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. More...

#include <Inventor/nodes/SoLevelOfDetail.h>

Inheritance diagram for SoLevelOfDetail:

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 run-time 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 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

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)

uint32_t	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)

virtual void	addWriteReference (SoOutput *out, SbBool isfromfield=FALSE)

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 SoAuditorList &	getAuditors (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 SoNode *	getByName (const SbName &name)

static int	getByName (const SbName &name, SoNodeList &l)

static void	initClass (void)

static void	initClasses (void)

static uint32_t	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 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
uint32_t	uniqueId

Protected Attributes inherited from SoFieldContainer
SbBool	isBuiltIn

Static Protected Attributes inherited from SoNode
static uint32_t	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 run-time rendering system then, upon scenegraph 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 scenegraph 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 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 it's child geometry.

Along with this set of models of the same shape, a specification of when to switch between them is also provided.

Example scenegraph 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-scenegraph 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 modeled 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 scenegraph.)

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 noticable visual degradation.

FILE FORMAT/DEFAULTS:

LevelOfDetail {
    screenArea 0
}

See also: SoLOD

Constructor & Destructor Documentation

SoLevelOfDetail::SoLevelOfDetail ( void )

Default constructor.

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 ( )

protectedvirtual

Destructor.

Member Function Documentation

SoType SoLevelOfDetail::getTypeId ( void ) const

virtual

Returns the type identification of an object derived from a class inheriting SoBase. This is used for run-time 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 pre-defined 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 toplevel superclasses for the various class groups.

Reimplemented from SoGroup.

const SoFieldData * SoLevelOfDetail::getFieldData ( void ) const

protectedvirtual

Returns a pointer to the class-wide field data storage object for this instance. If no fields are present, returns NULL.

Reimplemented from SoGroup.

void SoLevelOfDetail::doAction ( SoAction * action )

virtual

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

Reimplemented from SoGroup.

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.

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 who wants to throw geometry primitives at OpenGL overrides this method.

Reimplemented from SoGroup.

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 overrides this method.

Reimplemented from SoNode.

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 calculates their bounding box also overrides this method to change the relevant state variables.

Reimplemented from SoGroup.

void SoLevelOfDetail::audioRender ( SoAudioRenderAction * action )

virtual

Action method for SoAudioRenderAction.

Does common processing for SoAudioRenderAction action instances.

Reimplemented from SoGroup.

void SoLevelOfDetail::notify ( SoNotList * l )

virtual

Notifies all auditors for this instance when changes are made.

Reimplemented from SoNode.

Member Data Documentation

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

Public Member Functions

Static Public Member Functions

Public Attributes

Protected Member Functions

Static Protected Member Functions

Additional Inherited Members

Detailed Description

Constructor & Destructor Documentation

Member Function Documentation

Member Data Documentation