
SbBool | enableNotify (const SbBool flag)
SbBool | isNotifyEnabled (void) const
SbBool | set (const char *fielddata, SoInput *input)
void | get (SbString &fielddata, SoOutput *out)
virtual SbBool | validateNewFieldValue (SoField *field, void *newval)
SbBool | getIsBuiltIn (void) const
virtual void | getFieldsMemorySize (size_t &managed, size_t &unmanaged) const
void | setUserData (void *userdata) const
void * | getUserData (void) const
Public Member Functions inherited from SoBase
void | ref (void) const
void | unref (void) const
void | unrefNoDelete (void) const
int32_t | getRefCount (void) const
void | touch (void)
SbBool | isOfType (SoType type) const
| Returns `TRUE` if the type of this object is either of the same type or inherited from type.
virtual SbName | getName (void) const
virtual void | setName (const SbName &newname)
void | addAuditor (void *const auditor, const SoNotRec::Type type)
void | removeAuditor (void *const auditor, const SoNotRec::Type type)
const SoAuditorList & | getAuditors (void) const
SbBool | shouldWrite (void)
void | assertAlive (void) const

## Static Public Member Functions

static SoType | getClassTypeId (void)
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.
Static Public Member Functions inherited from SoGroup
static SoType | getClassTypeId (void)
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.
Static Public Member Functions inherited from SoNode
static uint32_t | getCompatibilityTypes (const SoType &nodetype)
static SoType | getClassTypeId (void)
static SoNode * | getByName (const SbName &name)
static int | getByName (const SbName &name, SoNodeList &l)
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.
static void | initClasses (void)
static SbUniqueId | getNextNodeId (void)
static int | getActionMethodIndex (const SoType type)
static void | getBoundingBoxS (SoAction *action, SoNode *node)
static void | GLRenderS (SoAction *action, SoNode *node)
static void | callbackS (SoAction *action, SoNode *node)
static void | getMatrixS (SoAction *action, SoNode *node)
static void | handleEventS (SoAction *action, SoNode *node)
static void | pickS (SoAction *action, SoNode *node)
static void | rayPickS (SoAction *action, SoNode *node)
static void | searchS (SoAction *action, SoNode *node)
static void | writeS (SoAction *action, SoNode *node)
static void | audioRenderS (SoAction *action, SoNode *node)
static void | getPrimitiveCountS (SoAction *action, SoNode *node)
Static Public Member Functions inherited from SoFieldContainer
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.
static SoType | getClassTypeId (void)
| This static method returns the SoType object associated with objects of this class.
static void | cleanupClass (void)
static void | initCopyDict (void)
static void | addCopy (const SoFieldContainer *orig, const SoFieldContainer *copy)
static SoFieldContainer * | checkCopy (const SoFieldContainer *orig)
static SoFieldContainer * | findCopy (const SoFieldContainer *orig, const SbBool copyconnections)
static void | copyDone (void)
Static Public Member Functions inherited from SoBase
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.
static SoType | getClassTypeId (void)
| This static method returns the SoType object associated with objects of this class.
static void | addName (SoBase *const base, const char *const name)
static void | removeName (SoBase *const base, const char *const name)
static void | incrementCurrentWriteCounter (void)
static void | decrementCurrentWriteCounter (void)
static SoBase * | getNamedBase (const SbName &name, SoType type)
static int | getNamedBases (const SbName &name, SoBaseList &baselist, SoType type)
static SbBool | read (SoInput *input, SoBase *&base, SoType expectedtype)
static void | setInstancePrefix (const SbString &c)
static void | setTraceRefs (SbBool trace)
static SbBool | getTraceRefs (void)
static SbBool | connectRoute (SoInput *input, const SbName &fromnodename, const SbName &fromfieldname, const SbName &tonodename, const SbName &tofieldname)
static SbBool | readRoute (SoInput *input)

## Public Attributes

SoMFFloat | screenArea

## Protected Member Functions

virtual const SoFieldData * | getFieldData (void) const
virtual | ~SoLevelOfDetail ()
Protected Member Functions inherited from SoGroup
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 Member Functions inherited from SoNode
| SoNode (void)
virtual | ~SoNode ()
Protected Member Functions inherited from SoFieldContainer
| SoFieldContainer (void)
virtual | ~SoFieldContainer ()
Protected Member Functions inherited from SoBase
| SoBase (void)
virtual | ~SoBase ()
virtual void | destroy (void)
SbBool | hasMultipleWriteRefs (void) const
SbBool | writeHeader (SoOutput *out, SbBool isgroup, SbBool isengine) const
void | writeFooter (SoOutput *out) const
virtual const char * | getFileFormatName (void) const

## Static Protected Member Functions

static const SoFieldData ** | getFieldDataPtr (void)
Static Protected Member Functions inherited from SoGroup
static const SoFieldData ** | getFieldDataPtr (void)
Static Protected Member Functions inherited from SoNode
static const SoFieldData ** | getFieldDataPtr (void)
static void | setNextActionMethodIndex (int index)
static int | getNextActionMethodIndex (void)
static void | incNextActionMethodIndex (void)
static void | setCompatibilityTypes (const SoType &nodetype, const uint32_t bitmask)
Static Protected Member Functions inherited from SoBase
static uint32_t | getCurrentWriteCounter (void)
static void | staticDataLock (void)
static void | staticDataUnlock (void)

## Additional Inherited Members

Public Types inherited from SoNode

enum

NodeType {
INVENTOR = 0x0000 , VRML1 = 0x0001 , VRML2 = 0x0002 , INVENTOR_1 = 0x0004 ,
INVENTOR_2_0 = 0x0008 , INVENTOR_2_1 = 0x0010 , INVENTOR_2_5 = 0x0020 , INVENTOR_2_6 = 0x0040 ,
COIN_1_0 = 0x0080 , COIN_2_0 = 0x0100 , EXTENSION = 0x0200 , COIN_2_2 = 0x0400 ,
COIN_2_3 = 0x0800 , COIN_2_4 = 0x1000 , INVENTOR_5_0 = 0x2000 , COIN_2_5 = 0x4000 ,
COIN_3_0 = 0x8000 , INVENTOR_6_0 = 0x10000 , COIN_4_0 = 0x20000
}

Protected Types inherited from SoBase
enum | BaseFlags { IS_ENGINE = 0x01 , IS_GROUP = 0x02 }
Protected Attributes inherited from SoGroup
SoChildList * | children
Protected Attributes inherited from SoNode
SbUniqueId | uniqueId
Protected Attributes inherited from SoFieldContainer
SbBool | isBuiltIn
Static Protected Attributes inherited from SoNode
static SbUniqueId | nextUniqueId = 1
static int | nextActionMethodIndex = 0

## Detailed Description

The SoLevelOfDetail class is used to choose a child based on projected size.

A level-of-detail mechanism is typically used by application programmers to assist the library in speeding up the rendering.

The way a level-of-detail mechanism works is basically like this:

Several versions of varying complexity of the same geometry / shape is provided by the application programmer in sorted order from "most complex" to "least complex" (where "complex" in this context should be taken to mean more or less detailed in the number of polygons / shapes used for rendering it).

The runtime rendering system then, upon scene graph traversal, will on-the-fly calculate either the distance from the camera to the 3D-model in question, or the number of pixels in the screen projection of the 3D-model. This value is then used to decide which version of the model to actually render: as the model is moved farther away from the camera, a less detailed version of the model is used. And vice versa, as the model moves closer to the camera, more and more detailed versions of it are rendered.

This is under many different circumstances a very effective way to let the application programmer assist to profoundly optimize the rendering of her 3D-scene.

There is of course a trade-off with the level-of-detail technique: more versions of the same 3D model means the scene graph will use up more application memory resources. Also, generating the set of less and less detailed versions of a 3D model from the original is often not a trivial task to do properly. The process is often assisted by software like what Kongsberg Oil & Gas Technologies offers in their <a href="http://www.rational-reducer.com>Rational Reducer</a> package. The SoLevelOfDetail node implements the "projected size" variety level-of-detail technique (as opposed to the "object distance" technique, as done by the SoLOD node). The node works by comparing the current projected size of the smallest rectangle covering the bounding box of its child geometry. Along with this set of models of the same shape, a specification of when to switch between them is also provided. Example scene graph layout: @code LevelOfDetail { screenArea [ 2000, 500, 50 ] DEF version-0 Separator { # most complex / detailed / heavy version of subgraph } DEF version-1 Separator { # less complex version of subgraph } DEF version-2 Separator { # even less complex version of subgraph } DEF version-3 Separator { # simplest / "lightest" version of subgraph } } \endcode The way the above sub-scene graph would work would be the following: if the rectangular area around the model's projected bounding box covers \e more than 2000 pixels (meaning it will be up pretty close to the camera), the most complex version of the model (\c version-0) would be traversed (and rendered, of course). If the projected area would be \e between 500 and 2000 pixels, the \c version-1 model would be used. Ditto if the projected area was between 50 and 500 pixels, the \c version-2 version of the model would be used. Finally, if the projected bounding box area would be \e less than 50 square pixels, the presumably least detailed version of the model would be used. (A common "trick" is to let the last of the SoLevelOfDetail node's children be just an empty subgraph, so no geometry will be rendered at all if the model is sufficiently far away. This will of course have a positive effect on the total rendering time for the complete scene graph.) Note that the SoLevelOfDetail::screenArea vector will be influenced by preceding SoComplexity nodes in the following way: if SoComplexity::value is set from 0.0 up to 0.5, lower detail levels than normal will be selected for traversal. If SoComplexity::value is above 0.5, higher level details than normal will be used. An SoComplexity::value equal to 1.0 will cause the first child of SoLevelOfDetail to always be used. As mentioned above, there is one other level-of-detail node in the Coin library: SoLOD. The difference between that one and this is just that instead of projected bounding box area, SoLOD uses the distance between the camera and the object to find out when to switch between the different model versions. Using SoLOD is faster, since figuring out the projected bounding box area needs a certain amount of calculations. But using SoLevelOfDetail is often "better", in the sense that it's really a model's size and visibility in the viewport that determines whether we could switch to a less complex version without losing enough detail that it gives a noticeable visual degradation.

FILE FORMAT/DEFAULTS:

LevelOfDetail {
screenArea 0
}
SoLevelOfDetail::screenArea
SoMFFloat screenArea
Definition SoLevelOfDetail.h:53

See also
  SoLOD

## Constructor & Destructor Documentation

## SoLevelOfDetail() [1/2]

SoLevelOfDetail::SoLevelOfDetail | ( | void |  | ) |

Default constructor.

## SoLevelOfDetail() [2/2]

SoLevelOfDetail::SoLevelOfDetail | ( | int | numchildren | ) |

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.

## ~SoLevelOfDetail()

SoLevelOfDetail::~SoLevelOfDetail | ( |  | ) |

protected virtual

Destructor.

## Member Function Documentation

## getClassTypeId()

SoType SoLevelOfDetail::getClassTypeId | ( | void |  | ) |

static

This static method returns the SoType object associated with objects of this class.

## getTypeId()

SoType SoLevelOfDetail::getTypeId | ( | void |  | ) | const

virtual

Returns the type identification of an object derived from a class inheriting SoBase. This is used for runtime type checking and "downward" casting.

Reimplemented from SoGroup.

## getFieldDataPtr()

const SoFieldData ** SoLevelOfDetail::getFieldDataPtr | ( | void |  | ) |

static protected

This API member is considered internal to the library, as it is not likely to be of interest to the application programmer.
Returns the SoFieldData class which holds information about fields in this node.

## getFieldData()

const SoFieldData * SoLevelOfDetail::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 SoGroup.

## doAction()

void SoLevelOfDetail::doAction | ( | SoAction * | action | ) |

virtual

This function performs the typical operation of a node for any action.

Reimplemented from SoGroup.

## callback()

void SoLevelOfDetail::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 SoGroup.

## GLRender()

void SoLevelOfDetail::GLRender | ( | SoGLRenderAction * | action | ) |

virtual

Action method for the SoGLRenderAction.

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

Reimplemented from SoGroup.

## rayPick()

void SoLevelOfDetail::rayPick | ( | SoRayPickAction * | action | ) |

virtual

Action method for SoRayPickAction.

Checks the ray specification of the action and tests for intersection with the data of the node.

Nodes influencing relevant state variables for how picking is done also override this method.

Reimplemented from SoNode.

## getBoundingBox()

void SoLevelOfDetail::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 calculate their bounding box also override this method to change the relevant state variables.

Reimplemented from SoGroup.

## audioRender()

void SoLevelOfDetail::audioRender | ( | SoAudioRenderAction * | action | ) |

virtual

Action method for SoAudioRenderAction.

Does common processing for SoAudioRenderAction action instances.

Reimplemented from SoGroup.

## notify()

void SoLevelOfDetail::notify | ( | SoNotList * | l | ) |

virtual

Notifies all auditors for this instance when changes are made.

Reimplemented from SoNode.

## Member Data Documentation

## screenArea

SoMFFloat SoLevelOfDetail::screenArea

The screen area limits for the children. See usage example in main class documentation of SoLevelOfDetail for an explanation of how this vector should be set up correctly.

By default this vector just contains a single value 0.0f.

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

- SoLevelOfDetail.h
- SoLevelOfDetail.cpp