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SoLevelOfDetail Class Reference

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

#include <Inventor/nodes/SoLevelOfDetail.h>

Inheritance diagram for SoLevelOfDetail:
SoGroup SoNode SoFieldContainer SoBase

Public Member Functions

virtual SoType getTypeId (void) const
 Returns the type identification of an object derived from a class inheriting SoBase. This is used for runtime type checking and "downward" casting. More...
 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 SoNodegetChild (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 SoChildListgetChildren (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 SoNodecopy (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 SoNodeaddToCopyDict (void) const
virtual SoFieldContainercopyThroughConnection (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 SoFieldgetField (const SbName &name) const
virtual SoFieldgetEventIn (const SbName &name) const
virtual SoFieldgetEventOut (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. More...
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 SoAuditorListgetAuditors (void) const
SbBool shouldWrite (void)
void assertAlive (void) const

Static Public Member Functions

static SoType getClassTypeId (void)
static void initClass (void)
- Static Public Member Functions inherited from SoGroup
static SoType getClassTypeId (void)
static void initClass (void)
- Static Public Member Functions inherited from SoNode
static uint32_t getCompatibilityTypes (const SoType &nodetype)
static SoType getClassTypeId (void)
static SoNodegetByName (const SbName &name)
static int getByName (const SbName &name, SoNodeList &l)
static void initClass (void)
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)
static SoType getClassTypeId (void)
static void cleanupClass (void)
static void initCopyDict (void)
static void addCopy (const SoFieldContainer *orig, const SoFieldContainer *copy)
static SoFieldContainercheckCopy (const SoFieldContainer *orig)
static SoFieldContainerfindCopy (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 SoBasegetNamedBase (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 SoFieldDatagetFieldData (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
- 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=">Rational Reducer 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:

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

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 more than 2000 pixels (meaning it will be up pretty close to the camera), the most complex version of the model (version-0) would be traversed (and rendered, of course). If the projected area would be between 500 and 2000 pixels, the version-1 model would be used. Ditto if the projected area was between 50 and 500 pixels, the version-2 version of the model would be used. Finally, if the projected bounding box area would be 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.


LevelOfDetail {
See also

Constructor & Destructor Documentation

◆ SoLevelOfDetail() [1/2]

SoLevelOfDetail::SoLevelOfDetail ( void  )

Default constructor.

◆ SoLevelOfDetail() [2/2]

SoLevelOfDetail::SoLevelOfDetail ( int  numchildren)


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 ( )


Member Function Documentation

◆ getTypeId()

SoType SoLevelOfDetail::getTypeId ( void  ) const

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

Usage example:

void foo(SoNode * node)
if (node->getTypeId() == SoFile::getClassTypeId()) {
SoFile * filenode = (SoFile *)node; // safe downward cast, knows the type

For application programmers wanting to extend the library with new nodes, engines, nodekits, draggers or others: this method needs to be overridden in all subclasses. This is typically done as part of setting up the full type system for extension classes, which is usually accomplished by using the predefined macros available through for instance Inventor/nodes/SoSubNode.h (SO_NODE_INIT_CLASS and SO_NODE_CONSTRUCTOR for node classes), Inventor/engines/SoSubEngine.h (for engine classes) and so on.

For more information on writing Coin extensions, see the class documentation of the top level superclasses for the various class groups.

Reimplemented from SoGroup.

◆ getFieldData()

const SoFieldData * SoLevelOfDetail::getFieldData ( void  ) const

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)

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

Reimplemented from SoGroup.

◆ callback()

void SoLevelOfDetail::callback ( SoCallbackAction action)

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)

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)

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)

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)

Action method for SoAudioRenderAction.

Does common processing for SoAudioRenderAction action instances.

Reimplemented from SoGroup.

◆ notify()

void SoLevelOfDetail::notify ( SoNotList l)

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: